SIMBAD references

2013ApJ...770...20K - Astrophys. J., 770, 20 (2013/June-2)

A state transition of the luminous X-ray binary in the low-metallicity blue compact dwarf galaxy I Zw 18.


Abstract (from CDS):

We present a measurement of the X-ray spectrum of the luminous X-ray binary in I Zw 18, the blue compact dwarf galaxy with the lowest known metallicity. We find the highest flux yet observed, corresponding to an intrinsic luminosity near 1x1040 erg/s establishing it as an ultraluminous X-ray source (ULX). The energy spectrum is dominated by disk emission with a weak or absent Compton component and there is no significant timing noise; both are indicative of the thermal state of stellar-mass black hole X-ray binaries and inconsistent with the Compton-dominated state typical of most ULX spectra. A previous measurement of the X-ray spectrum shows a harder spectrum that is well described by a power law. Thus, the binary appears to exhibit spectral states similar to those observed from stellar-mass black hole binaries. If the hard state occurs in the range of luminosities found for the hard state in stellar-mass black hole binaries, then the black hole mass must be at least 85 M. Spectral fitting of the thermal state shows that disk luminosities for which thin disk models are expected to be valid are produced only for relatively high disk inclinations, ≳ 60°, and rapid black hole spins. We find a* > 0.98 and M > 154 M for a disk inclination of 60°. Higher inclinations produce higher masses and somewhat lower spins.

Abstract Copyright:

Journal keyword(s): black hole physics - galaxies: individual (I Zw 18) - X-rays: binaries - X-rays: galaxies

Simbad objects: 7

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