Swift Observations of GRB 180103A

A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB) and N.P.M. Kuin (UCL-MSSL) for the Swift team

1. Introduction

At 01:08:30 UT on 3 Jan 2018, BAT detected a rate increase (Beardmore et al. GCN Circ. 22305). However further analysis was truncated by a pre-planned slew. 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.

Standard analysis products for this burst are available at https://gcn.gsfc.nasa.gov/swift_gnd_ana.html.

2. BAT Observations and Analysis

BAT refined results are not available.

3. XRT Observations and Analysis

XRT refined results are not available.

4. UVOT Observations and Analysis

The Swift/UVOT performed observations of the field of GRB 180103A (Kuin and .P. Beardmore GCN Circ. 22309). No optical afterglow consistent with the XRT position (Melandri et al. GCN. 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 0.48 mag. in the direction of the GRB (Schlegel et al. 1998).

BAT light curve

Figure 1. The BAT mask-weighted light curve in the four individual and total energy bands. The units are counts s-1 illuminated-detector-1. The vertical green dash-dotted lines show the T50 interval, the vertical black dashed lines show the T90 interval, and vertical blue (orange) solid lines show the start (stop) of slews.

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
10h38m24.37s -53°33'21.6" 3.8" XRT Melandri et al. GCN Circ. 22326
10h38m20.3s -53°33'16.9" 3' BAT-initial Beardmore et al. GCN Circ. 22305

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Guidorzi et al. 22315 LCO Sutherland 1-m telescope
observations		 LCO
Gamma-ray Sharma et al. 22310 AstroSat CZTI detection CZTI T90=147.1 seconds
Gamma-ray Svinkin et al. 22314 Konus-Wind observation Konus-Wind Epeak=282 (-33,+40) keV
Duration=~237 seconds
Fluence=3.41(-0.36,+0.33)x10-4erg cm-2

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

Filter Tstart(ks) Tstop(ks) Exp(s) Mag
v 344.2 350.7 1044 >19.9
u 344.2 350.7 848 >20.4

Table 3. UVOT observations reported by Kuin and .P. Beardmore (GCN Circ. 22309). 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 14, 2018