GRB 230423A
GCN Circular 33679
Subject
GRB 230423A: Swift-XRT afterglow detection
Date
2023-04-24T14:11:56Z (2 years ago)
From
Chiara Salvaggio at INAF OABrera <chiara.salvaggio@inaf.it>
C. Salvaggio (INAF-OAB), P. D’avanzo (INAF-OAB), T. Sbarrato (INAF-OAB), R.
Brivio (INAF-OAB), M. Ferro (INAF-OAB), M.G. Bernardini (INAF-OAB), A. Y.
Lien (U Tampa), K.L. Page (U. Leicester), P.A. Evans (U. Leicester) report
on behalf of the Swift-XRT team:
We have analysed 852s of Swift/XRT data for GRB 230423A (R.Brivio et al.,
GCN CIrc. 33677), from t-t0=704.5 s to t+t0=4893.3 s after the BAT trigger
1165354. The trigger was previously indicated as non-burst due to a low BAT
significance detection and the absence of an XRT counterpart (GCN circ.
33677).
We found an uncatalogued fading source with coordinates:
RA (J2000): 08h 10m 19.94s
DEC (J2000): -21d 55’ 33.5”
with an uncertainty of 3.8” (radius, 90% confidence).
We propose this source as the X-ray afterglow of GRB 230423A.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01165354
This circular is an official product of the Swift-XRT team
GCN Circular 33681
Subject
GRB 230423A: Swift-XRT refined Analysis
Date
2023-04-25T04:27:05Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), P.A.
Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V.
D'Elia (SSDC & INAF-OAR) and report on behalf of the Swift-XRT team:
We have analysed 2.5 ks of XRT data for GRB 230423A, from 680 s to 57.3
ks after the BAT trigger. The data comprise 22 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. The refined
XRT position is RA, Dec = 122.5830, -21.9259 which is equivalent to:
RA (J2000): 08 10 19.91
Dec(J2000): -21 55 33.1
with an uncertainty of 3.7 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.19 (+0.39, -0.28).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.6 (+/-0.8). The
best-fitting absorption column is 3.3 (+1.5, -1.3) x 10^22 cm^-2, in
excess of the Galactic value of 2.0 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 5.9 x 10^-11 (2.8 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.3 (+1.5, -1.3) x 10^22 cm^-2
Galactic foreground: 2.0 x 10^21 cm^-2
Excess significance: 4.1 sigma
Photon index: 2.6 (+/-0.8)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01165354.
This circular is an official product of the Swift-XRT team.
GCN Circular 33683
Subject
GRB 230423A: Swift/UVOT Upper Limits
Date
2023-04-25T20:34:48Z (2 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. Paul Kuin (UCL-MSSL) and Riccardo Brivio (INAF-OAB)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 230423A
731 s after the BAT trigger (Brivio et al., GCN Circ. 33677). No optical
afterglow consistent with the XRT position Salvaggio et al., GCN
Circulars 33679, is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 731 881 147 >20.9
white 731 5415 491 >21.4
b 5010 5210 197 >20.0
u 4805 5004 197 >19.2
w2 5420 5544 122 >19.5
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.137 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 33694
Subject
GRB 230423A(trigger #1165354): Swift-BAT refined analysis
Date
2023-04-27T21:21:35Z (2 years ago)
From
Sibasish Laha at GSFC <sibasish.laha@nasa.gov>
T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC),
M. Stamatikos (OSU)(i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we have found that BAT trigger #1165354 is a GRB 230423A even though
the original GCN Circular (Brivio et al., GCN Circ. 33677) based on the immediately
available data suggested that it was probably a statistical fluctuation.
The BAT ground-calculated position is
RA, Dec = 122.618, -21.901 deg which is
RA(J2000) = 08h 10m 28.2s
Dec(J2000) = -21d 54' 03.6"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The BAT light curve showed a complex structure with a duration of about 30 sec.
T90 (15-350 keV) is 23.60 +- 4.27 sec (estimated error including systematics).
The time-averaged spectrum from T-2.25 to T+24.49 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.69 +- 0.27. The fluence in the 15-150 keV band is 4.6 +- 0.8 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+10.62 sec in the 15-150 keV band
is 0.6 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1165354/BA/