We present a comprehensive analysis of AstroSat/LAXPC data of the second spin-up and second spin-down phases of the persistent X-ray pulsar 4U 1626-67.Flares followed by a broad dip are detected in the spin-up observa...We present a comprehensive analysis of AstroSat/LAXPC data of the second spin-up and second spin-down phases of the persistent X-ray pulsar 4U 1626-67.Flares followed by a broad dip are detected in the spin-up observations.The pulse profiles changed from a shoulder-like structure to a broad sinusoidal shape as the source underwent a torque reversal from spin-up to spin-down.Energy-resolved pulse profiles in lower energies showed a double-horned profile in the spin-up state and a flat top with multiple peaks in the spin-down state.Regardless of the torque state,the pulse profiles exhibit a broad single-peaked shape at higher energies.The observation in the spin-down era is characterized by the presence of a prominent QPO at 46.5±1.0 mHz frequency.The QPO rms and center frequency show a correlation with energy.Spin-up and spin-down states show a difference in the shape of the power density spectrum.After the torque reversal,a gradual flux drop and the hardening of the spectra were observed.The difference in the shape of the pulse profiles and the presence and absence of QPOs can be explained by the change in accretion flow geometry of the pulsar,from pencil-beam to fan-beam,between spin-down and spin-up states.展开更多
Using data from the Large Area X-ray Proportional Counter(LAXPC)on the AstroSat satellite,we observed Type-1 thermonuclear X-ray bursts from the low mass X-ray binary neutron star 4 U 1323-62.Observations of 4 U 1323-...Using data from the Large Area X-ray Proportional Counter(LAXPC)on the AstroSat satellite,we observed Type-1 thermonuclear X-ray bursts from the low mass X-ray binary neutron star 4 U 1323-62.Observations of 4 U 1323-62 that were carried out during the performance verification phase of the AstroSat satellite indicated six thermonuclear X-ray bursts in a total effective exposure of^49.5 ks for about two consecutive days.Recurrence time of the detected thermonuclear bursts is in accordance with the orbital period of the source,~9400 s.Moreover,the light curve of 4 U 1323-62 revealed the presence of two dips.We present the results from time-resolved spectroscopy performed during all of the six X-ray bursts and also report the detection of a known low frequency quasi-periodic oscillation(LFQPO)at^1 Hz from the source.However,any evidence of kilohertz QPO was not found.We have shown the burst profile at different energy ranges.Assuming a distance of 10 kpc,we observed a mean flux of^1.8×10^-9 erg cm^2 s^-1.The radius of the blackbody is found to be highly consistent with the blackbody temperature and the blackbody flux of the bursts.展开更多
基金financial support from ISRO(Sanction Order:No.DS_2B-13013(2)/3/2021-Sec.2)。
文摘We present a comprehensive analysis of AstroSat/LAXPC data of the second spin-up and second spin-down phases of the persistent X-ray pulsar 4U 1626-67.Flares followed by a broad dip are detected in the spin-up observations.The pulse profiles changed from a shoulder-like structure to a broad sinusoidal shape as the source underwent a torque reversal from spin-up to spin-down.Energy-resolved pulse profiles in lower energies showed a double-horned profile in the spin-up state and a flat top with multiple peaks in the spin-down state.Regardless of the torque state,the pulse profiles exhibit a broad single-peaked shape at higher energies.The observation in the spin-down era is characterized by the presence of a prominent QPO at 46.5±1.0 mHz frequency.The QPO rms and center frequency show a correlation with energy.Spin-up and spin-down states show a difference in the shape of the power density spectrum.After the torque reversal,a gradual flux drop and the hardening of the spectra were observed.The difference in the shape of the pulse profiles and the presence and absence of QPOs can be explained by the change in accretion flow geometry of the pulsar,from pencil-beam to fan-beam,between spin-down and spin-up states.
基金support from the Indian Space Research Organization(ISRO)and AstroSat science support cell in various aspects of instrument building,testing,software development and mission operation during the payload verification phase。
文摘Using data from the Large Area X-ray Proportional Counter(LAXPC)on the AstroSat satellite,we observed Type-1 thermonuclear X-ray bursts from the low mass X-ray binary neutron star 4 U 1323-62.Observations of 4 U 1323-62 that were carried out during the performance verification phase of the AstroSat satellite indicated six thermonuclear X-ray bursts in a total effective exposure of^49.5 ks for about two consecutive days.Recurrence time of the detected thermonuclear bursts is in accordance with the orbital period of the source,~9400 s.Moreover,the light curve of 4 U 1323-62 revealed the presence of two dips.We present the results from time-resolved spectroscopy performed during all of the six X-ray bursts and also report the detection of a known low frequency quasi-periodic oscillation(LFQPO)at^1 Hz from the source.However,any evidence of kilohertz QPO was not found.We have shown the burst profile at different energy ranges.Assuming a distance of 10 kpc,we observed a mean flux of^1.8×10^-9 erg cm^2 s^-1.The radius of the blackbody is found to be highly consistent with the blackbody temperature and the blackbody flux of the bursts.
