Swift Observations of GRB 180113A

T.N. Ukwatta (LANL) for the Swift team

1. Introduction

At 02:47:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180113A (trigger=804999) (Ukwatta et al. GCN Circ. 22325). Due to an observing constraint, Swift could not slew to this burst. At the time of the trigger, the initial BAT position was 108° from the Sun (5.7 hours East) and 120° from the 14%-illuminated Moon. 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

As reported by Ukwatta et al. (GCN Circ. 22332), the BAT ground-calculated position is RA, Dec = 19.211, 68.682 deg which is RA(J2000) = 01h16m50.7s Dec(J2000) = +68°40'55.9" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 75%.

The mask-weighted light curve (Figure 1) shows some weak emissions that starts at ~T-15 s, followed by the main structure with several overlapping pulses from ~ T0 to ~T+15 s, and a weak tail that lasts until ~T+70 s. T90 (15-350 keV) is 64 ± 16 s (estimated error including systematics).

The time-averaged spectrum from T-12.98 to T+67.02 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.08 ± 0.06. The fluence in the 15-150 keV band is 4.8 ± 0.2 x 10-6 erg cm-2. This fluence is larger than that of 82% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+10.52 s in the 15-150 keV band is 2.5 ± 0.2 ph cm-2 s-1. All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/804999/BA/.

3. XRT Observations and Analysis

XRT refined results are not available.

4. UVOT Observations and Analysis

UVOT results are not available.

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.

RA (J2000) Dec (J2000) Error Note Reference
01h16m50.7s +68°40'55.9" 1.0' BAT-refined Ukwatta et al. GCN Circ. 22332

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Zheng and Filippenko 22330 KAIT Optical Observations KAIT
Gamma-ray Veres 22328 Fermi GBM observation Fermi GBM Epeak=247±12 keV
T90=11 seconds
Fluence=1.007±0.012x10-5erg cm-2
(75th percentile for long GRBs)
Gamma-ray Frederiks et al. 22344 Konus-Wind observation Konus-Wind Epeak=293 (-29,+36) keV
Gamma-ray Torii et al. 22359 CALET Gamma-Ray Burst Monitor detection CALET
Gamma-ray Sharma et al. 22363 AstroSat CZTI detection CZTI T90=14.3 seconds

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

April 13, 2018