Swift Observations of GRB 200215A

M.G. Bernardini (INAF-OAB), M. Perri (ASDC) and N.P.M. Kuin (UCL-MSSL) for the Swift team

1. Introduction

At 14:39:31 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200215A (trigger=956639) (Bernardini et al. GCN Circ. 27079). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 70° from the Sun (4.4 hours East) and 164° from the 54%-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 Barthelmy et al. (GCN Circ. 27098), the BAT ground-calculated position is RA, Dec = 34.100, 12.775 deg which is RA(J2000) = 02h16m24.1s Dec(J2000) = +12°46'31.7" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 73%.

The mask-weighted light curve (Figure 1) shows a single symmetrical peak from roughly

The time-averaged spectrum from T-9.97 to T+5.37 s is best fit by a simple

The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/956639/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Perri et al. (GCN Circ. 27091). We have analysed 17 ks of XRT data for GRB 200215A, from 72 s to 339.9 ks after the BAT trigger. The data comprise 24 s in Windowed Timing (WT) mode (the first 9 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 Evans et al. (GCN Circ. 27089).

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.016 (+0.030, -0.028).

A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.50 ± 0.17. The best-fitting absorption column is 2.0 (+0.8, -0.7) x 1021 cm-2, in excess of the Galactic value of 1.2 x 1021 cm-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.8 x 10-11 (5.6 x 10-11) erg cm-2 count-1.

A summary of the PC-mode spectrum is thus:
Total column: 2.0 (+0.8, -0.7) x 1021 cm-2
Galactic foreground: 1.2 x 1021 cm-2
Excess significance: 1.9 σ
Photon index: 1.50 ± 0.17

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00956639.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 200215A 90 s after the BAT trigger (Kuin and Bernardini GCN Circ. 27090). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 27089) 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 0.15 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
02h16m19.06s +12°46'15.6" 1.4" XRT-final UKSSDC
02h16m19.06s +12°46'14.9" 1.5" XRT-enhanced Evans et al. GCN Circ. 27089
02h16m24.1s +12°46'31.7" 1.0' BAT-refined Barthelmy et al. GCN Circ. 27098

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 27080 Swift GRB200215.61: Global MASTER-Net
observations report 		MASTER
Optical Xu et al. 27081 Nanshan/NEXT optical upper limit Xinjiang Astro. Obs. upper limits
Optical Perley and Cockeram 27086 Liverpool Telescope upper limits Liverpool Telescope upper limits
Optical de Ugarte Postigo et al. 27088 Optical observations form Calar Alto
2.2m		 Calar Alto detection
Optical Xu et al. 27099 UKIRT H-band observations UKIRT
Optical Watson et al. 27105 RATIR Optical Observations RATIR upper limits
Optical Strausbaugh and Cucchiara 27150 LCO Optical Upper Limits LCO upper limits
Gamma-ray Fermi 27078 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Poolakkil and Meegan 27087 Fermi GBM detection Fermi GBM Epeak=162±25 keV
T90=24 seconds
Fluence=1.858±0.175x10-6erg cm-2
(28th percentile for long GRBs)
Gamma-ray Sakamoto et al. 27113 CALET Gamma-Ray Burst Monitor detection CALET
Other Kann and de Ugarte Postigo 27083 Possible host galaxy in PanSTARRS

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 90 240 147 >20.0
uFC 302 552 246 >20.0
white 90 7290 581 >21.2
v 634 5070 294 >18.5
b 559 7092 294 >19.8
u 302 6885 481 >20.3
w1 1087 6680 216 >19.2
w2 10534 11091 547 >19.8

Table 3. UVOT observations reported by Kuin and Bernardini (GCN Circ. 27090). 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.

February 21, 2020