Swift Observations of GRB 200122A

E. Sonbas (Adiyaman Univ.), J.D. Gropp (PSU) and A. Belles (PSU) for the Swift team

1. Introduction

At 01:41:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200122A (trigger=950330) (Sonbas et al. GCN Circ. 26844). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 102° from the Sun (6.2 hours West) and 75° from the 8%-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 Lien et al. (GCN Circ. 26861), the BAT ground-calculated position is RA, Dec = 210.010, 27.548 deg which is RA(J2000) = 14^h00^m02.4^s Dec(J2000) = +27°32'52.2" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 78%.

The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts from ~T-10 s and ends at ~T+200 s. The main emission interval is around T-10 s to T+50 s, with the highest peak occurs at ~T+10 s. In addition, there is a weak pulse around ~T+192 s. T₉₀ (15-350 keV) is 174.96 ± 14.54 s (estimated error including systematics).

The time-averaged spectrum from T-8.572 to T+201.832 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.60 ± 0.05. The fluence in the 15-150 keV band is 1.1 ± 0.03 x 10^-5 erg cm^-2. This fluence is larger than that of 93.2% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+10.18 s in the 15-150 keV band is 9.1 ± 0.4 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/950330/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Gropp et al. (GCN Circ. 26852). We have analysed 6.4 ks of XRT data for GRB 200122A, from 63 s to 35.2 ks after the BAT trigger. The data comprise 296 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. 26846).

The late-time light curve (Figure 2) (from T0+5.3 ks) can be modelled with a power-law decay with a decay index of α=0.67 (+0.08, -0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.84 ± 0.05. The best-fitting absorption column is 1.44 ± 0.07 x 10²² cm^-2, in excess of the Galactic value of 1.5 x 10²⁰ cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.26 (+0.14, -0.13) and a best-fitting absorption column of 1.67 (+0.17, -0.16) x 10²² cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.0 x 10^-11 (1.3 x 10^-10) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column: 1.67 (+0.17, -0.16) x 10²² cm^-2
Galactic foreground: 1.5 x 10²⁰ cm^-2
Excess significance: 16.7 σ
Photon index: 2.26 (+0.14, -0.13)

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00950330.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 200122A 82 s after the BAT trigger (Belles and Sonbas GCN Circ. 26859). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 26846) 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 E_B-V of 0.03 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

14^h00^m04.31^s +27°32'55.5" 1.4" XRT-final UKSSDC

14^h00^m04.34^s +27°32'55.8" 1.7" XRT-enhanced Osborne et al. GCN Circ. 26846

14^h00^m02.4^s +27°32'52.2" 1.0' BAT-refined Lien et al. GCN Circ. 26861

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 26845 Swift GRB 200122A: Global MASTER-Net
observations report MASTER

Optical Wiersema et al. 26853 GOTO non-detection of optical afterglow Gravitational-wave Optical Transient Observer

Optical Jelinek et al. 26854 FRAM-ORM optical limit FRAM upper limits

Optical Liu et al. 26860 Xinglong-2.16m optical upper limit Xinglong upper limits

Optical Watson et al. 26862 RATIR Optical Observations RATIR upper limits

Optical Adachi et al. 26864 MITSuME Akeno optical upper limits MITSuME Akeno upper limits

Optical Belkin et al. 26869 Mondy optical upper limit Mondy upper limits

Optical Dimple et al. 26870 Optical upper limit Devasthal Opt.Tel. upper limits

Optical Dimple et al. 26873 Optical upper limit: correction to the
GCN Circ. 26870 Devasthal Opt.Tel. upper limits

Gamma-ray Frederiks et al. 26865 Konus-Wind observation Konus-Wind E_peak=148 (-16,+15) keV

Gamma-ray Gaikwad et al. 26871 AstroSat CZTI detection CZTI T₉₀=39.3 seconds

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

Filter T_start(s) T_stop(s) Exp(s) Mag

white_fc 82 232 147 >21.1

u_fc 294 544 246 >20.9

white 82 5672 627 >21.7

v 624 6083 352 >19.4

b 550 5467 333 >20.6

u 294 1844 363 >20.7

w1 674 1472 58 >20.1

m2 6088 6276 186 >19.5

w2 5678 5878 197 >20.3

RA (J2000)	Dec (J2000)	Error	Note	Reference
14^h00^m04.31^s	+27°32'55.5"	1.4"	XRT-final	UKSSDC
14^h00^m04.34^s	+27°32'55.8"	1.7"	XRT-enhanced	Osborne et al. GCN Circ. 26846
14^h00^m02.4^s	+27°32'52.2"	1.0'	BAT-refined	Lien et al. GCN Circ. 26861

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	26845	Swift GRB 200122A: Global MASTER-Net observations report	MASTER
Optical	Wiersema et al.	26853	GOTO non-detection of optical afterglow	Gravitational-wave Optical Transient Observer
Optical	Jelinek et al.	26854	FRAM-ORM optical limit	FRAM	upper limits
Optical	Liu et al.	26860	Xinglong-2.16m optical upper limit	Xinglong	upper limits
Optical	Watson et al.	26862	RATIR Optical Observations	RATIR	upper limits
Optical	Adachi et al.	26864	MITSuME Akeno optical upper limits	MITSuME Akeno	upper limits
Optical	Belkin et al.	26869	Mondy optical upper limit	Mondy	upper limits
Optical	Dimple et al.	26870	Optical upper limit	Devasthal Opt.Tel.	upper limits
Optical	Dimple et al.	26873	Optical upper limit: correction to the GCN Circ. 26870	Devasthal Opt.Tel.	upper limits
Gamma-ray	Frederiks et al.	26865	Konus-Wind observation	Konus-Wind	E_peak=148 (-16,+15) keV
Gamma-ray	Gaikwad et al.	26871	AstroSat CZTI detection	CZTI	T₉₀=39.3 seconds

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white_fc	82	232	147	>21.1
u_fc	294	544	246	>20.9
white	82	5672	627	>21.7
v	624	6083	352	>19.4
b	550	5467	333	>20.6
u	294	1844	363	>20.7
w1	674	1472	58	>20.1
m2	6088	6276	186	>19.5
w2	5678	5878	197	>20.3

Table 3. UVOT observations reported by Belles and Sonbas (GCN Circ. 26859). 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.

January 25, 2020