Swift Observations of GRB 191213A

S.B. Cenko (GSFC) for the Swift team

1. Introduction

At 04:06:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 191213A (trigger=944091) (Cenko et al. GCN Circ. 26398). Due to a Sun constraint, Swift did not slew to this burst. At the time of the trigger, the initial BAT position was 36° from the Sun (2.4 hours West) and 132° from the 99%-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 Lien et al. (GCN Circ. 26418), the BAT ground-calculated position is RA, Dec = 224.530, -9.745 deg which is RA(J2000) = 14h58m07.2s Dec(J2000) = -09°44'41.9" with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 56%.

The mask-weighted light curve (Figure 1) shows some weak emission that starts at ~T-30 s and remains detectable until the burst went out of the BAT FOV at T+139 s. It is likely that the emission continues beyond T+139 s. The burst did not come back into the BAT FOV within the next ~ 2 hours.

The time-averaged spectrum from T-33.52 to T+104.01 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.49 ± 0.16. The fluence in the 15-150 keV band is 2.1 ± 0.2 x 10-6 erg cm-2. This fluence is larger than that of 60% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+99.95 s in the 15-150 keV band is 0.5 ± 0.2 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/944091/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
14h58m07.2s -09°44'41.9" 2.2' BAT-refined Lien et al. GCN Circ. 26418

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Carrasco et al. 26420 BOOTES-5/JGT optical limit BOOTES upper limits
Gamma-ray Ridnaia et al. 26484 Konus-Wind observation of GRB 191213A
(ulong)		 Konus-Wind Epeak=409 (-71,+110) keV

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

December 19, 2019