Swift Observations of GRB 140402A

M. Perri (SSDC and INAF-OAR) and A.A. Breeveld (UCL-MSSL) for the Swift team

1. Introduction

Bissaldi et al. (GCN Circ. 16069) reported the GRB detection. At 00:10:07.00 on April 02, 2014, Fermi-LAT detected high-energy emission from GRB 140402A, which was also detected by Fermi-GBM (trigger 418090209/140402007). 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

The mask-weighted lightcurve (Figure 1) shows a single nearly square pulse. T₉₀ was about 0.031 ± 0.003 seconds (estimated 90% confidence).

A powerlaw fit to the spectrum from 15 to 150 keV has a photon index of 0.89 ± 0.44 (90% confidence). In 0.034 seconds the fluence was (3.8 ± 1.2) x 10^-8 ergs/cm² (62% confidence). This fluence is larger than that of 32% of the short GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011).

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Perri et al. (GCN Circ. 29370). We have analysed 4.5 ks of XRT data for the Fermi/GBM-detected burst GRB 140402A (Cummings et al. GCN Circ. 16071), from 32.8 ks to 51.2 ks after the Fermi/GBM trigger. The data are entirely in Photon Counting (PC) mode. We cannot determine at the present time whether the source is fading.

4. UVOT Observations and Analysis

The Swift/UVOT took exposures at both the pointings for GRB140402A described in Pagani et al., GCN Circ. 16075 (Breeveld and Pagani GCN Circ. 16077). No optical afterglow consistent with the BAT position given by Cummings (GCN Circ. 16081) is detected in 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 0.03 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

13^h50^m23.67^s +05°46'28.0" 5.6" XRT-refined Perri et al. GCN Circ. 29370

13^h50^m22.2^s +05°58'16" 2.8' BAT-refined Cummings GCN Circ. 16073

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Xin et al. 16072 Xinglong TNT upper limit TNT upper limits

Optical Yurkov et al. 16074 MASTER optical observations MASTER upper limits

Optical Fong et al. 16080 Deep limit on the optical afterglow
from Magellan observations Magellan upper limits

Gamma-ray Bissaldi et al. 16069 Fermi-LAT detection of a burst Fermi LAT E_max=3.5 GeV

Gamma-ray Jenke and Yu 16070 Fermi GBM detection Fermi GBM T₉₀=0.3 seconds
Fluence=4.0±0.4x10^-7erg cm^-2
(57^th percentile for short GRBs)

Other Cummings et al. 16071 Marginal BAT detection 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

white 57023 57665 632 >21.5

u 56375 61574 649 >20.5

v 57672 58344 659 >19.8

RA (J2000)	Dec (J2000)	Error	Note	Reference
13^h50^m23.67^s	+05°46'28.0"	5.6"	XRT-refined	Perri et al. GCN Circ. 29370
13^h50^m22.2^s	+05°58'16"	2.8'	BAT-refined	Cummings GCN Circ. 16073

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Xin et al.	16072	Xinglong TNT upper limit	TNT	upper limits
Optical	Yurkov et al.	16074	MASTER optical observations	MASTER	upper limits
Optical	Fong et al.	16080	Deep limit on the optical afterglow from Magellan observations	Magellan	upper limits
Gamma-ray	Bissaldi et al.	16069	Fermi-LAT detection of a burst	Fermi LAT	E_max=3.5 GeV
Gamma-ray	Jenke and Yu	16070	Fermi GBM detection	Fermi GBM	T₉₀=0.3 seconds Fluence=4.0±0.4x10^-7erg cm^-2 (57^th percentile for short GRBs)
Other	Cummings et al.	16071	Marginal BAT detection		detection

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	57023	57665	632	>21.5
u	56375	61574	649	>20.5
v	57672	58344	659	>19.8

Table 3. UVOT observations reported by Breeveld and Pagani (GCN Circ. 16077). 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.

January 30, 2021