The 1996 outburst of GRO J1655-40: the challenge of interpreting the multiwavelength spectra

被引:50
作者
Hynes, RI [1 ]
Haswell, CA
Shrader, CR
Chen, W
Horne, K
Harlaftis, ET
O'Brien, K
Hellier, C
Fender, RP
机构
[1] Univ Sussex, Ctr Astron, Brighton BN1 9QH, E Sussex, England
[2] Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
[3] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[4] Univ St Andrews, Sch Phys & Astron, St Andrews KY16 9SS, Fife, Scotland
[5] Univ Keele, Dept Phys, Keele ST5 5BG, Staffs, England
[6] Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[7] Univ Amsterdam, Ctr High Energy Astrophys, NL-1098 SJ Amsterdam, Netherlands
关键词
accretion; accretion discs; binaries : close; stars : individual : Nova Sco 1994 (GRO J1655-40); ultraviolet : stars; X-rays : stars;
D O I
10.1046/j.1365-8711.1998.01835.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report on the results of a multiwavelength campaign to observe the soft X-ray transient (SXT) and superluminal jet source GRO J1655-40 in outburst using HST, RXTE and CGRO together with ground-based facilities. This outburst was qualitatively quite different from other SXT outbursts and from previous outbursts of this source, The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with the standard disc instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. Based on the strength of the 2175-Angstrom interstellar absorption feature we constrain the reddening to be E(B - V) - 1.2 +/- 0.1, a result which is consistent with the known properties of the source and with the strength of interstellar absorption lines. Using this result we find that our dereddened spectra are dominated by a component peaking, in the optical, with the expected nu(1/3) disc spectrum seen only in the ultraviolet. We consider possible interpretations of this spectrum in terms of thermal emission from the outer accretion disc and/or secondary star, both with and without X-ray irradiation, and also as non-thermal optical synchrotron emission from a compact self-absorbed central source. In addition to the prominent He Ir 4686-Angstrom line, we see Bowen fluorescence Lines of N III and O III, and possible P Cygni profiles in the ultraviolet resonance lines, which can be interpreted in terms of an accretion disc wind. The X-ray spectra broadly resemble the high-soft state commonly seen in black hole candidates, but evolve through two substates. Taken as a whole, the outburst data set cannot readily be interpreted by any standard model for SXT outbursts. We suggest that many of the characteristics could be interpreted in the context of a model combining X-ray irradiation with the limit-cycle disc instability, but with the added ingredient of a very large disc in this long-period system.
引用
收藏
页码:64 / 82
页数:19
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