Swift Observations of GRB 220302A

E. Troja (NASA/GSFC/UMCP), M. Perri (SSDC and INAF-OAR) and M.H. Siegel (PSU) for the Swift team

1. Introduction

At 07:40:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220302A (trigger=1094950) (Troja et al. GCN Circ. 31661). Swift did not slew to the burst. At the time of the trigger, the initial BAT position was 67° from the Sun (2.8 hours West) and 72° from the 0%-illuminated Moon. Table 1 contains the best reported positions from Swift, and the latest XRT position can be viewed at http://www.swift.ac.uk/xrt_positions.

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

BAT refined results are not available.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Perri et al. (GCN Circ. 31673). We have analysed 7.7 ks of XRT data for GRB 220302A, from 32.5 ks to 241.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 31666).

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=0.7 ± 0.3.

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01094950.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 220302A 32464 s after the BAT trigger (Siegel and Troja GCN Circ. 31682). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 31666) 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 0.217 mag. in the direction of the GRB (Schlegel et al. 1998).

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.

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
20h05m43.30s +49°23'13.1" 2.9" XRT-final UKSSDC
20h05m43.30s +49°23'13.1" 2.9" XRT-enhanced Osborne et al. GCN Circ. 31666
20h05m44s +49°23'20" 3' BAT-initial Troja et al. GCN Circ. 31661

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 31662 Swift GRB 220302A: Global MASTER-Net
observations report 		MASTER
Optical Hu et al. 31669 BOOTES-5/JGT optical upper limit BOOTES upper limits

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
whiteFC 32464 32614 147 >19.9
white 32464 32614 147 >19.9
v 32621 33528 885 >19.2
m2 33533 34194 651 >19.7

Table 3. UVOT observations reported by Siegel and Troja (GCN Circ. 31682). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.

March 5, 2022