Radio imaging campaign on newly-detected jets in GRS1915+105

ATel #758; J. C.A. Miller-Jones (Univ. of Amsterdam), M. P. Rupen (NRAO), S. A. Trushkin (SAO RAS), G. G. Pooley (MRAO), R. P. Fender (Univ. of Southampton)
on 3 Mar 2006; 12:56 UT
Credential Certification: James C.A. Miller-Jones (jmiller@science.uva.nl)

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We report the detection of a large-scale radio jet in the black hole X-ray binary GRS 1915+105 following an X-ray and radio outburst, and announce the start of an intensive radio imaging campaign.

Daily observations with the RATAN-600 radio telescope showed a major radio flare in GRS 1915+105, peaking at ~350 mJy at 2.3 GHz on Feb. 23rd, 2006. X-ray measurements by the RXTE ASM, combined with radio monitoring with the RATAN-600 and the Ryle Telescope, suggest the outburst began at most a day before this. In response to the RATAN-600 report we have begun a series of radio imaging observations with the Very Large Array (VLA), the Very Long Baseline Array (VLBA), and the Multi-Element Radio-Linked Interferometer Network (MERLIN). Here we report the results of the first two 43 GHz VLA observations, taken on Feb. 24th and 28th.

Extended emission was detected on Feb. 24th. This emission was reasonably well fit by two point sources, the brightest one (18.0 +/- 0.7 mJy) at a position consistent with that of the core (V. Dhawan, priv. comm.), and a second component to the southeast, with a flux density of 5.3 +/- 0.7 mJy. The separation of the two components was 45.4 +/- 2.2 milliarcseconds [mas], at a position angle of 140.4 +/- 2.7 degrees, in good agreement with previous observations of the orientation of the radio jets in this source (e.g., Mirabel & Rodriguez 1994, Nature, 371, 46-48; Fender et al. 1999, MNRAS 304, 865-876). Assuming no contamination by the receding (northern) jet, and taking the proper motion of the approaching component to be the same as that reported by Fender et al. (23.6 +/- 0.5 mas/day), the implied ejection date is Feb. 22nd, consistent with the X-ray and radio light curves.

By the time of the second observation on Feb. 28th, the source had faded markedly, with an integrated flux density of only 3.7 +/- 0.9 mJy at 43 GHz. The approaching (southeastern) component had faded below detectability, although there appeared to be a hint of extension to the NW of the core position, possibly corresponding to the receding jet.

Weekly observations with the VLA will continue through mid-May; VLBA observations were taken on Feb. 28th, and are scheduled for Mar. 4th, 6th, and 9th; MERLIN has also made one observation. The combination should give the best imaging sequence yet on this source, probing the evolving morphology over three orders of magnitude in angular scale. Daily radio monitoring with the RATAN-600 and the Ryle Telescope is on-going, and we encourage parallel observations at other wavelengths.

The results of this radio campaign, including contour plots of the two observations detailed above, may be found at http://remote.science.uva.nl/~jmiller/grs1915/monitoring.html which we plan to update weekly.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.