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Register a new userMulti-Wavelength Study of X-ray Pulsar 2S 1553-542 During Outburst in 2021
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We summarize the results of temporal and spectral analysis of the X-ray pulsar 2S 1553-542 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift during the outburst in January-February 2021. During the outburst, the spin period of the neutron star was $P = 9.2822pm 0.0001$ s based on NuSTAR data. The temporal evolution of the spin period, pulse profile, and pulse fraction is studied during the outburst. The spectra of the source are studied for different days of the outburst and can be well described by a model consisting of -- a black body emission or a power law. We have investigated the inter-day evolution of different timing and spectral parameters during the outburst. The energy dependence of the pulse profile was studied to investigate the evolution of the individual peaks and emission geometry of the pulsar with a different energy. The pulse profile of the source shows strong single peak nature with a hump-like feature of relatively lower intensity and it evolves significantly with different energy ranges. The evolution of the pulse profile is studied during different phases of the outburst and the pulse fraction shows a positive correlation with energy.
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We report results of a spectral and timing analysis of the poorly studied transient X-ray pulsar 2S 1553-542 using data collected with the NuSTAR and Chandra observatories and the Fermi/GBM instrument during an outburst in 2015. Properties of the source at high energies (>30 keV) are studied for the first time and the sky position had been essentially improved. The source broadband spectrum has a quite complicated shape and can be reasonably described by a composite model with two continuum components - a black body emission with the temperature about 1 keV at low energies and a power law with an exponential cutoff at high energies. Additionally an absorption feature at $sim23.5$ keV is discovered both in phase-averaged and phase-resolved spectra and interpreted as the cyclotron resonance scattering feature corresponding to the magnetic field strength of the neutron star $Bsim3times10^{12}$ G. Based on the Fermi/GBM data the orbital parameters of the system were substantially improved, that allowed us to determine the spin period of the neutron star P = 9.27880(3) s and a local spin-up $dot P simeq -7.5times10^{-10}$ s s$^{-1}$ due to the mass accretion during the NuSTAR observations. Assuming accretion from the disk and using standard torque models we have estimated the distance to the system $d=20pm4$ kpc.
We have studied the evolution of different timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observations. The spin period during the outburst is $P sim$17.3622 s based on the NICER data and the period decreases slowly with time. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate was found to be varied between $simeq$(0.8--1.8)$times$10$^{-11}$ Hz s$^{-1}$. The pulse profile shows strong energy dependence and variability. The pulse profile shows multiple peaks and dips which evolve significantly with energy. The pulsed fraction shows a positive correlation with energy. The evolution of the spectral state is also studied. The NICER energy spectrum is well described with a composite model of -- power-law and a blackbody emission along with a photo-electric absorption component. An iron emission line is detected near 6.4 keV in the NICER spectrum with an equivalent width of about 0.05 keV. During the recent outburst, the flux was relatively low compared to the 2018 outburst and the mass accretion rate was also low. The mass accretion rate is estimated to be $simeq$1.3 $times$ 10$^{17}$ g s$^{-1}$ near the peak of the outburst. We have found a positive correlation between the pulse frequency derivatives and luminosity. The GL model was applied to estimate the magnetic field in low mass accretion rate and different spin-up rates, which is compared to the earlier estimated magnetic field at a relatively high mass accretion rate. The magnetic field is estimated to be $simeq$10$^{14}$ G from the torque-luminosity model, which is comparatively higher than most of the other Be/XBPs.
We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during which the source was initially discovered with a periodicity of 2.1652$pm$0.0001 seconds which we associate with the spin period of the neutron star. A systematic temporal analysis of long term Swift/BAT data reveals a periodic signal of 82.5$pm$0.7 days, in contrast with a similar analysis of long base line OGLE I-band light curves which reveals an 83.67$pm$0.05 days also found in this work. Interpreting the longer X-ray periodicity as indicative of binary motion of the neutron star, we find that outbursts detected by INTEGRAL and Swift between 2014 and 2016 are consistent with Type I outbursts seen in Be/XRBs, occurring around periastron. Comparing these outbursts with the OGLE data, we see a clear correlation between outburst occurrence and increasing I-band flux. A periodic analysis of subdivisions of OGLE data reveals three epochs during which short periodicities of $sim$1 day are significantly detected which we suggest are non-radial pulsations (NRPs) of the companion star. These seasons immediately precede those exhibiting clear outburst behaviour, supporting the suggested association between the NRPs, decretion disk growth and the onset of Type I outbursts.
With the observations from textit{Rossi X-ray Timing Explorer}, we search and study the X-ray bursts of accreting millisecond X-ray pulsar SAX~J1748.9-2021 during its 2010 outburst. We find 13 X-ray bursts, including 12 standard type-uppercaseexpandafter{romannumeral1} X-ray bursts and an irregular X-ray burst which lacks cooling tail. During the outburst, the persistent emission occurred at $sim$(1-5)$%rm {dot{M}_{Edd}}$. We use a combination model of a blackbody (BB), a powerlaw, and a line component to fit the persistent emission spectra. Another BB is added into the combination model to account for the emission of the X-ray bursts due to the thermonuclear burning on the surface of the neutron star. Finally, we modify the combination model with a multiplicative factor $f_{rm a}$, plus a BB to fit the spectra during the X-ray bursts. It is found that the $f_{rm a}$ is inversely correlated with the burst flux in some cases. Our analysis suggests that the ignition depth of the irregular X-ray burst is obviously smaller than those of the type-uppercaseexpandafter{romannumeral1} X-ray bursts. We argue that the detected type-uppercaseexpandafter{romannumeral1} X-ray bursts originate from helium-rich or pure-helium environment, while the irregular X-ray burst originates from the thermonuclear flash in a shallow ocean.
We present the spectral and timing analysis of the X-ray pulsar GRO J1744-28 during its 2014 outburst using data collected with the X-ray satellites Swift, INTEGRAL, Chandra, and XMM-Newton. We derived, by phase-connected timing analysis of the observed pulses, an updated set of the source ephemeris. We were also able to investigate the spin-up of the X-ray pulsar as a consequence of the accretion torque during the outburst. Relating the spin-up rate and the mass accretion rate as $dot{ u}proptodot{M}^{beta}$, we fitted the pulse phase delays obtaining a value of $beta=0.96(3)$. Combining the results from the source spin-up frequency derivative and the flux estimation, we constrained the source distance to be between 3.4-4.1 kpc, assuming a disc viscous parameter $alpha$ to be in the range 0.1-1. Finally, we investigated the presence of a possible spin-down torque by adding a quadratic component to the pulse phase delay model. The marginal statistical improvement of the updated model does not allow us to firmly confirm the presence of this component.
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