A.Y. Lien (GSFC/UMBC), K.L. Page (U. Leicester) and M.H. Siegel (PSU) for the Swift team
At 21:52:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210207B (trigger=1031297) (Lien et al. GCN Circ. 29420). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 81° from the Sun (3.4 hours West) and 78° from the 17%-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.
Lien et al. (GCN Circ. 29420) reported the discovery with UVOT of an optical afterglow. 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. 29435),
the BAT ground-calculated position is RA, Dec = 270.614, 53.700 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts at ~
The time-averaged spectrum from T-0.25 to T+106.40 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.20 ± 0.07.
The fluence in the 15-150 keV band is 4.3 ± 0.2 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1031297/BA/.
Analysis of the initial XRT data was reported by Page et al. (GCN Circ. 29427). We have analysed 20 ks of XRT data for GRB 210207B, from 80 s to 302.1 ks after the BAT trigger. The data comprise 329 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 29422).
The late-time light curve (Figure 2) (from T0+3.9 ks) can be modelled with an initial power-law decay with an index of α=0.99 (+0.13, -0.27), followed by a break at T+11.4 ks to an α of 1.69 (+0.32, -0.11).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.99 ± 0.04. The best-fitting absorption column is 1.38 ± 0.13 x 1
A summary of the PC-mode spectrum is thus:
Total column: 7.2 (+2.9, -2.6) x 1
Galactic foreground: 3.5 x 1
Excess significance: 2.3 σ
Photon index: 1.78 (+0.11, -0.10)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01031297.
The Swift/UVOT began settled observations of the field of GRB 210207B 82 s after the BAT trigger
(Siegel and Lien GCN Circ. 29436).
A source consistent with the XRT position is detected in the initial UVOT exposures, as reported in the initial circular and confirmed by ARIES (Kumar et al., GCN Circ. 29421), KAIT (Zheng & Filippenko, GCN Circ. 29430) and LCO (Strausbaugh & Cucchiara, GCN Circ. 294311).
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 |
+53°40'55.8" | 0.42" | UVOT-refined | Siegel and Lien GCN Circ. 29436 |
| 1 |
+53°40'55.8" | 2.0" | XRT-final | UKSSDC |
| 1 |
+53°40'55.5" | 1.7" | XRT-enhanced | Beardmore et al. GCN Circ. 29422 |
| 1 |
+53°42'01.1" | 1.4' | BAT-refined | Krimm et al. GCN Circ. 29435 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Kumar et al. | 29421 | optical detection with 3.6m Devasthal Optical Telescope |
Devasthal Opt.Tel. | detection |
| Optical | Belkin et al. | 29423 | AbAO optical upper limit | Abastumani Astro. Obs. | upper limits |
| Optical | Zheng and Filippenko | 29430 | KAIT Optical Observations | KAIT | marginal detection |
| Optical | Strausbaugh and Cucchiara | 29431 | LCO Optical Afterglow Detection | LCO | detection |
| Optical | Strausbaugh and Cucchiara | 29441 | Continued LCO Observations | LCO | |
| Optical | Sutaria and Ray | 29759 | Prompt and very late time observations with HCT. |
Himalayan Chandra Telescope | |
| Gamma-ray | Frederiks et al. | 29426 | Konus-Wind detection | Konus-Wind | |
| Gamma-ray | Ursi et al. | 29428 | AGILE observations | AGILE | |
| Gamma-ray | Zheng et al. | 29434 | Insight-HXMT/HE detection | Insight-HXMT | |
| Gamma-ray | Waratkar et al. | 29437 | AstroSat CZTI detection | CZTI | |
| Other | Zhao et al. | 29486 | GECAM detection | detection |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| white (fc) | 83 | 233 | 147 | 13.66±1.13 |
| white | 4081 | 5717 | 393 | 17.91±0.04 |
| white | 61938 | 62307 | 361 | 21.06±0.32 |
| v | 4492 | 4692 | 196 | 17.61±0.10 |
| v | 9433 | 10341 | 885 | 18.54±0.09 |
| v | 56912 | 74907 | 1297 | >19.84 |
| b | 3876 | 5512 | 393 | 17.95±0.05 |
| b | 44686 | 45593 | 885 | >20.99 |
| b | 61025 | 79012 | 1770 | 20.79±0.18 |
| u (fc) | 295 | 410 | 113 | 14.42±0.03 |
| u | 5106 | 5306 | 196 | 17.80±0.09 |
| u | 43773 | 44680 | 885 | 20.47±0.26 |
| u | 51795 | 69087 | 612 | >19.80 |
| uvw1 | 4901 | 5101 | 196 | 18.23±0.18 |
| uvw1 | 11254 | 11428 | 171 | >18.90 |
| uvw1 | 39917 | 40544 | 616 | >19.72 |
| uvw1 | 50889 | 68646 | 1771 | >20.53 |
| uvm2 | 4697 | 4896 | 196 | >19.12 |
| uvm2 | 10346 | 11246 | 885 | >20.23 |
| uvw2 | 4287 | 5871 | 342 | >19.39 |
| uvw2 | 56005 | 74346 | 1771 | >20.68 |
Table 3. UVOT observations reported by Siegel and Lien (GCN Circ. 29436). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary detections and 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.
April 5, 2021