A. Tohuvavohu (PSU), J.A. Kennea (PSU) and S.J. LaPorte (PSU) for the Swift team
At 04:22:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181103A (trigger=870201) (Tohuvavohu et al. GCN Circ. 23402). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 70° from the Sun (1.4 hours West) and 49° from the 23%-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.
LaPorte and Tohuvavohu (GCN Circ. 23407) reported the detection 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. 23405),
the BAT ground-calculated position is RA, Dec = 197.093, 52.220 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) s shows a single FRED-shaped peak from
The time-averaged spectrum from T-0.89 to T+10.18 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.90 ± 0.27.
The fluence in the 15-150 keV band is 2.8 ± 0.5 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/870201/BA/.
Analysis of the initial XRT data was reported by Kennea et al. (GCN Circ. 23404). We have analysed 20 ks of XRT data for GRB 181103A, from 76 s to 235.8 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 23403).
The light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=0.36 (+0.08, -0.06), followed by a break at T+7798 s to an α of 0.82 (+0.35, -0.08).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.20 (+0.20, -0.19). The best-fitting absorption column is 6.3 (+1.3, -1.1) x 1
A summary of the PC-mode spectrum is thus:
Total column: 6.3 (+1.3, -1.1) x 1
Galactic foreground: 1.3 x 1
Excess significance: 8.9 σ
Photon index: 2.20 (+0.20, -0.19)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00870201.
The Swift/UVOT began settled observations of the field of GRB 181103A 92 s after the BAT trigger
(LaPorte and Tohuvavohu GCN Circ. 23407).
A fading source is detected in the initial UVOT exposures at a position consistent with the XRT position (Evans et al., GCN Circ. 23403).
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 |
+52°13'32.5" | 1.6" | XRT-final | UKSSDC |
1 |
+52°13'33.1" | 1.6" | XRT-enhanced | Evans et al. GCN Circ. 23403 |
1 |
+52°13'11.8" | 2.0' | BAT-refined | Krimm et al. GCN Circ. 23405 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Liu et al. | 23406 | Nanshan-1m optical upper limit | Xinjiang Astro. Obs. | upper limits |
Optical | Murata et al. | 23408 | MITSuME Okayama optical upper limits | MITSuME Okayama | upper limits |
Optical | Volnova et al. | 23410 | AbAO optical upper limit | Abastumani Astro. Obs. | upper limits |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
b | 534 | 898 | 58 | >19.08 |
uvm2 | 632 | 1126 | 57 | >18.19 |
u | 279 | 874 | 530 | 19.58± 0.25 |
v | 608 | 1103 | 58 | >18.21 |
uvw1 | 657 | 849 | 38 | >18.16 |
uvw2 | 584 | 1079 | 58 | >18.36 |
whit |
121 | 271 | 294 | 20.47± 0.29 |
white | 559 | 6763 | 579 | >21.12 |
Table 3. UVOT observations reported by LaPorte and Tohuvavohu (GCN Circ. 23407). 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.
November 6, 2018