Swift Observations of GRB 131224A

B. Gompertz (U. Leicester) and A.A. Breeveld (UCL-MSSL) for the Swift team

1. Introduction

Mereghetti et al. (GCN Circ. 15607) reported the GRB detection. a short gamma ray burst lasting about 0.8 s has been detected by IBAS in the IBIS/ISGRI data at 16:54:37 UT of 24 December. 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 xx ks of XRT data for the INTEGRAL-detected burst: GRB 131224A, from 0 s to 0 s after the INTEGRAL trigger. The data are entirely in Photon Counting (PC) mode. We cannot determine at the present time whether the source is fading.

If the light curve (Figure 2) continues to decay with a power-law decay index of , the count rate at T+24 hours will be 0.27 count s^-1

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 131224A 10748 s after the INTEGRAL trigger (Mereghetti et al., GCN Circ. 15607) (Breeveld and De Pasquale GCN Circ. 15615). The field is very crowded and no optical afterglow consistent with the INTEGRAL position 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 E_B-V of 0.96 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

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Gorbovskoy et al. 15608 MASTER-Net early optical observations MASTER upper limits

Radio Fong et al. 15626 5.8 GHz VLA observations VLA

Gamma-ray Mereghetti et al. 15607 A short GRB detected by INTEGRAL INTEGRAL detection

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

Filter T_start(s) T_stop(s) Exp(s) Mag

u 10748 18662 3918 >21.1

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Gorbovskoy et al.	15608	MASTER-Net early optical observations	MASTER	upper limits
Radio	Fong et al.	15626	5.8 GHz VLA observations	VLA
Gamma-ray	Mereghetti et al.	15607	A short GRB detected by INTEGRAL	INTEGRAL	detection

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
u	10748	18662	3918	>21.1

Table 3. UVOT observation reported by Breeveld and De Pasquale (GCN Circ. 15615). 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.

December 28, 2013