Stars getting close enough to black holes(BHs)can be torn apart by strong tidal forces,producing electromagnetic flares.To date,more than 100 tidal disruption events(TDEs)have been observed,each involving invariably n...Stars getting close enough to black holes(BHs)can be torn apart by strong tidal forces,producing electromagnetic flares.To date,more than 100 tidal disruption events(TDEs)have been observed,each involving invariably normal gaseous stars whose debris falls onto the BH,sustaining the flares over years.White dwarfs(WDs),which are the most prevalent compact stars and a million times denser-and therefore tougher-than gaseous stars,can only be disrupted by intermediate-mass black holes(IMBHs)of 10^(2)–10^(5) solar masses.WD-TDEs are considered to generate more powerful and short-lived flares,but their evidence has been lacking.Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe.Its one-day-long X-ray peak as luminous as 10^(47−49) erg s^(−1) showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays,as detected by Fermi/GBM and Konus-Wind,indicating relativistic jet emission.The jet's X-rays dropped sharply from 3×10^(49) erg s^(−1) to around 1044 erg s^(−1) within 20 days(10 days in the source rest frame).These characteristics are inconsistent with any previously known transient phenomena.We suggest that this fast-evolving event over the unprecedentedly short timescale arises likely from disruption of a WD by an IMBH.At late times,a soft component progressively dominates the X-ray spectrum,reaching a luminosity as high as 1044 erg s^(−1),which is consistent with being extreme super-Eddington emission from an accretion disk expected to form in an IMBH-WD TDE.WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments,and they are prime sources of gravitational waves in the band of space-based interferometers.展开更多
I reminisce on my early life in Section 1;on my education in Sections 2 and 3;on the years at Princeton as a research astronomer in Section 4;on the years on the faculty at Chicago in Section 5;on research on Diffuse ...I reminisce on my early life in Section 1;on my education in Sections 2 and 3;on the years at Princeton as a research astronomer in Section 4;on the years on the faculty at Chicago in Section 5;on research on Diffuse Interstellar Bands(DIBs) in Section 6;on construction of the 3.5 m telescope at Apache Point Observatory(APO)in Section 7;on work on the Sloan Digital Sky Survey(SDSS) in Section 8;on work in public education in Chicago in Section 9;and on my travels in Section 10. My main science research is of an observational nature,concerning Galactic and intergalactic interstellar gas. Highlights for me included my work on the orbiting telescope Copernicus, including the discovery of interstellar deuterium;early observations of absorption associated with fivetimes ionized oxygen;and discoveries concerning the phases of gas in the local interstellar medium, based on previously unobservable interstellar UV spectral lines. With other instruments and collaborations, I extended interstellar UV studies to the intergalactic cool gas using quasi-stellar object QSO absorption lines redshifted to the optical part of the spectrum;provided a better definition of the emission and morphological character of the source of absorption lines in QSO spectra;and pursued the identification of the unidentified DIBs. For several of these topics, extensive collaborations with many scientists were essential over many years. The conclusions developed slowly, as I moved from being a graduate student at Chicago, to a research scientist position at Princeton and then to a faculty position at Chicago. At each stage of life, I was exposed to new technologies adaptable to my science and to subsequent projects. From high school days, I encountered several management opportunities which were formative. I have been extremely fortunate both in scientific mentors I had and in experimental opportunities I encountered.展开更多
This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interst...This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interstellar medium(ISM) configurations: a uniform density distribution and a medium with a sharp density discontinuity. Compared to the uniform density distribution, the ISM with this density discontinuity better reflects the actual conditions and explains the overall morphological characteristics of specific types of SNR-PWN composite systems. These systems exhibit asymmetries, such as an SNR shell with differing radii or an inner PWN located nearer to the shell on one side. The simulation results suggest that the density discontinuity in the ISM is a contributing factor to both the shell asymmetry and the PWN displacement. Specifically, this density variation directly causes the inconsistency in the forward shock speeds of the SNR between high and low density regions, resulting in discrepancies in the shell layer radii. Furthermore, the asymmetric morphology of the PWN and its positional offset emerge through interactions with the reverse shock. The PWN tends to shift toward the SNR shell on one side. The greater the density jump in the background field, the more pronounced the shell radius differences and PWN offset become.展开更多
Based on the RXTE observations of Sco X-1,we identified a clear dichotomy in the behavior of its X-ray crosscorrelation functions(CCFs)which is possibly associated with two different radio jet ejection events.Twenty s...Based on the RXTE observations of Sco X-1,we identified a clear dichotomy in the behavior of its X-ray crosscorrelation functions(CCFs)which is possibly associated with two different radio jet ejection events.Twenty six observations display asymmetric CCFs of low correlation coefficients with soft or hard delays of a few hundred seconds along with no oscillation feature in the power density spectrum associated with horizontal branch/hard apex.All the observations belonging to NB/FB have symmetric CCFs with NBO/NBO+HBO/FBO in the PDS.Based on radio observations,two different types of jets were associated with Sco X-1 i.e.,ballistic radio jets and an ultra-relativistic flow(URF).We noted that asymmetric CCFs with delays were connected with ballistic or lobe radio jets and symmetric CCFs with URFs in Sco X-1.We interpret these findings as evidence of two different states of the inner accretion disk.We propose that the launch of a ballistic jet triggers significant instability within the inner accretion region,likely the boundary layer and corona.This disruption explains the observed delays in the CCF and simultaneously quenches the conditions required for coherent oscillations,leaving only flat-topped noise in the PDS.We constrain the size of this unstable region in the inner region of accretion to be~10-40 km.In contrast,the symmetric CCFs and persistent oscillations(NBO/NBO+HBO)during URF events suggest a more stable,steady accretion flow.Although connecting the URF to a specific oscillation is difficult,its strong association with the NB phase of variation suggests a common underlying physical mechanism.Therefore,the CCF's asymmetry acts as a powerful diagnostic,linking ballistic jets to disk instability and URFs to a stable accretion state.Various physical scenarios are discussed to understand the connection among X-ray CCFs,PDS,and radio ejections in Sco X-1.展开更多
Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion mo...Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion model to investigate the mechanism by which high-energy protons escaping from SNRs interact with dense MCs through proton–proton interactions to produce high-energyγ-rays.Using the W51 complex,a typical star-forming region,as a research sample,we analyze the production and propagation characteristics of γ-rays.By employing the Exponential Cutoff Power-Law model and the Markov Chain Monte Carlo method,we fit theγ-ray observational data of W51C,successfully constraining the key physical parameters.Additionally,we systematically search for 1LHAASO sources spatially coincident with SNR-MC systems to explore the potential origins of ultra-high-energy(UHE) γ-ray sources.The results indicate that the radiation characteristics of the UHE γ-ray sources are highly consistent with the SNR-MC systems,further supporting their candidacy as PeVatrons in the Galaxy.展开更多
SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56...SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56)Ni model to fit the multiband light curves(LCs)of SN 2014av.For the CSI and CSI plus^(56)Ni models,we assume that the CSM is a constant density shell(“shell”)or a steady-state stellar wind(“wind”)with density∝r-2.We find that both the^(56)Ni and CSI models fail to fit the multiband LCs of SN 2014av,while the CSI plus^(56)Ni model can account for the LCs.In the last scenario,the LCs around the peaks were mainly powered by the CSI,while the flattening of the LCs was mainly powered by the radioactive decay of^(56)Ni.For the wind case,the derived mass-loss rate of the progenitor is≈20.5-205.5 M_(⊙)yr^(-1),whose lower limit is significantly larger than the upper limit of normal stellar winds,and comparable the upper limit of hyper-winds.Hence,we suggest that the wind case is disfavored.For the shell case,the best-fitting values of the ejecta,^(56)Ni,and the CSM are2.29 M_(⊙),0.09 M_(⊙),and 5.00 M_(⊙),respectively.Provided the velocity of the CSM shell is 100-1000 km s^(-1),we infer that the shell might be expelled≈0.49-5.20 yr before the SN exploded.展开更多
We present 17 cataclysmic variables(CVs) obtained from the crossmatch between the Sloan Digital Sky Survey(SDSS) and eROSITA Final Equatorial Depth Survey(eFEDS),including eight known CVs before eFEDS and nine identif...We present 17 cataclysmic variables(CVs) obtained from the crossmatch between the Sloan Digital Sky Survey(SDSS) and eROSITA Final Equatorial Depth Survey(eFEDS),including eight known CVs before eFEDS and nine identified from eFEDS.The photometric periods of four CVs are derived from the Zwicky Transient Facility and Catalina Real-Time Transient Survey.We focus on two CVs,SDSS J084309.3-014858 and SDSS J093555.0+042916,and confirm that their photometric periods correspond to the orbital periods by fitting the radial velocity curves.Furthermore,by the combination of the Gaia distance,the spectral energy distribution,and the variations of Ha emission lines,the masses of the white dwarf and the visible star can be well constrained.展开更多
We present systematic identifications of supergiants in M31/M33 based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST)spectroscopic survey.Radial velocities of nearly 5000 photometrically selec...We present systematic identifications of supergiants in M31/M33 based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST)spectroscopic survey.Radial velocities of nearly 5000 photometrically selected M31/M33 supergiant candidates have been properly derived from the qualified spectra released in LAMOST DR10.By comparing their radial velocities with those predicted from the rotation curve of M31,as well as utilizing Gaia astrometric measurements to exclude foreground contaminations,199 supergiant members in M31,including 168“Rank1”and 31“Rank2,”have been successfully identified.This sample contains 62 blue supergiants(BSGs,all“Rank1”),134 yellow supergiants(YSGs,103“Rank1”and 31“Rank2”)and three red supergiants(RSGs,all“Rank1”).For M33,we identify 84 supergiant members(56“Rank1”and 28“Rank2”),which include 28 BSGs(all“Rank1”),53 YSGs(25“Rank1”and 28“Rank2”)and three RSGs(all“Rank1”).So far,this is one of the largest supergiant samples of M31/M33 with full optical wavelength coverage(3700<λ<9100Å).This sample is valuable for understanding star formation and stellar evolution under different environments.展开更多
Slitless spectroscopy onboard space telescopes is a powerful tool to detect emission-line objects such as emissionline galaxies(ELGs)and quasars.In this work,we present a study of ELGs observed with slitless spectrosc...Slitless spectroscopy onboard space telescopes is a powerful tool to detect emission-line objects such as emissionline galaxies(ELGs)and quasars.In this work,we present a study of ELGs observed with slitless spectroscopy by the Hubble Space Telescope(HST)in a deep field of~44 arcmin^(2).This is one of the deepest HST fields with a wealth of imaging and spectral data.In particular,previous VLT/MUSE observations have covered this field and identified a large number of ELGs.We reduce the HST spectra using the latest pipeline with a forward modeling algorithm and construct a sample of ELGs.By comparing with the MUSE spectra,we characterize our ELG detection in the HST spectra,including the impact of the line flux,line width,signal-to-noise ratio,etc.We find that the morphological broadening may affect the detection of ELGs,such that more compact sources are easier to be detected in slitless spectra.We discuss its implications to future slitless spectroscopic surveys that will be carried out by the China Space Station Telescope(CSST)and find that the CSST slitless spectroscopy has a capability comparable to that of HST in terms of the detection of emission lines.展开更多
Previous X-ray and optical studies of the galaxy cluster pair A222/223 suggested the possible presence of a=lamentary structure connecting the two clusters,a result that appears to be supported by subsequent weak-lens...Previous X-ray and optical studies of the galaxy cluster pair A222/223 suggested the possible presence of a=lamentary structure connecting the two clusters,a result that appears to be supported by subsequent weak-lensing analyses.This=lament has been reported to host a primordial warm-hot intergalactic medium,which existed prior to being heated by the interactions of the clusters.In this study,we made an attempt to examine the reported emission feature with data from an archival Suzaku observation,taking advantage of its low detector background.Because the emission is expected to be very weak,we=rst carefully examined all potential sources of“contamination,”and then modeled the residual emission.Due to large uncertainties,unfortunately,our results can neither con=rm the presence of the reported emission feature nor rule it out.We discuss the sources of uncertainties.展开更多
We analyze the absorption features in the public 73 ks XMM-Newton spectra of the Seyfert 1 galaxy PG 0052+251.Our analysis reveals the presence of a warm absorber(WA)intrinsic to the source and the hot circumgalactic ...We analyze the absorption features in the public 73 ks XMM-Newton spectra of the Seyfert 1 galaxy PG 0052+251.Our analysis reveals the presence of a warm absorber(WA)intrinsic to the source and the hot circumgalactic medium at zero redshift.The identified WA is inflowing toward the central black hole,with a velocity shift of■.The ionization parameter of the WA is■,showing strong O II and O III absorption lines,along with a significant absorption of the spectral continuum at?10?.The line of sight toward PG 0052+251 intersects the halo of M31 at an impact parameter of approximately 218 kpc.Several local(z~0)absorption lines,like O VII,O VIII,and Ne IX,were detected.The derived hydrogen column density of the local hot gas is 2.2–2.6σhigher than those estimated by several models of the Galactic hot halo,suggesting a likely contribution from the M31 halo.We also find two absorption features at24.305?and 21.410?,which are unlikely to be associated with the hot halos or the warm-hot intergalactic medium but imply the presence of an additional WA component with an outflow velocity of approximately-7000 km s^(-1).展开更多
According to the standard“inside-out”galaxy formation scenario,galaxies first form a dense core and then gradually assemble their outskirts.This implies that galaxies with similar central stellar mass densities migh...According to the standard“inside-out”galaxy formation scenario,galaxies first form a dense core and then gradually assemble their outskirts.This implies that galaxies with similar central stellar mass densities might have evolutionary links.We use the UVJ color-color diagram to select quiescent galaxies in the redshift interval from 0.5 to 2.5 and classify them into different subsamples based on their central stellar mass densities,stellar mass,morphological type and redshift.We then infer the intrinsic axis ratiosμ_(B/A) andμC/A of different subsamples based on the apparent axis ratio q distributions,where A,B,and C refer to,respectively,the major,intermediate and minor axis of a triaxial ellipsoidal model.We find that(1)massive quiescent galaxies have typical intrinsic shapes similarly close to thick oblate structures,withμ_(B/A)0.9,regardless of stellar mass,redshift,or central stellar mass densities,and(2)galaxies at higher redshift are systematically thinner than their lower-redshift counterparts,and(3)when splitting the sample into early type and late type with Sérsic indices,ETGs at higher redshift are slightly more prolate(smaller averageμ_(B/A))than those at lower redshift.Minor mergers of galaxies may have played important roles in the structural evolution of quiescent galaxies found in this work.展开更多
In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at ...In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at a constant velocity at early epochs,and the photosphere temperature increased slightly after reaching a minimum.These features are reminiscent of those of SN 2017dio.Based on the photosphere module that can describe the photosphere evolution of PTF11rka,we use the ^(56)Ni cascade decay model to fit its multiband light curves (LCs),finding that the model can well fit the photometric data.The derived ejecta mass and ^(56)Ni mass are respectively 8.76■ and 0.29-0.41■;the derived peak luminosity and the rise time of the theoretical bolometric LC of PTF11rka are ~8.24×10^(42)erg s^(-1) and ~35 days,respectively.Moreover,we find that the theoretical multiband LCs and the theoretical bolometric LC of PTF11rka do not show early-time excesses proposed in the literature.This indicates that additional energy sources (e.g.,the interaction between the ejecta and the circumstellar material)suggested to be responsible for the early-time excess can be neglected.展开更多
We estimate halo spins for H I-rich galaxies in the Arecibo Legacy Fast ALFA survey using a semi-analytic approach,examining the relationship between halo spin and stellar surface density.Our findings reveal an invers...We estimate halo spins for H I-rich galaxies in the Arecibo Legacy Fast ALFA survey using a semi-analytic approach,examining the relationship between halo spin and stellar surface density.Our findings reveal an inverse correlation in both low-and high-mass galaxy samples,with stellar surface density decreasing as halo spin increases.This trend highlights the pivotal role of halo spin in galaxy evolution and suggests a universal formation scenario:high-spin halos,accompanied by high-spin accreted gas,retain angular momentum,preventing gas from efficiently condensing in the galactic center and thus suppressing star formation.Consequently,weak feedback redistributes gas to the halo outskirts without significant expulsion.The shallower central gravitational potential in high-spin halos promotes outward stellar migration,leading to more extended stellar distributions and lower stellar surface densities.展开更多
The nature of progenitors of Type Ia supernovae(SNe Ia)and their explosion mechanism remains unclear.It has been suggested that SNe Ia may have resulted from thermonuclear explosions of hybrid carbon-oxygen-neon white...The nature of progenitors of Type Ia supernovae(SNe Ia)and their explosion mechanism remains unclear.It has been suggested that SNe Ia may have resulted from thermonuclear explosions of hybrid carbon-oxygen-neon white dwarfs(CONe WDs)when they grow in mass to approach the Chandrasekhar mass limit by accreting matter from a binary main-sequence(MS)companion.In this work,we combine the results of detailed binary evolution calculations with population synthesis models to investigate the rates and delay times of SNe Ia in the CONe WD+MS channel at a low metallicity environment of Z=0.0001.For a constant star formation rate of 5M_(⊙)yr^(−1),our calculations predict that the SN Ia rates in the CONe WD+MS channel at low metallicity of Z=0.0001 is about 0.11−3.89×10^(−4) yr^(−1).In addition,delay times in this channel cover a wide range of 0.05−2.5 Gyr.We further compare our results to those given by a previous study for the CONe WD+MS channel with a higher metallicity of Z=0.02 to explore the influence of metallicity on the results.We find that these two metallicity environments give a slight difference in rates and delay times of SNe Ia from the CONe WD+MS channel,although SNe Ia produced at a low metallicity environment of Z=0.0001 have relatively longer delay times.展开更多
We investigate the small-scale clustering of star-forming galaxies(SFGs) in the local universe, using both observational samples from the final data release of the Sloan Digital Sky Survey and IllustrisTNG300, one of ...We investigate the small-scale clustering of star-forming galaxies(SFGs) in the local universe, using both observational samples from the final data release of the Sloan Digital Sky Survey and IllustrisTNG300, one of the state-of-the-art hydrodynamic simulations of galaxy formation. We measure the projected two-point crosscorrelation function, wp(rp), for subsamples of SFGs with different specific star formation rates(sSFRs) and stellar masses(M*), with respect to reference samples of galaxies with early-type or late-type morphology. On scales smaller than ~100 kpc and at fixed M*, SFGs with higher sSFR are more strongly clustered, reflecting the interaction-induced central star formation found in previous studies. More importantly, the small-scale clusteringsSFR correlation is stronger when the reference sample is limited to late-type galaxies only. This confirms the previous finding that the enhancement of star formation in close pairs depends on the morphology of companion galaxies. These observational trends are broadly reproduced by IllustrisTNG300, indicating that current hydrodynamic simulations are capable of capturing the main recipes governing star formation in interacting/merging galaxies, although further work is needed to identify the exact physical processes involved.展开更多
Superluminous supernovae(SLSNe)and luminous supernovae(LSNe)exhibit extreme luminosities,which require additional energy supply mechanisms such as central engines or circumstellar interaction.In the centralengine scen...Superluminous supernovae(SLSNe)and luminous supernovae(LSNe)exhibit extreme luminosities,which require additional energy supply mechanisms such as central engines or circumstellar interaction.In the centralengine scenario,jets inject energy into the polar ejecta,modifying its evolution and shaping the explosion geometry.This study investigates the polarization signatures of jet-driven bipolar explosions in SLSNe/LSNe,where the asymmetric ejecta structure and differential photospheric evolution imprint distinct observational features.We develop a two-component ejecta model,consisting of fast-expanding polar ejecta(powered by jets)and slower equatorial ejecta.We find that polarization exhibits complex temporal evolution,where the ejecta geometry and flux asymmetry between the two regions jointly produce a double-peaked feature.In addition,the line opacity in the polar region further enhances the wavelength dependence of the polarization.Spectropolarimetric observations,particularly during early phases,can constrain the geometry and energy sources of SLSNe/LSNe,advancing our understanding of their explosion mechanisms.展开更多
The effective field theory of dark energy(EFTofDE)provides a systematic and model-independent framework to study dark energy(DE)and modified gravity(MG)with one additional scalar degree of freedom.It can describe the ...The effective field theory of dark energy(EFTofDE)provides a systematic and model-independent framework to study dark energy(DE)and modified gravity(MG)with one additional scalar degree of freedom.It can describe the known models such as Quintessence,k-essence,DGP,f(R),and Horndeski theories.In this work,we update constraints on EFTofDE by utilizing the most up-to-date public data including the Baryon Acoustic Oscillations(DESI DR2),CMB(Planck 2018 and ACT DR6),SNIa(DESY5),weak lensing(DESY3)and full-shape galaxy power(BOSS DR 12).We find with the ACDM background,general relativity(GR)is favored by the data,while with the w_(0)w_(a)CDM background,slight modification to GR is favored,but still consistent with GR within 1.5σ.We also find the significance level for dynamical DE is greatly reduced within EFTofDE compared to within GR,indicating the degeneracy between dynamical DE and MG.展开更多
Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a compreh...Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120,through re-analyzing its six XMMNewton observations taken between 2003 and 2014.We find a clear“softer-when-brighter”trend in the 2-10 keV power-law component over long timescales,with this trend being timescale dependent,as it is much weaker on shorter timescales,similar to that previously detected in NGC 4051.Notably,a rare“harder-when-brighter”trend is observed during one exposure,indicating dynamic changes in the spectral variability behavior of the power-law component.This exceptional exposure,with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of~2 keV,suggests intricate variations in the thermal Comptonization processes within the corona.Furthermore,when the data below 2 keV are included,we identify that the soft excess component adds significant complexity to the spectral variability,such as evidenced by a transition from“harder-when-brighter”to“softer-when-brighter”during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.展开更多
Multiband afterglow observations of gamma-ray bursts(GRBs)are important for studying the central engine.GRB 201223A is a GRB with prompt optical detection by GWAC.Here we report on the early optical afterglow of GRB 2...Multiband afterglow observations of gamma-ray bursts(GRBs)are important for studying the central engine.GRB 201223A is a GRB with prompt optical detection by GWAC.Here we report on the early optical afterglow of GRB 201223A detected by NEXT(only 2.8 minutes after the Swift/BAT trigger),which smoothly connects the prompt optical emission and the afterglow phase.Utilizing Amati diagrams and considering the detection of afterglow emission in the Swift u-band,we suggest a redshift range of 0.26–1.85.Based on our optical data and combined with early optical observation from GWAC and early X-ray data from Swift/XRT,a multiband fitting is performed using PyFRS,and we obtain the best afterglow parameters(assuming a redshift of z=1.0):=5.01+10/_(1.70)^(1.91)×^(54)erg,G=-426.58+_(138.18)/^(148.86),θj=-25.98+_(-10.54)^/(9.67)deg,=-n0=0.30+_(-0.26)^(+3.78)cm^(−3),=-p2.32+_(-0.01)/^(+0.01),εe=-3.31+_(-0.86)/^(+1.59)×10^(-5),εB=-3.47+_(-2.62)/^(+4.12)×10^(-1).The late-time X-ray shows a re-brightening,indicating late-time central engine activities.After comparing the leading two central engine models,i.e.,magnetar model and hyperaccreting black hole model,we find that the fallback accretion onto a newborn black hole provides a better explanation for the X-ray re-brightening with fallback accretion rate Mp≈2.76×10^(-9)M⊙s^(-1)and the total fallback accreted mass Mfb≈1.41×10^(−6)M⊙.展开更多
文摘Stars getting close enough to black holes(BHs)can be torn apart by strong tidal forces,producing electromagnetic flares.To date,more than 100 tidal disruption events(TDEs)have been observed,each involving invariably normal gaseous stars whose debris falls onto the BH,sustaining the flares over years.White dwarfs(WDs),which are the most prevalent compact stars and a million times denser-and therefore tougher-than gaseous stars,can only be disrupted by intermediate-mass black holes(IMBHs)of 10^(2)–10^(5) solar masses.WD-TDEs are considered to generate more powerful and short-lived flares,but their evidence has been lacking.Here we report observations of a fast and luminous X-ray transient EP250702a detected by Einstein Probe.Its one-day-long X-ray peak as luminous as 10^(47−49) erg s^(−1) showed strong recurrent flares with hard spectra extending to several tens of MeV gamma-rays,as detected by Fermi/GBM and Konus-Wind,indicating relativistic jet emission.The jet's X-rays dropped sharply from 3×10^(49) erg s^(−1) to around 1044 erg s^(−1) within 20 days(10 days in the source rest frame).These characteristics are inconsistent with any previously known transient phenomena.We suggest that this fast-evolving event over the unprecedentedly short timescale arises likely from disruption of a WD by an IMBH.At late times,a soft component progressively dominates the X-ray spectrum,reaching a luminosity as high as 1044 erg s^(−1),which is consistent with being extreme super-Eddington emission from an accretion disk expected to form in an IMBH-WD TDE.WD-TDEs open a new window for investigating the elusive IMBHs and their surrounding stellar environments,and they are prime sources of gravitational waves in the band of space-based interferometers.
文摘I reminisce on my early life in Section 1;on my education in Sections 2 and 3;on the years at Princeton as a research astronomer in Section 4;on the years on the faculty at Chicago in Section 5;on research on Diffuse Interstellar Bands(DIBs) in Section 6;on construction of the 3.5 m telescope at Apache Point Observatory(APO)in Section 7;on work on the Sloan Digital Sky Survey(SDSS) in Section 8;on work in public education in Chicago in Section 9;and on my travels in Section 10. My main science research is of an observational nature,concerning Galactic and intergalactic interstellar gas. Highlights for me included my work on the orbiting telescope Copernicus, including the discovery of interstellar deuterium;early observations of absorption associated with fivetimes ionized oxygen;and discoveries concerning the phases of gas in the local interstellar medium, based on previously unobservable interstellar UV spectral lines. With other instruments and collaborations, I extended interstellar UV studies to the intergalactic cool gas using quasi-stellar object QSO absorption lines redshifted to the optical part of the spectrum;provided a better definition of the emission and morphological character of the source of absorption lines in QSO spectra;and pursued the identification of the unidentified DIBs. For several of these topics, extensive collaborations with many scientists were essential over many years. The conclusions developed slowly, as I moved from being a graduate student at Chicago, to a research scientist position at Princeton and then to a faculty position at Chicago. At each stage of life, I was exposed to new technologies adaptable to my science and to subsequent projects. From high school days, I encountered several management opportunities which were formative. I have been extremely fortunate both in scientific mentors I had and in experimental opportunities I encountered.
基金supported by the National Natural Science Foundation of China(NSFC,grants No.12393852)the Yunnan Fundamental Research Projects(grant No.202501AS070068)the Program of Graduate Research and Innovation Fund Project of Yunnan University(KC-24249493).
文摘This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interstellar medium(ISM) configurations: a uniform density distribution and a medium with a sharp density discontinuity. Compared to the uniform density distribution, the ISM with this density discontinuity better reflects the actual conditions and explains the overall morphological characteristics of specific types of SNR-PWN composite systems. These systems exhibit asymmetries, such as an SNR shell with differing radii or an inner PWN located nearer to the shell on one side. The simulation results suggest that the density discontinuity in the ISM is a contributing factor to both the shell asymmetry and the PWN displacement. Specifically, this density variation directly causes the inconsistency in the forward shock speeds of the SNR between high and low density regions, resulting in discrepancies in the shell layer radii. Furthermore, the asymmetric morphology of the PWN and its positional offset emerge through interactions with the reverse shock. The PWN tends to shift toward the SNR shell on one side. The greater the density jump in the background field, the more pronounced the shell radius differences and PWN offset become.
基金the support of the DST-ANRF(Anusandhan National Research Foundation)Core Research Grant project,Government of India。
文摘Based on the RXTE observations of Sco X-1,we identified a clear dichotomy in the behavior of its X-ray crosscorrelation functions(CCFs)which is possibly associated with two different radio jet ejection events.Twenty six observations display asymmetric CCFs of low correlation coefficients with soft or hard delays of a few hundred seconds along with no oscillation feature in the power density spectrum associated with horizontal branch/hard apex.All the observations belonging to NB/FB have symmetric CCFs with NBO/NBO+HBO/FBO in the PDS.Based on radio observations,two different types of jets were associated with Sco X-1 i.e.,ballistic radio jets and an ultra-relativistic flow(URF).We noted that asymmetric CCFs with delays were connected with ballistic or lobe radio jets and symmetric CCFs with URFs in Sco X-1.We interpret these findings as evidence of two different states of the inner accretion disk.We propose that the launch of a ballistic jet triggers significant instability within the inner accretion region,likely the boundary layer and corona.This disruption explains the observed delays in the CCF and simultaneously quenches the conditions required for coherent oscillations,leaving only flat-topped noise in the PDS.We constrain the size of this unstable region in the inner region of accretion to be~10-40 km.In contrast,the symmetric CCFs and persistent oscillations(NBO/NBO+HBO)during URF events suggest a more stable,steady accretion flow.Although connecting the URF to a specific oscillation is difficult,its strong association with the NB phase of variation suggests a common underlying physical mechanism.Therefore,the CCF's asymmetry acts as a powerful diagnostic,linking ballistic jets to disk instability and URFs to a stable accretion state.Various physical scenarios are discussed to understand the connection among X-ray CCFs,PDS,and radio ejections in Sco X-1.
基金supported by NSFC grant No.12393852the Yunnan Fundamental Research Project(grant No.202501AS070068).
文摘Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion model to investigate the mechanism by which high-energy protons escaping from SNRs interact with dense MCs through proton–proton interactions to produce high-energyγ-rays.Using the W51 complex,a typical star-forming region,as a research sample,we analyze the production and propagation characteristics of γ-rays.By employing the Exponential Cutoff Power-Law model and the Markov Chain Monte Carlo method,we fit theγ-ray observational data of W51C,successfully constraining the key physical parameters.Additionally,we systematically search for 1LHAASO sources spatially coincident with SNR-MC systems to explore the potential origins of ultra-high-energy(UHE) γ-ray sources.The results indicate that the radiation characteristics of the UHE γ-ray sources are highly consistent with the SNR-MC systems,further supporting their candidacy as PeVatrons in the Galaxy.
基金supported by the National Key R&D Program(2024YFA1611700)the National Natural Science Foundation of China(grant Nos.12133003,12494571 and 11963001)supported by the Guangxi Talent Program(“Highland of Innovation Talents”)and Program of Bagui Scholars(LHJ)。
文摘SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56)Ni model to fit the multiband light curves(LCs)of SN 2014av.For the CSI and CSI plus^(56)Ni models,we assume that the CSM is a constant density shell(“shell”)or a steady-state stellar wind(“wind”)with density∝r-2.We find that both the^(56)Ni and CSI models fail to fit the multiband LCs of SN 2014av,while the CSI plus^(56)Ni model can account for the LCs.In the last scenario,the LCs around the peaks were mainly powered by the CSI,while the flattening of the LCs was mainly powered by the radioactive decay of^(56)Ni.For the wind case,the derived mass-loss rate of the progenitor is≈20.5-205.5 M_(⊙)yr^(-1),whose lower limit is significantly larger than the upper limit of normal stellar winds,and comparable the upper limit of hyper-winds.Hence,we suggest that the wind case is disfavored.For the shell case,the best-fitting values of the ejecta,^(56)Ni,and the CSM are2.29 M_(⊙),0.09 M_(⊙),and 5.00 M_(⊙),respectively.Provided the velocity of the CSM shell is 100-1000 km s^(-1),we infer that the shell might be expelled≈0.49-5.20 yr before the SN exploded.
基金supported by the National Key R&D Program of China under grants 2023YFA1607901 and 2021YFA1600401the National Natural Science Foundation of China under grants 12433007, 11925301, 12033006, 12221003, and 12263003+1 种基金the fellowship of China National Postdoctoral Program for Innovation Talents under grant BX20230020the science research grants from the China Manned Space Project with No. CMS-CSST-2025-A13。
文摘We present 17 cataclysmic variables(CVs) obtained from the crossmatch between the Sloan Digital Sky Survey(SDSS) and eROSITA Final Equatorial Depth Survey(eFEDS),including eight known CVs before eFEDS and nine identified from eFEDS.The photometric periods of four CVs are derived from the Zwicky Transient Facility and Catalina Real-Time Transient Survey.We focus on two CVs,SDSS J084309.3-014858 and SDSS J093555.0+042916,and confirm that their photometric periods correspond to the orbital periods by fitting the radial velocity curves.Furthermore,by the combination of the Gaia distance,the spectral energy distribution,and the variations of Ha emission lines,the masses of the white dwarf and the visible star can be well constrained.
基金funded by the National Natural Science Foundation of China(NSFC,grant Nos.12090040,12090044,12133001,and 12422303)Beijing Natural Science Foundation(no.1242016)+2 种基金the science research grants from the China Manned Space Projectsupported by the Talents Program(24CE-YS-08)the Popular Science Project(24CD012)of the Beijing Academy of Science and Technology.
文摘We present systematic identifications of supergiants in M31/M33 based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST)spectroscopic survey.Radial velocities of nearly 5000 photometrically selected M31/M33 supergiant candidates have been properly derived from the qualified spectra released in LAMOST DR10.By comparing their radial velocities with those predicted from the rotation curve of M31,as well as utilizing Gaia astrometric measurements to exclude foreground contaminations,199 supergiant members in M31,including 168“Rank1”and 31“Rank2,”have been successfully identified.This sample contains 62 blue supergiants(BSGs,all“Rank1”),134 yellow supergiants(YSGs,103“Rank1”and 31“Rank2”)and three red supergiants(RSGs,all“Rank1”).For M33,we identify 84 supergiant members(56“Rank1”and 28“Rank2”),which include 28 BSGs(all“Rank1”),53 YSGs(25“Rank1”and 28“Rank2”)and three RSGs(all“Rank1”).So far,this is one of the largest supergiant samples of M31/M33 with full optical wavelength coverage(3700<λ<9100Å).This sample is valuable for understanding star formation and stellar evolution under different environments.
基金support from the National Key R&D Program of China(2022YFF0503401)the China Manned Space Project with No.CMS-CSST-2021-A05the National Natural Science Foundation of China(12225301)。
文摘Slitless spectroscopy onboard space telescopes is a powerful tool to detect emission-line objects such as emissionline galaxies(ELGs)and quasars.In this work,we present a study of ELGs observed with slitless spectroscopy by the Hubble Space Telescope(HST)in a deep field of~44 arcmin^(2).This is one of the deepest HST fields with a wealth of imaging and spectral data.In particular,previous VLT/MUSE observations have covered this field and identified a large number of ELGs.We reduce the HST spectra using the latest pipeline with a forward modeling algorithm and construct a sample of ELGs.By comparing with the MUSE spectra,we characterize our ELG detection in the HST spectra,including the impact of the line flux,line width,signal-to-noise ratio,etc.We find that the morphological broadening may affect the detection of ELGs,such that more compact sources are easier to be detected in slitless spectra.We discuss its implications to future slitless spectroscopic surveys that will be carried out by the China Space Station Telescope(CSST)and find that the CSST slitless spectroscopy has a capability comparable to that of HST in terms of the detection of emission lines.
基金supported in part by the National Natural Science Foundation of China through Grant 11821303by the Ministry of Science and Technology of China through Grant 2018YFA0404502+1 种基金support from the China Scholarship Councilthe nancial support of the GA?R EXPRO grant No.21-13491X.
文摘Previous X-ray and optical studies of the galaxy cluster pair A222/223 suggested the possible presence of a=lamentary structure connecting the two clusters,a result that appears to be supported by subsequent weak-lensing analyses.This=lament has been reported to host a primordial warm-hot intergalactic medium,which existed prior to being heated by the interactions of the clusters.In this study,we made an attempt to examine the reported emission feature with data from an archival Suzaku observation,taking advantage of its low detector background.Because the emission is expected to be very weak,we=rst carefully examined all potential sources of“contamination,”and then modeled the residual emission.Due to large uncertainties,unfortunately,our results can neither con=rm the presence of the reported emission feature nor rule it out.We discuss the sources of uncertainties.
基金supported by the National Natural Science Foundation of China under Nos.11890692,12133008 and 12221003We acknowledge the science research grant from the China Manned Space Project with No.CMS-CSST-2021-A04.
文摘We analyze the absorption features in the public 73 ks XMM-Newton spectra of the Seyfert 1 galaxy PG 0052+251.Our analysis reveals the presence of a warm absorber(WA)intrinsic to the source and the hot circumgalactic medium at zero redshift.The identified WA is inflowing toward the central black hole,with a velocity shift of■.The ionization parameter of the WA is■,showing strong O II and O III absorption lines,along with a significant absorption of the spectral continuum at?10?.The line of sight toward PG 0052+251 intersects the halo of M31 at an impact parameter of approximately 218 kpc.Several local(z~0)absorption lines,like O VII,O VIII,and Ne IX,were detected.The derived hydrogen column density of the local hot gas is 2.2–2.6σhigher than those estimated by several models of the Galactic hot halo,suggesting a likely contribution from the M31 halo.We also find two absorption features at24.305?and 21.410?,which are unlikely to be associated with the hot halos or the warm-hot intergalactic medium but imply the presence of an additional WA component with an outflow velocity of approximately-7000 km s^(-1).
基金support from the National Key Research and Development Program of China (grant No.2023YFA1608100)from the National Natural Science Foundation of China(NSFC,grant Nos.12122303 and 11973039)+2 种基金supported by the China Manned Space Project (grant Nos.CMSCSST-2021-B02 and CMS-CSST-2021-A07)support from the CAS Pioneer Hundred Talents Programthe Cyrus Chun Ying Tang Foundations
文摘According to the standard“inside-out”galaxy formation scenario,galaxies first form a dense core and then gradually assemble their outskirts.This implies that galaxies with similar central stellar mass densities might have evolutionary links.We use the UVJ color-color diagram to select quiescent galaxies in the redshift interval from 0.5 to 2.5 and classify them into different subsamples based on their central stellar mass densities,stellar mass,morphological type and redshift.We then infer the intrinsic axis ratiosμ_(B/A) andμC/A of different subsamples based on the apparent axis ratio q distributions,where A,B,and C refer to,respectively,the major,intermediate and minor axis of a triaxial ellipsoidal model.We find that(1)massive quiescent galaxies have typical intrinsic shapes similarly close to thick oblate structures,withμ_(B/A)0.9,regardless of stellar mass,redshift,or central stellar mass densities,and(2)galaxies at higher redshift are systematically thinner than their lower-redshift counterparts,and(3)when splitting the sample into early type and late type with Sérsic indices,ETGs at higher redshift are slightly more prolate(smaller averageμ_(B/A))than those at lower redshift.Minor mergers of galaxies may have played important roles in the structural evolution of quiescent galaxies found in this work.
基金supported by the National Natural Science Foundation of China (NSFC,grant Nos.12494571,11963001 and 12133003)supported by the Program of Bagui Scholars (LHJ)。
文摘In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at a constant velocity at early epochs,and the photosphere temperature increased slightly after reaching a minimum.These features are reminiscent of those of SN 2017dio.Based on the photosphere module that can describe the photosphere evolution of PTF11rka,we use the ^(56)Ni cascade decay model to fit its multiband light curves (LCs),finding that the model can well fit the photometric data.The derived ejecta mass and ^(56)Ni mass are respectively 8.76■ and 0.29-0.41■;the derived peak luminosity and the rise time of the theoretical bolometric LC of PTF11rka are ~8.24×10^(42)erg s^(-1) and ~35 days,respectively.Moreover,we find that the theoretical multiband LCs and the theoretical bolometric LC of PTF11rka do not show early-time excesses proposed in the literature.This indicates that additional energy sources (e.g.,the interaction between the ejecta and the circumstellar material)suggested to be responsible for the early-time excess can be neglected.
基金supports from the CAS Pioneer Hundred Talents Program (Category B)the National Natural Science Foundation of China (NSFC, grant No. 12273037)+2 种基金Funds of the Double First-Class Initiativesupported by the research grants from the China Manned Space Project (the second-stage CSST science projects:“Investigation of small-scale structures in galaxies and forecasting of observations” and “CSST study on specialized galaxies in ultraviolet and multi-band”)supported by the China Postdoctoral Science Foundation grant No. 2024M763213
文摘We estimate halo spins for H I-rich galaxies in the Arecibo Legacy Fast ALFA survey using a semi-analytic approach,examining the relationship between halo spin and stellar surface density.Our findings reveal an inverse correlation in both low-and high-mass galaxy samples,with stellar surface density decreasing as halo spin increases.This trend highlights the pivotal role of halo spin in galaxy evolution and suggests a universal formation scenario:high-spin halos,accompanied by high-spin accreted gas,retain angular momentum,preventing gas from efficiently condensing in the galactic center and thus suppressing star formation.Consequently,weak feedback redistributes gas to the halo outskirts without significant expulsion.The shallower central gravitational potential in high-spin halos promotes outward stellar migration,leading to more extended stellar distributions and lower stellar surface densities.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(grant Nos.XDB1160303,XDB1160000)the National Natural Science Foundation of China(NSFC,Nos.12288102,12333008,12090040/1,11873016,11973080,and 11803030)+3 种基金the National Key R&D Program of China(Nos.2021YFA1600403,2021YFA1600401 and 2021YFA1600400)the Chinese Academy of Sciences(CAS),the Yunnan Ten Thousand Talents Plan–Young&Elite Talents Project,and the CAS“Light of West China”Program,the International Centre of Supernovae,Yunnan Key Laboratory(No.202302AN360001)the Yunnan Fundamental Research Projects(grant Nos.202401BC070007,202201BC070003,and 202001AW070007)the“Yunnan Revitalization Talent Support Program”—Science&Technology Champion Project and Yunling Scholar Project(No.202305AB350003).
文摘The nature of progenitors of Type Ia supernovae(SNe Ia)and their explosion mechanism remains unclear.It has been suggested that SNe Ia may have resulted from thermonuclear explosions of hybrid carbon-oxygen-neon white dwarfs(CONe WDs)when they grow in mass to approach the Chandrasekhar mass limit by accreting matter from a binary main-sequence(MS)companion.In this work,we combine the results of detailed binary evolution calculations with population synthesis models to investigate the rates and delay times of SNe Ia in the CONe WD+MS channel at a low metallicity environment of Z=0.0001.For a constant star formation rate of 5M_(⊙)yr^(−1),our calculations predict that the SN Ia rates in the CONe WD+MS channel at low metallicity of Z=0.0001 is about 0.11−3.89×10^(−4) yr^(−1).In addition,delay times in this channel cover a wide range of 0.05−2.5 Gyr.We further compare our results to those given by a previous study for the CONe WD+MS channel with a higher metallicity of Z=0.02 to explore the influence of metallicity on the results.We find that these two metallicity environments give a slight difference in rates and delay times of SNe Ia from the CONe WD+MS channel,although SNe Ia produced at a low metallicity environment of Z=0.0001 have relatively longer delay times.
基金supported by the National Key R&D Program of China through grant 2020YFC2201400the NSFC Key Program through grants 11733010 and 11333008.
文摘We investigate the small-scale clustering of star-forming galaxies(SFGs) in the local universe, using both observational samples from the final data release of the Sloan Digital Sky Survey and IllustrisTNG300, one of the state-of-the-art hydrodynamic simulations of galaxy formation. We measure the projected two-point crosscorrelation function, wp(rp), for subsamples of SFGs with different specific star formation rates(sSFRs) and stellar masses(M*), with respect to reference samples of galaxies with early-type or late-type morphology. On scales smaller than ~100 kpc and at fixed M*, SFGs with higher sSFR are more strongly clustered, reflecting the interaction-induced central star formation found in previous studies. More importantly, the small-scale clusteringsSFR correlation is stronger when the reference sample is limited to late-type galaxies only. This confirms the previous finding that the enhancement of star formation in close pairs depends on the morphology of companion galaxies. These observational trends are broadly reproduced by IllustrisTNG300, indicating that current hydrodynamic simulations are capable of capturing the main recipes governing star formation in interacting/merging galaxies, although further work is needed to identify the exact physical processes involved.
基金supported by the National Natural Science Foundation of China(Projects 12373040 and 12021003)the National SKA Program of China(2022SKA0130100)the Fundamental Research Funds for the Central Universities.
文摘Superluminous supernovae(SLSNe)and luminous supernovae(LSNe)exhibit extreme luminosities,which require additional energy supply mechanisms such as central engines or circumstellar interaction.In the centralengine scenario,jets inject energy into the polar ejecta,modifying its evolution and shaping the explosion geometry.This study investigates the polarization signatures of jet-driven bipolar explosions in SLSNe/LSNe,where the asymmetric ejecta structure and differential photospheric evolution imprint distinct observational features.We develop a two-component ejecta model,consisting of fast-expanding polar ejecta(powered by jets)and slower equatorial ejecta.We find that polarization exhibits complex temporal evolution,where the ejecta geometry and flux asymmetry between the two regions jointly produce a double-peaked feature.In addition,the line opacity in the polar region further enhances the wavelength dependence of the polarization.Spectropolarimetric observations,particularly during early phases,can constrain the geometry and energy sources of SLSNe/LSNe,advancing our understanding of their explosion mechanisms.
基金supported by the National Key R&D Program of China grant No.2022YFF0503404 and No.2021YFC2203100by the National Natural Science Foundation of China(NSFC,grant Nos.12173036 and 11773024)+2 种基金by the China Manned Space Program with grant No.CMS-CSST-2025-A04by Cyrus Chun Ying Tang Foundationsby the 111 Project for"Observational and Theoretical Research on Dark Matter and Dark Energy"(B23042)。
文摘The effective field theory of dark energy(EFTofDE)provides a systematic and model-independent framework to study dark energy(DE)and modified gravity(MG)with one additional scalar degree of freedom.It can describe the known models such as Quintessence,k-essence,DGP,f(R),and Horndeski theories.In this work,we update constraints on EFTofDE by utilizing the most up-to-date public data including the Baryon Acoustic Oscillations(DESI DR2),CMB(Planck 2018 and ACT DR6),SNIa(DESY5),weak lensing(DESY3)and full-shape galaxy power(BOSS DR 12).We find with the ACDM background,general relativity(GR)is favored by the data,while with the w_(0)w_(a)CDM background,slight modification to GR is favored,but still consistent with GR within 1.5σ.We also find the significance level for dynamical DE is greatly reduced within EFTofDE compared to within GR,indicating the degeneracy between dynamical DE and MG.
基金supported by the National Natural Science Foundation of China (NSFC,grant Nos.12033006,12192221,and 123B2042)the Cyrus Chun Ying Tang Foundationsfunded by ESA Member States and NASA
文摘Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120,through re-analyzing its six XMMNewton observations taken between 2003 and 2014.We find a clear“softer-when-brighter”trend in the 2-10 keV power-law component over long timescales,with this trend being timescale dependent,as it is much weaker on shorter timescales,similar to that previously detected in NGC 4051.Notably,a rare“harder-when-brighter”trend is observed during one exposure,indicating dynamic changes in the spectral variability behavior of the power-law component.This exceptional exposure,with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of~2 keV,suggests intricate variations in the thermal Comptonization processes within the corona.Furthermore,when the data below 2 keV are included,we identify that the soft excess component adds significant complexity to the spectral variability,such as evidenced by a transition from“harder-when-brighter”to“softer-when-brighter”during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.
基金supported by the MINECO/FEDER through grant AyA2017-84089.7the science research grants from the China Manned Space Project with NO.CMSCSST-2021-A13CMS-CSST-2021-B11.W.H.Lei acknowledges support by the National Key R&D Program of China(No.2020YFC2201400)。
文摘Multiband afterglow observations of gamma-ray bursts(GRBs)are important for studying the central engine.GRB 201223A is a GRB with prompt optical detection by GWAC.Here we report on the early optical afterglow of GRB 201223A detected by NEXT(only 2.8 minutes after the Swift/BAT trigger),which smoothly connects the prompt optical emission and the afterglow phase.Utilizing Amati diagrams and considering the detection of afterglow emission in the Swift u-band,we suggest a redshift range of 0.26–1.85.Based on our optical data and combined with early optical observation from GWAC and early X-ray data from Swift/XRT,a multiband fitting is performed using PyFRS,and we obtain the best afterglow parameters(assuming a redshift of z=1.0):=5.01+10/_(1.70)^(1.91)×^(54)erg,G=-426.58+_(138.18)/^(148.86),θj=-25.98+_(-10.54)^/(9.67)deg,=-n0=0.30+_(-0.26)^(+3.78)cm^(−3),=-p2.32+_(-0.01)/^(+0.01),εe=-3.31+_(-0.86)/^(+1.59)×10^(-5),εB=-3.47+_(-2.62)/^(+4.12)×10^(-1).The late-time X-ray shows a re-brightening,indicating late-time central engine activities.After comparing the leading two central engine models,i.e.,magnetar model and hyperaccreting black hole model,we find that the fallback accretion onto a newborn black hole provides a better explanation for the X-ray re-brightening with fallback accretion rate Mp≈2.76×10^(-9)M⊙s^(-1)and the total fallback accreted mass Mfb≈1.41×10^(−6)M⊙.
