It has recently been pointed out (Halpern 2006, GCN 4614) that the nature of GRB 051221B has still not been definitively settled (GRB vs hard X-ray transient). Prompted by this report, we are providing further analysis details of the Swift-XRT observation of this source....Full Text

"I revise here the report in GCN 4381 of an optical object at the Swift XRT position of the possible GRB 051221B (Boyd et al. GCN 4376, Page et al. GCN 4378, Fenimore et al. GCN 4382), prompted by the non-detections at this position by Milne (GCN 4420) and Sharapov et al. (GCN 4612). The position and magnitude given in GCN 4381 were both in error as a result of using an incorrect entry...Full Text

We observed the field of GRB 051221B (SWIFT-BAT trigger 173904) on Dec. 21, 2005, starting at UT=02:35:53 (06:32:33 after the burst) with the 61" Kuiper telescope at Mt. Bigelow, AZ. We obtained 11 x 300-sec R-band images. Observing conditions were considered good. The field was subsequently observed the next night starting at UT=01:33:50. We obtained 7 x 300 second images in the R-band...Full Text

"We used the Very Large Array to observe the Swift burst GRB 051221B (GCN 4376; GCN 4382) at a frequency of 8.46 GHz on 2005 Dec. 27.92 UT (i.e. 6.9 days after the burst). No radio emission is detected within the XRT error circle (GCN 4378). The rms noise was 31 uJy....Full Text

ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe, Turkey, responded to GRB 051221B (Swift trigger 173904), producing images beginning 10 s after the GCN notice time. An automated response took the first image at 20:06:57.2 UT, 217.1 s after the burst, under excellent conditions. We took 10 5-sec, 138 20-sec eposures. These unfiltered images are calibrated relative to USNO...Full Text

We imaged the entire field of GRB 051221B (173904) detected by SWIFT (Boyd et al. GCN 4376) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. Observations started 9 seconds after the GCN notice (and 216 sec. after the GRB). The field had an elevation of 35 degrees above horizon at the beginning of the observations and then decreased. The humidity was rather...Full Text

Using the full data set from the recent telemetry downlink covering T-300 to T+300 sec, we report further analysis of Swift-BAT GRB 051221B (trigger #173904) (Boyd, et al., GCN 4376). The ground-analysis position is RA,Dec 312.359,+53.040 {RA 20h 49m 26.1s,DEC +53d 02' 23.4"} (J2000) with an uncertainty of 1.6 arcmin (radius, 90%, stat+sys). The partial coding fraction is 45%. The lightcurve...Full Text

"We observed the position of possible Swift GRB 051221B in the R-band with the MDM 1.3m for 30 minutes starting on Dec. 22 01:31 UT, or 5.5 hours after the BAT trigger (Boyd et al., GCN 4376)....Full Text

"BOOTES-1 in South Spain (El Arenosillo, INTA, Huelva), responded under non-optimal conditions to GRB 051221 (Swift trigger 173904, Boyd et al. GCN 4376). A sequence of RVI-band exposures started at 20:07:15 UT (235s after the GRB onset). Preliminary analysis does not reveal any transient optical source in the 3' radius SWIFT/BAT error box, and in particular at the position reported by...Full Text

We have analysed the first orbit of XRT data for BAT trigger 173904 (GCN 4376, Boyd et al.) and find a fading, uncatalogued source located at...Full Text

At 20:03:20 UT, Swift-BAT triggered and located a source (trigger=173904). The spacecraft slewed promptly after the end of the image trigger. The BAT on-board calculated location is RA,Dec 312.395d,+53.054d {RA 20h 49m 35s,DEC +53d 03' 14"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). All we have at this time is the TDRSS lightcurve. This plus the fact...Full Text