Gamma-ray Burst 220408B

(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:     Fri 08 Apr 22 07:28:29 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      46
TRIGGER_NUM:     671095689
GRB_RA:          101.367d {+06h 45m 28s} (J2000),
                 101.412d {+06h 45m 39s} (current),
                 101.264d {+06h 45m 03s} (1950)
GRB_DEC:         -63.133d {-63d 07' 59"} (J2000),
                 -63.158d {-63d 09' 27"} (current),
                 -63.079d {-63d 04' 42"} (1950)
GRB_ERROR:       8.38 [deg radius, statistical plus systematic]
GRB_INTEN:       358 [cnts/sec]
DATA_SIGNIF:     15.90 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        19677 TJD;    98 DOY;   22/04/08
GRB_TIME:        26884.65 SOD {07:28:04.65} UT
GRB_PHI:         176.00 [deg]
GRB_THETA:        35.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.67
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,1,0, 1,0,1, 0,0,
SUN_POSTN:        17.02d {+01h 08m 06s}   +7.23d {+07d 13' 57"}
SUN_DIST:         93.93 [deg]   Sun_angle= -5.6 [hr] (East of Sun)
MOON_POSTN:       98.72d {+06h 34m 53s}  +26.92d {+26d 55' 01"}
MOON_DIST:        90.10 [deg]
MOON_ILLUM:      41 [%]
GAL_COORDS:      273.12,-24.66 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      149.89,-84.09 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_lc_medres34_bn220408311.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 129.58,12.18 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 08 Apr 22 07:28:38 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     671095689
GRB_RA:           94.367d {+06h 17m 28s} (J2000),
                  94.476d {+06h 17m 54s} (current),
                  94.121d {+06h 16m 29s} (1950)
GRB_DEC:         -54.900d {-54d 53' 59"} (J2000),
                 -54.910d {-54d 54' 33"} (current),
                 -54.879d {-54d 52' 45"} (1950)
GRB_ERROR:       4.23 [deg radius, statistical plus systematic]
GRB_INTEN:       1037 [cnts/sec]
DATA_SIGNIF:     101.20 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19677 TJD;    98 DOY;   22/04/08
GRB_TIME:        26884.65 SOD {07:28:04.65} UT
GRB_PHI:         190.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.59
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,1,0, 1,0,1, 0,0,
SUN_POSTN:        17.02d {+01h 08m 06s}   +7.23d {+07d 13' 57"}
SUN_DIST:         88.80 [deg]   Sun_angle= -5.2 [hr] (East of Sun)
MOON_POSTN:       98.72d {+06h 34m 54s}  +26.92d {+26d 55' 01"}
MOON_DIST:        81.91 [deg]
MOON_ILLUM:      41 [%]
GAL_COORDS:      263.41,-26.66 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      102.31,-78.15 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_lc_medres34_bn220408311.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 129.58,12.18 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 08 Apr 22 07:28:48 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     671095689
GRB_RA:           94.540d {+06h 18m 10s} (J2000),
                  94.678d {+06h 18m 43s} (current),
                  94.229d {+06h 16m 55s} (1950)
GRB_DEC:         -49.920d {-49d 55' 11"} (J2000),
                 -49.930d {-49d 55' 47"} (current),
                 -49.899d {-49d 53' 54"} (1950)
GRB_ERROR:       1.59 [deg radius, statistical only]
DATA_SIGNIF:     83.90 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        19677 TJD;    98 DOY;   22/04/08
GRB_TIME:        26884.65 SOD {07:28:04.65} UT
GRB_PHI:         200.00 [deg]
GRB_THETA:        30.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        17.02d {+01h 08m 06s}   +7.23d {+07d 13' 57"}
SUN_DIST:         87.70 [deg]   Sun_angle= -5.2 [hr] (East of Sun)
MOON_POSTN:       98.73d {+06h 34m 54s}  +26.92d {+26d 55' 01"}
MOON_DIST:        76.93 [deg]
MOON_ILLUM:      41 [%]
GAL_COORDS:      258.00,-25.58 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      100.16,-73.20 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_lc_medres34_bn220408311.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_671095689.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        Bright hard burst in the GBM.  
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:     Fri 08 Apr 22 13:38:19 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     671095689
GRB_RA:           94.800d {+06h 19m 12s} (J2000),
                  94.933d {+06h 19m 44s} (current),
                  94.501d {+06h 18m 00s} (1950)
GRB_DEC:         -50.910d {-50d 54' 35"} (J2000),
                 -50.920d {-50d 55' 12"} (current),
                 -50.887d {-50d 53' 13"} (1950)
GRB_ERROR:       2.22 [deg radius, statistical only]
GRB_DATE:        19677 TJD;    98 DOY;   22/04/08
GRB_TIME:        26884.65 SOD {07:28:04.65} UT
GRB_PHI:         198.05 [deg]
GRB_THETA:        30.26 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        17.26d {+01h 09m 02s}   +7.33d {+07d 19' 43"}
SUN_DIST:         88.02 [deg]   Sun_angle= -5.2 [hr] (East of Sun)
MOON_POSTN:      102.12d {+06h 48m 30s}  +26.88d {+26d 53' 05"}
MOON_DIST:        78.06 [deg]
MOON_ILLUM:      43 [%]
GAL_COORDS:      259.11,-25.63 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      101.15,-74.16 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_lc_medres34_bn220408311.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_locplot_all_bn220408311.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 #31854
The Fermi GBM team reports the detection of a likely LONG GRB.
At 07:28:04.65 UT on 8 Apr 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 220408B (trigger 671095689.64512 / 220408311).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 94.8, Dec = -50.9 (J2000 degrees, equivalent to J2000 06h 19m, -50d 54'), with a statistical uncertainty of 2.2 degrees.
The angle from the Fermi LAT boresight is 30.3 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_skymap_all_bn220408311.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_healpix_all_bn220408311.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220408311/quicklook/glg_lc_medres34_bn220408311.gif

GCN Circular #31858
V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, G.Antipov, D.Zimnukhov, V.Senik, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D.Cheryasov, Ya.Kechin (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev (Irkutsk State University, API),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational State University)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 220408B ( Fermi GBM team, GCN 31854) errorbox 38858 sec after notice time and 38887 sec after trigger time at 2022-04-08 18:16:12 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 33 deg. The sun altitude is -24.1 deg.
The galactic latitude b = -25 deg., longitude l = 259 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1936782
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   38918 | 2022-04-08 18:16:12 |         MASTER-SAAO | (06h 12m 56.98s , -50d 05m 58.3s) |   C |    60 | 17.8 |        
   39007 | 2022-04-08 18:17:42 |         MASTER-SAAO | (06h 25m 30.38s , -50d 06m 55.8s) |   C |    60 | 17.9 |        
   39088 | 2022-04-08 18:19:03 |         MASTER-SAAO | (06h 04m 01.42s , -52d 01m 53.5s) |   C |    60 | 17.5 |        
   39180 | 2022-04-08 18:20:34 |         MASTER-SAAO | (06h 16m 56.43s , -52d 00m 18.7s) |   C |    60 | 17.4 |        
   39498 | 2022-04-08 18:25:52 |         MASTER-SAAO | (06h 33m 41.72s , -48d 11m 39.6s) |   C |    60 | 17.5 |        
   39589 | 2022-04-08 18:27:23 |         MASTER-SAAO | (06h 20m 15.24s , -53d 55m 36.6s) |   C |    60 | 17.6 |        
   39669 | 2022-04-08 18:28:43 |         MASTER-SAAO | (06h 33m 53.81s , -53d 55m 10.9s) |   C |    60 | 17.6 |        
   39997 | 2022-04-08 18:34:11 |         MASTER-SAAO | (06h 13m 03.64s , -50d 07m 10.9s) |   C |    60 | 17.4 |        
   40088 | 2022-04-08 18:35:42 |         MASTER-SAAO | (06h 25m 31.89s , -50d 05m 38.5s) |   C |    60 | 17.6 |        
   40172 | 2022-04-08 18:37:07 |         MASTER-SAAO | (06h 03m 58.08s , -52d 00m 16.1s) |   C |    60 | 17.5 |        
   40263 | 2022-04-08 18:38:37 |         MASTER-SAAO | (06h 16m 57.23s , -51d 59m 13.9s) |   C |    60 | 17.3 |        
   40354 | 2022-04-08 18:40:09 |         MASTER-SAAO | (06h 21m 52.59s , -48d 12m 07.9s) |   C |    60 | 17.5 |        
   40434 | 2022-04-08 18:41:28 |         MASTER-SAAO | (06h 33m 43.84s , -48d 13m 07.6s) |   C |    60 | 17.5 |        
   40537 | 2022-04-08 18:43:11 |         MASTER-SAAO | (06h 20m 24.77s , -53d 54m 58.6s) |   C |    60 | 17.3 |        
   40669 | 2022-04-08 18:45:23 |         MASTER-SAAO | (06h 33m 53.42s , -53d 53m 27.9s) |   C |    60 | 17.4 |        
   40840 | 2022-04-08 18:48:14 |         MASTER-SAAO | (06h 11m 00.85s , -48d 11m 45.8s) |   C |    60 | 17.5 |        
   40919 | 2022-04-08 18:49:33 |         MASTER-SAAO | (06h 13m 02.11s , -50d 04m 46.1s) |   C |    60 | 17.4 |        
   41011 | 2022-04-08 18:51:05 |         MASTER-SAAO | (06h 25m 34.52s , -50d 05m 46.3s) |   C |    60 | 17.7 |        
   41106 | 2022-04-08 18:52:40 |         MASTER-SAAO | (06h 04m 01.19s , -52d 00m 39.5s) |   C |    60 | 17.1 |        
   41195 | 2022-04-08 18:54:09 |         MASTER-SAAO | (06h 17m 05.09s , -52d 00m 21.5s) |   C |    60 | 17.2 |        
   41291 | 2022-04-08 18:55:45 |         MASTER-SAAO | (06h 21m 50.81s , -48d 10m 39.6s) |   C |    60 | 17.8 |        
   41370 | 2022-04-08 18:57:05 |         MASTER-SAAO | (06h 33m 49.29s , -48d 12m 25.5s) |   C |    60 | 17.3 |        
   41474 | 2022-04-08 18:58:48 |         MASTER-SAAO | (06h 20m 25.74s , -53d 52m 38.1s) |   C |    60 | 17.2 |        
   41565 | 2022-04-08 19:00:19 |         MASTER-SAAO | (06h 33m 52.54s , -53d 53m 31.3s) |   C |    60 | 17.6 |        
   41738 | 2022-04-08 19:03:12 |         MASTER-SAAO | (06h 36m 42.34s , -50d 06m 22.0s) |   C |    60 | 17.6 |        
   41817 | 2022-04-08 19:04:32 |         MASTER-SAAO | (06h 11m 06.65s , -48d 11m 50.7s) |   C |    60 | 17.7 |        
   42081 | 2022-04-08 19:08:55 |         MASTER-SAAO | (06h 01m 51.27s , -50d 04m 52.3s) |   C |    60 | 17.6 |        
   42252 | 2022-04-08 19:11:46 |         MASTER-SAAO | (06h 08m 09.12s , -53d 53m 57.1s) |   C |    60 | 17.7 |        
   42785 | 2022-04-08 19:20:39 |         MASTER-SAAO | (06h 36m 45.22s , -50d 05m 41.5s) |   C |    60 | 17.6 |

Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN Circular #31863
R. Gopalakrishnan (IUCAA), V. Prasad (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed detection of a long GRB 220408B which was also detected by Fermi-GBM (GCN 31854).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2022-04-08 07:28:08.50 UT. The measured peak count rate associated with the burst is 1181 (+79, -36) counts/s above the background in the combined data of all four quadrants, with a total of 12408 (+531, -419) counts. The local mean background count rate was 516 (+2, -4) counts/s. Using cumulative rates, we measure a T90 of 25 (+3, -1) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2022-04-08 07:28:08.19 UT. The measured peak count rate is 1215 (+93, -70) counts/s above the background in the combined Veto data of four quadrants, with a total of 10873 (+743, -663) counts. The local mean background count rate was 1882 (+4, -5) counts/s. We measure a T90 of 24 (+2, -6) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb [1]. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
Links:
------
[1] http://astrosat.iucaa.in/czti/?q=grb
GCN Circular #31878
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the MGNS/BepiColombo team,
J. Benkhoff on behalf of the BepiColombo team,
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, and C. Wilson-Hodge on behalf of the Fermi GBM team, report:
The bright, long-duration GRB 220408B (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 31854; AstroSat-CZTI detection: Gopalakrishnan et al., GCN Circ. 31863) was detected by Fermi (GBM trigger 671095689), Konus-Wind, BepiColombo (MGNS), and AstroSat (CZTI) at about 26884 s UT (07:28:04).
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:
```
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
    92.538 (06h 10m 09s) -49.610 (-49d 36' 36")
  Corners:
    93.180 (06h 12m 43s) -49.644 (-49d 38' 40")
    93.133 (06h 12m 32s) -47.629 (-47d 37' 43")
    91.896 (06h 07m 35s) -49.572 (-49d 34' 20")
    91.889 (06h 07m 33s) -51.597 (-51d 35' 50")
  ---------------------------------------------
```
The error box area is 1.7 sq. deg, and its maximum dimension is 4.0 deg (the minimum one is 48 arcmin). The Sun distance was 86 deg.
This box may be improved.
The IPN localization is consistent with, but reduces the area of, the Fermi GBM final position (GCN 31854).
A triangulation map is posted at A href="http://www.ioffe.ru/LEA/GRBs/GRB220408_T26885/IPN/"> http://www.ioffe.ru/LEA/GRBs/GRB220408_T26885/IPN/
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
GCN Circular #31896
E. Bissaldi (Politecnico and INFN Bari), M. Arimoto (Kanazawa Univ.), S. Ciprini (INFN and ASI), F. Giacchino (INFN Roma Tor Vergata and ASI), M. Giroletti (INAF/IRA Bologna), and L. Scotton (CNRS/IN2P3/LUPM) report on behalf of the Fermi-LAT team:
"On April 8, 2022, Fermi-LAT detected high-energy emission from GRB 220408B, which was also detected by Fermi-GBM (trigger 671095689 / 220408311, GCN 31854), AstroSat CZTI (Gopalakrishnan et al. 2022, GCN 31863) and was reported by the IPN (Kozyrev et al. 2022. GCN 31878).
The best LAT on-ground location is found to be
RA, Dec = 92.48, -50.97 (degrees, J2000)
with an error radius of 0.06 deg (90 % containment, statistical error only). This was 30 deg from the LAT boresight at the time of the GBM trigger:
T0 = 07:28:04.65 UT.
The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-2500s after the GBM trigger is (2.0 +/- 0.5)E-06 ph/cm2/s.
The estimated photon index above 100 MeV is -1.9 +/- 0.2.
The highest-energy photon is a 22 GeV event which is observed 42 seconds after the GBM trigger.
The Fermi-LAT point of contact for this burst is Elisabetta Bissaldi (elisabetta.bissaldi@ba.infn.it).
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 #31905
A. Lysenko, D. Frederiks, D. Svinkin, M. Ulanov, A. Tsvetkova, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, report:
The long-duration GRB 220408B (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 31854; AstroSat-CZTI detection: Gopalakrishnan et al., GCN Circ. 31863; IPN triangulation: Kozyrev et al., GCN Circ. 31878; Fermi-LAT detection: Bissaldi et al., GCN Circ. 31896;) triggered Konus-Wind at T0=26885.231 s UT (07:28:05.231).
The burst light curve shows a multipeaked structure which starts at ~T0-0.5 s and has a total duration of ~35 s. The emission is seen up to ~3 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB220408_T26885/
As observed by Konus-Wind, the burst had a fluence of 4.1(-0.4,+0.5)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+3.760 s, of 7.26(-1.60,+1.63)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst (measured from T0 to T0+30.976 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.80(-0.09,+0.11), the high energy photon index beta = -2.72(-0.54,+0.29), the peak energy Ep = 231(-20,+20) keV (chi2 = 84/81 dof).
The spectrum near the maximum count rate (measured from T0+0.256 to T0+6.400 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.27(-0.16,+0.18), the high energy photon index beta = -2.39(-0.21,+0.15), the peak energy Ep = 211(-20,+23) keV (chi2 = 80/82 dof).
All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
GCN Circular #31906
E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 07:28:04.65 UT on 8 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220408B (trigger 671095689 / 220408311), which was also detected by the AstroSat CZTI (Gopalakrishnan et al. 2022, GCN 31863), Fermi-LAT (Bissaldi et al. 2022, GCN 31896), and Konus-Wind (Lysenko et al. 2022, GCN 31905). The Fermi GBM Final Localization (GCN 31854) is consistent with the LAT position.
The angle from the Fermi LAT boresight at the GBM trigger time is 29 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 33 s (50-300 keV). The time-averaged spectrum from T0 to T0+33 s is best fit by a Band function with Epeak = 214 +/- 8 keV, alpha = -0.80 +/- 0.02 and beta = -2.33 +/- 0.09.
The event fluence (10-1000 keV) in this time interval is (3.68 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.6 s in the 10-1000 keV band is 17.1 +/- 0.3 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: 15-Apr-2022 [Disclaimer]