Gamma-ray Burst 230911D

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 11 Sep 23 07:53:29 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      70
TRIGGER_NUM:     716111594
GRB_RA:           13.250d {+00h 53m 00s} (J2000),
                  13.500d {+00h 54m 00s} (current),
                  12.720d {+00h 50m 53s} (1950)
GRB_DEC:         -60.250d {-60d 15' 00"} (J2000),
                 -60.122d {-60d 07' 17"} (current),
                 -60.521d {-60d 31' 16"} (1950)
GRB_ERROR:       3.68 [deg radius, statistical plus systematic]
GRB_INTEN:       2424 [cnts/sec]
DATA_SIGNIF:     87.00 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:         345.00 [deg]
GRB_THETA:       160.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.52
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       169.28d {+11h 17m 06s}   +4.61d {+04d 36' 39"}
SUN_DIST:        121.50 [deg]   Sun_angle= 10.4 [hr] (West of Sun)
MOON_POSTN:      131.44d {+08h 45m 46s}  +23.27d {+23d 16' 15"}
MOON_DIST:       123.85 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      302.58,-56.88 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      333.48,-57.33 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 39.58,-0.08 [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 07:53:13 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     716111594
GRB_RA:          352.567d {+23h 30m 16s} (J2000),
                 352.912d {+23h 31m 39s} (current),
                 351.830d {+23h 27m 19s} (1950)
GRB_DEC:         -68.450d {-68d 27' 00"} (J2000),
                 -68.319d {-68d 19' 08"} (current),
                 -68.726d {-68d 43' 32"} (1950)
GRB_ERROR:       9.82 [deg radius, statistical plus systematic]
GRB_INTEN:       342 [cnts/sec]
DATA_SIGNIF:     8.10 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:          12.00 [deg]
GRB_THETA:       155.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.84
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      98%  GRB
2nd_MOST_LIKELY:   1%  Generic Transient
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       169.28d {+11h 17m 06s}   +4.61d {+04d 36' 39"}
SUN_DIST:        116.24 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      131.44d {+08h 45m 45s}  +23.27d {+23d 16' 17"}
MOON_DIST:       128.42 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      313.69,-46.95 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      311.37,-56.56 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 39.58,-0.08 [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 07:53:21 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      59
TRIGGER_NUM:     716111594
GRB_RA:           12.800d {+00h 51m 12s} (J2000),
                  13.052d {+00h 52m 12s} (current),
                  12.267d {+00h 49m 04s} (1950)
GRB_DEC:         -60.500d {-60d 30' 00"} (J2000),
                 -60.371d {-60d 22' 16"} (current),
                 -60.772d {-60d 46' 17"} (1950)
GRB_ERROR:       3.92 [deg radius, statistical plus systematic]
GRB_INTEN:       1586 [cnts/sec]
DATA_SIGNIF:     57.50 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:         345.00 [deg]
GRB_THETA:       160.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.66
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       169.28d {+11h 17m 06s}   +4.61d {+04d 36' 39"}
SUN_DIST:        121.39 [deg]   Sun_angle= 10.4 [hr] (West of Sun)
MOON_POSTN:      131.44d {+08h 45m 45s}  +23.27d {+23d 16' 16"}
MOON_DIST:       124.01 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      302.99,-56.63 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      332.86,-57.34 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 39.58,-0.08 [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 07:53:28 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     716111594
GRB_RA:          153.610d {+10h 14m 26s} (J2000),
                 153.889d {+10h 15m 33s} (current),
                 153.021d {+10h 12m 05s} (1950)
GRB_DEC:         -22.540d {-22d 32' 23"} (J2000),
                 -22.658d {-22d 39' 29"} (current),
                 -22.291d {-22d 17' 27"} (1950)
GRB_ERROR:       3.41 [deg radius, statistical only]
DATA_SIGNIF:     36.70 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:         348.00 [deg]
GRB_THETA:        69.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       169.28d {+11h 17m 06s}   +4.61d {+04d 36' 39"}
SUN_DIST:         31.14 [deg]   Sun_angle= 1.0 [hr] (West of Sun)
MOON_POSTN:      131.44d {+08h 45m 46s}  +23.27d {+23d 16' 15"}
MOON_DIST:        50.85 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      261.72, 27.50 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      164.84,-31.00 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_716111594.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
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 07:53:36 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      73
TRIGGER_NUM:     716111594
GRB_RA:           13.550d {+00h 54m 12s} (J2000),
                  13.799d {+00h 55m 12s} (current),
                  13.021d {+00h 52m 05s} (1950)
GRB_DEC:         -60.100d {-60d 06' 00"} (J2000),
                 -59.972d {-59d 58' 18"} (current),
                 -60.371d {-60d 22' 14"} (1950)
GRB_ERROR:       3.50 [deg radius, statistical plus systematic]
GRB_INTEN:       3968 [cnts/sec]
DATA_SIGNIF:     136.40 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:         345.00 [deg]
GRB_THETA:       160.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.43
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,1,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       169.28d {+11h 17m 06s}   +4.61d {+04d 36' 39"}
SUN_DIST:        121.56 [deg]   Sun_angle= 10.4 [hr] (West of Sun)
MOON_POSTN:      131.44d {+08h 45m 46s}  +23.27d {+23d 16' 14"}
MOON_DIST:       123.73 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      302.30,-57.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      333.87,-57.33 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 39.58,-0.08 [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 08:23:36 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     716111594
GRB_RA:          154.850d {+10h 19m 24s} (J2000),
                 155.132d {+10h 20m 32s} (current),
                 154.255d {+10h 17m 01s} (1950)
GRB_DEC:         -20.920d {-20d 55' 11"} (J2000),
                 -21.039d {-21d 02' 21"} (current),
                 -20.669d {-20d 40' 06"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.73 SOD {07:53:09.73} UT
GRB_PHI:         348.58 [deg]
GRB_THETA:        67.16 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:       169.29d {+11h 17m 11s}   +4.60d {+04d 36' 11"}
SUN_DIST:         29.16 [deg]   Sun_angle= 0.9 [hr] (West of Sun)
MOON_POSTN:      131.70d {+08h 46m 48s}  +23.20d {+23d 12' 02"}
MOON_DIST:        49.78 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:      261.57, 29.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      165.28,-29.05 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_locplot_all_bn230911329.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 has human-in-the-loop processing.

GCN Circular #34656
The Fermi GBM team reports the detection of a likely long GRB.
At 07:53:09.73 UT on 11 September 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230911D (trigger 716111594 / 230911329).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 154.9, Dec = -20.9 (J2000 degrees, equivalent to J2000 +10h 19m, -20d 55'), with a statistical uncertainty of 1.0 degree.
The angle from the Fermi LAT boresight is 67 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_skymap_all_bn230911329.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/bn230911329/quicklook/glg_healpix_all_bn230911329.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230911329/quicklook/glg_lc_medres34_bn230911329.gif
GCN Circular #34657
B. Biltzinger, T. Preis, J. Burgess & J. Greiner (all MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger at 07:53:09 on 11 Sept. 2023 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60).
The best-fit position (1 sigma statistical errors) is:
```
RA(2000.0) = 148.9+/-0.2 deg
Decl.(2000.0) = -23.4+/-0.7 deg
```
We estimate an additional systematic error of 1 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB230911329/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB230911329/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB230911329/json

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 11 Sep 23 15:00:25 UT
NOTICE_TYPE:     Fermi-LAT Offline Position
TRIGGER_NUM:     230911329
GRB_RA:          151.900d {+10h 07m 36s} (J2000),
                 152.173d {+10h 08m 42s} (current),
                 151.324d {+10h 05m 18s} (1950)
GRB_DEC:         -25.970d {-25d 58' 11"} (J2000),
                 -26.086d {-26d 05' 10"} (current),
                 -25.725d {-25d 43' 29"} (1950)
GRB_ERROR:       14.39 [arcmin radius, 90% containment, statistical only]
GRB_DATE:        20198 TJD;   254 DOY;   23/09/11
GRB_TIME:        28389.72 SOD {07:53:09.72} UT
TRIGGER_ID:      0x0
MISC:            0x40000000
SUN_POSTN:       169.54d {+11h 18m 10s}   +4.50d {+04d 29' 53"}
SUN_DIST:         34.91 [deg]   Sun_angle= 1.2 [hr] (West of Sun)
MOON_POSTN:      135.07d {+09h 00m 18s}  +22.24d {+22d 14' 15"}
MOON_DIST:        51.08 [deg]
MOON_ILLUM:      10 [%]
GAL_COORDS:      262.81, 23.86 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      164.88,-34.76 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi LAT Offline position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.
COMMENTS:        It is the result of human-in-the-loop processing.  
COMMENTS:        This is a human generated position of a LAT ground detection.  
COMMENTS:        This source corresponds to GBM trigger.

GCN Circular #34659
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 230911D (Fermi GBM team, GCN 34656) triggered Konus-Wind (KW) at T0=3D28387.687 s UT (07:53:07.687).
The burst light curve shows a bright, multi-peaked emission complex, which starts at ~T0-3 s, peaks at ~T0+15 s, and has a total duration of ~60 s. The emission is seen up to ~5 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB230911_T28387/
As observed by Konus-Wind, the burst had a fluence of (1.57 =C2=B1 0.12)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 14.848 s, of (1.42 =C2=B1 0.15)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+54.272 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -0.74 (-0.06,+0.06), the high energy photon index beta =3D -2.44 (-0.28,+0.17), the peak energy Ep =3D 343 (-22,+23) keV, chi2 =3D 126/96 dof.
The spectrum near the peak count rate (measured from T0+14.336 to T0+16.384 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -0.13 (-0.16,+0.18), the high energy photon index beta =3D -2.56 (-0.32,+0.21), the peak energy Ep =3D 405 (-43,+48) keV, chi2 =3D 95/73 dof.
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #34660
D. Frederiks, on behalf of the KW team,
the subject line of GCN 34659 contains a typo in the GRB name and should read as "Konus-Wind detection of GRB 230911D"
We are sorry for the inconvenience.
GCN Circular #34668
F. Longo (University and INFN, Trieste), D. Kocevski (NASA/MSFC), N. Omodei (Stanford University), N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT Collaboration:
On September 11, 2023 Fermi-LAT detected high-energy emission from GRB 230911D, which was also detected by Fermi-GBM (trigger 716111594 / 230911329, GCN 34656) and Konus-Wind (GCN 34659).
The best LAT on-ground location is found to be
RA, Dec = 151.9, -26.0 (degrees, J2000)
with an error radius of 0.3 deg (90% containment, statistical error only). This was 73 deg from the LAT boresight at the time of the GBM trigger:
T0 = 07:53:09.73 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-1000 s after the GBM trigger is (2.3 +/- 0.8)E-5 ph/cm2/s.
The estimated photon index above 100 MeV is -1.9 +/- 0.2. The highest-energy photon is a 4.6 GeV event which is observed 154 seconds after the GBM trigger.
A Swift ToO has been requested for this burst.
The Fermi-LAT point of contact for this burst is Makoto Arimoto (arimoto@se.kanazawa-u.ac.jp )
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular #34669
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report:
The bright, short-duration GRB 230911D (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 34656; BALROG localization: Biltzinger et al., GCN Circ. 34657; Konus-Wind detection: Frederiks et al., GCN Circ. 34659; Fermi-LAT detection: Longo et al., GCN Circ. 34668) was detected by Fermi (GBM trigger 716111594), INTEGRAL (SPI-ACS), Konus-Wind, Swift (BAT), and Mars-Odyssey (HEND) at about 28389 s UT (07:53:09). The burst was outside the coded field of view of the BAT.
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:
```
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  151.360 (10h 05m 26s) -25.633 (-25d 38' 00")
 Corners:
  151.696 (10h 06m 47s) -26.192 (-26d 11' 31")
  151.638 (10h 06m 33s) -26.200 (-26d 12' 01")
  151.036 (10h 04m 09s) -25.072 (-25d 04' 18")
  151.093 (10h 04m 22s) -25.064 (-25d 03' 51")
 ---------------------------------------------
```
The error box area is 226 sq. arcmin, and its maximum dimension is 1.3 deg (the minimum one is 3 arcmin). The Sun distance was 35 deg.
The IPN localization is consistent with, but reduces the area of, the Fermi-LAT localization (GCN 34668).
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB230911_T28387/IPN
GCN Circular #34670
L. Scotton (UAH), R. Hamburg (CNRS/IJCLab), and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 07:53:09.72 UT on 11 September 2023, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 230911D (trigger 716111594 / 230911329), which was also detected by the Fermi LAT (F. Longo et al. 2023, GCN 34668) and Konus-Wind (D. Frederiks et al. 2023, GCN 34659).
The Fermi GBM Final Localization (GCN 34656) is consistent with the Fermi LAT position.
The angle from the Fermi LAT boresight at the GBM trigger time is 72 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 45.6 s (50-300 keV). The time-averaged spectrum from T0-4.4 s to T0+77.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.00 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 429.9 +/- 7.8 keV
The event fluence (10-1000 keV) in this time interval is (1.214 +/- 0.007)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+16.1 s in the 10-1000 keV band is 24.8 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak= 420.6 +/- 9.0 keV, alpha = -1.00 +/- 0.01 and beta = -3.02 +/- 0.25.
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/"
GCN Circular #34678
B. Grefenstette and A. Jaodand (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of prompt emission from the Long GRB 230911D in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe hard X-ray imagers. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR GRB search algorithm triggered at 2023-09-11T07:53:11, which is roughly 1.25-s after the Fermi detection (Hamburg et al., GCN Circ. 34656). When we consider the 1-s resolution of the shield data combined with the smoothing of the search algorithm, we consider the NuSTAR GRB time to be consistent with the time reported by Fermi.
Using the GRB localization (Greiner, et al., GCN Circ. 34657) and the NuSTAR trigger time, we estimate that the GRB was above the Earth's horizon as seen by NuSTAR and roughly 83-degrees off-axis from the NuSTAR boresight at the time of the GRB (e.g., through the side of the instrument).
The CsI data are recorded at 1 Hz and show a broad burst with multiple peaks. 1-sec count rates peaked at ~4,000 counts per second in both the FPMA and FPMB shield units. Typical background rates are ~1,000 counts per second.
The burst was also coincidentally detected in both CdZnTe detectors, with peak count rates of ~30 counts above 100 keV in 5-s time bins.
Flux calibration from the CdZnTe detectors for far off-axis is currently not possible since the X-rays observed by the CdZnTe detectors this far off-axis likely have multiple scatters in the instrument before being recorded by the X-ray detectors. Work on understanding the response and converting measured rates to incident fluxes is on-going.
The automated light curve report for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2023/230911D/
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA=E2=80=99s Science Mission Directorate in Washington.
View this GCN Circular online at https://gcn.nasa.gov/circulars/34678.
GCN Circular #34712
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner= (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (= Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Kolar, J.-P. = Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. o= f Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, = M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U.= of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. = Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.= ), G. Dalya (Eotvos U.), yyT. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Fr= iss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya= U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Ob= servatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (U= niv of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso= , M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. = Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 230911D (Fermi/GBM detection: GCN 34656; Fermi/LAT de= tection: GCN 34668; Konus/Wind detection: GCN 34659; NuSTAR detection: GCN = 34678; INTEGRAL/SPI-ACS peak detection at 2023-09-11 ~07:53:25 UT) was obse= rved by the GRBAlpha 1U CubeSat (Pal et al. 2023; arXiv:2302.10048).
The detection was confirmed at the peak time 2023-09-11 07:53:26 UTC. The T= 90 duration measured by GRBAlpha is 45 s and the overall significance durin= g T90 reaches 56 sigma.
The light curve obtained by GRBAlpha is available here:=20 https://grbalpha.konkoly.hu/static/share/GRB230911D_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/he= a/GRBAlpha/=20 GRBAlpha, launched on 2021 March 22, is a demonstration mission for a futur= e CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GR= BAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM ar= ray, covering the energy range from ~50 keV to ~1000 keV. To increase the d= uty cycle and the downlink rate, the upgrade of the on-board data acquisiti= on software stack is in progress. The ground segment is also supported by t= he radio amateur community and it takes advantage of the SatNOGS network fo= r increased data downlink volume.

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Jochen Greiner, last update: 16-Sep-2023 [Disclaimer]