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Swift Detection of a Bright, Multiple-Peaked Burst: GRB050525a

GRB050525a

From GCN 3466:

At 00:02:53 UT, the BAT instrument on the Swift spacecraft triggered (trigger=130088) and located GRB 050525. The BAT on-board calculated location is RA,Dec 278.144 , +26.340 (18h 32m 35s +26d 20' 23") (J2000) with an uncertainty of 3 arcmin (radius, 3-sigma, including systematic uncertainty). This is a very bright burst, yielding about 1500 counts over background in 64 ms (preliminary) in the 25-100 keV range in the BAT instrument. This would correspond to a rate of 10 counts/sec/cm2 in that 64 ms interval, but the peak rate in a later interval may be greater. Although light curves are not yet available, the BAT rate trigger continued to evaluate different timescales while data from the first 64 ms was being imaged. The merit parameters indicate that the highest significance rate trigger is for a 1 second interval, consistent with a short burst. More details will be available after the full data pass.

The XRT was pointed promptly at the burst and took an image at 00:04:58 UT (125 s after the BAT burst trigger). The XRT found a bright X-ray source near the center of the field of view, with position RA(J2000) = 18h 32m 32.3s Dec(J2000) = +26d 20' 17.5" We estimate an uncertainty of about 6 arcseconds radius (90% containment). This position is 31 arcseconds from the BAT position and 8 arcseconds from the ROTSE position (Rykoff et al, GCN 2465).

We caution that the XRT is in the middle of engineering tests and is in an unusual mode. While the X-ray afterglow looks unusually strong, there are also indications that the XRT instrument configuration is abnormal due to the tests being performed.

The XRT position is outside of the UVOT-TDRSS image. Analysis of the UVOT data will take place after the next full data pass.

This is a bright burst that appears to be in the short category; the Sun and moon angles are conducive for optical observations. Followup observations are strongly encouraged.

From GCN 3467:
GRB 050525 (Swift trigger 130088) was observed by Swift BAT. At the present, only rate data are available. This initial data indicate that the burst was very intense (peak rate of 80,000 ct/s above background). The light curve consists of at least two ragged peaks, with a total duration of approximately 10 seconds (15 - 200 keV).

Thus, this is not a short burst as initially speculated (Band et al. GCN #3466), but it is one of the brightest bursts of the year.