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

Swift Mission Director's Status Report Log - July 2005

July 20, 2005

Swift has continued to amaze us with its record of burst discoveries. We've learned first hand what 'random' truly means. From June 7 to July 1, the BAT detected no new GRBs. After July 1, we had no GRBs until July 12. Since July 12, the BAT has found seven new bursts! So in these six weeks, we've seen eight bursts [which is not too far from the average rate of 100 per year] but almost all of them are in the last week!

In addition to the eight BAT bursts, we also commanded Swift to observe one HETE-2 and one INTEGRAL-discovered bursts. Here is the break-down of BAT bursts: July 1, July 12, July 13a and b, July 14 b, July 15, July 16 and July 17. The XRT and UVOT observed the locations of nine of the ten GRBs (GRB 050715 was too close to the Sun to be observed by the XRT and UVOT.) The XRT found X-ray counterparts in eight of the nine cases. (The only non-detection came from the HETE-2 burst, on July 9, which was only reported about 24 hours after the burst occurred.) The UVOT only detected a definite optical counterpart for GRB050712.

Six times Swift was able to respond autonomously, and started XRT and UVOT observation in less than three minutes after the gamma-ray emission from the burst started. In one case we reached the burst in time to have simultaneous X-ray and gamma-ray detections.

Swift was also a major player in the follow-up to the Deep Impact collision with Comet Tempel 1. Swift has done daily monitoring both before and after the impact (except for a four day period when the Moon and comet were too close together). Swift has seen a beautiful UV light curve for the comet, and an impressive X-ray flare. More details can be found at the following website:

Swift is also a valuable asset for responding to new supernova discoveries, and we have monitored the optical and UV rise of SN2005cs and 2005cf. Peter Brown and Stephen Holland led the analysis of Swift data for SN2005am, which was recently accepted for publication.

The dramatic X-ray flares in GRB050406 and 050502b have been accepted for publication in Science, in a paper led by David Burrows. The Swift-discovered early X-ray light curves have been accepted in a paper for Nature, in a paper led by Gianpiero Tagliaferri. The press release on the discovery of the first counterpart to a short GRB was covered in the August 'Discover' magazine, and a paper to Nature has been submitted. The Swift team has many other papers accepted, submitted or in preparation to technical journals.

Kim Page and Dave Burrows have collected the following statistics on the allocation of Swift observing time. Since the start of normal operations on April 5 to July 11, we have divided our time as follows:
     GRBs - new, followup, ToOs:    58%
     Calibration targets:           11%
     Non-GRB ToOs:                   8%
     Fill-in Targets:               15%
     SAA cold points/ non-science:   8%
On the technical side, the observatory and the instruments continue to work well. During the Memorial Day weekend, Swift encountered two un-related Attitude Control System problems. We have now diagnosed both, and believe they were low-probability occurrences. On May 28 the ACS/Star Tracker system produced a bad quaternion (the ACS orientation matrix that measures where Swift is looking on the sky). On May 30 it appears the Star Tracker suffered a particle hit which corrupted memory, forcing us to carry out a cold reboot of the tracker.

Neither problem has recurred, and we believe that we can respond quickly to any reoccurrences, keeping Swift efficiently observing the sky. The Swift team will be holding a team meeting at Goddard Space Flight Center, at which we will bring together our first major summary of the Swift results to date. We have been enjoying the excitement of the flow of discoveries and hope for many more to come!