The Neil Gehrels Swift Observatory

Swift Mission Director's Status Report Log - March 2005

Mar. 11 - Mar. 17, 2005

Observatory Status: A memory leak identified in the BAT resulted in a spontaneous reboot on Day 070, prior to a planned reboot. The array was not affected, and the BAT IP was returned to normal functioning by mid-afternoon on Day 071. Triggering was re-enabled, monitored and adjusted for about a day, and automated slewing was re-enabled on Day 072.

UVOT's safety circuit has tripped several times, particularly during grism tests. Steps have been taken in PPST planning to avoid the grism trips. Upcoming FSW modifications will also reduce safety circuit trips.

The first steps to lower the Earth Limb constraint were executed this week. The effect will be to increase the observable area of the sky and create a larger buffer for spacecraft slews to avoid "constraint traps."

New Bursts: GRB050315 sparked lengthy discussions of how best to followup the initial detection by BAT and XRT and lack of detection by UVOT. Ground detections in the near-IR prompted extension of Automated Target observations (80,000 secs total) and frequent PPST observations through this weekend.

Old bursts: Occasional observations of three February bursts continue.

SN2005am: Daily UVOT observations of SN2005am continue in broadband filters and grisms. The SN is fading slowly in the optical and faster in the UV.

Mar. 10, 2005

Swift reobserved the location of the GRB050306 Markwardt et al., GCN 3071). The initial observations were conducted two days after the burst due to the proximity of the Moon to the target. On the initial look XRT found a faint X-ray source inside the BAT error circle, but no source was seen by UVOT. On the second look the XRT source had faded below detectability, strengthening the association of the X-ray source with the GRB.

Swift autonomously responded to a threshold level trigger on March 9. BAT ground analysis suggested that the significance of this trigger was quite low, but a faint X-ray source was found by XRT within the BAT error circle (Barthelmy et al., GCN 3082). We will re-observe this source to look if this sources fades as well.

We the UVOT observations of SN2005am continue. UVOT is conduct filter and grism observations of this object, which we will follow through the peak brightness of the source.

Mar. 8, 2005

Swift discovered one GRB over the weekend (GRB050306, Markwardt et al., GCN 3071). Unfortunately the GRB was located too close to the Moon to be observed by the XRT and UVOT. On Monday the GRB emerged from the Moon exclusion, and we collected 20 ksec of data. XRT found a faint X-ray source inside the BAT error circle, but no source was seen by UVOT. We will re-observe 050306 tomorrow to see if the X-ray source has faded (and hence strengthen the identification between the X-ray source and the GRB).

We have started a sequence of UVOT observations of SN2005am, which is a supernova still on the rise to maximum. UVOT will conduct filter and grism observations of this object, projected to reach a peak brightness of 12.4.

The UVOT has turned on its Build 7 software. This revision allows the UVOT to compensate for spacecraft induced motions, thus allowing them to collect images on board the instrument. Starting on Thursday UVOT will accelerate its calibration measurements by collecting data in imaging mode (greatly reducing the telemetry requirements over event mode).

Mar. 4, 2005

Swift has been passing through a quiet period, as far as GRBs. The last burst discovered by BAT was GRB050223 (Mitani et al., GCN 3055). Significant X-ray afterglow emission faded from this burst within about 1000 seconds after the burst, and no UVOT detection has been reported. We have scheduled followup observations for this weekend in case an optical brightening (such as a supernova light curve might predict) were to happen. (The distribution of intervals between bursts is following the prediction of random intervals, and we should expect to continue to see gaps of 12, 20 and 10 days, as we have seen to this point, in the future. The overall Swift rate is consistent with the pre-launch prediction of 100 bursts per year.)

The Swift team has been busy with uploads to code changes for the XRT and UVOT teams. The XRT modifications reflect in-flight experience, and attempt to moderate the effect of loss of the XRT Thermal-Electric Cooler. This load was successful and initial tests suggest that the XRT can now operate as warm as -47 C and remain in Auto State. (Auto State is the preferred state for responding to new GRBs.)

The UVOT has completed the code upload for its Build 7 software. This revision will allow the UVOT to compensate for spacecraft induced motions, thus allowing them to collect images on board the instrument. Once this load is enabled (probably early next week) the UVOT will be able to efficiently collect images and transmit them to the ground. (To this point the full imaging response required each photon location be telemetered to the ground, forcing limitations to the amount of UVOT data collected.) After Build 7 is operational UVOT will accelerate its calibration measurements.

This week also included the first Swift Science Team meeting since launch. More than 90 participants met in State College to review the initial results. We heard that BAT, XRT and UVOT are all performing well, and many papers are being prepared for submission to scientific journals. The SGR1806-20 was the most recent NASA press release, with large Swift participation. The BAT has prepared an early version of its hard X-ray sky survey, and reported several new sources. Surprising light curves of XRT afterglows and the lack of bright UVOT afterglows were also discussed. We sensed the start of a new era in GRB science, and Swift stands at the center!