Swift Observations of GRB 210403A

K.L. Page (U. Leicester) for the Swift team

1. Introduction

At 08:27:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210403A (trigger=1040345) (Page and Lien GCN Circ. 29748). Swift did not slew immediately to the burst due to an observing constraint. At the time of the trigger, the initial BAT position was 39° from the Sun (0.6 hours West) and 79° from the 62%-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 Krimm et al. (GCN Circ. 29754), the BAT ground-calculated position is RA, Dec = 2.813, -33.024 deg which is RA(J2000) = 00^h11^m15.2^s Dec(J2000) = -33°01'27.2" with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 80%.

The lightcurve (Figure 1) has multiple peaks starting at T-40 s and ending at T+140 s. T₉₀ (15-350 keV) is 168.3 ± 9.2 s (estimated error including systematics).

The time-averaged spectrum from T-41.51 to T+137.18 s is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.93 ± 0.52, and E_peak of 37.4 ± 4.8 keV (χ² 52.21 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.7 ± 0.2 x 10^-6 erg cm^-2 and the 1-s peak flux measured from T+0.18 s in the 15-150 keV band is 1.1 ± 0.2 ph cm^-2 s^-1. This fluence is larger than that of 69% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). A fit to a simple power law gives a photon index of 2.13 ± 0.10 (χ² 73.02 for 57 d.o.f.). 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/1040345/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

00^h11^m15.2^s -33°01'27.2" 2.6' BAT-refined Krimm et al. GCN Circ. 29754

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 29751 Swift GRB210403.35: 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
00^h11^m15.2^s	-33°01'27.2"	2.6'	BAT-refined	Krimm et al. GCN Circ. 29754

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	29751	Swift GRB210403.35: Global MASTER-Net observations report	MASTER

April 5, 2021