Recent VLA radio observations of XTE J1118+480

ATel #404; M. P. Rupen (NRAO/GSFC), V. Dhawan, A. J. Mioduszewski (NRAO)
on 2 Feb 2005; 21:32 UT
Credential Certification: Michael P. Rupen (mrupen@nrao.edu)

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We report further Very Large Array (VLA) observations of the continuing outburst of the black hole candidate binary XTE J1118+480 (e.g., ATEL #399, ATEL #400, ATEL #402). Our most recent observation (31 January 2005, MJD 53401.306) showed a 1.4+/-0.1 mJy source at 8.46 GHz. Multi-frequency observations taken on MJD 53399 show a rising (nu^0.3) spectrum between 4.86 and 8.46 GHz, as is also seen from 4.86 to 22.46 GHz on MJD 53396. Our data show the radio emission has decayed roughly exponentially with a time constant of 10 days since the original radio detection on MJD 53383, a decay punctuated by a few-mJy radio flare sometime between our observations on MJD 53386 and MJD 53391. A plot of the current radio light curve is available at

http://www.aoc.nrao.edu/~mrupen/XRT/X1118+480/x1118+480.shtml
Further frequencies will be added to this light curve over the next week or so, together with the results of on-going VLA observations. We will post further ATels if warranted by departures from the current gradual decay.

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

X1118+480 radio light curve