Gamma-ray Burst 220426A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 26 Apr 22 06:50:24 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      60
TRIGGER_NUM:     672648596
GRB_RA:          335.867d {+22h 23m 28s} (J2000),
                 336.178d {+22h 24m 43s} (current),
                 335.167d {+22h 20m 40s} (1950)
GRB_DEC:         -27.183d {-27d 10' 59"} (J2000),
                 -27.070d {-27d 04' 10"} (current),
                 -27.437d {-27d 26' 11"} (1950)
GRB_ERROR:       3.32 [deg radius, statistical plus systematic]
GRB_INTEN:       9873 [cnts/sec]
DATA_SIGNIF:     628.40 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        19695 TJD;   116 DOY;   22/04/26
GRB_TIME:        24591.23 SOD {06:49:51.23} UT
GRB_PHI:          70.00 [deg]
GRB_THETA:        70.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.62
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      67%  GRB
2nd_MOST_LIKELY:  30%  Distant Particles
DETECTORS:       1,0,0, 0,0,1, 0,0,0, 1,0,0, 0,0,
SUN_POSTN:        33.72d {+02h 14m 53s}  +13.53d {+13d 31' 51"}
SUN_DIST:         69.01 [deg]   Sun_angle= 3.8 [hr] (West of Sun)
MOON_POSTN:      344.82d {+22h 59m 17s}  -11.89d {-11d 53' 13"}
MOON_DIST:        17.21 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:       24.16,-57.21 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      327.59,-15.93 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_lc_medres34_bn220426285.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 117.55,-25.58 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 26 Apr 22 06:50:15 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     672648596
GRB_RA:          335.767d {+22h 23m 04s} (J2000),
                 336.078d {+22h 24m 19s} (current),
                 335.067d {+22h 20m 16s} (1950)
GRB_DEC:         -27.017d {-27d 01' 00"} (J2000),
                 -26.903d {-26d 54' 11"} (current),
                 -27.270d {-27d 16' 11"} (1950)
GRB_ERROR:       3.38 [deg radius, statistical plus systematic]
GRB_INTEN:       6412 [cnts/sec]
DATA_SIGNIF:     205.50 [sigma]
INTEG_TIME:      0.512 [sec]
GRB_DATE:        19695 TJD;   116 DOY;   22/04/26
GRB_TIME:        24591.23 SOD {06:49:51.23} UT
GRB_PHI:          70.00 [deg]
GRB_THETA:        70.00 [deg]
DATA_TIME_SCALE: 0.5120 [sec]
HARD_RATIO:      0.37
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      65%  GRB
2nd_MOST_LIKELY:  33%  Distant Particles
DETECTORS:       1,0,0, 0,0,1, 0,0,0, 1,0,0, 0,0,
SUN_POSTN:        33.72d {+02h 14m 53s}  +13.53d {+13d 31' 51"}
SUN_DIST:         69.01 [deg]   Sun_angle= 3.8 [hr] (West of Sun)
MOON_POSTN:      344.82d {+22h 59m 17s}  -11.89d {-11d 53' 16"}
MOON_DIST:        17.11 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:       24.44,-57.09 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      327.57,-15.74 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_lc_medres34_bn220426285.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 117.55,-25.58 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 26 Apr 22 06:50:31 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      59
TRIGGER_NUM:     672648596
GRB_RA:          335.780d {+22h 23m 07s} (J2000),
                 336.085d {+22h 24m 20s} (current),
                 335.096d {+22h 20m 23s} (1950)
GRB_DEC:         -20.480d {-20d 28' 47"} (J2000),
                 -20.367d {-20d 21' 59"} (current),
                 -20.733d {-20d 43' 59"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     684.10 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19695 TJD;   116 DOY;   22/04/26
GRB_TIME:        24591.23 SOD {06:49:51.23} UT
GRB_PHI:          67.00 [deg]
GRB_THETA:        76.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        33.72d {+02h 14m 53s}  +13.53d {+13d 31' 52"}
SUN_DIST:         66.02 [deg]   Sun_angle= 3.8 [hr] (West of Sun)
MOON_POSTN:      344.82d {+22h 59m 17s}  -11.89d {-11d 53' 12"}
MOON_DIST:        11.92 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:       35.91,-55.56 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      330.07, -9.68 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_lc_medres34_bn220426285.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_672648596.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
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:     Tue 26 Apr 22 06:59:17 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     672648596
GRB_RA:          335.820d {+22h 23m 17s} (J2000),
                 336.127d {+22h 24m 31s} (current),
                 335.131d {+22h 20m 31s} (1950)
GRB_DEC:         -22.800d {-22d 48' 00"} (J2000),
                 -22.687d {-22d 41' 10"} (current),
                 -23.053d {-23d 03' 11"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
GRB_DATE:        19695 TJD;   116 DOY;   22/04/26
GRB_TIME:        24591.23 SOD {06:49:51.23} UT
GRB_PHI:          68.00 [deg]
GRB_THETA:        74.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        33.73d {+02h 14m 54s}  +13.53d {+13d 31' 59"}
SUN_DIST:         67.02 [deg]   Sun_angle= 3.8 [hr] (West of Sun)
MOON_POSTN:      344.90d {+22h 59m 35s}  -11.85d {-11d 51' 11"}
MOON_DIST:        13.68 [deg]
MOON_ILLUM:      21 [%]
GAL_COORDS:       31.97,-56.26 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      329.24,-11.85 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_lc_medres34_bn220426285.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_locplot_all_bn220426285.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:        Bright hard burst in the GBM.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(2.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9876).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 26 Apr 22 09:56:11 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     672648596
GRB_RA:          335.800d {+22h 23m 12s} (J2000),
                 336.105d {+22h 24m 25s} (current),
                 335.116d {+22h 20m 28s} (1950)
GRB_DEC:         -20.530d {-20d 31' 47"} (J2000),
                 -20.416d {-20d 24' 58"} (current),
                 -20.783d {-20d 46' 58"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
GRB_DATE:        19695 TJD;   116 DOY;   22/04/26
GRB_TIME:        24591.23 SOD {06:49:51.23} UT
GRB_PHI:          67.01 [deg]
GRB_THETA:        75.73 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        33.84d {+02h 15m 22s}  +13.57d {+13d 34' 21"}
SUN_DIST:         66.14 [deg]   Sun_angle= 3.8 [hr] (West of Sun)
MOON_POSTN:      346.42d {+23h 05m 40s}  -11.17d {-11d 10' 12"}
MOON_DIST:        13.55 [deg]
MOON_ILLUM:      20 [%]
GAL_COORDS:       35.84,-55.59 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      330.07, -9.73 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_lc_medres34_bn220426285.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220426285/quicklook/glg_locplot_all_bn220426285.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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(2.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9876).

GCN Circular #31950
B. Biltzinger, F. Kunzweiler, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 672648596 at 06:49:51 on 26 April 2022 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) = 339.6+/-0.3 deg
Decl.(2000.0) = -24.0+/-0.3 deg
```
We estimate an additional systematic error of 2 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB220426285/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB220426285/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB220426285/json
GCN Circular #31954
Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay (UAlabama), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 220426A onboard (T0: 2022-04-26T06:49:51 UTC, Fermi/GBM trig #672648596, INTEGRAL/SPI-ACS trig #9876).
The Fermi and INTEGRAL notices, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu, arXiv:2111.01769), detects the burst with a sqrt(TS) of 169 in a 4.096 s analysis time bin. The burst episode as seen by BAT is ~6s long.
NITRATES results strongly indicate a burst coming from outside the coded FoV, with DeltaLLHOut of -1550, consistent with the Fermi/GBM BALROG localization (GCN 31950).
See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular #31955
C. Malacaria (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
At 06:49:51.23 UT on 26 April 2022, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 220426A (trigger 672648596 / 220426285).
The on-ground calculated location, using the GBM trigger data, is RA = 335.8, DEC = -20.5 (J2000 degrees, equivalent to 22h 23m, -20d 30'), with an uncertainty of 1.0 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).
The angle from the Fermi LAT boresight at the GBM trigger time is 76 degrees.
The GBM light curve consists of a double pulse on top of a broader peak with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0+0.002 s to T0+9.856 s is best fit by a Band function with Epeak = 146.3 +/- 0.9 keV, alpha = -0.05 +/- 0.01, and beta = -3.08 +/- 0.04 .
The event fluence (10-1000 keV) in this time interval is (1.084+/-0.005)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.9 s in the 10-1000 keV band is 180.7 +/- 0.9 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/

GCN Circular #31956
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-OAGH robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 220426A ( C. Malacaria et al., GCN 31955) errorbox 13914 sec after notice time and 13944 sec after trigger time at 2022-04-26 10:42:15 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 87 deg. The sun altitude is -23.6 deg.
The galactic latitude b = -57 deg., longitude l = 33 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1954577
We obtain a following upper limits.

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

   13974 | 2022-04-26 10:42:15 |         MASTER-OAGH | (22h 26m 58.35s , -22d 47m 13.6s) |   C |    60 | 14.0 |        
   13974 | 2022-04-26 10:42:15 |         MASTER-OAGH | (22h 18m 46.43s , -23d 14m 51.0s) |   C |    60 | 14.2 |        
   14195 | 2022-04-26 10:45:55 |         MASTER-OAGH | (22h 27m 04.78s , -22d 46m 50.5s) |   C |    60 | 14.4 |        
   14195 | 2022-04-26 10:45:55 |         MASTER-OAGH | (22h 18m 53.88s , -23d 14m 54.4s) |   C |    60 | 14.3 |        
   14416 | 2022-04-26 10:49:36 |         MASTER-OAGH | (22h 27m 01.55s , -22d 45m 08.6s) |   C |    60 | 14.7 |        
   14416 | 2022-04-26 10:49:36 |         MASTER-OAGH | (22h 18m 52.02s , -23d 13m 27.6s) |   C |    60 | 14.4 |        
   14638 | 2022-04-26 10:53:19 |         MASTER-OAGH | (22h 27m 01.61s , -22d 46m 16.7s) |   C |    60 | 15.0 |        
   14638 | 2022-04-26 10:53:19 |         MASTER-OAGH | (22h 18m 53.98s , -23d 13m 57.4s) |   C |    60 | 14.4 |        
   15069 | 2022-04-26 11:00:29 |         MASTER-OAGH | (22h 26m 59.82s , -22d 44m 34.8s) |   C |    60 | 13.5 |        
   15069 | 2022-04-26 11:00:29 |         MASTER-OAGH | (22h 18m 47.92s , -23d 13m 32.3s) |   C |    60 | 15.3 |        
   15399 | 2022-04-26 11:05:59 |         MASTER-OAGH | (22h 26m 59.62s , -22d 44m 54.8s) |   C |    60 | 16.0 |        
   15399 | 2022-04-26 11:05:59 |         MASTER-OAGH | (22h 18m 51.90s , -23d 13m 10.4s) |   C |    60 | 15.5 |        
   15621 | 2022-04-26 11:09:42 |         MASTER-OAGH | (22h 27m 05.08s , -22d 45m 53.1s) |   C |    60 | 15.9 |        
   15621 | 2022-04-26 11:09:42 |         MASTER-OAGH | (22h 18m 57.09s , -23d 14m 19.4s) |   C |    60 | 15.3 |        
   15843 | 2022-04-26 11:13:23 |         MASTER-OAGH | (22h 27m 00.35s , -22d 46m 49.8s) |   C |    60 | 16.0 |        
   15843 | 2022-04-26 11:13:23 |         MASTER-OAGH | (22h 18m 53.16s , -23d 14m 44.6s) |   C |    60 | 15.2 |        
   16335 | 2022-04-26 11:20:36 |         MASTER-OAGH | (22h 27m 03.19s , -22d 44m 58.7s) |   C |   180 | 16.9 |        
   16335 | 2022-04-26 11:20:36 |         MASTER-OAGH | (22h 18m 54.54s , -23d 13m 07.3s) |   C |   180 | 16.1 |        
   16677 | 2022-04-26 11:26:18 |         MASTER-OAGH | (22h 27m 03.75s , -22d 46m 34.8s) |   C |   180 | 18.1 |        
   16677 | 2022-04-26 11:26:18 |         MASTER-OAGH | (22h 18m 54.96s , -23d 14m 42.0s) |   C |   180 | 18.0 |        
   17018 | 2022-04-26 11:31:59 |         MASTER-OAGH | (22h 27m 07.01s , -22d 45m 21.0s) |   C |   180 | 18.2 |        
   17018 | 2022-04-26 11:31:59 |         MASTER-OAGH | (22h 18m 58.09s , -23d 13m 28.3s) |   C |   180 | 18.1 |        
   17360 | 2022-04-26 11:37:41 |         MASTER-OAGH | (22h 27m 01.27s , -22d 45m 58.8s) |   C |   180 | 18.2 |        
   17360 | 2022-04-26 11:37:41 |         MASTER-OAGH | (22h 18m 52.06s , -23d 14m 06.9s) |   C |   180 | 18.0 |        
   17703 | 2022-04-26 11:43:23 |         MASTER-OAGH | (22h 27m 02.75s , -22d 44m 59.6s) |   C |   180 | 17.6 |        
   17703 | 2022-04-26 11:43:23 |         MASTER-OAGH | (22h 18m 53.37s , -23d 13m 07.8s) |   C |   180 | 17.6 |        
   18045 | 2022-04-26 11:49:05 |         MASTER-OAGH | (22h 27m 08.28s , -22d 46m 00.6s) |   C |   180 | 16.9 |        
   18045 | 2022-04-26 11:49:05 |         MASTER-OAGH | (22h 18m 58.55s , -23d 14m 08.2s) |   C |   180 | 16.8 |

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

GCN Circular #31958
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. 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,
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 very bright, long-duration GRB 220426A (BALROG localization: Biltzinger et al., GCN Circ. 31950; Swift/BAT-GUANO detection: Tohuvavohu et al., GCN Circ. 31954; Fermi-GBM detection: Malacaria and Meegan, GCN Circ. 31955) has been detected by Fermi (GBM trigger 672648596), INTEGRAL (SPI-ACS), Swift (BAT), Konus-Wind, and Mars-Odyssey (HEND), so far, at about 24591 s UT (06:49:51). 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:
   338.692 (22h 34m 46s) -22.994 (-22d 59' 38")
  Corners:
   337.871 (22h 31m 29s) -22.760 (-22d 45' 38")
   337.994 (22h 31m 59s) -23.010 (-23d 00' 37")
   339.494 (22h 37m 59s) -23.176 (-23d 10' 35")
   339.374 (22h 37m 30s) -22.943 (-22d 56' 35")
  ---------------------------------------------
```
The error box area is 1131 sq. arcmin, and its maximum dimension is 1.6 deg (the minimum one is 13.6 arcmin). The Sun distance was 64 deg.
This box may be improved.
The IPN localization is consistent with, but reduces the area of, the Fermi GBM Final Real-time position (GCN Circ. 31955) and BALROG (GCN 31950) localizations.
A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB220426_T24589/IPN/
Swift ToO has been approved.
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
GCN Circular #31959
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 220426A (BALROG localization: Biltzinger et al., GCN Circ. 31950; Swift/BAT-GUANO detection outside the coded FOV: Tohuvavohu et al., GCN Circ. 31954; Fermi-GBM detection: Malacaria & Meegan, GCN Circ. 31955; IPN localization: Kozyrev et al., GCN 31958) triggered Konus-Wind (KW) at T0=24589.598 s UT (06:49:49.598).
The burst light curve shows a bright, double-peaked pulse which starts at ~T0-0.5 s and has a total duration of ~11 s. The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB220426_T24589/
As observed by Konus-Wind, the burst had a fluence of (9.2 � 0.2)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 2.432 s, of (2.9 � 0.2)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+13.312 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.29 (-0.07,+0.07), the high energy photon index beta = -4.00 (-0.71,+0.32), the peak energy Ep = 158 (-3,+4) keV, chi2 = 112/97 dof.
The spectrum near the peak count rate (measured from T0+2.304 s to T0+2.560 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = 0.10 (-0.17,+0.21), the high energy photon index beta = -5.6 (-4.3,+1.7), the peak energy Ep = 227 (-15,+13) keV, chi2 = 47/38 dof.
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #31961
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the IPN GRB 220426A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00104
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the IPN event is high: 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 #31966
V. D’Elia (ASI-SSDC & INAF-OAR) and M. H. Siegel (PSU) report on behalf of the Swift team:
Swift has performed follow-up observations of the Fermi/GBM-detected burst GRB 220426A (GCN Circ. 31950, 31955), which was also detected by Swift/BAT-GUANO (GCN Circ. 31954), Konus-Wind (GCN Circ. 31959), INTEGRAL/SPI-ACS, and HEND/Mars-Odyssey (GCN Circ. 31958).
The XRT observations consist of three tiles of 1 ks each, to cover the GRB error region. The data were acquired between 45 and 47 hours after the burst and are entirely in PC mode.
One bright, uncatalogued X-ray source has been detected:
Source 1: >pre> RA (J2000.0): 22h 32m 34.33s Dec (J2000.0): -22° 57′ 01.0″ Error: 3.7 arcsec (radius, 90% conf.) Count-rate: (1.4 +/- 0.5)e-2 ct s^-1 Distance: 3.2 arcmin from the IPN position Flux: (4.1 +/- 1.4)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Nevertheless, we note that at the XRT position the RASS PSPC 3 sigma upper limit is 0.05 cts/s (XRT equivalent count-rate).
The UVOT took images of 616s each on the three XRT tiles with the white filter 160-170 ks after the trigger. We identify one source at 1.9” from the XRT coordinates of Source 1, with a white magnitude of 18.01.
The UVOT position is:
```
   RA  (J2000) =  22:32:34.39 = 338.14330 (deg.)
   Dec (J2000) = -22:57:02.7  =  22.95074 (deg.)
```
with an estimated uncertainty of 0.5 arc sec. (radius, 90% confidence).
However, we note that this is a known source in the DSS and is therefore unlikely to be the afterglow. No other sources are detected to a limiting magnitude in the white filter of 20.8.
More Swift observations are planned in the next days to assess for variability
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00104/
This circular is an official product of the Swift team.

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Jochen Greiner, last update: 28-Apr-2022 [Disclaimer]