Name: Ashwin Devaraj
Affiliation: Raman Research Institute / Indian Institute of Science
Conference ID : ASI2022_730
Title : Discovery of a cyclotron line feature in GRO J1750-27 using NuSTAR
Authors : Ashwin Devaraj, Biswajit Paul
Abstract Type: Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : The Be/X-ray binary, GRO J1750-27 was discovered in 1995 with the CGRO-BATSE during a major outburst. The source has shown significant activity only three more times since then i.e, in 2008, 2014 and most recently in 2021. It is a relatively poorly studied source and is one of the farthest known galactic X-ray pulsars located almost behind the galactic centre at a distance between 14-22 kpc. Previously, during the 2014-2015 outburst, using the standard theory of accretion torque on magnetized neutron stars and the spin-up rate of this pulsar measured with Fermi-GBM along with its X-ray flux measured with Swift-BAT, the magnetic field strength was determined to be ~3.5-4.5 x 10^12 G. The uncertainty in the distance measurement led to the large uncertainty in the estimated magnetic field. The source was observed during the latest outburst using the NuSTAR telescope during the rising phase of the outburst. We estimate the spin period of the source to be ~ 4.45s using which we produced energy-resolved pulse profiles between 3 and 79 keV. We find that the profiles appear to be double-peaked at low energies (<20 keV) while evolving into a single peak at higher energies (>20 keV). The broadband spectrum of this source was described by a power-law modified by an exponential cut off and we report the discovery of a cyclotron resonant scattering feature (CRSF) in this hard x-ray spectrum of this source at ~43 keV indicating a magnetic field strength of 3.7 x 10^12 G. Our estimate of the magnetic field strength using the cyclotron line is consistent with the estimate made using the accretion torque model.