Subjects: Radio, Binaries, Black Holes, Neutron Stars, Transients
We have observed the X-ray binary SS 433 on November 6, 2008 between 13:48-18:35 UT at 5 GHz with the European VLBI Network (EVN) using the e-VLBI technique. The radio telescopes participating in the experiment were: Medicina, Onsala 25m, Torun, Jodrell Bank MkII and Cambridge.
The X-ray binary SS 433 is in outburst. Trushkin & Nizhelskij (ATel #1819) reported a major flare already active during the RATAN-600 observations in the 1-22 GHz band on 2008 October 28. The same radio facility recorded a rebrightening event on November 3/4 (spectra).
Our preliminary e-VLBI map shows three pairs (two of which are resolved) of radio emitting blobs located symmetrically on both sides of the presumed position of the core of the system. It is well known that in SS 433 the matter is ejected along a direction close to the plane of the sky with quite a stable speed, but the jet is precessing and the proper motion of the individual blobs varies accordingly. Assuming that the blobs
are moving at a rate of about 8 mas/day (corresponding to the proper motion in the plane of the sky of a blob moving with a speed of 0.26c at 5.5 kpc; e.g. Vermeulen et al. 1993 A&A 270, 177; Stirling et al. 2002 MNRAS 337, 657), then the pair the furthest away from the core, at about 100 mas, has been ejected around October 24 and perhaps the RATAN-600 observations on October 28 caught the aftermath of this event. It is interesting that the north-western blob is considerably brighter than its south-eastern counterpart and in fact dominates the radio emission at this scale. It is situated well beyond the "rebrightening zone" (i.e. about 50 mas from the core; Vermeulen et al. 1988 IAUS 129, 275) and perhaps interactions with the external medium are involved in producing the observed radio emission.
Following the same line of reasoning, the two blobs at about 25 mas from the core could have been ejected around November 3, date which also corresponds to the rebrightening event witnessed by RATAN-600.
The nature of the fainter radio blobs, closest to the core is not clear. They might be new ejections launched roughly a day before the e-VLBI observations or radio emission from the core.
More e-VLBI observations are planned.
e-VLBI is a technique in which signals from widely separated radio telescopes are directly streamed to the central data processor (correlator) in real-time. The data are then immediately made available to the astronomers for further data analysis. For information about e-EVN observing opportunities, please see the EVN e-VLBI web pages. In case of further questions, please e-mail to support(at)expres-eu.org
e-VLBI developments in Europe are supported by the EC DG-INFSO funded Communication Network Developments project 'EXPReS', Contract No. 02662. The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils.
