A. D'Ai (INAF-IASFPA), K.L. Page (U. Leicester) and N.J. Klingler (GSFC/UMBC/CRESTII) for the Swift team
At 18:16:28 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220711B (trigger=1115766) (D'Ai et al. GCN Circ. 32366). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 126° from the Sun (10.1 hours East) and 50° from the 94%-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.
Malesani et al. (GCN Circ. 32368) reported the position from NOT for the optical afterglow of this GRB. 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 Krimm et al. (GCN Circ. 32374),
the BAT ground-calculated position is RA, Dec = 262.018, 24.674 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts at ~T-40 s and ends at ~T+100 s.
The main peak occurs at ~
The time-averaged spectrum from T-37.72 to T+98.89 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.75 ± 0.08.
The fluence in the 15-150 keV band is 6.0 ± 0.3 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1115766/BA/.
Analysis of the initial XRT data was reported by Page et al. (GCN Circ. 32372). We have analysed 21 ks of XRT data for GRB 220711B, from 93 s to 704.3 ks after the BAT trigger. The data comprise 414 s in Windowed Timing (WT) mode (the first 8 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 Beardmore et al. (GCN Circ. 32370).
The late-time light curve (Figure 2) (from T0+4.2 ks) can be modelled with a power-law decay with a decay index of α=1.04 (+0.07, -0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 ± 0.04. The best-fitting absorption column is 2.59 ± 0.16 x 1
A summary of the PC-mode spectrum is thus:
Total column: 2.3 ± 0.6 x 1
Galactic foreground: 7.4 x 1
Excess significance: 4.3 σ
Photon index: 2.08 (+0.18, -0.17)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01115766.
The Swift/UVOT began settled observations of the field of GRB 220711B 114 s after the BAT trigger
(Klingler and D'Ai GCN Circ. 32371).
No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 32370) 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 |
+24°40'51.5" | 2.0" | XRT-final | UKSSDC |
| 1 |
+24°40'51.5" | 2.1" | XRT-enhanced | Beardmore et al. GCN Circ. 32370 |
| 1 |
+24°40'27.1" | 1.3' | BAT-refined | Krimm et al. GCN Circ. 32374 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Strausbaugh and Cucchiara | 32367 | LCO Optical Upper Limits | LCO | upper limits |
| Optical | Malesani et al. | 32368 | NOT optical observations | NOT | |
| Optical | Lipunov et al. | 32378 | Fermi GRB 220711B: Global MASTER-Net observations report |
MASTER | |
| Optical | Swain et al. | 32380 | GIT optical upper limits | GROWTH-India Tel. | upper limits |
| Optical | Komesh et al. | 32381 | NUTTelA-TAO / BSTI Early Optical Limits (Preliminary) |
NUTTelA | upper limits |
| Optical | Guelbenzu et al. | 32383 | GROND observations | GROND | detection |
| Optical | Sanchez-Ramirez et al. | 32386 | 10.4 m GTC(+EMIR) observations | GTC | detection |
| Optical | Sanchez-Ramirez et al. | 32387 | 10.4 m GTC(+EMIR) observations | GTC | detection |
| Optical | Hu | 32388 | Retraction of GRB 220711B: 10.4 m GTC(+EMIR) observations (GCN Circ. 32387) |
GTC | retraction |
| Gamma-ray | Fermi | 32365 | Fermi GBM Final Real-time Localization | Fermi GBM | |
| Gamma-ray | Lesage and Meegan | 32369 | Fermi GBM Detection | Fermi GBM | Fluence=1.02±0.04x1 (brighter than 75% of long GRBs) |
| Gamma-ray | Shimizu et al. | 32416 | CALET Gamma-Ray Burst Monitor detection | CALET |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| whit |
114 | 264 | 147 | >21.0 |
| 326 | 576 | 246 | >20.2 | |
| white | 114 | 915 | 221 | >21.0 |
| v | 655 | 4601 | 236 | >19.7 |
| b | 581 | 773 | 39 | >19.7 |
| u | 326 | 5120 | 368 | >20.4 |
| w1 | 704 | 5011 | 216 | >20.5 |
| m2 | 852 | 4806 | 216 | >19.4 |
| w2 | 631 | 4396 | 216 | >20.4 |
Table 3. UVOT observations reported by Klingler and D'Ai (GCN Circ. 32371). 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 20, 2022