A.Y. Lien (GSFC/UMBC), S.J. LaPorte (PSU) and J.D. Gropp (PSU) for the Swift team
At 16:42:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180111A (trigger=804692) (Lien et al. GCN Circ. 22318). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 140° from the Sun (9.5 hours West) and 94° from the 24%-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. 22318) 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 Stamatikos et al. (GCN Circ. 22324),
the BAT ground-calculated position is RA, Dec = 149.782, 48.254 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows several overlapping pulses that starts at ~
The time-averaged spectrum from T-0.30 to T+68.59 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.30 ± 0.03.
The fluence in the 15-150 keV band is 1.02 ± 0.02 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/804692/BA/.
Analysis of the initial XRT data was reported by LaPorte et al. (GCN Circ. 22322). We have analysed 12 ks of XRT data for GRB 180111A, from 76 s to 74.4 ks after the BAT trigger. The data comprise 117 s in Windowed Timing (WT) mode (the first 10 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 Evans et al. (GCN Circ. 22319).
The late-time light curve (Figure 2) (from T0+4.0 ks) can be modelled with a power-law decay with a decay index of α=1.42 (+0.28, -0.23).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.48 ± 0.09. The best-fitting absorption column is 4.0 (+3.0, -2.6) x 1
A summary of the PC-mode spectrum is thus:
Total column: 1.6 (+4.9, -0.5) x 1
Galactic foreground: 1.1 x 1
Excess significance: <1.6 σ
Photon index: 1.68 (+0.20, -0.13)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00804692.
The Swift/UVOT began settled observations of the field of GRB 180111A 98 s after the BAT trigger
(Gropp and Lien GCN Circ. 22327).
A fading source consistent with the XRT position (Evans et al. GCN Circ. 22319) 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 |
---|---|---|---|---|
0 |
+48°16'03.3" | UVOT-initial | Lien et al. GCN Circ. 22318 | |
0 |
+48°16'02.7" | 1.5" | XRT-final | UKSSDC |
0 |
+48°16'03.7" | 1.8" | XRT-enhanced | Evans et al. GCN Circ. 22319 |
0 |
+48°15'14.6" | 1.0' | BAT-refined | Stamatikos et al. GCN Circ. 22324 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Xin et al. | 22320 | Xinglong TNT possible optical detection | TNT | possible detection |
Optical | Butler et al. | 22323 | RATIR Optical and NIR Observations | RATIR | |
Optical | Mazaeva et al. | 22331 | AbAO optical observations | Abastumani Astro. Obs. | detection |
Optical | Kitaoka and Sakamoto | 22352 | AROMA-N optical observation | AROMA-N | |
Gamma-ray | Verrecchia et al. | 22321 | AGILE/MCAL detection | AGILE | |
Gamma-ray | Asaoka et al. | 22333 | CALET Gamma-Ray Burst Monitor detection | CALET | |
Gamma-ray | Svinkin et al. | 22336 | Konus-Wind observation | Konus-Wind | Duration=~61 seconds Fluence=8.44(-0.57,+0.64)x1 |
Gamma-ray | Li et al. | 22341 | Insight-HXMT/HE observation | Insight-HXMT |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
white | 84 | 233 | 147 | 19.95± 0.21 |
white | 86 | 6202 | 552 | 20.37± 0.16 |
v | 64 | 5181 | 206 | >19.23 |
b | 4365 | 6002 | 393 | >20.60 |
u | 296 | 5795 | 639 | 20.25± 0.35 |
w1 | 5391 | 5591 | 196 | >19.50 |
m2 | 650 | 670 | 19 | >17.15 |
w2 | 4776 | 6407 | 393 | 19.60± 0.27 |
Table 3. UVOT observations reported by Gropp and Lien (GCN Circ. 22327). 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.
January 17, 2018