J.D. Gropp (PSU), A. D'Ai (INAF-IASFPA) and A.A. Breeveld (UCL-MSSL) for the Swift team
At 19:24:34 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180510A (trigger=831810) (Gropp et al. GCN Circ. 22695). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 134° from the Sun (8.7 hours West) and 75° from the 25%-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.
BAT refined results are not available.
Analysis of the initial XRT data was reported by D'Ai et al. (GCN Circ. 22707). We have analysed 7.9 ks of XRT data for GRB 180510A, from 77 s to 130.4 ks after the BAT trigger. The data comprise 228 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.
The late-time light curve (Figure 2) (from T0+15.8 ks) can be modelled with a power-law decay with a decay index of α=1.33 (+0.20, -0.17).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 (+0.08, -0.07). The best-fitting absorption column is 5.2 ± 0.5 x 1
A summary of the PC-mode spectrum is thus:
Total column: 3.5 (+1.4, -1.2) x 1
Galactic foreground: 2.1 x 1
Excess significance: 1.9 σ
Photon index: 2.01 (+0.30, -0.28)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00831810.
The Swift/UVOT began settled observations of the field of GRB 180510A 97 s after the BAT trigger
(Breeveld et al. GCN Circ. 22709).
A source is detected at the edge of the refined XRT position (D’Ai et al. GCN Circ. 22707) but this is consistent with the position of a USNO-B1.0 source (at 276.332, -31.908), and it is not clear if we see any fading.
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 |
-31°54'29.1" | 3.6" | XRT-final | UKSSDC |
| 1 |
-31°54'29.1" | 3.6" | XRT-refined | D'Ai et al. GCN Circ. 22707 |
| 1 |
-31°54'38" | 3' | BAT-initial | Gropp et al. GCN Circ. 22695 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Horiuchi et al. | 22730 | MITSuME Ishigakijima optical upper limits |
MITSuME Ishigakijima | upper limits |
| Gamma-ray | Tsvetkova et al. | 22722 | Konus-Wind observation | Konus-Wind | Duration=~23.5 seconds Fluence=1.07(-0.14,+0.21)x1 |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| whit |
97 | 247 | 147 | 20.0 ± 0.3 |
| white | 28989 | 29010 | 21 | >19.2 |
| v | 22961 | 23272 | 301 | >19.4 |
| b | 28076 | 28983 | 885 | 20.2 ± 0.2 |
| u | 310 | 322 | 12 | >17.6 |
| uvw1 | 15854 | 16753 | 886 | >20.6 |
| uvw2 | 22055 | 22955 | 886 | >20.5 |
Table 3. UVOT observations reported by Breeveld et al. (GCN Circ. 22709). 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.
May 15, 2018