Swift Observations of GRB 210708B

B. Sbarufatti (PSU) for the Swift team

1. Introduction

At 13:23:24 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 210708B (trigger=1059494) (Sbarufatti et al. GCN Circ. 30417). Due to an observing constraint, Swift did not slew immediately to the burst. At the time of the trigger, the initial BAT position was 34° from the Sun (2.3 hours East) and 51° from the 2%-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 Stamatikos et al. (GCN Circ. 30429), the BAT ground-calculated position is RA, Dec = 142.594, 14.523 deg which is RA(J2000) = 09h30m22.5s Dec(J2000) = +14°31'22.6" with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 74%.

The mask-weighted light curve (Figure 1) shows a broad peak with some sub-structure. Emission begins around T-100 s, peaks near the trigger time and decays to background by T+200 s. The burst position was not in the field of view of the BAT until about T-150 s. T90 (15-350 keV) is 298.43 ± 47.32 s (estimated error including systematics).

The time-averaged spectrum from -99.8 to 263.7 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.62 ± 0.26. The fluence in the 15-150 keV band is 2.2 ± 0.4 x 10-6 erg cm-2. This fluence is larger than that of 62% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+2.84 s in the 15-150 keV band is 0.0 ± 0.3 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/1059494/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
09h30m22.5s +14°31'22.6" 2.5' BAT-refined Stamatikos et al. GCN Circ. 30429

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 30426 Swift GRB 210708B: Global MASTER-Net
observations report 		MASTER

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

July 10, 2021