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# Constraining distance and inclination angle of V4641 Sgr using SWIFT and NuSTAR observations during low soft spectral state

Pahari, Mayukh and Misra, Ranjeev and Dewangan, Gulab C and Pawar, Pramod (2015) Constraining distance and inclination angle of V4641 Sgr using SWIFT and NuSTAR observations during low soft spectral state. Astrophysical Journal, 814 (2). Art No 158. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20160203-100150948

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## Abstract

We present results from NuSTAR and Swift/XRT joint spectral analysis of V4641 Sgr during a disk dominated or soft state, as well as a power law dominated or hard state. The soft state spectrum is well modeled by a relativistically blurred disk emission, a power law, a broad iron line, two narrow emission lines, and two edges. The Markov Chain Monte Carlo simulation technique and the relativistic effects seen in the disk and broad iron line allow us to self-consistently constrain the inner disk radius, disk inclination angle, and distance to the source at ${2.43}_{-0.17}^{+0.39}$Rg (GM/c2), ${69.5}_{-4.2}^{+12.8}$ degrees and ${10.8}_{-2.5}^{+1.6}$ kpc respectively. For the hard state, the spectrum is a power law with a weakly broad iron line and an edge. The distance estimate gives a measure of the Eddington fraction, ${L}_{2.0-80.0\;\mathrm{keV}}/{L}_{\mathrm{Edd}},$ to be ~1.3 × 10−2 and ~1.9 × 10−3 for the soft and hard states, respectively. Unlike many other typical black hole systems, which are always in a hard state at such a low Eddington fraction, V4641 Sgr shows a soft, disk dominated state. The soft state spectrum shows narrow emission lines at ~6.95 and ~8.31 keV which can be identified as being due to emission from highly ionized iron and nickel in an X-ray irradiated wind respectively. If this is not due to instrumental effect or calibration error, this would be the first detection of a Ni fluorescent line in a black hole X-ray binary.

Item Type:Article
Related URLs:
URLURL TypeDescription
http://iopscience.iop.org/article/10.1088/0004-637X/814/2/158/metaPublisherArticle
http://dx.doi.org/10.1088/0004-637X/814/2/158DOIArticle
Additional Information: © 2015 The American Astronomical Society. Received 2015 April 25; accepted 2015 October 19; published 2015 December 1. We thank the referee for useful discussions and comments. We are thankful to the NuSTAR team for making data publicly available. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). RXTE/PCA data obtained through the High Energy Astrophysics Science Archive Research Center online service, provided by the NASA/ Goddard Space Flight Center and the Swift data center. MAXI data are obtained from the MAXI team, RIKEN, JAXA.
Group:NuSTAR
Issue or Number:2
Record Number:CaltechAUTHORS:20160203-100150948
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160203-100150948
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64194
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:03 Feb 2016 18:07