X-ray Binaries

http://bear.ras.ucalgary.ca/X-ray_binaries.html (Einblicke ins Internet, 10/1995)

X-ray Binaries

The class of radio emitting X-ray binaries consists of only 17 members. Members of the laboratory are investigating several of these objects using VLBI and x-ray telescope. The X-ray binaries LSI +61 +303 and GT2318 are the focus of most efforts.

LSI +61 +303

LSI +61 +303 is an X-ray binary system featuring large-amplitude radio outbursts with a period of 26.5 days. It is situated in the Perseus arm at a distance of 2.3 kpc. The outburts are non-thermal in nature and vary in amplitude between ~60 mJy and ~320 mJy with a four year modulation. Between outbursts the system has a typical flux density between 20-40 mJy. The 26.5d variability has been detected in the optical and infrared as well as the radio. Detections have been reported in the ultraviolet and possibly in gamma-rays. The optical component has been classified as a rapidly rotating B0-B0.5 Ve star with a circumstellar envelope and mass loss. The data implies masses of about 10 sloar masses for the primary and 1.5 solar masses for the secondary.

Three models have been proposed to account for the radio behaviour of LSI +61 +303.

Verstrand (1983) proposes a central pulsar enshrouded with matter and producing copious amounts of X-rays.
Marashi and Treves (1981) propose a young pulsar companion with a relativistic wind. Relativistic electrons are produced at the interaction front between the primary wind and the pulsar wind. Modulation results from variations in magnetic field intensity in the emitting region as the orbits progress.
Taylor and Gregory (1982, 1984) suggest that outbursts result from blast waves caused by supercritical accretion near periastron passage.

Russ Taylor (russ@ras.ucalgary.ca) and Glen Young (young@ras.ucalgary.ca) , along with Marta Peracuala (U of Barcelona) and Phil Gregory (UBC) are investigating these possibilities using VLBI radio data and ROSAT X-ray data..

GT 2318

The radio source GT 2318+620 lies in the error box or the UHURU x-ray source 4U 2316+61. A neutral hydrogen absorption spectrum in the direction of the source indicates that it lies within our Galaxy at a distance of 3 - 6 kpc. High resolution radio imaging reveals an unresolved core source with a jet-like feature extending to either side. The radio source is coincident with an ~20 magnitude optical star. The properties of the source suggest that it is a member of the small class of radio emitting, low-mass x-ray binary systems. GT 2318+620 may be a further example of the jet phenomenon seen in the x-ray binary system SS 433. SS 433 is unique among Galactic radio sources in showing relativistic motion of jets on arcsecond scales. Such jets are thought to result from accretion onto a collapsed stellar object. For more information on this object contact Russ Taylor (russ@ras.ucalgary.ca).

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Brad Wallace: brad@ras.ucalgary.ca