B. Sbarufatti (PSU), D.N. Burrows (PSU) and M.H. Siegel (PSU) for the Swift team
At 02:25:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210708A (trigger=1059460) (Sbarufatti et al. GCN Circ. 30413). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 93° from the Sun (4.4 hours East) and 108° from the 4%-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 Sakamoto et al. (GCN Circ. 30422),
the BAT ground-calculated position is RA, Dec = 173.759, -49.164 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a single peak of duration about 3 seconds, starting just before
The time-averaged spectrum from T-0.69 to T+2.44 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 2.05 ± 0.29.
The fluence in the 15-150 keV band is 1.1 ± 0.2 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1059460/BA/.
Analysis of the initial XRT data was reported by Burrows et al. (GCN Circ. 30416). We have analysed 9.1 ks of XRT data for GRB 210708A, from 85 s to 46.0 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode.
The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.7 (+0.3, -0.8).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+0.4, -0.3). The best-fitting absorption column is 2.9 (+1.2, -1.0) x 1
A summary of the PC-mode spectrum is thus:
Total column: 2.9 (+1.2, -1.0) x 1
Galactic foreground: 1.6 x 1
Excess significance: 2.2 σ
Photon index: 2.5 (+0.4, -0.3)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01059460.
The Swift/UVOT began settled observations of the field of GRB 210708A 121 s after the BAT trigger
(Siegel and Sbarufatti GCN Circ. 30425).
No optical afterglow consistent with the XRT position 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 |
|---|---|---|---|---|
| 1 |
-49°08'03.2" | 4.0" | XRT-final | UKSSDC |
| 1 |
-49°09'05.4" | 7.0" | XRT-refined | Burrows et al. GCN Circ. 30416 |
| 1 |
-49°09'50.2" | 2.2' | BAT-refined | Sakamoto et al. GCN Circ. 30422 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Lipunov et al. | 30412 | Swift GRB210708.10: Global MASTER-Net observations report |
MASTER | |
| Gamma-ray | Fletcher | 30421 | Fermi GBM Sub-Threshold Detection | Fermi GBM |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| 121 | 370 | 246 | >19.4 | |
| v | 427 | 4406 | 236 | >19.6 |
| b | 377 | 5077 | 108 | >19.3 |
| u | 121 | 5021 | 481 | >19.4 |
| w1 | 476 | 4816 | 236 | >18.9 |
| m2 | 452 | 4611 | 236 | >19.4 |
| w2 | 403 | 4201 | 236 | >19.5 |
Table 3. UVOT observations reported by Siegel and Sbarufatti (GCN Circ. 30425). 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.
July 10, 2021