Swift Observations of GRB 210119A

M.J. Moss (GWU) for the Swift team

1. Introduction

At 02:54:09 UT, the Swift Burst Alert Telescope (BAT) triggered and located a short burst which would be either an unknown Soft Gamma Repeater or GRB 210119A (trigger=1017711) (Moss et al. GCN Circ. 29323). Due to an observing constraint, Swift did not slew immediately to the burst. At the time of the trigger, the initial BAT position was 43° from the Sun (1.2 hours West) and 89° from the 34%-illuminated Moon. Table 1 contains the best reported positions from Swift.

Tiurina et al. (GCN Circ. 29325) reported the position from MASTER for the optical afterglow of this GRB. 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 Ukwatta et al. (GCN Circ. 29332), the BAT ground-calculated position is RA, Dec = 282.822, -61.767 deg which is RA(J2000) = 18h51m17.4s Dec(J2000) = -61°45'59.7" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%.

The mask-weighted light curve (Figure 1) shows a single spike with a FRED-like shape, rising sharply at T+0 s and decaying to background by T+0.1 s. T90 (15-350 keV) is 0.06 ± 0.02 s (estimated error including systematics).

The time-averaged spectrum from T+0.00 to T+0.08 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.41 ± 0.22. The fluence in the 15-150 keV band is 7.1 ± 0.9 x 10-8 erg cm-2. This fluence is larger than that of 53% of the short GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T-0.46 s in the 15-150 keV band is 1.0 ± 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/1017711/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
18h51m17.4s -61°45'59.7" 1.5' BAT-refined Ukwatta et al. GCN Circ. 29332

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 29324 Fermi GRB 210119A: Global MASTER-Net
observations report 		MASTER
Optical Tiurina et al. 29325 Short Fermi GRB 210119A or new SGR
Swift J1851.2-6148: Possible MASTER
Short OT detection 		MASTER possible detection
Gamma-ray Fermi 29322 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Mangan et al. 29328 Fermi GBM observation Fermi GBM Epeak=515±168 keV
T90=0.05 seconds
Fluence=3.432±0.397x10-7erg cm-2
(51st percentile for short GRBs)
Gamma-ray 29329 Insight-HXMT/HE detection Insight-HXMT T90=0.03 seconds

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

January 21, 2021