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Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst

Hynes, R. I. and Robinson, E. L. and Pearson, K. J. and Gelino, D. M. and Cui, W. and Xue, Y. Q. and Wood, M. A. and Watson, T. K. and Winget, D. E. and Silver, I. M. (2006) Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst. Astrophysical Journal, 651 (1). pp. 401-407. ISSN 0004-637X. doi:10.1086/507669.

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We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ~10 s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHK_s photometry, as in the previous outburst, exhibits especially large-amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power law of slope α = -0.78 ± 0.07, where F_ν ∝ ν_α. There is no compelling evidence for evolution in the slope over five nights, during which time the source brightness decayed along almost the same track as seen in variations within the nights. We conclude that both short-term variability and longer timescale fading are dominated by a single component of constant spectral shape. We cannot fit the SED of the IR variability with a credible thermal component, either optically thick or thin. This IR SED is, however, approximately consistent with optically thin synchrotron emission from a jet. These observations therefore provide indirect evidence to support jet-dominated models for XTE J1118+480 and also provide a direct measurement of the slope of the optically thin emission, which is impossible, based on the average spectral energy distribution alone.

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Gelino, D. M.0000-0003-1274-2784
Additional Information:© 2006 American Astronomical Society. Received 2005 November 15; accepted 2006 July 11. We are grateful to Michael Merrill for technical assistance with SQIID and John Robertson for assistance with the SARA observations. W. C. acknowledges support from NASA grant NNG 04GI54G. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work has made use of the NASA Astrophysics Data System Abstract Service.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:accretion, accretion disks; binaries: close; stars: individual (XTE J1118+480)
Issue or Number:1
Record Number:CaltechAUTHORS:20110428-115554074
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Official Citation:Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst R. I. Hynes et al. 2006 ApJ 651 401
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23490
Deposited On:28 Apr 2011 21:31
Last Modified:09 Nov 2021 16:15

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