A large-scale view of the magnetospheric cusp is expected to be obtained by the Soft X-ray Imager(SXI)onboard the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE).However,it is challenging to trace the three-d...A large-scale view of the magnetospheric cusp is expected to be obtained by the Soft X-ray Imager(SXI)onboard the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE).However,it is challenging to trace the three-dimensional cusp boundary from a two-dimensional X-ray image because the detected X-ray signals will be integrated along the line of sight.In this work,a global magnetohydrodynamic code was used to simulate the X-ray images and photon count images,assuming an interplanetary magnetic field with a pure Bz component.The assumption of an elliptic cusp boundary at a given altitude was used to trace the equatorward and poleward boundaries of the cusp from a simulated X-ray image.The average discrepancy was less than 0.1 RE.To reduce the influence of instrument effects and cosmic X-ray backgrounds,image denoising was considered before applying the method above to SXI photon count images.The cusp boundaries were reasonably reconstructed from the noisy X-ray image.展开更多
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
The main scientific payload of Macao Science Satellite-1B is a solar soft X-ray detection unit.To obtain an accurate solar X-ray spectrum,we have designed low-noise,high-throughput electronics.Solar radiation is detec...The main scientific payload of Macao Science Satellite-1B is a solar soft X-ray detection unit.To obtain an accurate solar X-ray spectrum,we have designed low-noise,high-throughput electronics.Solar radiation is detected using a low-leakage silicon drift detector(SDD),which is cooled to-30℃.The SDD output is processed using two parallel shaping amplifiers with peaking times of 315 ns and 65 ns.The amplifiers are designed using two-pole multiple-feedback active low-pass filters optimized to achieve a Bessel response.The differential output of the shaping amplifier generates a bipolar signal.The phase of the differential stage is tuned to ensure zero crossing corresponding to the peak of the shaping amplifier.A high-speed switch is inserted between the shaping amplifier and the peak-hold capacitor,and the peak value is maintained by turning off the switch.Fast and slow peak-hold circuits share a common ADC via time-division multiplexing.Both peak values are sampled for space-background rejection.Traditional pile-up detection methods cannot distinguish pulses that overlap in a fast channel.In this study,the differential of the“fast shaping”is selected,enabling the distinction of events separated by as little as 65ns,which is crucial for solar flare detection.The energy resolution is measured to be 138 eV at 5.90 keV.The centroid drift is less than 3.6 eV between-5℃ and 20℃.Compared with other solar X-ray instruments,this study demonstrates improved energy resolution with a lower peaking time,indicating a higher solar flare detection capability.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
基金funded by the National Natural Science Foundation of China(NNSFC)under Grant Numbers 42322408,42188101,and 42441809Additional support was provided by the Climbing Program of the National Space Science Center(NSSC,Grant No.E4PD3005)as well as the Specialized Research Fund for State Key Laboratories of China.
文摘A large-scale view of the magnetospheric cusp is expected to be obtained by the Soft X-ray Imager(SXI)onboard the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE).However,it is challenging to trace the three-dimensional cusp boundary from a two-dimensional X-ray image because the detected X-ray signals will be integrated along the line of sight.In this work,a global magnetohydrodynamic code was used to simulate the X-ray images and photon count images,assuming an interplanetary magnetic field with a pure Bz component.The assumption of an elliptic cusp boundary at a given altitude was used to trace the equatorward and poleward boundaries of the cusp from a simulated X-ray image.The average discrepancy was less than 0.1 RE.To reduce the influence of instrument effects and cosmic X-ray backgrounds,image denoising was considered before applying the method above to SXI photon count images.The cusp boundaries were reasonably reconstructed from the noisy X-ray image.
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.
基金supported by the National Natural Science Foundation of China(No.12035020)National Key Scientific Instrument and Equipment Development Projects of China(No.42327802).
文摘The main scientific payload of Macao Science Satellite-1B is a solar soft X-ray detection unit.To obtain an accurate solar X-ray spectrum,we have designed low-noise,high-throughput electronics.Solar radiation is detected using a low-leakage silicon drift detector(SDD),which is cooled to-30℃.The SDD output is processed using two parallel shaping amplifiers with peaking times of 315 ns and 65 ns.The amplifiers are designed using two-pole multiple-feedback active low-pass filters optimized to achieve a Bessel response.The differential output of the shaping amplifier generates a bipolar signal.The phase of the differential stage is tuned to ensure zero crossing corresponding to the peak of the shaping amplifier.A high-speed switch is inserted between the shaping amplifier and the peak-hold capacitor,and the peak value is maintained by turning off the switch.Fast and slow peak-hold circuits share a common ADC via time-division multiplexing.Both peak values are sampled for space-background rejection.Traditional pile-up detection methods cannot distinguish pulses that overlap in a fast channel.In this study,the differential of the“fast shaping”is selected,enabling the distinction of events separated by as little as 65ns,which is crucial for solar flare detection.The energy resolution is measured to be 138 eV at 5.90 keV.The centroid drift is less than 3.6 eV between-5℃ and 20℃.Compared with other solar X-ray instruments,this study demonstrates improved energy resolution with a lower peaking time,indicating a higher solar flare detection capability.
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.
