Swift Observations of GRB 230204B

V. D'Elia (SSDC and INAF-OAR) and M.H. Siegel (PSU) for the Swift team

1. Introduction

Serino et al. (GCN Circ. 33265) reported the GRB detection. The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 21:47:51 UT on 4 Feb 2023. Table 1 contains the best reported positions from Swift.

Saccardi et al. (GCN Circ. 33281) determined a redshift of 2.142 from VLT. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.

2. BAT Observations and Analysis

BAT did not observe this burst.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Elia et al. (GCN Circ. 33285). The source is below the RASS limit but does not show definitive signs of fading. This is most likely the afterglow, given also the reported redshift of z=2.14 (Saccardi et al. GCN Circ. 33281) but further observations are required to assess for fading.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Siegel and D’Elia GCN Circ. 33292) of the field of GRB 230204B 80 ks after the MAXI trigger (Serino et al., GCN Circ. 33265). No optical afterglow consistent with the optical or XRT positions (Swain et al., GCN Circ. 33269, Smartt et al., GCN Circ. 33278, D’Elia et al., GCN Circ. 33285) 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 0.109 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

RA (J2000) Dec (J2000) Error Note Reference

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Swain et al. 33269 GIT discovery of the likely optical
afterglow GROWTH-India Tel. detection

Optical Smartt et al. 33278 ATLAS detection of the optical
afterglow and a projected location in a
nearby galaxy group

Optical Saccardi et al. 33281 VLT/X-shooter redshift VLT redshift

Optical Ror et al. 33284 3.6m DOT optical observation DOT detection

Optical Strausbaugh and Cucchiara 33293 LCOGT Optical Upper Limits Las Cumbres Obs. Global Tele.Network upper limits

Optical Lipunov et al. 33301 MASTER early OT detection MASTER detection

Optical O'Connor et al. 33333 Lowell Discovery Telescope Observations Lowell Discovery Telescope

Optical Lipunov et al. 33441 MASTER detection of an object near NTT
Optical Afterglow Candidate MASTER detection

Radio Gulati et al. 33321 ATCA radio detection ATCA detection

X-ray Serino et al. 33265 MAXI/GSC detection MAXI detection

Gamma-ray Waratkar et al. 33268 AstroSat CZTI detection CZTI

Gamma-ray Casentini et al. 33272 AGILE detection AGILE

Gamma-ray Dafcikova et al. 33273 Detection by GRBAlpha GRBAlpha

Gamma-ray Poolakkil and Meegan 33288 Fermi GBM detection Fermi GBM E_peak=783±40 keV
T₉₀=216 seconds
Fluence=138.9±1.5x10^-6erg cm^-2
(brighter than 98.6% of long GRBs)

Gamma-ray Asaoka et al. 33322 CALET Gamma-Ray Burst Monitor detection CALET

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

v 81062 109630 314 >19.1

b 80652 109220 314 >20.1

u 80567 109136 314 >19.8

w1 80403 109052 629 >20.1

m2 81146 109877 2154 >20.9

w2 80737 109546 1259 >20.7

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Swain et al.	33269	GIT discovery of the likely optical afterglow	GROWTH-India Tel.	detection
Optical	Smartt et al.	33278	ATLAS detection of the optical afterglow and a projected location in a nearby galaxy group
Optical	Saccardi et al.	33281	VLT/X-shooter redshift	VLT	redshift
Optical	Ror et al.	33284	3.6m DOT optical observation	DOT	detection
Optical	Strausbaugh and Cucchiara	33293	LCOGT Optical Upper Limits	Las Cumbres Obs. Global Tele.Network	upper limits
Optical	Lipunov et al.	33301	MASTER early OT detection	MASTER	detection
Optical	O'Connor et al.	33333	Lowell Discovery Telescope Observations	Lowell Discovery Telescope
Optical	Lipunov et al.	33441	MASTER detection of an object near NTT Optical Afterglow Candidate	MASTER	detection
Radio	Gulati et al.	33321	ATCA radio detection	ATCA	detection
X-ray	Serino et al.	33265	MAXI/GSC detection	MAXI	detection
Gamma-ray	Waratkar et al.	33268	AstroSat CZTI detection	CZTI
Gamma-ray	Casentini et al.	33272	AGILE detection	AGILE
Gamma-ray	Dafcikova et al.	33273	Detection by GRBAlpha	GRBAlpha
Gamma-ray	Poolakkil and Meegan	33288	Fermi GBM detection	Fermi GBM	E_peak=783±40 keV T₉₀=216 seconds Fluence=138.9±1.5x10^-6erg cm^-2 (brighter than 98.6% of long GRBs)
Gamma-ray	Asaoka et al.	33322	CALET Gamma-Ray Burst Monitor detection	CALET

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
v	81062	109630	314	>19.1
b	80652	109220	314	>20.1
u	80567	109136	314	>19.8
w1	80403	109052	629	>20.1
m2	81146	109877	2154	>20.9
w2	80737	109546	1259	>20.7

Table 3. UVOT observations reported by Siegel and D’Elia (GCN Circ. 33292). 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 10, 2023