Swift Observations of GRB 220107A

D.N. Burrows (PSU) and M.H. Siegel (PSU) for the Swift team

1. Introduction

DeLaunay et al. (GCN Circ. 31402) reported the GRB detection. Swift/BAT did not localize GRB 220107A onboard (T0: 2022-01-07T14:45:31 UTC, Fermi/GBM GCN Circ. 31399), due to a slew. Table 1 contains the best reported positions from Swift.

Siegel (GCN Circ. 31415) reported the detection with UVOT of an optical afterglow. Castro-Tirado et al. (GCN Circ. 31423) determined a redshift of 1.246 from BTA. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.

2. BAT Observations and Analysis

BAT refined results are not available.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Burrows et al. (GCN Circ. 31410).

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=2.5 (+0.5, -2.4).

A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.84 (+0.27, -0.18). The best-fitting absorption column is 3.1 (+6.1, -0.9) x 10²⁰ cm^-2, consistent with the Galactic value of 2.2 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 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Siegel GCN Circ. 31415) of the field of GRB 220107A 26.7 ks after the Fermi detection (GCN Circ. 31399). An uncatalogued fading source consistent with the GUANO localization (DeLaunay et al., GCN Circ. 31402) and the XRT position (Burrows et al., GCN Circ. 31410) 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 0.056 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

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

11^h19^m13.71^s +34°10'14.5" 0.4" UVOT-refined Siegel GCN Circ. 31415

11^h19^m13.68^s +34°10'14.3" 2.0" XRT-final UKSSDC

11^h19^m13.55^s +34°10'12.5" 2.3" XRT Burrows et al. GCN Circ. 31410

11^h19^m02.58^s +34°08'19.26" 10' BAT-GUANO DeLaunay et al. GCN Circ. 31402

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 31403 Fermi GRB 220107A: Global MASTER-Net
observations report MASTER

Optical Hosokawa et al. 31413 MITSuME Akeno optical observation MITSuME Akeno

Optical Zhu et al. 31416 Nanshan/NEXT optical observations Xinjiang Astro. Obs. detection

Optical Pankov et al. 31419 AbAO and Terskol optical observations Abastumani Astro. Obs. detection

Optical Moskvitin et al. 31422 SAO RAS optical observations SAO RAS detection

Optical Castro-Tirado et al. 31423 6m BTA spectroscopic redshift BTA redshift

Optical Moskvitin and Medvedev 31426 further SAO RAS optical observations SAO RAS

Optical Moskvitin 31431 SAO RAS optical observations SAO RAS

Gamma-ray Fermi 31399 Fermi GBM Final Real-time Localization Fermi GBM

Gamma-ray Kunzweiler et al. 31400 BALROG localization (Fermi Trigger
663259536 / GRB 220107615) BALROG

Gamma-ray Veres and Meegan 31406 Fermi GBM observations Fermi GBM E_peak=168±11 keV
T₉₀=33 seconds
Fluence=2.24±0.05x10^-5erg cm^-2
(brighter than 88% of long GRBs)

Gamma-ray Suresh et al. 31408 AstroSat CZTI detection CZTI

Gamma-ray Ridnaia et al. 31429 Konus-Wind detection Konus-Wind E_peak=247 (-24,+30) keV
Duration=~110.8 seconds
Fluence=5.48(-0.30,+0.34)x10^-5erg cm^-2

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

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

white 26.7 28.5 1834 20.16 ± 0.08

white 32.4 33.0 2708 20.35 ± 0.07

white 37.6 39.4 247 20.43 ± 0.24

RA (J2000)	Dec (J2000)	Error	Note	Reference
11^h19^m13.71^s	+34°10'14.5"	0.4"	UVOT-refined	Siegel GCN Circ. 31415
11^h19^m13.68^s	+34°10'14.3"	2.0"	XRT-final	UKSSDC
11^h19^m13.55^s	+34°10'12.5"	2.3"	XRT	Burrows et al. GCN Circ. 31410
11^h19^m02.58^s	+34°08'19.26"	10'	BAT-GUANO	DeLaunay et al. GCN Circ. 31402

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	31403	Fermi GRB 220107A: Global MASTER-Net observations report	MASTER
Optical	Hosokawa et al.	31413	MITSuME Akeno optical observation	MITSuME Akeno
Optical	Zhu et al.	31416	Nanshan/NEXT optical observations	Xinjiang Astro. Obs.	detection
Optical	Pankov et al.	31419	AbAO and Terskol optical observations	Abastumani Astro. Obs.	detection
Optical	Moskvitin et al.	31422	SAO RAS optical observations	SAO RAS	detection
Optical	Castro-Tirado et al.	31423	6m BTA spectroscopic redshift	BTA	redshift
Optical	Moskvitin and Medvedev	31426	further SAO RAS optical observations	SAO RAS
Optical	Moskvitin	31431	SAO RAS optical observations	SAO RAS
Gamma-ray	Fermi	31399	Fermi GBM Final Real-time Localization	Fermi GBM
Gamma-ray	Kunzweiler et al.	31400	BALROG localization (Fermi Trigger 663259536 / GRB 220107615)	BALROG
Gamma-ray	Veres and Meegan	31406	Fermi GBM observations	Fermi GBM	E_peak=168±11 keV T₉₀=33 seconds Fluence=2.24±0.05x10^-5erg cm^-2 (brighter than 88% of long GRBs)
Gamma-ray	Suresh et al.	31408	AstroSat CZTI detection	CZTI
Gamma-ray	Ridnaia et al.	31429	Konus-Wind detection	Konus-Wind	E_peak=247 (-24,+30) keV Duration=~110.8 seconds Fluence=5.48(-0.30,+0.34)x10^-5erg cm^-2

Filter	T_start(ks)	T_stop(ks)	Exp(s)	Mag
white	26.7	28.5	1834	20.16 ± 0.08
white	32.4	33.0	2708	20.35 ± 0.07
white	37.6	39.4	247	20.43 ± 0.24

Table 3. UVOT observations reported by Siegel (GCN Circ. 31415). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary detections and 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.

January 11, 2022