Swift Observations of GRB 220101A

A. Tohuvavohu (U. Toronto), A. D'Ai (INAF-IASFPA) and N.P.M. Kuin (UCL-MSSL) for the Swift team

1. Introduction

At 05:09:55 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220101A (trigger=1091101) (Tohuvavohu et al. GCN Circ. 31347). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 137° from the Sun (9.6 hours West) and 65° from the 41%-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.

Tohuvavohu et al. (GCN Circ. 31347) reported the discovery with UVOT of an optical afterglow. Fu et al. (GCN Circ. 31353) determined a redshift of 4.61 from Xinglong, Perley (GCN Circ. 31357) determined a redshift from Liverpool Telescope, Fynbo et al. (GCN Circ. 31359) determined a redshift of 4.618 from NOT, Tomasella et al. (GCN Circ. 31363) determined a redshift of 4.61, and Kumar et al. (GCN Circ. 31442) determined a redshift of 4.618 from DFOT. 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 Markwardt et al. (GCN Circ. 31369), the BAT ground-calculated position is RA, Dec = 1.360, 31.758 deg.

The BAT lightcurve (Figure 1) shows a complex lightcurve extending to at least T+170 with a peak of 7000 counts/s (15-350 keV), at ~89 s after the trigger. T₉₀ (15-350 keV) is 173.36 ± 12.76 s (estimated error including systematics).

The time-averaged spectrum from T-58.08 to T+259.11 s is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.13 ± 0.13, and E_peak of 249.1 ± 161.8 keV (χ² 42.49 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.5 ± 0.0 x 10^-5 erg cm^-2 and the 1-s peak flux measured from T+89.07 s in the 15-150 keV band is 7.3 ± 0.3 ph cm^-2 s^-1. This fluence is larger than that of 98.5% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). A fit to a simple power law gives a photon index of 1.34 ± 0.03 (χ² 50.91 for 57 d.o.f.). 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/1091101/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Ai et al. (GCN Circ. 31355). We have analysed 19 ks of XRT data for GRB 211227A (Beardmore et al. GCN Circ. 31316), from 63 s to 257.6 ks after the BAT trigger. The data comprise 182 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 Goad et al. (GCN Circ. 31322).

The light curve (Figure 2) can be modelled with a series of power-law decays. The initial decay index is α=1.19 (+0.25, -0.20). At T+106 s the decay steepens to an α of 2.30 (+0.34, -0.18) before breaking again at T+219 s to a final decay with index α=5.26 (+0.35, -0.28).

A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.11 ± 0.07. The best-fitting absorption column is 2.2 (+0.5, -0.4) x 10²¹ cm^-2, in excess of the Galactic value of 2.4 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 6.1 x 10^-11 (6.6 x 10^-11) erg cm^-2 count^-1.

A summary of the WT-mode spectrum is thus:
Total column: 2.2 (+0.5, -0.4) x 10²¹ cm^-2
Galactic foreground: 2.4 x 10²⁰ cm^-2
Excess significance: 7.8 σ
Photon index: 1.11 ± 0.07

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01091101.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 220101 90 s after the BAT trigger (Kuin and Tohuvavohu GCN Circ. 31351). A rapidly decayig source consistent with the XRT position (Osborne et al., GCN Circ. 31349) 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).

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

00^h05^m24.80^s +31°46'08.4" 0.42" UVOT-refined Kuin and Tohuvavohu GCN Circ. 31351

00^h05^m24.89^s +31°46'07.7" 1.9" XRT-final UKSSDC

00^h05^m24.90^s +31°46'08.0" 2.1" XRT-enhanced Osborne et al. GCN Circ. 31349

00^h05^m26.4^s +31°45'28.3" 2.2' BAT-refined Markwardt et al. GCN Circ. 31369

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 31352 Swift GRB220101.22: Global MASTER-Net
observations report MASTER

Optical Fu et al. 31353 Xinglong-2.16m photometry and
spectroscopy Xinglong spectroscopy

Optical Hentunen et al. 31356 THO optical observations Taurus Hill Obs. detection

Optical Perley 31357 Liverpool telescope imaging of a
high-redshift afterglow Liverpool Telescope redshift

Optical de Ugarte Postigo et al. 31358 CAHA 2.2m/CAFOS detection CAHA detection

Optical Fynbo et al. 31359 NOT redshift confirmation NOT redshift

Optical Vinko et al. 31361 optical afterglow detection from
Konkoly Observatory Konkoly detection

Optical Mao et al. 31364 GMG observation Gao-Mei-Gu detection

Optical Noschese et al. 31366 OASDG optical observations S.Di Giacomo Obs. detection

Optical Mao et al. 31368 GMG observation (2nd epoch) Gao-Mei-Gu

Optical Guelbenzu et al. 31370 Tautenburg observations Tautenburg

Optical Strausbaugh and Cucchiara 31371 LCO Optical Observations LCO

Optical D'Avanzo et al. 31373 TNG NIR afterglow detection TNG detection

Optical Strausbaugh and Cucchiara 31383 LCO Continued Optical Observations LCO

Optical Dimple et al. 31384 1.3m DFOT observations DFOT

Optical 31387 iTelescope optical observations iTelescope

Optical Caballero-Garcia et al. 31388 2.2m CAHA (+CAFOS) first day optical
detection CAHA detection

Optical Strausbaugh and Cucchiara 31389 3rd LCO Optical Observation LCO

Optical Belkin et al. 31390 Mondy optical observations Mondy detection

Optical Ror et al. 31394 continued 1.3m DFOT Optical Observations DFOT detection

Optical D'Avanzo et al. 31395 further TNG NIR observations TNG detection

Optical Pankov et al. 31398 Continued Mondy optical observations Mondy detection

Optical Guelbenzu et al. 31401 Tautenburg observations Tautenburg

Optical Moskvitin et al. 31420 SAO RAS optical observations SAO RAS detection

Optical Perley 31425 Additional Liverpool telescope
photometry Liverpool Telescope

Optical Kumar et al. 31442 continued 1.3m DFOT optical
observations of a high-redshift
afterglow DFOT redshift

Optical Pankov et al. 31471 TSHAO optical observation, Terskol,
AbAO upper limits Abastumani Astro. Obs. upper limits

Optical Fouad et al. 31504 KAO optical-R observation Kottamia

Radio Laskar 31372 ALMA detection ALMA detection

Radio Laskar 31385 VLA detection VLA detection

Gamma-ray Arimoto et al. 31350 Fermi-LAT detection Fermi LAT

Gamma-ray Ursi et al. 31354 AGILE detection AGILE

Gamma-ray Lesage and Meegan 31360 Fermi GBM Detection Fermi GBM E_peak=330±15 keV
T₉₀=128 seconds
Fluence=7.7±0.1x10^-5erg cm^-2
(brighter than 97.0% of long GRBs)

Gamma-ray Tsvetkova et al. 31433 Konus-Wind detection Konus-Wind E_peak=257 (-27,+28) keV

Gamma-ray Tsvetkova 31436 Konus-Wind detection of GRB 220101A
(correction to GCN Circ. 31433) Konus-Wind

Other Tomasella et al. 31363 Asiago spectroscopic and photometric
detection detection

Other Atteia 31365 E_iso equals the maximum isotropic GRB
energy detection

Other Ruffini et al. 31465 The most powerful GRB and BDHN I in 26
years

Other Ruffini et al. 31648 The first example of a Petanova

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 90 240 147 14.68 ± 0.02

v 4448 4647 197 18.70 ± 0.18

b 3833 4032 197 >19.8

u 3628 5201 334 >20.1

w1 4858 5057 197 >20.1

m2 4652 4852 197 >20.2

w2 4243 4443 197 >20.4

RA (J2000)	Dec (J2000)	Error	Note	Reference
00^h05^m24.80^s	+31°46'08.4"	0.42"	UVOT-refined	Kuin and Tohuvavohu GCN Circ. 31351
00^h05^m24.89^s	+31°46'07.7"	1.9"	XRT-final	UKSSDC
00^h05^m24.90^s	+31°46'08.0"	2.1"	XRT-enhanced	Osborne et al. GCN Circ. 31349
00^h05^m26.4^s	+31°45'28.3"	2.2'	BAT-refined	Markwardt et al. GCN Circ. 31369

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	31352	Swift GRB220101.22: Global MASTER-Net observations report	MASTER
Optical	Fu et al.	31353	Xinglong-2.16m photometry and spectroscopy	Xinglong	spectroscopy
Optical	Hentunen et al.	31356	THO optical observations	Taurus Hill Obs.	detection
Optical	Perley	31357	Liverpool telescope imaging of a high-redshift afterglow	Liverpool Telescope	redshift
Optical	de Ugarte Postigo et al.	31358	CAHA 2.2m/CAFOS detection	CAHA	detection
Optical	Fynbo et al.	31359	NOT redshift confirmation	NOT	redshift
Optical	Vinko et al.	31361	optical afterglow detection from Konkoly Observatory	Konkoly	detection
Optical	Mao et al.	31364	GMG observation	Gao-Mei-Gu	detection
Optical	Noschese et al.	31366	OASDG optical observations	S.Di Giacomo Obs.	detection
Optical	Mao et al.	31368	GMG observation (2nd epoch)	Gao-Mei-Gu
Optical	Guelbenzu et al.	31370	Tautenburg observations	Tautenburg
Optical	Strausbaugh and Cucchiara	31371	LCO Optical Observations	LCO
Optical	D'Avanzo et al.	31373	TNG NIR afterglow detection	TNG	detection
Optical	Strausbaugh and Cucchiara	31383	LCO Continued Optical Observations	LCO
Optical	Dimple et al.	31384	1.3m DFOT observations	DFOT
Optical		31387	iTelescope optical observations	iTelescope
Optical	Caballero-Garcia et al.	31388	2.2m CAHA (+CAFOS) first day optical detection	CAHA	detection
Optical	Strausbaugh and Cucchiara	31389	3rd LCO Optical Observation	LCO
Optical	Belkin et al.	31390	Mondy optical observations	Mondy	detection
Optical	Ror et al.	31394	continued 1.3m DFOT Optical Observations	DFOT	detection
Optical	D'Avanzo et al.	31395	further TNG NIR observations	TNG	detection
Optical	Pankov et al.	31398	Continued Mondy optical observations	Mondy	detection
Optical	Guelbenzu et al.	31401	Tautenburg observations	Tautenburg
Optical	Moskvitin et al.	31420	SAO RAS optical observations	SAO RAS	detection
Optical	Perley	31425	Additional Liverpool telescope photometry	Liverpool Telescope
Optical	Kumar et al.	31442	continued 1.3m DFOT optical observations of a high-redshift afterglow	DFOT	redshift
Optical	Pankov et al.	31471	TSHAO optical observation, Terskol, AbAO upper limits	Abastumani Astro. Obs.	upper limits
Optical	Fouad et al.	31504	KAO optical-R observation	Kottamia
Radio	Laskar	31372	ALMA detection	ALMA	detection
Radio	Laskar	31385	VLA detection	VLA	detection
Gamma-ray	Arimoto et al.	31350	Fermi-LAT detection	Fermi LAT
Gamma-ray	Ursi et al.	31354	AGILE detection	AGILE
Gamma-ray	Lesage and Meegan	31360	Fermi GBM Detection	Fermi GBM	E_peak=330±15 keV T₉₀=128 seconds Fluence=7.7±0.1x10^-5erg cm^-2 (brighter than 97.0% of long GRBs)
Gamma-ray	Tsvetkova et al.	31433	Konus-Wind detection	Konus-Wind	E_peak=257 (-27,+28) keV
Gamma-ray	Tsvetkova	31436	Konus-Wind detection of GRB 220101A (correction to GCN Circ. 31433)	Konus-Wind
Other	Tomasella et al.	31363	Asiago spectroscopic and photometric detection		detection
Other	Atteia	31365	E_iso equals the maximum isotropic GRB energy		detection
Other	Ruffini et al.	31465	The most powerful GRB and BDHN I in 26 years
Other	Ruffini et al.	31648	The first example of a Petanova

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	90	240	147	14.68 ± 0.02
v	4448	4647	197	18.70 ± 0.18
b	3833	4032	197	>19.8
u	3628	5201	334	>20.1
w1	4858	5057	197	>20.1
m2	4652	4852	197	>20.2
w2	4243	4443	197	>20.4

Table 3. UVOT observations reported by Kuin and Tohuvavohu (GCN Circ. 31351). 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.

February 26, 2022