We report on an extension of earlier work to search the archival database of the Differential Microwave Radiometers (DMR) aboard the COBE satellite for evidence of transient events at microwave wavelengths associated with cosmic gamma-ray bursts (GRBs). Over its four-year lifetime the DMR experiment repeatedly surveyed the sky to measure fluctuations in the cosmic microwave background. On a number of occasions over that period at least one of the horns of the DMR was also serendipitously pointing in the direction of a cosmic gamma-ray burst at the moment of burst occurrence, as recorded by the BATSE experiment aboard the Compton Gamma Ray Observatory (CGRO). Our original investigation covered the eight-month period April-December 1991 when a number of GRBs were observed by the COBE/DMR at or within a few seconds of the BATSE trigger time. Upper limits only were obtained for any simultaneous microwave flux from these events, in the range 7-42 kJy. Most recently, we have extended our search using the additional 24 months of COBE DMR data now publicly available, covering the time period January 1992 through December 1993, and the latest BATSE 4B Catalog of gamma-ray bursts. We review here the results of our original work, outline our current analysis plan, and estimate the improvement expected in any derived upper limits. Finally, we assess the implications of our results in the context of the most recent developments in burst counterpart searches and models.
Fifth Huntsville Gamma Ray Burst Symposium
Hunsville, Alabama, USA
18-22 October, 1999