Gamma-ray Burst 230911A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 11 Sep 23 03:10:02 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     716094577
GRB_RA:           51.167d {+03h 24m 40s} (J2000),
                  51.433d {+03h 25m 44s} (current),
                  50.604d {+03h 22m 25s} (1950)
GRB_DEC:         -19.717d {-19d 43' 00"} (J2000),
                 -19.634d {-19d 38' 02"} (current),
                 -19.892d {-19d 53' 31"} (1950)
GRB_ERROR:       14.95 [deg radius, statistical plus systematic]
GRB_INTEN:       116 [cnts/sec]
DATA_SIGNIF:     9.20 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        11372.88 SOD {03:09:32.88} UT
GRB_PHI:         144.00 [deg]
GRB_THETA:        65.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      1.44
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 0,0,0, 1,0,0, 1,0,1, 0,0,
SUN_POSTN:       169.10d {+11h 16m 24s}   +4.69d {+04d 41' 08"}
SUN_DIST:        117.60 [deg]   Sun_angle= 7.8 [hr] (West of Sun)
MOON_POSTN:      129.00d {+08h 35m 59s}  +23.91d {+23d 54' 38"}
MOON_DIST:        87.18 [deg]
MOON_ILLUM:      13 [%]
GAL_COORDS:      209.35,-54.22 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       42.38,-36.96 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_lc_medres34_bn230911132.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 115.48,-1.72 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 11 Sep 23 03:10:20 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     716094577
GRB_RA:           57.180d {+03h 48m 43s} (J2000),
                  57.422d {+03h 49m 41s} (current),
                  56.669d {+03h 46m 41s} (1950)
GRB_DEC:         -28.930d {-28d 55' 47"} (J2000),
                 -28.859d {-28d 51' 30"} (current),
                 -29.082d {-29d 04' 54"} (1950)
GRB_ERROR:       4.34 [deg radius, statistical only]
DATA_SIGNIF:     17.40 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        11372.88 SOD {03:09:32.88} UT
GRB_PHI:         148.00 [deg]
GRB_THETA:        55.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       169.10d {+11h 16m 24s}   +4.69d {+04d 41' 08"}
SUN_DIST:        111.21 [deg]   Sun_angle= 7.4 [hr] (West of Sun)
MOON_POSTN:      129.00d {+08h 36m 00s}  +23.91d {+23d 54' 36"}
MOON_DIST:        86.71 [deg]
MOON_ILLUM:      13 [%]
GAL_COORDS:      226.27,-51.06 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       45.48,-47.42 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_lc_medres34_bn230911132.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_716094577.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 11 Sep 23 03:18:57 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     716094577
GRB_RA:           59.780d {+03h 59m 07s} (J2000),
                  60.006d {+04h 00m 01s} (current),
                  59.304d {+03h 57m 13s} (1950)
GRB_DEC:         -34.410d {-34d 24' 35"} (J2000),
                 -34.344d {-34d 20' 37"} (current),
                 -34.551d {-34d 33' 03"} (1950)
GRB_ERROR:       4.09 [deg radius, statistical only]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        11372.88 SOD {03:09:32.88} UT
GRB_PHI:         152.00 [deg]
GRB_THETA:        50.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       169.10d {+11h 16m 25s}   +4.68d {+04d 40' 60"}
SUN_DIST:        108.38 [deg]   Sun_angle= 7.3 [hr] (West of Sun)
MOON_POSTN:      129.07d {+08h 36m 18s}  +23.89d {+23d 53' 28"}
MOON_DIST:        87.64 [deg]
MOON_ILLUM:      13 [%]
GAL_COORDS:      235.14,-49.39 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       45.95,-53.33 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_lc_medres34_bn230911132.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_locplot_all_bn230911132.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #34652
The Fermi GBM team reports the detection of a likely LONG GRB
At 03:09:32 UT on 11 Sep 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230911A (trigger 716094577.87568 / 230911132).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 59.8, Dec = -34.4 (J2000 degrees, equivalent to J2000 03h 59m, -34d 23'), with a statistical uncertainty of 4.1 degrees.
The angle from the Fermi LAT boresight is 50.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_skymap_all_bn230911132.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_healpix_all_bn230911132.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911132/quicklook/glg_lc_medres34_bn230911132.gif
GCN Circular #34681
S. Belkin; B. P. Gompertz; A. Kumar; K. Ackley; K. Wiersema; D. O=E2=80=99N= eill; T. Killestein; R. Starling; M. J. Dyer; J. Lyman; K. Ulaczyk; F. Jime= nez-Ibarra; D. Steeghs; D. K. Galloway; V. Dhillon; P. O'Brien; G. Ramsay; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Pall'e and D. Pollacc= o report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Obs= erver (GOTO; Steeghs et al. 2022) in response to GRB 230911A (Fermi GBM tea= m, GCN 34652). Observations were performed by GOTO North and South between 04:19:47 UT on 2023-09-11 and 17:08:39 UT on 2023-09-12 (1.17 to 37.98 hour= s after trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. Source candidates were initially filtered using a classifie= r (Killestein et al. 2021) and cross-matched against a variety of contextua= l and minor planet catalogues. Human vetting was carried out in real time o= n any candidates that passed the above checks.
We identify one candidate optical counterpart consistent within the GBM 90% localisation region. We find no evidence of this source prior to the GRB t= rigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry serv= er (Shingles et al. 2021). However, we caution that the last available obse= rvation of the field was taken by ATLAS nine days before the GRB trigger.
```
Name | RA(J2000) | Dec(J2000) | Filter | Mag(AB) | t - trig(hrs)

GOTO23akf | 03:50:00.51 | -29:49:30.66 | L | 19.22 +/- 0.10 | 1.17=20
```
This source is seen to decay as a power-law with an index of 0.61 +/- 0.07 across 7 epochs of observations. No object is present at this position in the Legacy Survey (Dey et al. 2019).
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is prin= cipally funded by the STFC and operated at the Roque de los Muchachos Obser= vatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash Univ= ersity, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Th= ailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular #34684
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/GBM GRB 230911A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021622
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #34702
P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 230911A, collecting 2.8 ks of Photon Counting (PC) mode data between T0+215.5 ks and T0+326.2 ks.
An uncatalogued X-ray source is detected consistent with the GOTO position (GCN Circ. 34681) of the fading optical counterpart candidate, and this is therefore believed to be the afterglow. The position of this source (astrometrically enhanced by using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec=57.5027, -29.8259 which is equivalent to:
```
RA (J2000): 03:50:0.65
Dec(J2000): -29:49:33.2
```
with an uncertainty of 3.4 arcsec (radius, 90% confidence). Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 177). This position is 3.1 arcsec from the GOTO position.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021622. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021622.
This circular is an official product of the Swift-XRT team.
GCN Circular #34720
O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 03:09:32.88 UT on 11 September 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230911A (trigger 716094577/230911132), which was also detected by Swift/XRT (P. D'Avanzo et al. 2023, GCN 34702) and GOTO (S. Belkin et al. 2023, GCN 34681). The Fermi GBM Final Real-time Localization reported in GCN 34652 is consistent with the Swift-XRT and GOTO localizations.
The angle from the Fermi LAT boresight is 54 degrees.
The GBM light curve consists of a single peak with a duration (T90) of about 36 s (50-300 keV). The time-averaged spectrum from T0-4 to T0+30 s is best fit by a Band function with Epeak= 98 +/- 21 keV, alpha = -1.1 +/- 0.1 and beta = -2.0 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is (6.2 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.0 s in the 10-1000 keV band is 3.7 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

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Jochen Greiner, last update: 17-Sep-2023 [Disclaimer]