K.K. Simpson (PSU), A. Tohuvavohu (U. Toronto) and F.E. Marshall (NASA/GSFC) for the Swift team
At 20:33:15 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200512A (trigger=971846) (Simpson et al. GCN Circ. 27726). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 47° from the Sun (2.8 hours West) and 63° from the 67%-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. 27742),
the BAT ground-calculated position is RA, Dec = 7.417, -2.217 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a single-pulse structure.
The main emission starts at ~T-3 s, peaks at ~T+3 s, and ends at ~T+40 s.
In addition, there are some weak emission that lasts until ~T+80 s.
The time-averaged spectrum from T-2.86 to T+78.14 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.68 ± 0.18.
The fluence in the 15-150 keV band is 8.1 ± 1.0 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/971846/BA/.
Analysis of the initial XRT data was reported by Tohuvavohu et al. (GCN Circ. 27729). We have analysed 10 ks of XRT data for GRB 200512A, from 63 s to 154.7 ks after the BAT trigger. The data comprise 153 s in Windowed Timing (WT) mode (the first 5 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 Goad et al. (GCN Circ. 27728).
The light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=0.42 (+0.20, -0.38), followed by a break at T+161 s to an α of 1.92 ± 0.10.
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.49 ± 0.13. The best-fitting absorption column is 2.6 (+0.7, -0.6) x 1
A summary of the PC-mode spectrum is thus:
Total column: 2.4 (+1.4, -1.2) x 1
Galactic foreground: 2.9 x 1
Excess significance: 3.0 σ
Photon index: 1.20 (+0.23, -0.22)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00971846.
Analysis of the UVOT data was reported by Marshall and Simpson (GCN Circ. 27730).
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 |
-02°12'37.3" | 1.4" | XRT-final | UKSSDC |
| 0 |
-02°12'37.3" | 1.4" | XRT-enhanced | Goad et al. GCN Circ. 27728 |
| 0 |
-02°13'01.1" | 1.5' | BAT-refined | Sakamoto et al. GCN Circ. 27742 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Strausbaugh and Cucchiara | 27733 | LCO Optical Upper Limits | LCO | upper limits |
| Gamma-ray | Veres | 27731 | Fermi GBM Sub-Threshold Detection | Fermi GBM |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| whit |
78 | 228 | 147 | >19.9 |
| 236 | 486 | 246 | >19.8 | |
| v | 567 | 760 | 39 | >17.1 |
| b | 493 | 858 | 58 | >19.0 |
| u | 236 | 833 | 285 | >19.7 |
| w1 | 617 | 809 | 39 | >17.9 |
Table 3. UVOT observations reported by Marshall and Simpson (GCN Circ. 27730). 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.
May 15, 2020