Swift Observations of GRB 160422A

A. Maselli (INAF-IASFPA) and F.E. Marshall (NASA/GSFC) for the Swift team

1. Introduction

Yassine et al. (GCN Circ. 19329) reported the GRB detection. Fermi LAT detected high-energy emission associated with GRB 160422A, which was also detected by Fermi GBM (trigger 483019143 / 160422499) at 11:59:00.81 on April 22, 2016. 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 did not observe this burst.

3. XRT Observations and Analysis

XRT results are not available.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Marshall GCN Circ. 19333) of the field of GRB 160422A 32624 s after the LAT trigger (Yassine et al. GCN Circ. 19329). A candidate optical afterglow 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 0.02 mag. in the direction of the GRB (Schlegel et al. 1998).

The Swift/UVOT began settled observations (Marshall GCN Circ. 19346) of the field of GRB 160422A 32624 s after the LAT trigger (Yassine et al., GCN Circ. 19329). The optical afterglow candidate (Marshall, GCN Circ. 19333) has faded in a later observation in the same filter. 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 0.02 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

02^h48^m22.78^s -57°52'30.4" 0.45" UVOT-refined Marshall GCN Circ. 19346

02^h48^m22.71^s -57°52'30.1" 1.7" XRT-final UKSSDC

02^h48^m22.74^s -57°52'32.6" 3.6" XRT Maselli et al. GCN Circ. 19334

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Schweyer et al. 19352 GROND NIR afterglow detection GROND detection

Gamma-ray Yassine et al. 19329 Fermi-LAT Detection Fermi LAT E_max=12 GeV

Gamma-ray Burns and Meegan 19331 Fermi GBM observation Fermi GBM E_peak=242±4 keV
T₉₀=12 seconds
Fluence=8.68±0.04x10^-5erg cm^-2
(97.2 percentile for long GRBs)

Gamma-ray Ricciarini et al. 19345 CALET Gamma-Ray Burst Monitor detection CALET

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 33427 34064 627 19.50 ą 0.05

white 44903 44701 785 19.91 ą 0.06

v 39970 45820 320 19.29 ą 0.23

u 32624 33420 783 19.09 ą 0.10

RA (J2000)	Dec (J2000)	Error	Note	Reference
02^h48^m22.78^s	-57°52'30.4"	0.45"	UVOT-refined	Marshall GCN Circ. 19346
02^h48^m22.71^s	-57°52'30.1"	1.7"	XRT-final	UKSSDC
02^h48^m22.74^s	-57°52'32.6"	3.6"	XRT	Maselli et al. GCN Circ. 19334

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Schweyer et al.	19352	GROND NIR afterglow detection	GROND	detection
Gamma-ray	Yassine et al.	19329	Fermi-LAT Detection	Fermi LAT	E_max=12 GeV
Gamma-ray	Burns and Meegan	19331	Fermi GBM observation	Fermi GBM	E_peak=242±4 keV T₉₀=12 seconds Fluence=8.68±0.04x10^-5erg cm^-2 (97.2 percentile for long GRBs)
Gamma-ray	Ricciarini et al.	19345	CALET Gamma-Ray Burst Monitor detection	CALET

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	33427	34064	627	19.50 ą 0.05
white	44903	44701	785	19.91 ą 0.06
v	39970	45820	320	19.29 ą 0.23
u	32624	33420	783	19.09 ą 0.10

Table 3. UVOT observations reported by Marshall (GCN Circ. 19346). 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.

April 29, 2016