Gamma-ray Burst 220418B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN NOTICE
  

  TITLE:           GCN/FERMI NOTICE
  NOTICE_DATE:     Mon 18 Apr 22 17:16:46 UT
  NOTICE_TYPE:     Fermi-GBM Flight Position
  RECORD_NUM:      45
  TRIGGER_NUM:     671994986
  GRB_RA:          216.233d {+14h 24m 56s} (J2000),
                   216.541d {+14h 26m 10s} (current),
                   215.545d {+14h 22m 11s} (1950)
  GRB_DEC:         -16.500d {-16d 30' 00"} (J2000),
                   -16.600d {-16d 35' 59"} (current),
                   -16.274d {-16d 16' 27"} (1950)
  GRB_ERROR:       35.32 [deg radius, statistical plus systematic]
  GRB_INTEN:       100 [cnts/sec]
  DATA_SIGNIF:     4.70 [sigma]
  INTEG_TIME:      1.024 [sec]
  GRB_DATE:        19687 TJD;   108 DOY;   22/04/18
  GRB_TIME:        62181.65 SOD {17:16:21.65} UT
  GRB_PHI:         190.00 [deg]
  GRB_THETA:        80.00 [deg]
  DATA_TIME_SCALE: 1.0240 [sec]
  HARD_RATIO:      1.10
  LOC_ALGORITHM:   3 (version number of)
  MOST_LIKELY:      96%  GRB
  2nd_MOST_LIKELY:   1%  Generic SGR
  DETECTORS:       0,0,0, 0,0,0, 0,1,0, 0,0,1, 0,0,
  SUN_POSTN:        26.63d {+01h 46m 31s}  +11.00d {+10d 59' 44"}
  SUN_DIST:        168.87 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:      232.16d {+15h 28m 39s}  -18.99d {-18d 59' 10"}
  MOON_DIST:        15.06 [deg]
  MOON_ILLUM:      95 [%]
  GAL_COORDS:      333.11, 40.83 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      219.30, -2.01 [deg] ecliptic lon,lat of the burst (or transient)
  LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_lc_medres34_bn220418720.gif
  COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
  COMMENTS:        This trigger occurred at longitude,latitude = 151.32,18.10 [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 18 Apr 22 17:17:04 UT
  NOTICE_TYPE:     Fermi-GBM Ground Position
  RECORD_NUM:      57
  TRIGGER_NUM:     671994986
  GRB_RA:          222.110d {+14h 48m 26s} (J2000),
                   222.438d {+14h 49m 45s} (current),
                   221.376d {+14h 45m 30s} (1950)
  GRB_DEC:         -26.800d {-26d 48' 00"} (J2000),
                   -26.892d {-26d 53' 30"} (current),
                   -26.592d {-26d 35' 31"} (1950)
  GRB_ERROR:       20.40 [deg radius, statistical only]
  DATA_SIGNIF:     4.80 [sigma]
  DATA_INTERVAL:   1.024 [sec]
  GRB_DATE:        19687 TJD;   108 DOY;   22/04/18
  GRB_TIME:        62181.65 SOD {17:16:21.65} UT
  GRB_PHI:         196.00 [deg]
  GRB_THETA:        90.00 [deg]
  E_RANGE:         44.032 - 279.965 [keV]
  LOC_ALGORITHM:   4173 (Gnd S/W Version number)
  SUN_POSTN:        26.63d {+01h 46m 31s}  +11.00d {+10d 59' 44"}
  SUN_DIST:        158.23 [deg]   Sun_angle= 10.9 [hr] (West of Sun)
  MOON_POSTN:      232.17d {+15h 28m 40s}  -18.99d {-18d 59' 14"}
  MOON_DIST:        11.94 [deg]
  MOON_ILLUM:      95 [%]
  GAL_COORDS:      332.90, 29.18 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      227.73,-10.11 [deg] ecliptic lon,lat of the burst (or transient)
  LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_lc_medres34_bn220418720.gif
  POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_671994986.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 18 Apr 22 17:25:39 UT
  NOTICE_TYPE:     Fermi-GBM Final Position
  RECORD_NUM:      0
  TRIGGER_NUM:     671994986
  GRB_RA:          216.520d {+14h 26m 05s} (J2000),
                   216.843d {+14h 27m 22s} (current),
                   215.798d {+14h 23m 11s} (1950)
  GRB_DEC:         -26.580d {-26d 34' 47"} (J2000),
                   -26.680d {-26d 40' 45"} (current),
                   -26.355d {-26d 21' 18"} (1950)
  GRB_ERROR:       29.78 [deg radius, statistical only]
  GRB_DATE:        19687 TJD;   108 DOY;   22/04/18
  GRB_TIME:        62181.65 SOD {17:16:21.65} UT
  GRB_PHI:         191.00 [deg]
  GRB_THETA:        90.00 [deg]
  E_RANGE:         44.032 - 279.965 [keV]
  LOC_ALGORITHM:   41731 (Gnd S/W Version number)
  SUN_POSTN:        26.64d {+01h 46m 33s}  +11.00d {+10d 59' 51"}
  SUN_DIST:        161.60 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:      232.25d {+15h 29m 01s}  -19.02d {-19d 00' 57"}
  MOON_DIST:        16.12 [deg]
  MOON_ILLUM:      95 [%]
  GAL_COORDS:      327.87, 31.67 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      222.83,-11.47 [deg] ecliptic lon,lat of the burst (or transient)
  LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_lc_medres34_bn220418720.gif
  LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_locplot_all_bn220418720.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:        This is likely a Short GRB.  
  

• GCN Circular #31915
  The Fermi GBM team reports the detection of a likely SHORT GRB
  At 17:16:21 UT on 18 Apr 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 220418B (trigger 671994986.650868 / 220418720).
  The on-ground calculated location, using the Fermi GBM trigger data, is RA = 216.5, Dec = -26.6 (J2000 degrees, equivalent to J2000 14h 26m, -26d 36'), with a statistical uncertainty of 29.8 degrees.
  The angle from the Fermi LAT boresight is 90.0 degrees.
  The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_skymap_all_bn220418720.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/bn220418720/quicklook/glg_healpix_all_bn220418720.fit
  The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_lc_medres34_bn220418720.gif
  
• GCN Circular #31919
  Aaron Tohuvavohu (U Toronto), James DeLaunay (UAlabama), Gayathri Raman (PSU), Jamie A. Kennea (PSU), report:
  Swift/BAT did not localize GRB 220418B onboard (T0: 2022-04-18T17:16:21 UTC, Fermi/GBM trig #671994986).
  The Fermi notice, 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 in a 2.048 s analysis time bin with a sqrt(TS) of 10.4.
  A candidate arcminute localization is found with DeltaLLHPeak of 11.8.
  See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
  The BAT position is RA, Dec = 224.329, -17.514 deg which is

     RA(J2000)  = 14h 57m 18.96s
     Dec(J2000) = -17d 30′ 15.4″
  

  with an estimated uncertainty of 5 arcmin.
  This position is consistent with the Fermi/GBM localization (GCN 31915).
  XRT and UVOT follow-up has been requested, but will be delayed due to the position's proximity to the Moon. We encourage prompt followup from other facilities.
  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 #31921
  James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), Jamie A. Kennea (PSU), report:
  Further analysis has improved the location of the short GRB reported in GCN 31919, and its confidence. This new position is fully consistent with the originally reported position, with a smaller uncertainty region.
  The BAT position is RA, Dec = 224.344 -17.539 deg which is

     RA(J2000)  = 14h 57m 22.56s
     Dec(J2000) = -17d 32′ 20.4″
  

  with an estimated uncertainty of 3 arcmin.
  We encourage followup from other instruments.
• GCN Circular #31923
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the Swift/BAT-GUANO GRB 220418B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021486
  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 Swift/BAT-GUANO 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 #31928
  C. Fletcher (USRA), S. Dalessi (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
  "At 17:16:21.65 UT on 18 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220418B (trigger 671994986 / 220418720). which was also detected by the Swift-BAT/GUANO (GCN 31919, 31921) The Fermi GBM Final Real-time Localization (GCN 31915) is consistent with the Swift position.
  The angle from the Fermi LAT boresight at the GBM trigger time is 80 degrees.
  The GBM light curve shows a single peak with a duration (T90) of about 1.7 s (50-300 keV). The time-averaged spectrum from T0-1.024 s to T0+1.024 s is best fit a simple power law function with index -1.6 +/- 0.1.
  The event fluence (10-1000 keV) in this time interval is (3.8 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0-0.57 s in the 10-1000 keV band is 121 +/- 76 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 #31930
  B. Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), J. D. Gropp (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the Swift/BAT-GUANO-detected burst GRB 220418B, collecting 4.8 ks of Photon Counting (PC) mode data between T0+113.8 ks and T0+148.8 ks. These observations were delayed due to the Moon observing constraint.
  Due to a high XRT temperature and consequent high background, the data contain many low significance detections (ranked as "poor") which are likely to be spurious, but no objects are detected within the BAT/GUANO error region. We therefore conclude that no XRT afterglow to this object has been found.
  The 3-sigma upper limit is 2.3e-3 ct/sec, which, assuming a typical GRB spectral, equates to an observed 0.3-10 keV flux of ~9e-14 erg/cm^2/s.
  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/ToO_GRBs/00021486.
  This circular is an official product of the Swift-XRT team.