O. Godet et al 2009 ApJ 705 L109 doi:10.1088/0004-637X/705/2/L109
O. Godet1, D. Barret1, N. A. Webb1, S. A. Farrell2 and N. Gehrels3
Show affiliationsThe brightest ultra-luminous X-ray source, ESO 243-49 HLX-1, with a 0.2-10 keV X-ray luminosity of up to 1042 erg s–1, provides the strongest evidence to date for the existence of intermediate mass black holes (BHs). Although small-scale X-ray spectral variability has already been demonstrated, we have initiated a monitoring campaign with the X-ray Telescope (XRT) onboard the Swift satellite to search for luminosity-related spectral changes and to compare its behavior with the better-studied stellar mass BHs. In this Letter, we report a drop in the XRT count rate by a factor of ~8 which occurred simultaneously with a hardening of the X-ray spectrum. A second observation found that the source had re-brightened by a factor of ~21 which occurred simultaneously with a softening of the X-ray spectrum. This may be the first evidence for a transition between the low/hard and high/soft states.
accretion, accretion disks; X-rays: binaries; X-rays: individual (HLX-1)
98.70.Qy X-ray sources; X-ray bursts
Issue 2 (2009 November 10)
Received 2009 August 24, accepted for publication 2009 September 23
Published 2009 October 20
O. Godet et al 2009 ApJ 705 L109
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