Inclusive Intermediate-Mass Fragments（IMFs）are measured at seven angles for the<sup>40</sup>Ar+Ag reaction at 25 MeV/u.The energy spectra of IMF from Li to F are obtained.A thermal mod-el with the same p...Inclusive Intermediate-Mass Fragments（IMFs）are measured at seven angles for the<sup>40</sup>Ar+Ag reaction at 25 MeV/u.The energy spectra of IMF from Li to F are obtained.A thermal mod-el with the same parameters well fits the energy spectra of all IMFs at backward angles.These IMFs areevaporated from hot nuclei formed in an incomplete fusion process.The angular distribution and Z distri-bution are calculated with the statistical code GEMINI.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
We propose a dynamical description of the ^(136)Xe + p spallation at 1000 MeV/nucleon with the aim of probing the mechanism which rules the production of intermediate-mass fragments(IMF). The isospin-dependent quantum...We propose a dynamical description of the ^(136)Xe + p spallation at 1000 MeV/nucleon with the aim of probing the mechanism which rules the production of intermediate-mass fragments(IMF). The isospin-dependent quantum molecular dynamics(IQMD) model is used to describe the dynamical process of spallation until hot fragments with excitation energy less than a certain value E_(stop) are formed. The statistical code GEMINI is applied to simulate the light-particle evaporation from hot fragments. It is found that IMF production is well described by the model when E_(stop)= 2 MeV/nucleon is used. Comparison of the calculated mean neutron-to-proton ratio and the experimental data indicates that E_(stop) should be 3 MeV/nucleon.展开更多
基金①The project supported by the National Natural Science Foundation of China
文摘Inclusive Intermediate-Mass Fragments（IMFs）are measured at seven angles for the<sup>40</sup>Ar+Ag reaction at 25 MeV/u.The energy spectra of IMF from Li to F are obtained.A thermal mod-el with the same parameters well fits the energy spectra of all IMFs at backward angles.These IMFs areevaporated from hot nuclei formed in an incomplete fusion process.The angular distribution and Z distri-bution are calculated with the statistical code GEMINI.
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(11405278)
文摘We propose a dynamical description of the ^(136)Xe + p spallation at 1000 MeV/nucleon with the aim of probing the mechanism which rules the production of intermediate-mass fragments(IMF). The isospin-dependent quantum molecular dynamics(IQMD) model is used to describe the dynamical process of spallation until hot fragments with excitation energy less than a certain value E_(stop) are formed. The statistical code GEMINI is applied to simulate the light-particle evaporation from hot fragments. It is found that IMF production is well described by the model when E_(stop)= 2 MeV/nucleon is used. Comparison of the calculated mean neutron-to-proton ratio and the experimental data indicates that E_(stop) should be 3 MeV/nucleon.
