Swift Observations of GRB 200115A

S.B. Cenko (GSFC) for the Swift team

1. Introduction

At 11:50:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200115A (trigger=949361) (Cenko et al. GCN Circ. 26771). Swift did not slew to the burst. At the time of the trigger, the initial BAT position was 120° from the Sun (8.0 hours East) and 122° from the 73%-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 Laha et al. (GCN Circ. 26780), the BAT ground-calculated position is RA, Dec = 56.453, 5.607 deg, which is RA(J2000) = 03h45m48.7s Dec(J2000) = +05°36'26.0" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 82%.

The mask-weighted light curve (Figure 1) starts before T-50 s, picking up at T-30 s, continued increasing until the peak at T+100 s, a couple weak following peaks, and having weak and flat emission out past the end of data at T+240 s. T90 (15-350 keV) is 158.4 ± 32.6 s (estimated error including systematics).

The time-averaged spectrum from T-40.29 to T+233.12 s is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.29 ± 0.24, and Epeak of 75.0 ± 17.5 keV (χ2 40.88 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.0 ± 0.0 x 10-5 erg cm-2 and the 1-s peak flux measured from T+99.75 s in the 15-150 keV band is 3.6 ± 0.3 ph cm-2 s-1. This fluence is larger than that of 92.5% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). A fit to a simple power law gives a photon index of 1.77 ± 0.06 (χ2 53.76 for 57 d.o.f.). 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/949361/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
03h45m48.7s +05°36'26.0" 1.1' BAT-refined Laha et al. GCN Circ. 26780

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 26770 Swift GRB200115.49: Global MASTER-Net
observations report 		MASTER
Optical Zhu et al. 26772 Nanshan-0.6m optical upper limit Xinjiang Astro. Obs. upper limits
Optical Niwano et al. 26776 MITSuME Okayama optical upper limits MITSuME Okayama upper limits
Optical Pozanenko et al. 26790 Mondy optical afterglow candidate Mondy detection
Optical Becerra et al. 26792 DDOTI/OAN optical observations report
Optical Nakamura and Sakamoto 26801 AROMA-N Optical Observation AROMA-N
Optical Volnova et al. 26818 Mondy optical observations and
correction to GCN Circ. 26790		 Mondy
Optical Volnova et al. 26872 Assy optical observations
Gamma-ray Tamura et al. 26809 CALET Gamma-Ray Burst Monitor detection CALET

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

January 25, 2020