Swift Observations of GRB 131014A

J.A. Kennea (PSU), A. Amaral-Rogers (U.Leicester) and C.A. Swenson (PSU) for the Swift team

1. Introduction

Kennea and Amaral-Rogers (GCN Circ. 15335) reported the initial Swift results. On October 14, 2013 at 17:24 UT, Swift began a series of target of opportunity observations to cover the region around GRB131014A (Fitzpatrick et al., GCN Circ. 15332, Evans, GCN Circ. 15334), approximately 12.3 hours after the burst was detected by Fermi. 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.

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

Analysis of the initial XRT data was reported by Amaral-Rogers et al. (GCN Circ. 15344). We have analysed 11 ks of XRT data for the Fermi/LAT-detected burst: GRB 131014A, from 44.1 ks to 173.4 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode.

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.53 ± 0.28.

A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.7, -0.6). The best-fitting absorption column is 6.8 (+4.0, -3.0) x 1021 cm-2, in excess of the Galactic value of 2.2 x 1021 cm-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10-11 (8.5 x 10-11) erg cm-2 count-1.

4. UVOT Observations and Analysis

The Swift/UVOT began observations of the field of GRB 131014A starting approximately 45.7 ks after the Fermi LAT detection (Desiante et al. 2013, GCN Circ. 15333) (Swenson and Amaral-Rogers GCN Circ. 15342). We do not detect any new source consistent with the NOT afterglow candidate (Schulze et al. 2013, GCN Circ. 15337). 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 0.22 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

RA (J2000) Dec (J2000) Error Note Reference
06h41m12.18s -19°05'49.4" 3.9" XRT-final UKSSDC
06h41m12.80s -19°05'49.6" 6" XRT Evans and Osborne GCN Circ. 15351

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Xu et al. 15336 Nanshan optical observations Xinjiang Astro.Obs.
Optical Schulze et al. 15337 NOT afterglow candidate NOT detection
Optical Troja et al. 15340 RATIR Optical and NIR Observations RATIR detection
Optical Troja et al. 15346 RATIR Optical/NIR Afterglow Confirmation RATIR detection
Optical Kann et al. 15347 GROND observations GROND
Optical Troja et al. 15364 RATIR Optical/NIR Afterglow Retraction RATIR retraction
Gamma-ray Fitzpatrick and Xiong 15332 Fermi GBM detection Fermi GBM Epeak = 318 ± 3 keV
Gamma-ray Desiante et al. 15333 Fermi-LAT detection Fermi LAT detection
Gamma-ray Golenetskii et al. 15338 Konus-Wind observation Konus-Wind Epeak = 346 ± 9 keV
Gamma-ray Kawano et al. 15348 Suzaku WAM observation of the prompt emission Suzaku WAM light curve
Gamma-ray Hurley et al. 15363 IPN Triangulation IPN

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

Filter Tstart Tstop Exposure Mag
u 45,688 74,324 1239 >20.9

Table 3. UVOT observation reported by Swenson and Amaral-Rogers (GCN Circ. 15342). The start and stop time of the exposure are given in seconds since the BAT trigger. The preliminary 3-σ upper limit is given. No correction has been made for extinction in the Milky Way.


October 22, 2013