Swift Observations of GRB 140808A

K.L. Page (U. Leicester) and S.R. Oates (IAA-CSIC/UCL-MSSL) for the Swift team

1. Introduction

Zhang (GCN Circ. 16669) reported the GRB detection. At 00:54:00.62 UT on 08 August 2014, the Fermi Gamma-Ray Burst  Monitor triggered and located GRB 140808A (trigger 429152043/140808038) for which a possible counterpart was detected by iPTF14eag  (Singer et al. 2014, GCN Circ. 16668). Table 1 contains the best reported positions from Swift.

Singer et al. (GCN Circ. 16668) reported the position from iPTF for the optical afterglow of this GRB. Gorosabel et al. (GCN Circ. 16671) determined a redshift of 3.29 from GTC. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.

2. BAT Observations and Analysis

BAT did not observe this burst.

3. XRT Observations and Analysis

We have analysed 7.9 ks of XRT data for the GBM-detected burst: GRB 140808A, from 41.9 ks to 269.9 ks after the GBM trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the GBM error circle. The source has a mean count rate of 4.3 x 10-3 ct s-1; we cannot determine at the present time whether it is fading.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Oates and Cenko GCN Circ. 16672) of the field of GRB 140808A 42 ks after the GBM trigger (Zhang et al., GCN Circ. 16669). No optical afterglow consistent with the candidate optical position (iPTF14eag; Singer et al. GCN Circ. 16668) 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 0.02 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 crosshatched region are not included in the fit.

RA (J2000) Dec (J2000) Error Note Reference
14h44m53.27s +49°12'52.7" 3.3" XRT-final UKSSDC
14h44m53.27s +49°12'52.7" 3.3" XRT Page et al. GCN Circ. 16670

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Singer et al. 16668 optical afterglow candidate iPTF14eag iPTF detection
Optical Gorosabel et al. 16671 Redshift from the 10.4m GTC telescope GTC redshift
Optical Sahu et al. 16684 iPTF14eag optical follow-up at HCT Himalayan Chandra Telescope
Radio Corsi and Horesh 16694 PTFeag: VLA K-band observations VLA
Radio Chandra and Nayana 16715 Radio upper limit on the GRB 140808A
with the GMRT		 GMRT upper limits
Radio Anderson et al. 16725 iPTF14eag: AMI 15 GHz detection AMI detection
Gamma-ray Zhang 16669 Fermi GBM detection Fermi GBM Fluence=3.2±0.2x10-6erg cm-2
Gamma-ray Golenetskii et al. 16673 Konus-Wind observation Konus-Wind Epeak=127 (-18,+25) 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 41951 47112 835 >22.3
v 42055 47902 857 >20.7
u 41848 51959 1212 >21.2

Table 3. UVOT observations reported by Oates and Cenko (GCN Circ. 16672). 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.

May 22, 2015