Chandra discovery of luminous supersoft X-ray sources in M81

被引:64
作者
Swartz, DA
Ghosh, KK
Suleimanov, V
Tennant, AF
Wu, KW
机构
[1] NASA, George C Marshall Space Flight Ctr, Univ Space Res Assoc, Huntsville, AL 35812 USA
[2] Kazan VI Lenin State Univ, Kazan 420008, Russia
[3] NASA, George C Marshall Space Flight Ctr, Dept Space Sci, Huntsville, AL 35812 USA
[4] UCL, Mullard Space Sci Lab, Dorking RH5 6NT, Surrey, England
[5] Univ Sydney, Sch Phys, Sydney, NSW 2006, Australia
关键词
binaries : symbiotic; stars : atmospheres; stars : evolution; white dwarfs; X-rays : stars;
D O I
10.1086/340926
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
A Chandra ACIS-S imaging observation of the nearby galaxy M81 (NGC 3031) reveals nine luminous soft X-ray sources. The local environments, X-ray spectral properties, and X-ray light curves of the sources are presented and discussed in the context of prevailing physical models for supersoft sources. It is shown that the sample falls within expectations based on population synthesis models taken from the literature, although the high observed luminosities (L(obs) similar to 2 x 10(36)-3 x 10(38) ergs s(-1) in the 0.2-2.0 keV band) and equivalent blackbody temperatures (T(eff) similar to 40-80 eV) place the brightest detected M81 objects at the high-luminosity end of the class of supersoft sources defined by previous ROSAT and Einstein studies of nearby galaxies. This is interpreted as a natural consequence of the higher sensitivity of Chandra to hotter and more luminous systems. Most of the sources can be explained as canonical supersoft sources: accreting white dwarfs powered by steady surface nuclear burning with X-ray spectra well fitted by hot white dwarf local thermodynamic equilibrium atmosphere models. An exceptionally bright source is scrutinized in greater detail since its estimated bolometric luminosity, L(bol) similar to 1.5 x 10(39) ergs s(-1), greatly exceeds theoretical estimates for supersoft sources. This source may be beyond the stability limit and undergoing a phase of mass outflow under extreme conditions. Alternatively, a model in which the observed X-ray spectrum arises from an accretion disk around a black hole of mass similar to1200/(cos i)(1/2) M. (viewed at an inclination angle i) cannot be excluded.
引用
收藏
页码:382 / 397
页数:16
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