Abstract Details

Name: Ashwin Devaraj
Affiliation: Raman Research Institute / Indian Institute of Science
Conference ID: ASI2021_260
Title : NuSTAR view of the cyclotron line source, XTE J1946+274
Authors and Co-Authors : Ashwin Devaraj ((JAP) Raman Research Institute / Indian Institute of Science), Biswajit Paul (Raman Research Institute)
Abstract Type : Oral
Abstract Category : Stars, ISM and Galaxy
Abstract : XTE J1946+274 is a transient Be/X-ray Binary that has shown significant activity three times in the last two decades, undergoing type-II outbursts in 1998, 2010, and 2018. During these outbursts, it was observed using several X-ray observatories such as RXTE, BeppoSAX, Suzaku, and NuSTAR. It is among a subset of sources that exhibit a Cyclotron Resonance Scattering Feature in the hard X-ray spectra, at 38 keV. These cyclotron lines are the best diagnostic tool that we have access to in determining the magnetic field strength near the Neutron Star. A variety of cyclotron line sources have exhibited a positive correlation between their cyclotron line energy with the luminosity at which they were observed, a few showing no correlation and some showing a negative correlation. Since the cyclotron lines indicate the magnetic field strength at the region where they're formed, theories have been put forward attributing these correlations to be due to the variation in the height (above the surface of the NS) at which these lines are formed. Over the two decades, XTE J1946+274 has been seen over a wide range of luminosities, nearly two orders of magnitude, but shows no clear variation with the luminosity. From the phase-resolved analysis of the 2018 outburst of this source using the NuSTAR observatory, we find that the cyclotron line is significantly observed in certain phases while it is absent in others. This result is in corroboration with the disappearance of the secondary peak in the double-peaked structure of the energy-resolved pulse profiles in the range of 32-42 keV.