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Session 84 - QSOs and BL Lacs.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[84.05] Rapid Variability in Faint Extragalactic Radio Sources

S. R. Das, D. J. Helfand (Columbia U.), R. H. Becker (UC Davis and IGPP, LLNL), R. L. White (STScI)

In the process of constructing Faint Images of the Radio Sky at Twenty-cm, our VLA FIRST survey generates a unique database for radio variability studies. To date, we have multiple observations of over 135,000 radio sources in 1550 square degrees of sky complete to 1.0 mJy; thus, we are probing a population over 1000 times fainter and 10,000 times larger than any previous such study. The intervals between observations range from 3 minutes to 3 weeks; most are either a few minutes or 1--3 days, with sources observed from 2--5 times. Of the more than half million flux measurements obtained to date, we have found over 300 sources which appear to vary by more than 25% between one day and the next; two dozen objects show fluctuations greater than a factor of two. We have independent evidence that we have selected a special population of objects in searching for such variability, since the rate of matching to optical counterparts on the POSS I plates is far greater than for the catalog as a whole (by a factor of \sim 3). A number of the sources are in the nuclei of relatively bright (15--18th magnitude) galaxies. We will report on the statistics of the complete variability study, detail our tests to eliminate spurious detections, present the optical identifications from the POSS plates and, weather permitting, report on the first spectroscopic followup of the optical counterparts.

This work is supported by the National Science Foundation, the National Geographic Society, NATO, the IGPP at Lawrence Livermore National Laboratory, and Columbia University.

Program listing for Wednesday