Swift Mission Director's Status Report Log - January 2005
Jan. 31, 2005
Swift passed an exciting weekend, if not one with new bursts. The BAT detected the X-ray burst source, Ara X-1 (4U1702-429), which is a classic Low Mass X-ray Binary. There were also two events associated with flares from the SGR1806-20 (Sato et al, GCN 3002).
Last week Swift found GRB050128 which had an X-ray afterglow (Antonelli et al, GCN 2991; Cummings et al, GCN 2992). Swift continued Automated Target observations covering 17 orbits, and found detectable X-ray emission all but the last two.
Calibration observations continue when the new GRBs are not visible. XRT temperatures have been generally kept below -50C, although the AT observations are not under manual control, and so can result in higher temperatures for the XRT.
UVOT has created its six filter first light image of M101 and will be making a press release soon.
Jan. 26, 2005
Another exciting day for Swift! GRB050126 was discovered by Swift's BAT, and Automated Target slewing had been enabled (Sato et al., GCN 2987). The XRT commenced observations within 2 minutes, showing a rapidly declining X-ray source (Kennea et al, GCN 2984). The identification was confirmed when the Keck/ NIRC found a fading Near Infra-Red source at the XRT position. (Unfortunately the UVOT was prevented from collecting data because this GRB is less than 3 degrees away from Vega - a 0th magnitude star!)
Following up GRB050124, the UVOT reported its observations, which resulted in an upper limit some three hours after the burst (Hunsberger et al., GCN 2982).
GRB050126 observations will continue while it is visible to Swift. At other times Swift will conduct observations of targets called out in the Swift Calibration Plan. Observations of GRB050124 have been discontinued.
Jan. 25, 2005
Swift conducted automated observations of the field of GRB050124. The XRT detected X-ray emission from a fading source, consistent with the BAT position, and also reported an X-ray spectrum (Osborne et al., GCN Circ 2975). The UVOT also observed the same field, and provided the standard GRB data products. Although no optical/UV source was detected, this was the first ToO UVOT data for a new GRB (starting about 3 hours after the BAT trigger.)
When the GRB050124 source is not visible to Swift, it will conduct calibration observations of targets called out in the Swift Calibration Plan.
Jan. 24, 2005
At 11:30:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050124 (Markwardt et al., GCN Circ 2972). The BAT on-board calculated location is RA,Dec 192.879, +13.026 (J2000) with an uncertainty of 6 arcmin radius. The structure of the burst is double-peaked with a duration of ~4 seconds.
Automated Target slewing was disabled due to XRT radiator orientation testing, but the new GRB was observed by both XRT and UVOT approximately 3 hours after the burst, via a Target of Opportunity (ToO) upload. Observations will continue while the GRB position is visible for the rest of the day.
Over the weekend XRT radiator orientation testing demonstrated that the XRT temperature can be affected by about 4-5 C, by varying the spacecraft roll angle within allowable limits.
Over the week Swift will commence calibration observations of targets called out in the Swift Calibration Plan.
Jan. 21, 2005
UVOT has successfully activated its safety circuit, after several days of testing. For the past two days they have been uploading a new set of flight parameters to control the UVOT response to GRBs and other observations. In addition they have been collecting data through various filters to create their first light image (a multi-color UV observation of the face-on galaxy M101). The first two color version of the image is very attractive and the UVOT team is planning a first-light data release - probably some time next week.
XRT has created a three day timeline of observations aimed at testing the thermal models for XRT radiatior performance (important for controlling the CCD temperature). This will be the first time that Swift will be expected to operate autonomously over a weekend. MOC personnel are on-call to respond to any spacecraft emergency, or important science discovery.
Jan. 17, 2005
Swift conducted its first fully autonomous response to a burst. At 12:52:36 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board GRB050117a. The spacecraft autonomously slewed to the burst for the first time with a real GRB. The BAT on-board calculated location is RA,Dec 358.427,+65.945 (J2000) with an uncertainty of 4 arcmin radius (Sakamoto et al. GCN Circ 2952). This is within 55 arcsec of the XRT position (Burrows et al., GCN Circ 2951). XRT position was measured 192 seconds after the burst occurred. Because the burst was quite long, the first XRT data were collected before the burst ended, a first for a focussed X-ray GRB/afterglow observation. Unfortunately the GRB happened to be located at the extreme Northern edge of the visibility allowed by our Earth constraint, and the short part of the orbit where we could observe was almost entirely within the South Atlantic Anomaly - complicating the data analysis.
BAT also discovered another weak burst, GRB050117b, but we decided that it was too weak to justify a Target of Opportunity slew with the XRT.
Jan. 15, 2005
UVOT has successfully conducted Earth Limb testing. Proceeding very carefully, they have determined that the rate of events coming from the Earth's Limb, through all the various filters, is in line with the preflight predictions. This means that it is considered safe for the UVOT to conduct observations all the way down to an Earth Limb constraint of 30 degrees (the pre-flight estimate). We will consider additional testing to see if we can safely shrink this constraint farther.
In addition UVOT has started focus testing. They have determined that the best focus will be found by applying heat to the aluminum mounting stub for the secondary mirror (thus shrinking the distance between the primary and secondary). Additional thermal changes will be made to conduct further tests to find the best focus.
Once the operational focus is set, we will have three days of tests to set the Safety Circuit values to protect UVOT from accidental observations of bright stars.
PS: My apologies for the interruption of these reports. The Swift team leadership was attending the AAS meeting in San Diego. All five talks (by Gehrels, Nousek, Barthelmy, Burrows and Roming) were very well received. We appreciate the great interest and excitement in the community over Swift, and we share your eagerness to reach full operational capability.
Jan. 13, 2005
UVOT focussing test sequences were completed during Day 13, despite one further interruption because of a safety circuit trigger. Reasons for this triggering problem are beginning to be better understood. Steps have been taken to speed up the distribution of processed image data needed to characterise UVOT focus.
Plans have been completed to resume UVOT scans to look to within 30 degrees of the Earth Limb, starting on Day 14. The back-log of focus-test data will be downloaded over the next 48 hours.
Overnight, UVOT has been safed, BAT remains operational, slews are enabled and XRT is in auto state. We are due a burst!
Jan. 11 and Jan. 12, 2005
UVOT was returned to operation, and focussing tests were resumed, using a progression of incremental steps, spread over several Malindi passes, to change the heat inputs to the metering rods, and to allow long settling periods between changes to check thermal stability. Two days of operation were set aside for this high priority activity. The data volumes involved in these tests consume a large fraction of storage space on Swift's on board memory. BAT and XRT have scaled down their operations to provide maximum storage capacity for UVOT.
Two further, unexplained safe circuit triggers occurred over this period, which also lost observing time and required further investigation and changes to commanding plans.
Overnight January 12, BAT continued to look for bursts but none were detected. With XRT not taking data, autonomous slewing was not enabled.
There is some latency in getting data from these tests to ground, because UVOT data fills the on-board memory more rapidly than can be dumped to ground during a day's worth of Malindi passes. Also, turn-round time of processing dumped data and distributing it via the SWIFT Data Center's Quick-Look site, leads to delays in being able to interpret data from focus tests.
Jan. 10, 2005
UVOT began focus checks. This involved heating the invar metering rods in the telescope and observing changes to the optical image. A preliminary heating cycle was initiated and some data obtained. The operation was interrupted when the safety circuit, which protects the UVOT detector against damage from bright object exposure, was triggered. UVOT was placed in safe state to allow careful investigation of the anomalous trigger.
XRT was switched to auto mode and autonomous slews were again enabled. No burst was detected, although BAT continues to detect catalogued sources at expected levels of sensitivity. XRT is gathering additional data to help optimize XRT radiator temperatures for future observations.
Jan. 9, 2005
UVOT observations were scheduled to observe at decreasing angles from the Earth's limb to measure instrument response to limb-brightening. XRT was also enabled to check whether optical light leakage in the optical blocking filter or x-ray fluorescence from the bright Earth was contributing to the XRT background. Closest approach of instrument pointings were limited to 40 degrees.
Correlated UVOT and XRT data have been obtained. UVOT measurements were restricted to the "blocked", UVW1 and UVW2 filters, and a limited data set for the white-light filter. Each Earth Limb test required real-time commanding via TDRSS and, as some command time with TDRSS was lost during the day, additional passes have to be scheduled in order to complete the filter set and to measure responses up to within 30 degrees of the limb. The results obtained so far are excellent and allow the UVOT commissioning to proceed to its next phase, that of determining optimum focus of the instrument.
Overnight, January 9, UVOT was safed, SWIFT autonomous slews were enabled, BAT remained operational and XRT was switched into auto state. No bursts were detected.
Jan. 8, 2005
UVOT spent the day preparing for tomorrow's Earth Limb testing. The requirements for this test are quite demanding on the science planners, so we spent the day working on the plan. Swift had AT slews enabled, so from 01:40 UT on Day 8 to 13:50 UT on Day 9 Swift should slew to any BAT discovered GRBs which are visible to the XRT.
Jan. 7, 2005
UVOT conducted tests to verify that the UVOT Safety Circuit does properly protect the UVOT detector from damage due to looking at bright stars. Proceeding carefully, during a real-time pass, Swift was commanded to offset point at a seventh magnitude A0 star, and the Safety Circuit correctly detected the presence of the star and properly triggered a safing transition for the UVOT detector. (The Safety Circuit is a new development for UVOT, as its predecessor instrument - the Optical Monitor on XMM-Newton - did not require it.) With the Safety Circuit demonstrated, UVOT can proceed with its activation program.
Jan. 6, 2005
UVOT has conducted four exposures to measure its intensity channels, channel boundaries, centroid confirmation, and flat field. It has also conducted focus testing and filter integrity testing.
Tomorrow it will conduct tests to measure the allowable limits on approaching the Earth limb.
Jan. 5, 2005
UVOT has enabled its High Voltage on the Telescope Module (This major commissioning step, of turning on the UVOT High Voltage and testing the Cathode, was successfully completed at 01:28 UT.) This is a major step, and congratulations to the UVOT for the successful completion.
The rest of the day consisted of collecting exposures of the Blocked filter setting (which prevents celestial light from reaching the UVOT detector) and the LED turned on. These data will be used to determine the UVOT flat field, and the corrections to the centroiding algorithm (which relates to the 8x8 fixed pattern structure in the UVOT response).
Tomorrow UVOT will conduct tests to assure the integrity of the UVOT filters, and start enabling of the UVOT safety circuitry.
Jan. 4, 2005
Autonomous slewing to BAT-detected targets was disabled today at ~13:00 UT in preparation for UVOT activities. The BAT detected a weak, apparent burst on Day 005 at 00:47 UT. XRT did not perform any centroiding tests today, but conducted observations of those sources (without centroiding).
UVOT prepared for turning on the detector High Voltages tomorrow. UVOT uploaded the flight RTSs that control exposures, performed tests to ramp up the high voltages, and verified that the high voltages are properly ramped up and down for Pre-planned Targets.
Jan. 3, 2005
Swift still has Automated Target (AT) slewing enabled. There have been no BAT triggers since the AT slewing was enabled, around 16:10 UT on Dec. 31. We plan to keep Swift in AT slewing mode through the morning of Jan. 4.
XRT collected centroiding data. The results for each single source show a high degree of repeatability, but the offsets vary from source to source. We are conducting analysis to produce the appropriate correction factors. The Pre-Planned Science Timeline needed to support the first day of UVOT High Voltage activation has been loaded onto the spacecraft, and UVOT activation should resume tomorrow.
Jan. 2, 2005
Swift still has Automated Target (AT) slewing enabled. There have been no BAT triggers since the AT slewing was enabled, around 16:10 UT on Dec. 31. We plan to keep Swift in AT slewing mode through at least Jan. 4.
XRT commenced taking centroiding measurements of bright X-ray sources to improve the accuracy of the XRT position determinations. If BAT triggers during this time, the AT slewing will take precedence over the XRT measurements. We look forward to resuming activation of the UVOT starting on Jan. 4.
Jan. 1, 2005
Swift currently has Automated Target (AT) slewing enabled. If a GRB is detected by a BAT trigger, (and if the GRB location is outside the Swift viewing constraints from the Sun, Earth and Moon), then Swift should autonomously slew to the new GRB. We will continue to manually inspect BAT GRB candidates to assure that they are reliable before posting them on the GCN.
There have been no BAT triggers since the AT slewing was enabled, around 16:10 UT yesterday. We plan to keep Swift in AT slewing mode through at least Jan. 4. We look forward to resuming activation of the UVOT starting on Jan. 4. XRT will observe centroiding alignment targets on Jan. 2 to improve the accuracy of the XRT position determinations.