SIMBAD references

2006ApJ...650L..75F - Astrophys. J., 650, L75-L78 (2006/October-2)

Spectral state transitions of the ultraluminous X-ray sources X-1 and X-2 in NGC 1313.


Abstract (from CDS):

X-ray spectral state transitions are a key signature of black hole X-ray binaries and follow a well-defined pattern. We examined 12 XMM-Newton observations of the nearby spiral galaxy NGC 1313, which harbors two compact ultraluminous X-ray sources (ULXs), X-1 and X-2, in order to determine if the state transitions in ULXs follow the same pattern. For both sources, the spectra were adequately fitted by an absorbed power law with the addition of a low-temperature (kT=0.1-0.3 keV) disk blackbody component required in six of the 12 observations. As the X-ray luminosity of X-1 increases to a maximum at 3x1040 ergs/s, the power-law photon index softens to 2.5-3.0. This behavior is similar to the canonical spectral state transitions in Galactic black hole binaries, but the source never enters the high/soft or thermal-dominant state and instead enters the steep power-law state at high luminosities. X-2 has the opposite behavior and appears to be in the hard state, with a photon index of Γ=1.7-2.0 at high luminosity, but can soften to Γ=2.5 at the lower luminosities.

Abstract Copyright:

Journal keyword(s): Accretion, Accretion Disks - Black Hole Physics - X-Rays: Binaries - X-Rays: Galaxies - X-rays: individual (NGC 1313 X-1) - X-rays: individual (NGC 1313 X-2)

CDS comments: NGC 1313 X-1 and X-2 are [CPS95] X- 1 and [CPS95] X- 2 in SIMBAD.

Simbad objects: 13

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