Swift Observations of GRB 150523A

A.P. Beardmore (U. Leicester) and F.E. Marshall (NASA/GSFC) for the Swift team

1. Introduction

Yu (GCN Circ. 17863) reported the GRB detection. At 09:29:48.08 UT on 23 May 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150523A (trigger 454066191 / 150523396). Table 1 contains the best reported positions from Swift.

Dichiara et al. (GCN Circ. 17868) reported the position from Las Cumbres Obs. Global Tele.Network for the optical afterglow of this GRB. Marshall and Vargas (GCN Circ. 17872) reported the detection with UVOT of an optical afterglow. 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 and Vargas GCN Circ. 17872) of the field of GRB 150523A 32968 s after the LAT trigger (Bissaldi et al. GCN Circ. 17864). A source consistent with the XRT position (Beardmore et al. GCN Circ. 17866) and the optical afterglow position (Dichiara et al. GCN Circ. 17868 and 17869) 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 0.30 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
07h41m08.67s -45°25'12.4" 0.78" UVOT-refined Marshall and Vargas GCN Circ. 17872
07h41m08.62s -45°25'15.1" 3.7" XRT Beardmore et al. GCN Circ. 17866

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Dichiara et al. 17868 LCOGT Cerro-Tololo optical afterglow
candidate		 Las Cumbres Obs. Global Tele.Network detection
Optical Dichiara et al. 17869 LCOGT FTS afterglow confirmation FTS detection
Gamma-ray Yu 17863 Fermi GBM detection Fermi GBM Epeak=574±24 keV
T90=74.2 seconds
Fluence=3.57±0.05x10-5erg cm-2
(92nd percentile for long GRBs)
Gamma-ray Bissaldi et al. 17864 Fermi-LAT detection Fermi LAT Emax=7 GeV
Gamma-ray Golenetskii et al. 17870 Konus-Wind observation Konus-Wind Fluence=4.44(-0.69,+0.71)x10-5erg cm-2
Gamma-ray Fujinuma et al. 17875 Suzaku WAM observation of the prompt
emission		 Suzaku WAM Epeak=417 (+56/-41) keV
T90=32 seconds
Fluence=1.81(+0.23,-0.25)x10-5erg cm-2

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
white 33590 39627 1150 21.83 ± 0.24
v 34212 40619 1433 >20.5
u 32968 44748 2077 >20.5

Table 3. UVOT observations reported by Marshall and Vargas (GCN Circ. 17872). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary detections and 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.

May 28, 2015