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The Mass of the Black Hole in XTE J1118+480

Khargharia, Juthika and Froning, Cynthia S. and Robinson, Edward L. and Gelino, Dawn M. (2013) The Mass of the Black Hole in XTE J1118+480. Astronomical Journal, 145 (1). Art. No. 21. ISSN 0004-6256.

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We present contemporaneous, broadband, near-infrared spectroscopy (0.9-2.45 μm) and H-band photometry of the black hole X-ray binary, XTE J1118+480. We determined the fractional dilution of the NIR ellipsoidal light curves of the donor star from other emission sources in the system by comparing the absorption features in the spectrum with field stars of known spectral type. We constrained the donor star spectral type to K7 V-M1 V and determined that the donor star contributed 54% ± 27% of the H-band flux at the epoch of our observations. This result underscores the conclusion that the donor star cannot be assumed to be the only NIR emission source in quiescent X-ray binaries. The H-band light curve shows a double-humped asymmetric modulation with extra flux at orbital phase 0.75. The light curve was fitted with a donor star model light curve, taking into account a constant second flux component based on the dilution analysis. We also fitted models that included emission from the donor star, a constant component from the accretion disk, and a phase-variable component from the bright spot where the mass accretion stream impacts the disk. These simple models with reasonable estimates for the component physical parameters can fully account for the observed light curve, including the extra emission at phase 0.75. From our fits, we constrained the binary inclination to 68° ≤ i ≤ 79°. This leads to a black hole mass of 6.9 M_☉ ≤ M_(BH) ≤ 8.2 M_☉. Long-term variations in the NIR light curve shape in XTE J1118+480 are similar to those seen in other X-ray binaries and demonstrate the presence of continued activity and variability in these systems even when in full quiescence.

Item Type:Article
Related URLs:
URLURL TypeDescription
Froning, Cynthia S.0000-0001-8499-2892
Gelino, Dawn M.0000-0003-1274-2784
Additional Information:© 2013 American Astronomical Society. Received 2012 September 21; accepted 2012 November 7; published 2012 December 12. We thank Emma Hogan for her assistance with Gemini-IRAF and Bernadette Rogers for letting us use her code to make GNIRS data compatible for use with Spextool. Facilities: Gemini:Gillett (GNIRS), ARC (NICFPS)
Group:Infrared Processing and Analysis Center (IPAC)
Subject Keywords:binaries: close; black hole physics; infrared: stars; stars: individual (XTE J1118+480)
Issue or Number:1
Record Number:CaltechAUTHORS:20130115-103312705
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Official Citation:The Mass of the Black Hole in XTE J1118+480 Juthika Khargharia et al. 2013 The Astronomical Journal 145 21
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36387
Deposited By: Ruth Sustaita
Deposited On:15 Jan 2013 19:01
Last Modified:09 Mar 2020 13:18

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