The Swift Gamma-Ray Burst Mission Italian site U.K. site

Swift Mission Director's Status Report Log - May 2005

May 13, 2005

The rate of Swift discovery has continued to increase. Key highlights include the discovery of the first XRT localization of a short GRB, the discovery of the second highest redshift GRB to date, and the discovery of a giant X-ray flare following a GRB. I discuss these highlights below. Please refer to the GCN archive or the Swift project pages for a complete list of Swift bursts.

Since April 22 Swift discovered, observed or will observe the following bursts: May 2a and b; May 4; May 5; May 7; May 9a, b and c.

May 2b was an amazing burst which was observed initially by the XRT to be fairly faint. Three hundred seconds after the gamma-ray burst started, XRT detected an increase in X-ray flux by more than 1000! Later time observations revealed two broad X-ray rises above the simple power law extrapolation.

May 9b was the long awaited first XRT observed short burst. Swift began observations only 62 seconds after the burst, and it was a good thing because the entire X-ray flux dropped below detection after only about 400 seconds. This burst has substantial world-wide attention, including Chandra and HST followups. (A press release was made about this burst, which was covered by many news outlets.)

The May 5 burst was measured by ground-based observations from the Keck Observatory to have a red-shift of z=4.27. This is the second largest GRB redshift ever seen.

We are also conducting long term light curves of persistent GRB afterglows. Thus we continue to collect data on GRB050408, 050416a and 050422. The very low background in the XRT allows us to easily detect objects with counting rates as low as 10^-4 cts/sec in 50 ksecond observations. (We note that UVOT has detected 050416a in late time observations [Fox GCN 3408]. We continue to monitor this source in case of the possibility of a supernova related rebrightening.)

We continue to refine the Swift on-board software. New instrument software builds have been completed or are in-work for the BAT, FoM, XRT and UVOT. These software builds fix small bugs or improve the efficiency and performance of the instruments and observatory. The BAT and FoM finished last week, the UVOT will upload next week and the XRT will upload the following week.

We conducted testing of the spacecraft and UVOT ability to point closer to the Moon. Based on the results of this test (and analysis from the full team) we decided to reduce the spacecraft Moon constraint from 30 to 21 degrees. The effect of this change will be to increase the fraction of sky in which Swift can promptly follow bursts.