P. D'Avanzo (INAF-OAB), J.P. Osborne (U. Leicester) and N.P.M. Kuin (UCL-MSSL) for the Swift team
At 02:39:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 181013A (trigger=866783) (D'Avanzo et al. GCN Circ. 23332). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 49° from the Sun (0.6 hours East) and 69° from the 17%-illuminated Moon. Table 1 contains the best reported positions from Swift.
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 Markwardt et al. (GCN Circ. 23335),
the BAT ground-calculated position is RA, Dec = 207.661, 40.107 deg, which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows peaks starting at ~T-5 s and ending at ~T+120 s.
The time-averaged spectrum from T+18.37 to T+123.97 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.82 ± 0.75.
The fluence in the 15-150 keV band is 3.0 ± 1.4 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/866783/BA/.
Analysis of the initial XRT data was reported by Osborne et al. (GCN Circ. 23334). We have analysed 190 s of Photon Counting (PC) mode XRT data for the Swift/BAT-detected burst GRB 181013A, collected between T0+115 s and T0+306 s. An uncatalogued X-ray source is detected consistent with being within 296 arcsec of the Swift/BAT position and is above the RASS limit and fading with 3-sigma significance, and is therefore likely the GRB afterglow.
The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=7.6 (+0.4, -1.0).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 0.98 (+0.30, -0.19). The
best-fitting absorption column is consistent with the Galactic value
of 9.4 x 1
The Swift/UVOT began settled observations of the field of GRB 181013A 106 s after the BAT trigger
(Kuin and D'Avanzo GCN Circ. 23336).
No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23334) 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
| RA (J2000) | Dec (J2000) | Error | Note | Reference |
|---|---|---|---|---|
| 1 |
+40°06'29.5" | 3.9" | XRT | Osborne et al. GCN Circ. 23334 |
| 1 |
+40°06'26.8" | 3.3' | BAT-refined | Markwardt et al. GCN Circ. 23335 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Lipunov et al. | 23333 | Global MASTER Net optical observations | MASTER | upper limits |
| Optical | Mazaeva et al. | 23341 | AbAO optical upper limit | Abastumani Astro. Obs. | upper limits |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| whit |
867 | 1017 | 147 | >20.2 |
| 266 | 516 | 246 | >19.1 | |
| white | 867 | 1017 | 147 | >20.2 |
| u | 266 | 516 | 246 | >19.1 |
| w1 | 818 | 7875 | 471 | >20.4 |
| m2 | 6035 | 7669 | 393 | >19.6 |
| w2 | 5624 | 7260 | 393 | >20.8 |
Table 3. UVOT observations reported by Kuin and D'Avanzo (GCN Circ. 23336). 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.
October 16, 2018