Swift Observations of GRB 211223C

P.A. Evans (U. Leicester) for the Swift team

1. Introduction

At 14:29:26 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 211223C (trigger=1090656) (Evans et al. GCN Circ. 31288). Swift did not slew to the burst due to a pointing constraint. At the time of the trigger, the initial BAT position was 40° from the Sun (3.0 hours West) and 92° from the 83%-illuminated Moon. Table 1 contains the best reported positions from Swift.

Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.

Standard analysis products for this burst are available at https://gcn.gsfc.nasa.gov/swift_gnd_ana.html.

2. BAT Observations and Analysis

As reported by Krimm et al. (GCN Circ. 31297), the BAT ground-calculated position is RA, Dec = 227.165, -26.878 deg.

The BAT light curve (Figure 1) showed a complex structure with a duration of about 20 s. T90 (15-350 keV) is 15.00 ± 5.00 s (estimated error including systematics).

The time-averaged spectrum from T-13.01 to T+8.99 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.15 ± 0.09. The fluence in the 15-150 keV band is 2.4 ± 0.1 x 10-6 erg cm-2. This fluence is larger than that of 65% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T-0.01 s in the 15-150 keV band is 3.1 ± 0.4 ph cm-2 s-1. All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1090656/BA/.

3. XRT Observations and Analysis

XRT refined results are not available.

4. UVOT Observations and Analysis

UVOT results are not available.

BAT light curve

Figure 1. The BAT mask-weighted light curve in the four individual and total energy bands. The units are counts s-1 illuminated-detector-1. The vertical green dash-dotted lines show the T50 interval, the vertical black dashed lines show the T90 interval, and vertical blue (orange) solid lines show the start (stop) of slews.

RA (J2000) Dec (J2000) Error Note Reference
15h08m39.7s -26°52'41.0" 1.2' BAT-refined Krimm et al. GCN Circ. 31297

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 31294 Swift GRB 211223C: Global MASTER-Net
observations report 		MASTER
Optical Hu et al. 31295 BOOTES-4/MET optical upper limit BOOTES-4 upper limits

Table 2. Summary of GCN Circulars from other observatories sorted by band and then circular number.

December 25, 2021