S. Laha (GSFC/UMBC/CRESST), A.P. Beardmore (U. Leicester) and M.H. Siegel (PSU) for the Swift team
At 06:53:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210419A (trigger=1044032) (Laha et al. GCN Circ. 29828). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 88° from the Sun (4.0 hours East) and 93° from the 40%-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.
As reported by Palmer et al. (GCN Circ. 29838),
the BAT ground-calculated position is RA, Dec = 86.912, -65.452 deg which is RA(J2000) = 0
The BAT light curve (Figure 1) showed a complex structure with a duration of about ~100 s.
The time-averaged spectrum from T+21.92 to T+95.01 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 2.17 ± 0.24.
The fluence in the 15-150 keV band is 7.8 ± 1.2 x 1
Analysis of the initial XRT data was reported by Beardmore et al. (GCN Circ. 29835). We have analysed 8.7 ks of XRT data for GRB 210419A, from 134 s to 126.7 ks after the BAT trigger. The data comprise 143 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 29830).
The late-time light curve (Figure 2) (from T0+5.5 ks) can be modelled with a power-law decay with a decay index of α=0.88 ± 0.21.
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.71 (+0.11, -0.10). The best-fitting absorption column is 1.4 (+0.4, -0.3) x 1
A summary of the PC-mode spectrum is thus:
Total column: 1.9 (+0.7, -0.6) x 1
Galactic foreground: 7.8 x 1
Excess significance: 2.9 σ
Photon index: 2.60 (+0.29, -0.27)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01044032.
The Swift/UVOT began settled observations of the field of GRB 210419A 136 s after the BAT trigger
(Siegel and Laha GCN Circ. 29841).
No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 29830) 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
Figure 1. The BAT
mask-weighted light curve in the four individual and total
energy bands. The units are counts
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 |
---|---|---|---|---|
0 |
-65°30'08.1" | 2.0" | XRT-final | UKSSDC |
0 |
-65°30'09.0" | 2.0" | XRT-enhanced | Osborne et al. GCN Circ. 29830 |
0 |
-65°27'07.2" | 2.7' | BAT-refined | Palmer et al. GCN Circ. 29838 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Strausbaugh and Cucchiara | 29829 | LCO Optical Upper Limit | LCO | upper limits |
Optical | Lipunov et al. | 29832 | Swift GRB 210419A: Global MASTER-Net observations report |
MASTER | |
Optical | Lipunov et al. | 29836 | Swift GRB210419.98: Global MASTER-Net observations report |
MASTER |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
136 | 286 | 147 | >18.1 |
294 | 544 | 246 | >17.9 | |
white | 136 | 1027 | 333 | >18.1 |
v | 627 | 1079 | 58 | >17.5 |
b | 550 | 746 | 39 | >17.7 |
u | 294 | 721 | 265 | >17.9 |
w1 | 677 | 871 | 39 | >17.8 |
m2 | 651 | 1103 | 58 | >18.3 |
w2 | 119 | 1053 | 67 | >19.3 |
Table 3. UVOT observations reported by Siegel and Laha (GCN Circ. 29841). 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.
April 21, 2021