Swift Observations of GRB 160521B

K.L. Page (U. Leicester) and F.E. Marshall (NASA/GSFC) for the Swift team

1. Introduction

Yu and Veres (GCN Circ. 19443) reported the GRB detection. At 09:13:58.03 UT on 21 May 2016, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 160521B (trigger 485514842 / 160521385). 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. 19449) of GRB 160521B centered on the LAT position (Axelsson et al., GCN Circ. 19444) 41882 seconds after the trigger. The exposures for the optical filters (white, b, and u) cover about 20% of the LAT statistical error circle, and the uv filters (uvw1 and uvm2) cover about 44%. 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

09^h50^m40.05^s +79°01'51.6" 3.2" XRT-final UKSSDC

09^h50^m39.96^s +79°01'49.7" 4.2" XRT Page et al. GCN Circ. 19464

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Radio Mooley et al. 19563 15 GHz upper limits from AMI AMI upper limits

X-ray Ruffini et al. 19456 Theoretical estimate of the redshift
and urgent need for further x-ray
observations redshift

Gamma-ray Yu and Veres 19443 Fermi GBM detection Fermi GBM E_peak=155±5 keV
T₉₀=2.8 seconds
Fluence=1.25±0.02x10^-5erg cm^-2
(80^th percentile for long GRBs)

Gamma-ray Axelsson et al. 19444 Fermi-LAT detection Fermi LAT E_max=12 GeV

Gamma-ray Kozlova et al. 19462 Konus-Wind observation Konus-Wind E_peak=165 (-16,+17) keV
Fluence=1.32(-0.15,+0.17)x10^-5erg cm^-2

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 42794 43127 324 >20.8

b 41882 49001 1180 >20.7

u 47789 48695 885 >20.2

uvw1 46882 54226 1578 >20.1

uvw2 52616 53065 886 >20.4

RA (J2000)	Dec (J2000)	Error	Note	Reference
09^h50^m40.05^s	+79°01'51.6"	3.2"	XRT-final	UKSSDC
09^h50^m39.96^s	+79°01'49.7"	4.2"	XRT	Page et al. GCN Circ. 19464

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Radio	Mooley et al.	19563	15 GHz upper limits from AMI	AMI	upper limits
X-ray	Ruffini et al.	19456	Theoretical estimate of the redshift and urgent need for further x-ray observations		redshift
Gamma-ray	Yu and Veres	19443	Fermi GBM detection	Fermi GBM	E_peak=155±5 keV T₉₀=2.8 seconds Fluence=1.25±0.02x10^-5erg cm^-2 (80^th percentile for long GRBs)
Gamma-ray	Axelsson et al.	19444	Fermi-LAT detection	Fermi LAT	E_max=12 GeV
Gamma-ray	Kozlova et al.	19462	Konus-Wind observation	Konus-Wind	E_peak=165 (-16,+17) keV Fluence=1.32(-0.15,+0.17)x10^-5erg cm^-2

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	42794	43127	324	>20.8
b	41882	49001	1180	>20.7
u	47789	48695	885	>20.2
uvw1	46882	54226	1578	>20.1
uvw2	52616	53065	886	>20.4

Table 3. UVOT observations reported by Marshall (GCN Circ. 19449). 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.

June 25, 2016