Gamma-ray Burst 230423A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:08:55 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1165354,   Seg_Num: 0
GRB_RA:          122.605d {+08h 10m 25s} (J2000),
                 122.860d {+08h 11m 26s} (current),
                 122.059d {+08h 08m 14s} (1950)
GRB_DEC:         -21.920d {-21d 55' 12"} (J2000),
                 -21.990d {-21d 59' 25"} (current),
                 -21.771d {-21d 46' 16"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       15544 [cnts]    Image_Peak=368 [image_cnts]
TRIGGER_DUR:     12.160 [sec] 
TRIGGER_INDEX:   478     E_range: 25-100 keV
BKG_INTEN:       74623 [cnts]
BKG_TIME:        68776.84 SOD {19:06:16.84} UT
BKG_DUR:         64 [sec]
GRB_DATE:        20057 TJD;   113 DOY;   23/04/23
GRB_TIME:        68875.46 SOD {19:07:55.46} UT
GRB_PHI:         -62.72 [deg]
GRB_THETA:         4.98 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     8.60 [sigma]
IMAGE_SIGNIF:    7.30 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +2  -3  +0  +1 +10  +0 
SUN_POSTN:        31.15d {+02h 04m 36s}  +12.64d {+12d 38' 19"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.24d {+05h 04m 57s}  +26.55d {+26d 33' 16"}
MOON_DIST:        66.28 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      131.32,-40.80 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 342.20,-5.10 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:09:52 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1165354,   Seg_Num: 0
POINT_RA:        122.609d {+08h 10m 26s} (J2000)
POINT_DEC:       -21.922d {-21d 55' 19"} (J2000)
IMG_START_DATE:  20057 TJD;   113 DOY;   23/04/23
IMG_START_TIME:  68976.55 SOD {19:09:36.55} UT,   101.1 [sec] since BAT Trigger 
Time
COUNTS:          34    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:12:17 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1165354,   Seg_Num: 0
GRB_RA:          122.605d {+08h 10m 25s} (J2000),
                 122.860d {+08h 11m 26s} (current),
                 122.059d {+08h 08m 14s} (1950)
GRB_DEC:         -21.920d {-21d 55' 12"} (J2000),
                 -21.990d {-21d 59' 25"} (current),
                 -21.771d {-21d 46' 16"} (1950)
GRB_DATE:        20057 TJD;   113 DOY;   23/04/23
GRB_TIME:        68875.46 SOD {19:07:55.46} UT
TRIGGER_INDEX:   478
GRB_PHI:         -62.72 [deg]
GRB_THETA:         4.98 [deg]
DELTA_TIME:      58.00 [sec]
TRIGGER_DUR:     12.160 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     8.60 [sigma]
IMAGE_SIGNIF:    7.30 [sigma]
LC_URL:          sw01165354000msb.lc
SUN_POSTN:        31.15d {+02h 04m 37s}  +12.64d {+12d 38' 22"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.27d {+05h 05m 05s}  +26.56d {+26d 33' 33"}
MOON_DIST:        66.26 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      131.32,-40.80 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 342.20,-5.10 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:26:24 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1165354,   Seg_Num: 0
POINT_RA:        122.610d {+08h 10m 26s} (J2000)
POINT_DEC:       -21.923d {-21d 55' 23"} (J2000)
POINT_ROLL:      281.220d
IMG_START_DATE:  20057 TJD;   113 DOY;   23/04/23
IMG_START_TIME:  69761.00 SOD {19:22:41.00} UT,   885.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.359
N_STARS:         190
X_OFFSET:        277 [pixels]
Y_OFFSET:        308 [pixels]
X_MAX:           1716 [pixels]
Y_MAX:           1747 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw01165354000msufc0885.fits
SUN_POSTN:        31.16d {+02h 04m 39s}  +12.64d {+12d 38' 34"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.41d {+05h 05m 38s}  +26.58d {+26d 34' 44"}
MOON_DIST:        66.19 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      131.33,-40.80 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:26:41 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1165354,   Seg_Num: 0
POINT_RA:        122.610d {+08h 10m 26s} (J2000)
POINT_DEC:       -21.923d {-21d 55' 23"} (J2000)
POINT_ROLL:      281.220d
IMG_START_DATE:  20057 TJD;   113 DOY;   23/04/23
IMG_START_TIME:  69761.00 SOD {19:22:41.00} UT,   885.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.359
N_STARS:         190
X_OFFSET:        277 [pixels]
Y_OFFSET:        308 [pixels]
X_MAX:           1716 [pixels]
Y_MAX:           1747 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw01165354000msufc0885.fits
SUN_POSTN:        31.16d {+02h 04m 39s}  +12.64d {+12d 38' 34"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.41d {+05h 05m 38s}  +26.58d {+26d 34' 45"}
MOON_DIST:        66.19 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      131.33,-40.80 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:27:52 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1165354,   Seg_Num: 0
POINT_RA:        122.610d {+08h 10m 26s} (J2000)
POINT_DEC:       -21.923d {-21d 55' 23"} (J2000)
ROLL:            281.220d
IMG_START_DATE:  20057 TJD;   113 DOY;   23/04/23
IMG_START_TIME:  69761.00 SOD {19:22:41.00} UT,   885.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703970592
X_OFFSET:        836 [pixels]
Y_OFFSET:        867 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       996
Y_GRB_POS:       1027
BINNING_INDEX:   1
IM_URL:          sw01165354000msuni0917.fits
SUN_POSTN:        31.16d {+02h 04m 39s}  +12.64d {+12d 38' 35"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.42d {+05h 05m 41s}  +26.58d {+26d 34' 51"}
MOON_DIST:        66.18 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      131.33,-40.80 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 23 Apr 23 19:28:08 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1165354,   Seg_Num: 0
POINT_RA:        122.610d {+08h 10m 26s} (J2000)
POINT_DEC:       -21.923d {-21d 55' 23"} (J2000)
ROLL:            281.220d
IMG_START_DATE:  20057 TJD;   113 DOY;   23/04/23
IMG_START_TIME:  69761.00 SOD {19:22:41.00} UT,   885.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     703970592
X_OFFSET:        836 [pixels]
Y_OFFSET:        867 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       996
Y_GRB_POS:       1027
BINNING_INDEX:   1
IM_URL:          sw01165354000msuni0917.fits
SUN_POSTN:        31.16d {+02h 04m 39s}  +12.64d {+12d 38' 35"}
SUN_DIST:         96.25 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:       76.42d {+05h 05m 42s}  +26.58d {+26d 34' 53"}
MOON_DIST:        66.18 [deg]
MOON_ILLUM:      14 [%]
GAL_COORDS:      241.49,  6.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      131.33,-40.80 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #33677
R. Brivio (INAF-OAB), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL), S. Laha (GSFC/UMBC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), C. Salvaggio (INAF-OAB) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team:
At 19:07:55 UT, the Swift Burst Alert Telescope (BAT) triggered and located a marginal image peak, which is possibly GRB 230423A (trigger=1165354). Swift slewed immediately to the image location. The BAT on-board calculated location is RA, Dec 122.605, -21.920 which is
```
   RA(J2000) = 08h 10m 25s
   Dec(J2000) = -21d 55' 12"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~600 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 19:09:36.5 UT, 101.1 seconds after the BAT trigger. No source was detected in 777 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart.
UVOT took a finding chart exposure of 150 seconds with the White filter starting 885 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' covers 25% of the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.136.
Due to the marginal significance (7.3 sigma) of this detection in BAT and the lack of an observed XRT counterpart, we cannot confirm that this is a real GRB. However, the XRT observation was interrupted by entry into the South Atlantic Anomaly (SAA) so the bulk of the XRT exposure time may have been after any source could have faded significantly. For this reason, we will not be able to verify or refute the reality of this detection until the full dataset is downloaded.
GCN Circular #33679
C. Salvaggio (INAF-OAB), P. D=E2=80=99avanzo (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=3D704.5 s to t+t0=3D4893.3 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=E2=80=99 33.5=E2=80=9D
with an uncertainty of 3.8=E2=80=9D (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
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: 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
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
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/

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Jochen Greiner, last update: 27-Apr-2023 [Disclaimer]