Study of Timing and Spectral Properties of the X-ray Pulsar A 0535+262 During the Giant Outburst in Nov-Dec 2020

Manoj Mandal, Sabyasachi Pal

Published 2020-12-31Version 1

We made a multi-wavelength study of the timing and spectral properties of the X-ray pulsar A 0535+262 at the time of a recent giant outburst in November and December 2020. The flux of the X-ray pulsar reached a record value of nearly 12.5 Crab on 19th November 2020 (MJD 59172) since its discovery. We have used the NuSTAR, Swift, and NICER data for our study. We have studied the evolution of pulse frequency, pulse profile, and different spectral parameters during the giant outburst. The variation of pulse fraction in different energy ranges has been studied. We have detected a q like feature for the X-ray pulsar during the flare from the hardness intensity diagram. We investigated the evolution of the pulse period and we found the spin period of the neutron star to be $P = 103.58\pm 0.01$ s based on NuSTAR data. It was found that the spin period decreased with time at a rate of $\dot P= -1.50\pm 0.05\times10^{-7}$ ss$^{-1}$ during the flare. The timing results revealed the presence of highly variable pulse profiles. The pulse profile evolved from a double peak feature to a single peak in a higher energy range (40$-$79 keV) and prominent energy dependence of the pulse profile was established. The pulse fraction showed a positive correlation with energy. The cyclotron resonant scattering feature (CRSF) from the spectrum have been detected at $\sim44$ keV and the corresponding magnetic field is B $\sim4.9\times10^{12}$ G. We have studied the broadband spectrum of the source which can be described by a composite model with two continuum components - a blackbody emission and a cut-off power law. An emission line of iron ($K_{\alpha}$) near 6.4 keV have been detected from the energy spectrum.