Swift Observations of GRB 130903A

D. Grupe (PSU) and S.T. Holland (STScI) for the Swift team

1. Introduction

Mereghetti et al. (GCN Circ. 15169) reported the GRB detection. a gamma ray burst lasting about 70 s has been detected by IBAS in the IBIS/ISGRI data at 00:47:20 UT of September 3. Table 1 contains the best reported positions from Swift.

Tanga et al. (GCN Circ. 15177) reported the position from GROND for the optical afterglow of this GRB. 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 13 ks of XRT data for the INTEGRAL-detected burst: GRB 130903A, from 39.6 ks to 1165.7 ks after the INTEGRAL trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the INTEGRAL error circle. The source is fading with α >0.3.

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020294.

4. UVOT Observations and Analysis

The Swift/UVOT began observations of the field of GRB 130903A starting 44.1 ks after the INTEGRAL/IBAS trigger (Mereghetti et al. 2013, GCN Circ. 15169) (Holland and Grupe GCN Circ. 15181). We do not detect any new source consistent with the GROND afterglow position (Tanga et al. 2013, GCN Circ. 15177) in any of the 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 0.12 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

05^h28^m31.23^s -00°07'36.0" 4.3" XRT-final UKSSDC

05^h28^m31.23^s -00°07'36.0" 4.3" XRT Grupe and Holland GCN Circ. 15173

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Sudilovsky et al. 15170 GROND Upper Limits GROND upper limits

Optical Volnova et al. 15171 ISON-Kislovodsk optical Upper Limits ISON-Kislovodsk upper limits

Optical Gorbovskoy et al. 15176 MASTER early optical limit MASTER upper limits

Optical Tanga et al. 15177 GROND Afterglow Discovery GROND detection

Optical Volnova et al. 15241 optical observations ISON-Kislovodsk

Gamma-ray Mereghetti et al. 15169 A long GRB detected by INTEGRAL INTEGRAL detection

Gamma-ray Xiong and Meegan 15175 Fermi GBM observation Fermi GBM E_peak = 41 ± 3 keV

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

Filter T_start T_stop Exposure Mag

v 44,128 51,114 2461 >21.2

u 45,378 51,795 1442 >21.3

RA (J2000)	Dec (J2000)	Error	Note	Reference
05^h28^m31.23^s	-00°07'36.0"	4.3"	XRT-final	UKSSDC
05^h28^m31.23^s	-00°07'36.0"	4.3"	XRT	Grupe and Holland GCN Circ. 15173

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Sudilovsky et al.	15170	GROND Upper Limits	GROND	upper limits
Optical	Volnova et al.	15171	ISON-Kislovodsk optical Upper Limits	ISON-Kislovodsk	upper limits
Optical	Gorbovskoy et al.	15176	MASTER early optical limit	MASTER	upper limits
Optical	Tanga et al.	15177	GROND Afterglow Discovery	GROND	detection
Optical	Volnova et al.	15241	optical observations	ISON-Kislovodsk
Gamma-ray	Mereghetti et al.	15169	A long GRB detected by INTEGRAL	INTEGRAL	detection
Gamma-ray	Xiong and Meegan	15175	Fermi GBM observation	Fermi GBM	E_peak = 41 ± 3 keV

Filter	T_start	T_stop	Exposure	Mag
v	44,128	51,114	2461	>21.2
u	45,378	51,795	1442	>21.3

Table 3. UVOT observations reported by Holland and Grupe (GCN Circ. 15181). 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.

September 22, 2013