Title:	Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC
Authors:	Varun Pradhan, Pragati Paul, Biswajit +2 Co-Authors
Keywords:	binaries: spectroscopic methods: data analysis pulsars: individual (4U 1907+09) radiation mechanisms: non-thermal stars: magnetic field X-rays: binaries
Issue Date:	20-Jul-2019
Publisher:	IOP Sciences for The American Astronomical Society
Citation:	Astrophysical Journal, 2019, Vol.880, p61
Abstract:	We present timing and spectral analysis of data from an observation of the high mass X-ray binary pulsar 4U 1907+09 with the Large Area X-ray Proportional Counter instrument on board AstroSat. The light curve consisted of a flare at the beginning of the observation, followed by persistent emission. The pulsar continues to spin down, and the pulse profile is found to be double-peaked up to 16 keV with the peaks separated by a phase of ~0.45. Significant energy dependence of the pulse profile is seen with diminishing amplitude of the secondary peak above 16 keV, and increasing amplitude of the main peak up to 40 keV with a sharp decline after that. We confirm earlier detection of the cyclotron resonance scattering feature (CRSF) in 4U 1907+09 at ~18.5 ± 0.2 keV in the phase-averaged spectrum with a high detection significance. An intensity resolved spectral analysis of the initial flare in the light curve shows that the CRSF parameters do not change with a change in luminosity by a factor of 2.6. We also performed pulse phase-resolved spectral analysis with 10 independent phase bins. The energy and the strength of the cyclotron line show pulse phase dependence that is in agreement with previous measurements. Two features from the current observation (different energy dependence of the two pulse peaks and a strong CRSF only around the secondary peak) both indicate a deviation from a dipole geometry of the magnetic field of the neutron star, or complex beaming pattern from the two poles.
Description:	Open Access
URI:	http://hdl.handle.net/2289/7270
ISSN:	0004-637X
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2019arXiv190602917B/abstract https://arxiv.org/abs/1906.02917 https://doi.org/10.3847/1538-4357/ab2763
Copyright:	2019, The American Astronomical Society
Appears in Collections:	Research Papers (A&A)

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