Swift Observations of GRB 210605B

A. D'Ai (INAF-IASFPA) for the Swift team

1. Introduction

Poolakkil and Meegan (GCN Circ. 30209) reported the GRB detection. At 14:55:58.08 UT on 5 June 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210605B (trigger 644597763 / 210605622) which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2021, GCN Circ. 30130) The Fermi GBM Final Real-time Localization (GCN Circ. 30129) is consistent with the Swift position. 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'Ai et al. (GCN Circ. 30234). Of the sources reported by D'Ai et al. (GCN Circ. 30146), "Source 1" is fading with 2.5 sigma significance and thus is believed to be the GRB afterglow.

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=0.8 (+0.7, -0.4).

4. UVOT Observations and Analysis

UVOT results are not available.

Figure 1. The BAT light curve is not available.

XRT light curve

Figure 2. The XRT light curve. Any data from a crosshatched region are not included in the fit.

RA (J2000) Dec (J2000) Error Note Reference
01h02m59.01s -06°25'48.7" 5.8" XRT-final UKSSDC
01h02m58.95s -06°25'44.3" 5.7" XRT D'Ai et al. GCN Circ. 30234

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Gamma-ray Fermi 30129 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Poolakkil and Meegan 30209 Fermi GBM detection Fermi GBM Epeak=150±11 keV
T90=110 seconds
Fluence=10.12±0.44x10-6erg cm-2
(75th percentile for long GRBs)

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

June 15, 2021