Astrophys. J., 644, 432-438 (2006/June-2)
The 2005 outburst of the halo black hole X-ray transient XTE J1118+480.
ZURITA C., TORRES M.A.P., STEEGHS D., RODRIGUEZ-GIL P., MUNOZ-DARIAS T., CASARES J., SHAHBAZ T., MARTINEZ-PAIS I.G., ZHAO P., GARCIA M.R., PICCIONI A., BARTOLINI C., GUARNIERI A., BLOOM J.S., BLAKE C.H., FALCO E.E., SZENTGYORGYI A. and SKRUTSKIE M.
Abstract (from CDS):
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 Ksbands. 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)/Loptresemble 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.
Accretion, Accretion Disks - Stars: Binaries: Close - Stars: Individual: Alphanumeric: XTE J1118+480 - stars: individual (KV UMa) - X-Rays: Stars
Parag. 5 : GS 1121-68 is a misprint for GRS 1121-68 (V* GU MUS)
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