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arXiv · 0909.4458

First evidence for spectral state transitions in the ESO243-49 hyper luminous X-ray source HLX-1

O. Godet·D. Barret·N. A. Webb·S. A. Farrell·N. Gehrels
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Abstract

The brightest Ultra-Luminous X-ray source (ULX), ESO 243-49 HLX-1, with a 0.2 - 10 keV X-ray luminosity of up to 10^42 erg s^-1, provides the strongest evidence to date for the existence of intermediate mass black holes. Although small scale X-ray spectral variability has already been demonstrated, we have initiated a monitoring campaign with the X-ray Telescope onboard the Swift satellite to search for luminosity-related spectral changes and to compare its behavior with the better studied stellar mass black holes. In this paper, 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.

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O. Godet, D. Barret, N. A. Webb, S. A. Farrell, N. Gehrels. 2009-09-24. First evidence for spectral state transitions in the ESO243-49 hyper luminous X-ray source HLX-1. https://doi.org/10.1088/0004-637x/705/2/l109

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