Swift Observations of GRB 160625B

A. Melandri (INAF-OAB) and S.R. Oates (U. Warwick) for the Swift team

1. Introduction

Dirirsa et al. (GCN Circ. 19580) reported the GRB detection. At 22:43:24 on June 25, 2016, Fermi/LAT detected a sharp increase in the rate of high-energy photons, resulting in an onboard trigger on GRB 160625B. Table 1 contains the best reported positions from Swift.

Troja et al. (GCN Circ. 19588) reported the position from RATIR for the optical afterglow of this GRB. Oates and D'Aì (GCN Circ. 19589) reported the detection with UVOT of an optical afterglow. Xu et al. (GCN Circ. 19600) determined a redshift of 1.406 from VLT, and D’Elia et al. (GCN Circ. 19601) determined a redshift of 1.41 from TNG. 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 (Oates and D'Aì GCN Circ. 19589) of the field of GRB 160625B 9616 s after the LAT trigger (Dirirsa et al., GCN Circ. 19580). A source consistent with the RATIR position (Troja et al. GCN Circ. 19588) and the edge of the XRT position (Melandri et al. GCN Circ. 19585) 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 EB-V of 0.12 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
20h34m23.51s +06°55'08.1" 0.50" UVOT ?
20h34m23.25s +06°55'10.5" 3.8" XRT Melandri et al. GCN Circ. 19585

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Troja et al. 19588 RATIR Optical and NIR Afterglow
Detection		 RATIR detection
Optical Kuroda et al. 19599 MITSuME Ishigakijima Optical Observation MITSuME Ishigakijima detection
Optical Xu et al. 19600 VLT/X-shooter redshift VLT redshift
Optical D’Elia et al. 19601 TNG redshift confirmation TNG redshift
Optical Watson et al. 19602 RATIR Optical and NIR Observations RATIR detection
Optical Karpov et al. 19603 Mini-MegaTORTORA detection of bright
optical flash simultaneous with LAT
event		 TORTORA detection
Optical Mazaeva et al. 19605 TSHAO optical observations Zeiss-1000 detection
Optical Moskvitin 19611 SAO RAS optical observations SAO RAS
Optical Gorbovskoy et al. 19612 Global MASTER-Net prompt optical
emission detection 		MASTER detection
Optical Batsch et al. 19615 Pi of the Sky detection of an optical
flash accompanying GRB 160625B		 Pi of the Sky detection
Optical Cobb 19616 SMARTS optical/IR afterglow observations SMARTS detection
Optical Mazaeva et al. 19619 TSHAO optical observations Zeiss-1000 detection
Optical Pozanenko 19620 TSHAO optical observations, correction
GCN Circ. 19619		 detection
Optical Guidorzi et al. 19640 LCOGT FTN observations FTN detection
Optical Valeev et al. 19642 SAO RAS monitoring SAO RAS detection
Optical Bikmaev et al. 19651 RTT150 optical observations RTT150 detection
Optical Mazaeva et al. 19680 TSHAO optical observations Zeiss-1000 detection
Optical Lipunov et al. 19683 Global MASTER-Crimea prompt optical
emission detection (fwd)		 MASTER detection
Radio Alexander et al. 19606 VLA Detection VLA detection
Radio Mooley et al. 19610 15 GHz detection from AMI AMI detection
Gamma-ray Dirirsa et al. 19580 Fermi-LAT detection of a bright burst Fermi LAT
Gamma-ray Burns 19581 Fermi GBM initial observations Fermi GBM
Gamma-ray Dirirsa et al. 19586 Fermi-LAT refined analysis Fermi LAT Emax=15 GeV
Gamma-ray Burns 19587 Fermi GBM refined analysis Fermi GBM Epeak=68±1 keV
T90=460 seconds
Fluence=1.65±0.03x10-6erg cm-2
(25th percentile for long GRBs)
Gamma-ray Svinkin et al. 19604 Konus-Wind observation Konus-Wind Epeak=554 (-19,+20) keV
Fluence=9.44(-0.16,+0.16)x10-4erg cm-2
Gamma-ray Nakahira et al. 19617 CALET Gamma-Ray Burst Monitor detection CALET

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
u 9616 9978 353 16.41 ± 0.04

Table 3. UVOT observation reported by Oates and D'Aì (GCN Circ. 19589). The start and stop time of the exposure are given in seconds since the BAT trigger. The preliminary detection is given. No correction has been made for extinction in the Milky Way.

July 13, 2016