Swift Observations of GRB 200219A

A.Y. Lien (GSFC/UMBC), V. D'Elia (ASDC) and M.H. Siegel (PSU) for the Swift team

1. Introduction

At 07:36:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200219A (trigger=957271) (Lien et al. GCN Circ. 27125). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 48° from the Sun (0.7 hours East) and 55° from the 17%-illuminated Moon. Table 1 contains the best reported positions from Swift, and the latest XRT position can be viewed at http://www.swift.ac.uk/xrt_positions.

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. 27148), the BAT ground-calculated position is RA, Dec = 342.595, -59.101 deg which is RA(J2000) = 22h50m22.7s Dec(J2000) = -59°06'04.5" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 99%.

The mask-weighted light curve (Figure 1) shows a short pulse that starts and peaks at ~T0, and ends at ~T+0.5 s. It is followed by an extended emission that lasting until ~T+90 s. In addition, there may be some even weaker emission until ~T+300 s. T90 (15-350 keV) is 288.0 ± 50.6 s (estimated error including systematics).

The time-averaged spectrum from T-0.2 to T+86.7 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.47 ± 0.25. The fluence in the 15-150 keV band is 7.4 ± 1.1 x 10-7 erg cm-2. This fluence is larger than that of 31% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T-0.268 s in the 15-150 keV band is 2.4 ± 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/957271/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Elia et al. (GCN Circ. 27139). We have analysed 19 ks of XRT data for GRB 200219A, from 57 s to 231.1 ks after the BAT trigger. The data comprise 192 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 27138).

The light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=1.04 (+0.18, -0.28), followed by a break at T+107 s to an α of 3.90 ± 0.26.

A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.36 ± 0.06. The best-fitting absorption column is 1.26 (+0.26, -0.24) x 1021 cm-2, in excess of the Galactic value of 1.9 x 1020 cm-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10-11 (5.4 x 10-11) erg cm-2 count-1.

A summary of the WT-mode spectrum is thus:
Total column: 1.26 (+0.26, -0.24) x 1021 cm-2
Galactic foreground: 1.9 x 1020 cm-2
Excess significance: 7.2 σ
Photon index: 1.36 ± 0.06

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00957271.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 200219A 75 s after the BAT trigger (Siegel and Lien GCN Circ. 27165). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 27138) 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 0.02 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
22h50m33.23s -59°07'10.4" 1.4" XRT-final UKSSDC
22h50m33.21s -59°07'10.4" 1.8" XRT-enhanced Osborne et al. GCN Circ. 27138
22h50m22.7s -59°06'04.5" 2.4' BAT-refined Laha et al. GCN Circ. 27148

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 27124 Swift GRB200219.32: Global MASTER-Net
observations report 		MASTER
Optical Tiurina et al. 27126 MASTER catalog automatic possible Host
Galaxy candidate		 MASTER
Optical Jelinek et al. 27164 FRAM-Auger optical limit FRAM upper limits
Radio Bell et al. 27245 ATCA 5/9 GHz radio observations ATCA
X-ray Sakamoto et al. 27218 Chandra rapid ToO upper limit Chandra upper limits
Gamma-ray Fermi 27123 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Bissaldi and Meegan 27137 Fermi GBM observation Fermi GBM Epeak=1.4±0.2 keV
T90=1.1 seconds
Fluence=2.8±0.1x10-6erg cm-2
(94th percentile for short GRBs)
Gamma-ray Svinkin et al. 27226 Konus-Wind observation Konus-Wind Epeak=952 (-173,+218) keV
Duration=~0.4 seconds
Fluence=4.12(-0.61,+0.67)x10-6erg cm-2
Gamma-ray Gupta et al. 27305 AstroSat CZTI detection CZTI

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
whiteFC 75 225 147 >20.2
uFC 287 537 246 >19.3
white 75 19365 1139 >21.2
v 617 30839 1770 >19.7
b 543 36572 2257 >20.9
u 287 25105 2431 >20.7
w1 666 40797 1248 >20.4
m2 641 40734 2104 >20.4
w2 592 28878 914 >20.2

Table 3. UVOT observations reported by Siegel and Lien (GCN Circ. 27165). 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.

March 4, 2020