Swift Observations of GRB 210827A

J.D. Gropp (PSU) and A.A. Breeveld (UCL-MSSL) for the Swift team

1. Introduction

DeLaunay et al. (GCN Circ. 30732) reported the GRB detection. Swift/BAT did not trigger on GRB 210827A (T0: 2021-08-27 09:59:24.34 UTC, Fermi/GBM trigger # 651751169, GCN Circ. 30724). 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 refined results are not available.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Avanzo et al. (GCN Circ. 30745).

The light curve (Figure 2) can be described with a single power-law with a decay index α = 1.0 (+0.5, -0.4).

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Breeveld and D'Avanzo GCN Circ. 30743) of the Swift/BAT-GUANO-detected burst GRB 210827A (DeLaunay et al., GCN Circ. 30732) 44720s after the Fermi-GBM trigger (Fermi GBM team, GCN Circ. 30724). No new optical source consistent with the candidate XRT positions (Gropp et al., GCN Circ. 30734) 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 E_B-V of 0.0111 mag. in the direction of the GRB (Schlegel et al. 1998).

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

11^h39^m36.07^s +55°43'26.2" 3.8" XRT-final UKSSDC

11^h39^m36.07^s +55°43'26.0" 3.8" XRT GCN Circ. 30734

11^h39^m40.34^s +55°47'08.88" 4' BAT-GUANO DeLaunay et al. GCN Circ. 30732

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 30736 Fermi GRB 210827A: Global MASTER-Net
observations report MASTER

Optical Hu et al. 30742 BOOTES-5/JGT optical upper limit BOOTES upper limits

Gamma-ray Fermi 30724 Fermi GBM Final Real-time Localization Fermi GBM

Gamma-ray Lesage et al. 30738 Fermi GBM Observation Fermi GBM T₉₀=9 seconds
Fluence=7±1x10^-7erg cm^-2
(9^th percentile for long GRBs)

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

Filter T_start(s) T_stop(s) Exp(s) Mag

white 44720 50434 1650 >21.6

RA (J2000)	Dec (J2000)	Error	Note	Reference
11^h39^m36.07^s	+55°43'26.2"	3.8"	XRT-final	UKSSDC
11^h39^m36.07^s	+55°43'26.0"	3.8"	XRT	GCN Circ. 30734
11^h39^m40.34^s	+55°47'08.88"	4'	BAT-GUANO	DeLaunay et al. GCN Circ. 30732

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	30736	Fermi GRB 210827A: Global MASTER-Net observations report	MASTER
Optical	Hu et al.	30742	BOOTES-5/JGT optical upper limit	BOOTES	upper limits
Gamma-ray	Fermi	30724	Fermi GBM Final Real-time Localization	Fermi GBM
Gamma-ray	Lesage et al.	30738	Fermi GBM Observation	Fermi GBM	T₉₀=9 seconds Fluence=7±1x10^-7erg cm^-2 (9^th percentile for long GRBs)

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	44720	50434	1650	>21.6

Table 3. UVOT observation reported by Breeveld and D'Avanzo (GCN Circ. 30743). 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.

August 31, 2021