Swift Observations of GRB 210422A

E. Troja (NASA/GSFC/UMCP) for the Swift team

1. Introduction

At 17:47:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210422A (trigger=1044678) (Troja et al. GCN Circ. 29886). Due to an observing constraint, Swift did not slew immediately to the burst. 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 Barthelmy et al. (GCN Circ. 29897), the BAT ground-calculated position is RA, Dec = 21.077, 42.100 deg which is RA(J2000) = 01^h24^m18.6^s Dec(J2000) = +42°05'58.2" with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 53%.

The BAT light curve (Figure 1) showed a complex structure with a duration of about ~30 s. T₉₀ (15-350 keV) is 39.00 ± 7.28 s (estimated error including systematics).

The time-averaged spectrum from -34.40 s to -20.56 s and -19.40s to 7.59 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.70 ± 0.22. The fluence in the 15-150 keV band is 7.2 ± 1.1 x 10^-7 erg cm^-2. This fluence is larger than that of 31% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+0.59 s in the 15-150 keV band is 1.3 ± 0.2 ph cm^-2 s^-1. All the quoted errors are at the 90% confidence level.

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

01^h24^m18.6^s +42°05'58.2" 2.1' BAT-refined Barthelmy et al. GCN Circ. 29897

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 29887 Swift GRB210422.74: Global MASTER-Net
observations report MASTER

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

RA (J2000)	Dec (J2000)	Error	Note	Reference
01^h24^m18.6^s	+42°05'58.2"	2.1'	BAT-refined	Barthelmy et al. GCN Circ. 29897

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	29887	Swift GRB210422.74: Global MASTER-Net observations report	MASTER

April 25, 2021