A Possible Phase-dependent Absorption Feature in the Transient X-Ray Pulsar SAX J2103.5+4545
Abstract
We present an X-ray spectral and timing analysis of two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the transient Be X-ray binary SAX J2103.5+4545 during its 2016 April outburst, which was characterized by the highest flux since NuSTAR's launch. These observations provide detailed hard X-ray spectra of this source during its bright precursor flare and subsequent fainter regular outburst for the first time. In this work, we model the phase-averaged spectra for these observations with a negative and positive power law with an exponential cutoff (NPEX) model and compare the pulse profiles at different flux states. We found that the broadband pulse profile changes from a three-peaked pulse in the first observation to a two-peaked pulse in the second observation, and that each of the pulse peaks has some energy dependence. We also perform pulse-phase spectroscopy and fit phase-resolved spectra with NPEX to evaluate how spectral parameters change with pulse phase. We find that while the continuum parameters are mostly constant with pulse phase, a weak absorption feature at ∼12 keV might, with further study, be classified as a cyclotron line, does show strong pulse-phase dependence.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2018
- DOI:
- 10.3847/1538-4357/aa9e91
- arXiv:
- arXiv:1711.11105
- Bibcode:
- 2018ApJ...852..132B
- Keywords:
-
- pulsars: individual: SAX J2103.5+4545;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 7 figures, accepted by ApJ, acknowledgements updated