Gamma-ray Burst 221006A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #32626
  T. Mihara (RIKEN), M. Nakajima, H. Negoro (Nihon U.), W. Iwakiri (Chuo U.), K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, J. Kohara (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba (Kyoto U.), M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team:
  The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 2022-10-06T00:57:09 UT. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (337.328 deg, 15.703 deg) = (22 29 18, +15 42 10) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.11 deg and 0.09 deg, respectively. The roll angle of long axis from the north direction is 26.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 909 +- 81 mCrab (4.0-10.0keV, 1 sigma error).
  There was no significant excess flux in the previous transit at 10/5 23:24 UT with an upper limit of 20 mCrab.
• GCN Circular #32627
  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 MAXI GRB 221006A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00108
  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 MAXI 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 #32628
  B. Sbarufatti (INAF-OAB), J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 221006A (Mihara et al. GCN Circ. 32626) in a series of observations tiled on the sky. The total exposure time is 1.9 ks, distributed over 3 tiles; the maximum exposure at a single sky location was 992 s. The data were collected between T0+37.6 ks and T0+39.8 ks, and are entirely in Photon Counting (PC) mode.
  Three uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below:
  Source 1:

    RA (J2000.0):  337.3524  =  22:29:24.58
    Dec (J2000.0): +15.6341  =  +15:38:02.8
    Error: 12.1 arcsec (radius, 90% conf.)
    Count-rate: 0.0104 [+0.0063, -0.0045] ct s^-1   
    Distance: 262 arcsec from MAXI position.
  

  Source 2:

    RA (J2000.0):  337.2458  =  22:28:58.99
    Dec (J2000.0): +15.7138  =  +15:42:49.6
    Error: 3.2 arcsec (radius, 90% conf. [Enhanced position])
    Count-rate: 0.0401 [+0.0076, -0.0070] ct s^-1   
    Distance: 287 arcsec from MAXI position.
    Flux: (1.67 [+0.32, -0.29])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)
  

  Source 3:

    RA (J2000.0):  337.3461  =  22:29:23.07
    Dec (J2000.0): +15.6941  =  +15:41:38.6
    Error: 8.2 arcsec (radius, 90% conf.)
    Count-rate: 0.0106 [+0.0043, -0.0034] ct s^-1   
    Distance: 70 arcsec from MAXI position.
    Flux: (2.00 [+0.81, -0.64])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
  

  The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00108.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #32674
  N. Cannady (GSFC/UMBC), A. Yoshida, T. Sakamoto, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:
  The long GRB 221006A (MAXI/GSC detection: Mihara et al., GCN Circ. 32626) was marginally detected in the ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data near the MAXI trigger time at 00:57:09 UTC on October 6, 2022. The burst signal was seen by only HXM detectors.
  The burst light curve shows a faint signal which starts at T+0.8 sec, peaks at T+9.8 sec and ends at T+26.8 sec. The T90 and T50 durations measured by the HXM2 data are 24.0 +/- 2.0 sec and 14.0 +/- 2.0 sec (7-100 keV), respectively. The highest significance during the burst is 4.6 sigma at T+15.8 sec with HXM2 data in the 7 - 10 keV band.
  The ground-processed light curve is available at
  http://cgbm.calet.jp/cgbm_trigger/ground/1349052973/
  The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University.
• GCN Circular #32682
  P. A. Evans (U. Leicester) reports on behalf of the Swift team:
  Swift has initiated a ToO observation of the MAXI GRB 221006A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021524
  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 MAXI 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 #32710
  R. O’Rourke Brogan (AIP), P. A. C. Cunha (Univ. do Porto/CAUP), G. Ma (DAWN/NBI) and C. C. Thoene (ASU-CAS) report:
  We observed the field of the MAXI GRB 221006A (GCN 32626, Mikhara et al; GCN 32628, Sbarufatti et al.) using the 1.2m telescope at the Observatoire de l’Haute Provence. Observations started on Oct. 06, 2022 at 20:49 UT, ~20h after the GRB under nearly full Moon conditions.
  In a combined exposure of 2600s in R-band we do not detect a counterpart at any of the positions of the three possible candidates (Source 1: RA 22:29:24.52, DEC +15:38:02.8; Source 2: RA 22:28:58.99, DEC +15:42:49.6; Source 3: RA 22:29:23.07, DEC +15:41:38.6) down to a limiting magnitude of R = 22 mag (3 sigma).
  At the position of source 2, confirmed to be fading with a significance of 4.6 sigma (https://www.swift.ac.uk/xrt_products/TILED_GRB00108/), there are two underlying galaxies also present in the SDSS, which we call G1 and G2. Our image shows a combined magnitude of R=21.2 +/- 0.4 for the two galaxies. The objects show no evidence of excess emission, which is consistent with our upper limit. G1 has a distance of 0.5 arcsec and G2 of 3.5 arcsec from the X-ray candidate afterglow, making G1 the likely host of GRB 221006A.
  We thank the NEON observing school and the support of the 1.2m telescope operator Stephane Favard for obtaining these data.
• GCN Circular #32731
  B. Sbarufatti (INAF-OAB), J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift-XRT has conducted further observations of the field of the MAXI-detected burst GRB 221006A (Mihara et al. GCN Circ. 32626). The observations now extend from T0+37.8 ks to T0+595.5 ks.
  Of the sources reported by Sbarufatti et al. (GCN Circ. 32628), "Source 2" is fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 1256 s of PC mode data and 2 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 = 337.24578, +15.71379 which is equivalent to:

  RA (J2000): 22h 28m 58.99s
  Dec(J2000): +15d 42' 49.6"
  

  with an uncertainty of 3.2 arcsec (radius, 90% confidence). This position is 4.8 arcmin from the MAXI position.
  The light curve can be modelled with a power-law decay with a decay index of alpha=1.01 (+0.34, -0.25).
  The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021521. The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00108.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #32742
  P. A. C. Cunha (Univ. do Porto/CAUP), G. Ma (DAWN/NBI), R. O’Rourke Brogan (AIP), C. C. Thoene (ASU-CAS), A. de Ugarte Postigo (OCA, Nice), D. A. Kann (Goethe Univ.), J. F. Agui Fernandez (IAA-CSIC), L. Izzo (DARK/NBI), J.P.U. Fynbo (DAWN/NBI), N. R. Tanvir (Univ. Leicester), M. Blazek (Prague) and D. Garcia Alvarez (GTC) report:
  We observed the possible host galaxies of the MAXI GRB (GCN 32626, Mikhara et al) underlying the candidate afterglow at RA 22:28:58.99, DEC +15:42:49.6 (GCN 32628, Sbarufatti et al., confirmed to be fading in GCN 32731, Sbarufatti et al.), which we already reported in GCN 32710, (O’Rourke Brogan et al.). Observations were obtained with OSIRIS at the 10.4m GTC telescope in La Palma starting on Oct. 10, 2022 at 20:10 UT with a total exposure time of 3x600s using the R1000R grism (5100-10100Å) and a 1 arcsec slit aligned across both putative hosts.
  We clearly detect the traces of both galaxies in the combined spectrum and determine redshifts of z=0.731 for G1 and z=0.464 for G2 based on emission lines of [OII], [OIII] Hb and Ha. Based on the distance from the X-ray afterglow candidate we determined G1 to be the likely host of GRB 221006A (GCN 32710, O’Rourke Brogan et al.) and hence assume a redshift of z=0.731 for its possible host galaxy.
  We acknowledge two very enjoyable weeks at the NEON observing school during which these follow-up observations were obtained.