Zurita, C., Torres, M. A. P., Steeghs, D., Rodríguez-Gil, P., Muñoz-Darias, T., Casares, J., Shahbaz, T., Martinez-Pais, I. G., Zhao, P., Garcia, M. R., Piccioni, A., Bartolini, C., Guarnieri, A., Bloom, Joshua S., Blake, C. H., Falco, E. E., Szentgyorgyi, A. and Skrutskie, M. (2006) The 2005 outburst of the halo black hole X-ray transient XTE J1118+480. The Astrophysical Journal, Vol.644 (No.1). pp. 432-438. doi:10.1086/503286

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Abstract

We present optical and infrared monitoring of the 2005 outburst of the halo black hole X-ray transient XTE J1118+480. We measured a total outburst amplitude of ~5.7 ± 0.1 mag in the R band and ~5 mag in the infrared J, H, and Ks bands. The hardness ratio HR2 (5-12 keV : 3-5 keV) from the RXTE ASM data is 1.53 ± 0.02 at the peak of the outburst, indicating a hard spectrum. Both the shape of the light curve and the ratio LX(1-10 keV)/Lopt resemble the minioutbursts observed in GRO J0422+32 and XTE J1859+226. During early decline, we find a 0.02 mag amplitude variation consistent with a superhump modulation, like the one observed during the 2000 outburst. Similarly, XTE J1118+480 displayed a double-humped ellipsoidal modulation distorted by a superhump wave when settled into a near-quiescence level, suggesting that the disk expanded to the 3 : 1 resonance radius after outburst, where it remained until early quiescence. The system reached quiescence at R = 19.02 ± 0.03, about 3 months after the onset of the outburst. The optical rise preceded the X-ray rise by at most 4 days. The spectral energy distributions (SEDs) at the different epochs during outburst are all quasi-power laws with Fν να increasing toward the blue. At the peak of the outburst, we derived α = 0.49 ± 0.04 for the optical data alone and α = 0.1 ± 0.1 when fitting solely the infrared. This difference between the optical and the infrared SEDs suggests that the infrared is dominated by a different component (a jet?), whereas the optical is presumably showing the disk evolution.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Black holes (Astronomy), X-ray bursts
Journal or Publication Title:	The Astrophysical Journal
Publisher:	Institute of Physics Publishing Ltd.
ISSN:	0004-637X
Official Date:	2006
Dates:	Date Event 2006 Published
Date of first compliant deposit:	22 December 2015
Date of first compliant Open Access:	22 December 2015
Volume:	Vol.644
Number:	No.1
Page Range:	pp. 432-438
DOI:	10.1086/503286
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	United States. National Aeronautics and Space Administration (NASA), Smithsonian Astrophysical Observatory, Harvard University, University of California, Berkeley
Grant number:	NAG-5-10889 (NASA)

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