Gamma-ray Burst 240606B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #36628
  James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
  Swift/BAT did not localize GRB 240606B onboard (T0: 2024-06-06T13:33:06.5 UTC, GECAM trigger 392).
  The GECAM 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 2022, ApJ, 941, 169), detects the burst in a 4.096 s analysis time bin starting at T0 - 2.048 s with a sqrt(TS) of 28.9. An arcminute localization is found with DeltaLLHOut of 29.3 and a DeltaLLHPeak of 17.9.
  See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
  The BAT position is RA, Dec =3D 40.234, -60.637 deg which is

     RA(J2000)  = 02h 40m 56.16s
     Dec(J2000) = -60d 38=E2=80=B2 13.2=E2=80=B3
  

  with an estimated uncertainty of 4 arcmin radius.
  XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
  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 #36629
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the GECAM GRB 240606B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021695
  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 GECAM 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 #36631
  J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the Swift/BAT-GUANO-detected burst GRB 240606B, collecting 4.0 ks of Photon Counting (PC) mode data between T0+22.9 ks and T0+35.1 ks.
  Four uncatalogued X-ray sources are detected consistent with being within 493 arcsec of the BAT-GUANO position, of which one ("Source 1") is fading with 2.1 sigma significance and is undetected by eRosita to deeper upper limits. It is likely the afterglow.
  Using 3507 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 40.29507, -60.61201 which is equivalent to:

  RA (J2000): 02h 41m 10.82s
  Dec(J2000): -60d 36' 43.2"
  

  with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position is 53 arcsec from the BAT-GUANO position.
  The light curve can be modelled with a power-law decay with a decay index of alpha=1.2 (+0.9, -1.0).
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.7 (+0.4, -0.3). The best-fitting absorption column is 6 (+11, -4) x 10^20 cm^-2, consistent with the Galactic value of 2.4 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.1 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     6 (+11, -4) x 10^20 cm^-2
  Galactic foreground: 2.4 x 10^20 cm^-2
  Excess significance: <1.6 sigma
  Photon index:	     1.7 (+0.4, -0.3)
  

  If the light curve continues to decay with a power-law decay index of 1.2, the count rate at T+24 hours will be 0.013 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.2 x 10^-13 (5.7 x 10^-13) erg cm^-2 s^-1.
  The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021695. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021695.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #36633
  Yue Wang, Shao-Lin Xiong, Chen-Wei Wang report on behalf of the GECAM team:
  GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 240606B, at 2024-06-06T13:33:06.050 UTC (T0), which initialized Swift/BAT-GUANO observation (GCN # 36628).
  According to the realtime alert data, the GECAM-B light curve shows a long pulse with a duration about ~10 sec (15-1020 keV).
  The time-averaged spectrum of GECAM-B realtime data from T0-2 to T0+2 s could be adequately fit by a cut-off power-law with a flux about 6.67E-7 erg/cm^2/s in 20-1000 keV.
  The GECAM light curve could be found here: https://twikinew.ihep.ac.cn/pubgecam/Sandbox/GRB/GRB240606B_lightcurve.png
  The GECAM-B localization is consistent with the Swift/BAT localization within the error. We note that these results are based on realtime alert data and thus very preliminary. Refined analysis will be reported later.
  Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
  
• GCN Circular #36640
  S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
  "At 13:33:06.09 UT on 06 June 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240606B (trigger 739373591/240606565). which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2024, GCN 36628). The Fermi GBM on-ground location is consistent with the Swift-BAT/GUANO position.
  The angle from the Fermi LAT boresight is 141 degrees.
  The GBM light curve consists of a single emission episode with a duration (T90) of about 11 s (50-300 keV). The time-averaged spectrum from T0-6.9 to T0+8.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.2 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 310 +/- 60 keV. A Band function fits the spectrum equally well with Epeak= 238 +/- 75 keV, alpha = -1.11 +/- 0.16 and beta = -2.28 +/- 0.41.
  The event fluence (10-1000 keV) in this time interval is (6.4 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.51 s in the 10-1000 keV band is 7.9 +/- 0.7 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 #36646
  A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
  The long-duration GRB 240606B (Swift/BAT-GUANO arcminute localization: DeLaunay et al., GCN 36628; GECAM-B detection: Wang et al., GCN 36633; Fermi-GBM detection: Bala & Meegan, GCN 36640) triggered Konus-Wind at T0=48787.583 s UT (13:33:07.583).
  The burst light curve shows a multipeaked structure which starts at ~T0-53.0 s and has a total duration of ~58.4 s. The emission is seen up to ~4 MeV.
  The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB240606_T48787/
  As observed by Konus-Wind, the burst had a fluence of 5.07(-0.10,+1.54)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+0.318 s, of 1.68(-0.34,+0.61)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
  Since the bulk of the burst emission was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data.
  Modelling the KW 3-channel time-integrated spectrum (measured from T0-53.014 s to T0+5.360 s) by a power law with exponential cutoff (CPL) model, dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = -0.55(-0.83,+3.21) and Ep = 116(-21,+62) keV.
  A CPL fit to the spectrum near the peak count rate, measured from T0-0.400 s to T0+0.816 s, gives alpha -1.20(-0.14,+0.14), and Ep = 475(-128,+239) keV.
  All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.