S.B. Cenko (GSFC), V. D'Elia (SSDC and INAF-OAR) and A. Belles (PSU) for the Swift team
At 11:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220930A (trigger=1125809) (Cenko et al. GCN Circ. 32603). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 121° from the Sun (8.1 hours West) and 170° from the 23%-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 Barthelmy et al. (GCN Circ. 32612),
the BAT ground-calculated position is RA, Dec = 64.725, 13.353 deg which is RA(J2000) = 0
The BAT light curve (Figure 1) showed a complex structure with a duration of about 200 s.
The time-averaged spectrum from T-0.42 to T+235.67 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.59 ± 0.13.
The fluence in the 15-150 keV band is 5.5 ± 0.4 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1125809/BA/.
Analysis of the initial XRT data was reported by D'Elia et al. (GCN Circ. 32611). We have analysed 15 ks of XRT data for GRB 220930A, from 159 s to 212.0 ks after the BAT trigger. The data comprise 390 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 32605).
The late-time light curve (Figure 2) (from T0+5.1 ks) can be modelled with a power-law decay with a decay index of α=1.23 (+0.08, -0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.59 ± 0.08. The best-fitting absorption column is 4.9 (+0.6, -0.5) x 1
A summary of the PC-mode spectrum is thus:
Total column: 6.4 (+1.2, -1.1) x 1
Galactic foreground: 2.8 x 1
Excess significance: 5.4 σ
Photon index: 1.82 (+0.16, -0.15)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01125809.
The Swift/UVOT began settled observations of the field of GRB 220930A 180 s after the BAT trigger
(Belles and Cenko GCN Circ. 32609).
No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 32608) 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 |
+13°20'56.8" | 2.0" | XRT-final | UKSSDC |
0 |
+13°20'56.5" | 2.2" | XRT-enhanced | Evans et al. GCN Circ. 32608 |
0 |
+13°21'12.0" | 1.7' | BAT-refined | Barthelmy et al. GCN Circ. 32612 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Watson et al. | 32604 | COATLI Upper Limits | COATLI | upper limits |
Optical | Hu et al. | 32606 | BOOTES-5/JGT early optical upper limit | BOOTES | upper limits |
Optical | Lipunov et al. | 32607 | Swift GRB 220930A: Global MASTER-Net observations report |
MASTER | |
Optical | Strausbaugh and Cucchiara | 32610 | LCOGT Optical Upper Limits | Las Cumbres Obs. Global Tele.Network | upper limits |
Optical | Pankov et al. | 32617 | AbAO Optical Upper Limit | Abastumani Astro. Obs. | upper limits |
Gamma-ray | Gopalakrishnan et al. | 32613 | AstroSat CZTI detection | CZTI | |
Gamma-ray | Ridnaia et al. | 32614 | Konus-Wind detection | Konus-Wind | Duration=~76.0 seconds Fluence=1.78(-0.64,+0.98)x1 |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
w |
180 | 330 | 147 | >20.71 |
338 | 588 | 245 | >19.95 | |
wh | 618 | 1368 | 225 | >20.93 |
v | 669 | 1418 | 97 | >18.73 |
b | 594 | 1343 | 77 | >19.59 |
u | 744 | 1318 | 58 | >18.99 |
w1 | 719 | 1467 | 77 | >18.83 |
m2 | 693 | 1442 | 77 | >18.59 |
w2 | 644 | 1393 | 97 | >19.10 |
Table 3. UVOT observations reported by Belles and Cenko (GCN Circ. 32609). 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.
October 3, 2022