Swift Observations of GRB 190727B

A.Y. Lien (GSFC/UMBC) for the Swift team

1. Introduction

At 20:18:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190727B (trigger=916733) (Lien et al. GCN Circ. 25176). Swift could not slew to the location due to an observing constraint. At the time of the trigger, the initial BAT position was 32° from the Sun (0.0 hours West) and 67° from the 23%-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 Stamatikos et al. (GCN Circ. 25211), the BAT ground-calculated position is RA, Dec = 126.500, -13.272 deg which is RA(J2000) = 08h25m59.9s Dec(J2000) = -13°16'18.9" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 70%.

The mask-weighted light curve (Figure 1) shows a structure with multiple bright pulses that starts at ~T-20 s and ends at ~T+45 s. The brightest peak occurs at ~T+2 s. T90 (15-350 keV) is 40.14 ± 1.40 s (estimated error including systematics).

The time-averaged spectrum from T-21.30 to T+44.47 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.41 ± 0.03. The fluence in the 15-150 keV band is 1.8 ± 0.03 x 10-5 erg cm-2. This fluence is larger than that of 96.4% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+1.13 s in the 15-150 keV band is 20.9 ± 0.7 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/916733/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
08h25m59.9s -13°16'18.9" 1.0' BAT-refined Stamatikos et al. GCN Circ. 25211

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Gamma-ray Fermi 25177 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Biltzinger et al. 25178 BALROG localization (Fermi Trigger
585951481 / GRB 190727846)		 BALROG
Gamma-ray Veres and Meegan 25180 Fermi GBM observations Fermi GBM Epeak=621±26 keV
T90=35 seconds
Fluence=7.02±0.05x10-5erg cm-2
(96.7 percentile for long GRBs)
Gamma-ray Kovacevic et al. 25186 Fermi-LAT detection Fermi LAT Emax=2.2 GeV
Gamma-ray Svinkin et al. 25218 Konus-Wind observation Konus-Wind Epeak=402 (-49,+64) keV
Duration=~62 seconds
Fluence=9.92(-1.04,+1.04)x10-5erg cm-2

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

July 30, 2019