Swift Observations of GRB 210826A

A. D'Ai (INAF-IASFPA) and A.A. Breeveld (UCL-MSSL) for the Swift team

1. Introduction

Ohno et al. (GCN Circ. 30721) reported the GRB detection. 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.

2. BAT Observations and Analysis

BAT did not observe this burst.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Avanzo et al. (GCN Circ. 30799).

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Breeveld and Sbarrato GCN Circ. 30729) of the field of GRB 210826A 36747 s after the LAT trigger (Ohno et al., GCN Circ. 30721). No new optical source consistent with the any of the 8 candidate XRT positions (D'Ai et al., GCN Circ. 30725) is detected in the initial UVOT exposures. Table 3 gives preliminary magnitudes using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc., 1358, 373). No correction has been made for the expected extinction in the Milky Way corresponding to a reddening of EB-V of 0.032 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

RA (J2000) Dec (J2000) Error Note Reference
03h02m14.12s -71°54'11.4" 9.90" XRT ?

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 30720 Fermi GRB 210826A: Global MASTER-Net
observations report 		MASTER
Gamma-ray Fermi 30716 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Biltzinger et al. 30717 BALROG localization (Fermi Trigger
651654110 / GRB 210826293)		 BALROG
Gamma-ray Ohno et al. 30721 Fermi-LAT detection Fermi LAT Emax=7.7 GeV
Gamma-ray Prasad et al. 30737 AstroSat CZTI detection CZTI

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
v 36747 49716 4869 >20.9

Table 3. UVOT observation reported by Breeveld and Sbarrato (GCN Circ. 30729). The start and stop time of the exposure are given in seconds since the BAT trigger. The preliminary 3-σ upper limit is given. No correction has been made for extinction in the Milky Way.

September 11, 2021