A. Deich (PSU), D.N. Burrows (PSU) and N.P.M. Kuin (UCL-MSSL) for the Swift team
At 22:01:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180512A (trigger=832119) (Deich et al. GCN Circ. 22710). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 132° from the Sun (10.2 hours East) and 156° from the 8%-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 Cummings et al. (GCN Circ. 22720),
the BAT ground-calculated position is RA, Dec = 201.940, 21.404 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a weak pulse that starts at ~T+30 s, peaks at ~T+40 s, and ends at ~T+55 s.
The short spike at T+54.4 s is due to detector noise.
The time-averaged spectrum from T+29.00 to T+55.00 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 2.10 ± 0.27.
The fluence in the 15-150 keV band is 4.2 ± 0.7 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/832119/BA/.
Analysis of the initial XRT data was reported by Burrows et al. (GCN Circ. 22721). We have analysed 8.4 ks of XRT data for GRB 180512A, from 230 s to 101.5 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 22715).
The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=0.87 (+0.12, -0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+0.9, -0.8). The best-fitting absorption column is 2.3 (+1.5, -1.1) x 1
A summary of the PC-mode spectrum is thus:
Total column: 2.3 (+1.5, -1.1) x 1
Galactic foreground: 1.7 x 1
Excess significance: 3.6 σ
Photon index: 2.5 (+0.9, -0.8)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00832119.
The Swift/UVOT began settled observations of the field of GRB 180512A 218 s after the BAT trigger
(Kuin and Deich GCN Circ. 22717).
No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 22715) 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 |
+21°24'12.8" | 1.9" | XRT-final | UKSSDC |
1 |
+21°24'12.8" | 1.9" | XRT-enhanced | Evans et al. GCN Circ. 22715 |
1 |
+21°24'15.7" | 1.9' | BAT-refined | Cummings et al. GCN Circ. 22720 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | de Ugarte Postigo et al. | 22711 | Upper limits from OSN | Obs.de Sierra Nevada | upper limits |
Optical | Izzo | 22712 | OASDG optical observations | S.Di Giacomo Obs. | |
Optical | Heintz et al. | 22713 | NOT upper limits | NOT | upper limits |
Optical | Bolmer | 22714 | GROND upper limits | GROND | upper limits |
Optical | Guidorzi et al. | 22716 | LT prompt observations | Liverpool Telescope | |
Optical | Rossi and Palazzi | 22718 | LBT optical detection | LBT | detection |
Optical | Watson et al. | 22719 | RATIR Optical Observations | RATIR | upper limits |
Optical | Rossi et al. | 22724 | VLT/HAWK-I NIR Observations | VLT |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
218 | 368 | 147 | >21.1 |
white | 218 | 4358 | 344 | >21.2 |
v | 5986 | 6120 | 132 | >19.0 |
b | 3953 | 4153 | 197 | >20.7 |
u | 3748 | 16254 | 422 | >20.7 |
w1 | 3543 | 16019 | 1107 | >20.3 |
m2 | 9380 | 10280 | 886 | >20.9 |
w2 | 5781 | 5981 | 197 | >20.1 |
Table 3. UVOT observations reported by Kuin and Deich (GCN Circ. 22717). 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, 2018