Swift Observations of GRB 131031A

J.R. Cummings (), B.P. Gompertz (U. Leicester) and P. Kuin (UCL/MSSL) for the Swift team

1. Introduction

At 11:33:31 UT, Swift-BAT rate-triggered on GRB 131031A (trigger 576277) (Cummings GCN Circ. 15421). No significant source was found onboard. Table 1 contains the best reported positions from Swift.

Gorosabel et al. (GCN Circ. 15426) reported the position from CAHA for the optical afterglow of this GRB. 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 http://gcn.gsfc.nasa.gov/swift_gnd_ana.html.

2. BAT Observations and Analysis

3. XRT Observations and Analysis

We have analysed 8.4 ks of XRT data for the Swift/BAT-detected burst: GRB 131031A, from 39.7 ks to 461.6 ks after the Swift/BAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Swift/BAT error circle. The source has a mean count rate of 8.8 x 10-3 ct s-1; we cannot determine at the present time whether it is fading.

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020317.

4. UVOT Observations and Analysis

The Swift/UVOT began observations of the field of GRB 131031A 39.7ks after the ground-detected BAT trigger (Kuin and Troja GCN Circ. 15433). An otical afterglow candidate was reported by Gorosabel et al. (GCN Circ. 15426) but no optical afterglow consistent with the XRT position (Gompertz et al., GCN Circ. 15423) 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 EB-V of 0.03 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

XRT light curve

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
01h58m26.45s -01°34'43.7" 4.7" XRT-final UKSSDC
01h58m26.45s -01°34'43.7" 4.7" XRT Gompertz and Page GCN Circ. 15424
01h58m28.3s -01°36'11" 4' BAT-initial Cummings GCN Circ. 15421

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Terron et al. 15422 1.23m CAHA I-band and 1.5m OSN R-band
observations of Swift/BAT error circle		 CAHA
Optical Gorosabel et al. 15426 1.23m CAHA afterglow candidate CAHA detection
Optical Yurkov et al. 15429 MASTER optical observation MASTER
Optical Cucchiara et al. 15438 RATIR Optical and NIR Observations RATIR detection
Optical Littlejohns et al. 15439 RATIR Optical and NIR Observations and Upper
Limits		 RATIR upper limits
Optical Volnova et al. 15486 Mondy optical observations Mondy
Gamma-ray Golenetskii et al. 15428 Konus-Wind observation Konus-Wind detection
Gamma-ray Fitzpatrick and Bhat 15434 Fermi GBM detection Fermi GBM Epeak = 92.1 ± 7.0 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 40274 52042 1559 >21.1
v 40825 47155 762 >20.1
u 39724 51207 1559 >21.1

Table 3. UVOT observations reported by Kuin and Troja (GCN Circ. 15433). 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.


November 15, 2013