GRB 230204A
GCN Circular 33260
Subject
GRB 230204A: Swift detection of a possible burst (or possible transient Swift J1552.8-5055)
Date
2023-02-04T03:45:02Z (2 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), J. A. Kennea (PSU), A. Y. Lien (U Tampa),
A. Melandri (INAF-OAB), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB),
M. H. Siegel (PSU), A. Tohuvavohu (U Toronto) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 02:56:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230204A (trigger=1152509). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 238.164d, -50.858d which is
RA(J2000) = 15h 52m 39s
Dec(J2000) = -50d 51' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). Due to a telemetry gap, the BAT lightcurve
before T+8s is not immediately available, and no obvious variation is
visible in the remainder of the lightcurve, as is typical for an
image trigger.
The XRT began observing the field at 02:59:24.1 UT, 146.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 238.1950, -50.9167 which is equivalent to:
RA(J2000) = 15h 52m 46.80s
Dec(J2000) = -50d 55' 00.1"
with an uncertainty of 5.0 arcseconds (radius, 90% containment).
The initial flux in the 2.5 s image was 2.77e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 156 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the large, but
uncertain, extinction expected.
We note that this source is near the Galactic plane (lat=2.38 deg)
and was detected as a 64 s image trigger, which raises the possibility
that this is a Galactic transient. We would name this source
Swift J1552.8-5055 if it is not a GRB.
Further analysis of the nature of this source will require the
full downlinked dataset.
Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.it).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular 33261
Subject
GRB 230204A: Enhanced Swift-XRT position
Date
2023-02-04T07:39:42Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1193 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 230204A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 238.19965, -50.91653 which is equivalent
to:
RA (J2000): 15h 52m 47.91s
Dec (J2000): -50d 54' 59.5"
with an uncertainty of 2.2 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 33263
Subject
GRB 230204A/Swift J1552.8-5055: LCOGT Optical Counterpart Candidate
Date
2023-02-04T14:02:18Z (2 years ago)
From
Robert Strausbaugh at University of Minnesota <rstrausb@umn.edu>
R. Strausbaugh (University of Minnesota), A. Cucchiara (NASA) report on
behalf of a larger collaboration:
We observed the GRB 230204A/Swift J1552.8-5055 (D'Ai et al., GCN 33260)
field with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo
Interamerican Observatory, Chile site, on February 4, from 07:24 to 7:57 UT
(corresponding to 4.47 to 5.02 hours after GRB trigger time) with the
Bessel R and I filters.
We performed a series of 3x300s exposures in both bands. We detect a
source consistent with the XRT enhanced error position (Evens et al., GCN
33261) that is not present in USNO, SkyMapper, or 2MASS catalogs. The
coordinates for this candidate are: 238.19844d, -50.917039d.
As the field is near the galactic plane, the field is quite crowded. It is
possible that this source is present in the catalogs mentioned, but was not
able to be resolved due to different plate scales. Future observations are
planned to determine if the detected source is fading and other follow-up
efforts are encouraged.
The following magnitudes are calculated using the USNO-B1.0 catalog as
reference:
R = 17.75 +/- 0.02
I = 17.16 +/- 0.01
Due to the crowded field, these magnitudes may be contaminated by a nearby
bright star. These magnitudes are not corrected for galactic extinction.
GCN Circular 33264
Subject
GRB 230204A: Swift-XRT refined Analysis
Date
2023-02-04T18:03:23Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P.
D'Avanzo (INAF-OAB), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto),
D.N. Burrows (PSU) and A. D'Ai report on behalf of the Swift-XRT team:
We have analysed 6.4 ks of XRT data for GRB 230204A (D'Ai et al. GCN
Circ. 33260), from 136 s to 46.9 ks after the BAT trigger. The data
comprise 250 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 Evans et
al. (GCN Circ. 33261).
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.37 (+0.16, -0.14).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.64 (+/-0.10). The
best-fitting absorption column is 2.61 (+0.21, -0.20) x 10^22 cm^-2,
in excess of the Galactic value of 1.0 x 10^22 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.5 (+/-0.4) and a
best-fitting absorption column of 2.1 (+0.7, -0.6) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 7.6 x 10^-11 (1.2 x 10^-10) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.1 (+0.7, -0.6) x 10^22 cm^-2
Galactic foreground: 1.0 x 10^22 cm^-2
Excess significance: 2.8 sigma
Photon index: 1.5 (+/-0.4)
If the light curve continues to decay with a power-law decay index of
2.37, the count rate at T+24 hours will be 1.2 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.2 x
10^-16 (1.4 x 10^-15) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01152509.
This circular is an official product of the Swift-XRT team.
GCN Circular 33266
Subject
GRB 230204A: Swift/UVOT Upper Limits
Date
2023-02-04T23:36:26Z (2 years ago)
From
Sam LaPorte at PSU <sjl5346@psu.edu>
S. J. LaPorte (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 230204A
156 s after the BAT trigger (D'Ai et al., GCN Circ. 33260).
No optical afterglow consistent with the XRT position
(Evans et al. GCN Circ. 33261)
is detected in the initial UVOT exposures.
A known source with no significant signs of fading
is detected 2.88 arcsec from the XRT position at:
RA (J2000): 15h 52m 47.83s
Dec (J2000): -50d 54' 56.74"
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 156 306 147 >17.5
u_FC 314 564 246 >19.1
white 156 1372 373 >17.8
v 645 1596 117 >15.9
b 570 1521 97 >17.9
u 314 5553 382 >19.1
w1 695 5489 274 >19.1
m2 670 1446 97 >18.8
w2 621 1571 117 >18.5
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 2.516 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 33279
Subject
GRB 230204A: Swift-BAT refined analysis
Date
2023-02-06T03:46:38Z (2 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
T. Parsotan (GSFC/UMBC), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 230204A (trigger #1152509)
(D'Ai et al., GCN Circ. 33260). The BAT ground-calculated position is
RA, Dec = 238.166, -50.848 deg which is
RA(J2000) = 15h 52m 39.8s
Dec(J2000) = -50d 50' 52.8"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.
The mask-weighted light curve shows a multi-peaked structure that
starts at ~T-10 and ends at ~T+200 s. The most prominent peak
occurs at ~T+148 s. T90 (15-350 keV) is 182.05 +- 16.73 sec
(estimated error including systematics).
The time-averaged spectrum from T-6.81 to T+195.62 sec is best fit by a
simple
power-law model. The power law index of the time-averaged spectrum is
1.72 +- 0.13. The fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+148.12 sec in the 15-150 keV band
is 0.9 +- 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/1152509/BA/