Swift Observations of GRB 131018B

1. Introduction

Vianello et al. (GCN Circ. 15357) reported the GRB detection. At 16:08:39 on 2013-10-18 Fermi LAT detected high energy emission from GRB 131018B, which was also detected by Fermi-GBM ( trigger bn131018673). 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.

2. BAT Observations and Analysis

BAT results are not available.

3. XRT Observations and Analysis

We have analysed 9.5 ks of XRT data for the Fermi/LAT-detected burst: GRB 131018B, from 83.1 ks to 1100.0 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Fermi/LAT error circle. We cannot determine at the present time whether the source is fading.

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020308.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 131018B 83 ks after the LAT trigger (Vianello et al., GCN Circ. 15357) (Oates and D'Avanzo GCN Circ. 15362). No new optical candidate is detected within the LAT error circle (Vianello et al., GCN Circ. 15357) 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 E_B-V of 0.58 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

Figure 2. The XRT light curve. Any data from a cross-hatched region are not included in the fit.

RA (J2000)	Dec (J2000)	Error	Note	Reference
20h18m08.86s	+23°11'15.3"	4.9"	XRT-final	UKSSDC
20h18m08.86s	+23°11'15.3"	4.9"	XRT	D'Avanzo et al. GCN Circ. 15361

Table 1. Positions from the Swift instruments.

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Troja et al.	15437	RATIR Optical/NIR Observations	RATIR
Gamma-ray	Vianello et al.	15357	Fermi-LAT detection of a burst	Fermi LAT	detection
Gamma-ray	Zhang	15360	Fermi GBM observation	Fermi GBM	Epeak = 77 ± 7 keV

Table 2. Summary of GCN Circulars from other observatories sorted by band and then circular number.

Filter	Tstart(s)	Tstop(s)	Exp(s)	Mag
white	90363	91160	785	>21.7
v	91168	91427	255	>19.4
u	88969	95244	1300	>20.6

Table 3. UVOT observations reported by Oates and D'Avanzo (GCN Circ. 15362). 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.