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

Swift Mission Director's Status Report Log - April 2005

Apr. 22, 2005

The rate of Swift discovery has reached astonishing proportions. I won't be able to discuss each burst in great detail, but will just touch the highlights. Please refer to the GCN archive or the Swift project pages for a list of Swift bursts.

For this month so far Swift discovered or observed the following bursts: April 1, April 6, April 8, April 10, April 12, April 16A, April 16B, April 21 and April 22!

April 8 was an astonishing demonstration of the Swift agility, and the responsiveness of the Swift science and flight operations team. The High Energy Transient Explorer-2 (HETE-2) discovered a new, bright GRB. The Swift team was able to respond immediately and Swift was observing the new GRB only 40 minutes after it happened! Previous satellites have taken at least ten, and typically twenty or thirty times longer to respond to such new discoveries.

After April 5, Swift transitioned to normal operations. In addition to all data being public immediately, this means that the full priority is now given to discovering and following up bursts. (During the previous 90 days we were conducting the initial in-flight calibrations of Swift, and so spent time on calibration targets.) We are now allocating only 5% of time to calibration targets, and these are observed only when no GRB afterglow is in view.

We have also started a plan to emphasize looking at targets in the anti-Sun direction. The initial results are a great increase in the number of ground-based observatories reporting observations of Swift GRBs on the GCN. We hope this will result in many great discoveries triggered by Swift GRB detections.

Last week we completed the Build 10 flight software upload for UVOT. This software will make the UVOT more robust and reduce the telemetry volume. As a result we expect to conduct observations with UVOT on a more efficient basis.

Next week we will upload a similar flight software improvement for the BAT and Figure of Merit. These changes will also make Swift easier to control and produce better science.

On a science note, the Swift team has submitted its first papers to Nature on Swift detected GRBs, and we hope this will start a landslide of excitement in the GRB community.

Apr. 1, 2005

The cadence of Swift activity has reached a stable state so we will reduce the frequency of these reports to a weekly basis.

Swift had another busy week. The BAT discovered a bright burst on Mar. 26 (Markwardt et al, GCN 3143). Unfortunately the GRB occurred inside the Earth Limb constraint, so Swift had to wait about an hour before the target could be observed by the XRT and UVOT. By this time, there was a detectable XRT source, but no UVOT source.

On Mar. 31, Swift's star trackers were unable to acquire a lock on the star pattern during an observation of the South Galactic Pole. As a result Swift continued to maneuver based on the attitude provided by the inertial gyro system. In successive maneuvers Swift did not come close enough to the desired targets to re-acquire lock, and hence Swift slowly deviated from the inertial attitude solution. As a result three rapid variations by the known X-ray source, Vela X-1, were interpreted as GRBs (three were reported in notices by the automated system; two were reported in circulars starting from 18:23 UT). When we detected the loss of attitude lock, we retracted the GRB detections at 21:17 UT. We have instituted both automatic and manual checking to prevent loss of attitude lock and false GRBs such as these in the future.

On Apr. 1, Swift detected a real GRB (Barbier et al., GCN 3162). XRT detected an X-ray afterglow (Angellini et al., GCN 3161), and ground based instrument detected on optical/IR afterglow. Follow-up at the VLT found a redshift of 2.90. Unfortunately the UVOT cannot observe this burst due to a nearby 4th magnitude star within the UVOT field of view.

Next week we plan to upload the Build 10 flight software for UVOT. This software will make the UVOT more robust and reduce the telemetry volume. As a result we expect to conduct observations with UVOT on a more efficient basis.