Journal article
Transition of an X-ray binary to the hard ultraluminous state in the blue compact dwarf galaxy VII Zw 403
Monthly notices of the Royal Astronomical Society, Vol.448(4), pp.3374-3381
02/11/2015
DOI: 10.1093/mnras/stv227
Abstract
We examine the X-ray spectra of VII Zw 403, a nearby low-metallicity blue
compact dwarf (BCD) galaxy. The galaxy has been observed to contain an X-ray
source, likely a high mass X-ray binary (HMXB), with a luminosity of
1.3-23x10^38 erg s^-1 in the 0.3-8 keV energy range. A new Suzaku observation
shows a transition to a luminosity of 1.7x10^40 erg s^-1 [0.3-8 keV], higher by
a factor of 7-130. The spectra from the high flux state are hard, best
described by a disk plus Comptonization model, and exhibit curvature at
energies above 5 keV. This is consistent with many high-quality ultraluminous
X-ray source spectra which have been interpreted as stellar mass black holes
(StMBH) accreting at super-Eddington rates. However, this lies in contrast to
another HMXB in a low-metallicity BCD, I Zw 18, that exhibits a soft spectrum
at high flux, similar to Galactic black hole binaries and has been interpreted
as a possible intermediate mass black hole. Determining the spectral properties
of HMXBs in BCDs has important implications for models of the Epoch of
Reionization. It is thought that the main component of X-ray heating in the
early universe was dominated by HMXBs within the first galaxies. Early galaxies
were small, metal-deficient, star forming galaxies with large H I mass
fractions --- properties shared by local BCDs we see today. Understanding the
spectral evolution of HMXBs in early universe analogue galaxies, such as BCDs,
is an important step in estimating their contribution to the heating of the
intergalactic medium during the Epoch of Reionization. The strong contrast
between the properties of the only two spectroscopically studied HMXBs within
BCDs motivates further study on larger samples of HMXBs in low metallicity
environments in order to properly estimate the X-ray heating in the early
universe.
Details
- Title: Subtitle
- Transition of an X-ray binary to the hard ultraluminous state in the blue compact dwarf galaxy VII Zw 403
- Creators
- Matthew Brorby - University of IowaPhilip Kaaret - University of IowaHua Feng - Tsinghua University
- Resource Type
- Journal article
- Publication Details
- Monthly notices of the Royal Astronomical Society, Vol.448(4), pp.3374-3381
- DOI
- 10.1093/mnras/stv227
- ISSN
- 0035-8711
- eISSN
- 1365-2966
- Publisher
- Oxford University Press
- Language
- English
- Date published
- 02/11/2015
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199680702771
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