Complete and Simultaneous Spectral Observations of the Black Hole X-Ray Nova XTE J1118+480
Garnavich, P. M.; Groot, P. J.; Miller, J. M.; Lewin, W. H. G.; Chaty, S.; McClintock, J. E.; Shrader, C. R.; Muno, M. P.; Drake, J. J.; Pooley, G. G.; Garcia, M. R.; Marshall, H. L.; Vrtilek, S. D.; Haswell, C. A.; Mauche, C. W.; Hynes, R. I.
United States, United Kingdom
Abstract
The X-ray nova XTE J1118+480 suffers minimal extinction (b=62deg) and therefore represents an outstanding opportunity for multiwavelength studies. Hynes et al. conducted the first such study, which was centered on 2000 April 8 using UKIRT, EUVE, HST, and RXTE. On 2000 April 18, the Chandra X-Ray Observatory obtained data coincident with a second set of observations using all of these same observatories. A 30 ks grating observation using Chandra yielded a spectrum with high resolution and sensitivity covering the range 0.24-7 keV. Our near-simultaneous observations cover ~80% of the electromagnetic spectrum from the infrared to hard X-rays. The UV/X-ray spectrum of XTE J1118+480 consists of two principal components. The first of these is an ~24 eV thermal component that is caused by an accretion disk with a large inner disk radius: >~35R Schw. The second is a quasi power-law component that was recorded with complete spectral coverage from 0.4 to 160 keV. A model for this two-component spectrum is presented in a companion paper by Esin et al.