Swift Mission Director's Status Report Log - February 2005
Feb. 21, 2005
Swift once again had a busy weekend. BAT discovered two new GRBs on Saturday, both of which showed X-ray emission seen by XRT - GRB050219A (Romano et al GCN 3036; Hullinger et al GCN 3038) and GRB050219B (Burrows et al GCN 3042; Cummings et al GCN 3044). UVOT also observed both bursts promptly, but no optical flux was seen (Schady et al GCN 3039; Ivanushkina et al GCN 3046).
In addition Swift continued to observe GRB050215B through a Pre-Planned Science Timeline. This is the first long duration followup of a GRB by Swift. We are currently conducting instrument calibrations, but once these are complete we expect to routinely followup new GRBs with longer duration observations.
UVOT is completing its calibration of the grism capability. BAT is conducting grids of exposures of the Crab and Sco X-1 to map out their spatial and spectral responses. XRT is calibrating the spectral line response of the detector and the point spread function of the mirrors.
In a very significant confirmation of Swift's positional accuracy, the XRT has now found 8 cases of X-ray afterglow counterparts of BAT discovered GRBs. The average difference between the X-ray and BAT locations was only 1.07 arc minutes! This clearly shows the BAT is already meeting or exceeding its pre-flight estimates.
On a similar analysis, ground based followup have found optical or infrared counterpart of XRT located afterglows in 4 cases. The average difference between these locations was only 3 arc seconds! Again the XRT is already meeting or exceeding the pre-flight estimates. (Thanks to Dave Burrows for collecting these results.)
Feb. 16, 2005
After a gap of 12 days with only triggers induced by non-GRB events (such as flares from SGR1806-20), the BAT reacted to two GRBs within just 20 minutes! (Barthelmy et al, GCN 3024)
Swift slewed promptly to GRB050215A, but no object was found in a 9 second exposure, commenced just 98 seconds after the burst occurred (Breeveld et al, GCN 3025). XRT was not able to conduct observations due to the instrument mode (chosen to complement the planned calibration target).
Swift also responded promptly to GRB050215B, which superceded 0215A, but the initial observations were blocked by Swift's passage through the SAA. On subsequent orbits Swift collected useful data from both the UVOT and XRT. UVOT again found no optical source (Roming et al, GCN 3026), and XRT found a faint, steady source which is unlikely to be related to the GRB (Page et al, GCN 3027). 0215B continues as a Swift target.
UVOT has activated both heaters and finds the telescope focus is improved. We expect to keep this configuration. BAT, XRT and UVOT continue to make progress on their initial calibrations. We estimate that we have collected about half the required data for the initial calibration data products.
Feb. 10, 2005
Swift conducted a Target of Opportunity observation of the HETE reported burst, GRB050209. The Swift team responded rapidly to the request by generating a Target of Opportunity observation about 90 minutes after the HETE report. Unfortunately, no useful XRT and UVOT observations were obtained due to a spacecraft pointing shift. The shift was caused by an SAA particle detected by the XRT near the edge of the GRB field that mimicked a GRB afterglow source. This will not occur in future observations because the automatic pointing adjustment feature of the observatory will be turned off, at least temporarily. The on-orbit source positioning capabilities of the BAT have been demonstrated to be good enough to make the pointing adjustment unnecessary.
UVOT has activated both heaters and have conducted tests of focus using both heaters. Later UVOT will explore reducing the Earth Limb constraint, and the Bright Star Avoidance constraint to increase the sky coverage in which UVOT can pursue bursts. Note that the UVOT was prevented from observing one burst due to proximity to Vega.
Feb. 7, 2005
Swift spent the weekend collecting calibration data for the BAT and UVOT. The observatory was in full mode for GRB autonomous detection, but no BAT triggered bursts were detected. (The SGR 1806-20 was active, and produced a flare detected by the BAT.)
Today UVOT turned on its alternate DEM, in preparation for activating the second heater. This will extend the range of heater adjustments to its focus, and thus reach the final operational settings later this week. On Friday, UVOT will conduct Earth Limb testing to evaluate whether the Earth Limb restraint can be relaxed - thus offering greater portions of the sky accessible to Swift maneuvers, and GRB observations.
Feb. 2, 2005
The Swift BAT detected its first short GRB (GRB050202). The BAT on-board calculated location is RA,Dec 290.560, -38.720 (J2000) with an uncertainty of 4 arcmin. This appears to be a short burst (single spike, duration of ~0.4 second), dominated by emission in the 25-100 keV band (Tueller et al., GCN 3005).
Unfortunately the GRB was located only 31 degrees from the Sun, and could not be observed as either an automated target or as a Target of Opportunity. This discovery does confirm that BAT is capable of locating short bursts, and we look forward to later bursts which are more fortuitously located so that we can collect XRT and UVOT data.
Swift continues its calibration activities. XRT centroiding is improving out understanding of the systematics of the XRT positions, so we hope to soon decrease our XRT position uncertainties from the 30 arc second range to perhaps 5 arc seconds. UVOT is planning to extend the range of heater adjustments to its focus, and thus reach the final operational settings as early as next week.