Gamma-ray Burst 180923A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN NOTICE
  

  TITLE:           GCN/MAXI NOTICE
  NOTICE_DATE:     Sun 23 Sep 18 05:33:26 UT
  NOTICE_TYPE:     MAXI Unknown Source Position
  EVENT_ID_NUM:    384142869
  EVENT_RA:         38.30d {+02h 33m 13s} (J2000),
                    38.55d {+02h 34m 12s} (current),
                    37.64d {+02h 30m 35s} (1950)
  EVENT_DEC:        +6.30d {+06d 18' 04"} (J2000),
                    +6.38d {+06d 22' 58"} (current),
                    +6.08d {+06d 04' 54"} (1950)
  EVENT_ERROR:     1.0 [deg radius, stat+sys, 90% containment]
  EVENT_FLUX:      162.0 +- 0.0 [mCrab]
  EVENT_DATE:      18384 TJD;   266 DOY;   18/09/23
  EVENT_TIME:      14910.00 SOD {04:08:30.00} UT
  EVENT_TSCALE:    30s
  EVENT_EBAND:     Low, 2-4 keV
  SUN_POSTN:       180.14d {+12h 00m 34s}   -0.06d {-00d 03' 38"}
  SUN_DIST:        141.15 [deg]
  MOON_POSTN:      341.40d {+22h 45m 35s}  -10.87d {-10d 51' 53"}
  MOON_DIST:        59.44 [deg]
  MOON_ILLUM:      97 [%]
  GAL_COORDS:      163.04,-48.48 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:       37.98, -8.30 [deg] ecliptic lon,lat of the burst (or transient)
  COMMENTS:        MAXI Unknown Source Position. GRB or unknown X-ray Transient. 
  

• GCN Circular #23257
  W. Maruyama, H. Negoro (Nihon U.), M. Serino (AGU), M. Nakajima, A. Sakamaki (Nihon U.), T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.) report on behalf of the MAXI team:
  The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2018-09-23T04:08:25 UT . We obtain the source position at
  (R.A., Dec) = (38.304 deg, 6.301 deg) = (02 33 12, +06 18 03) (J2000)
  with a rectangular error box with the following corners:

  (R.A., Dec) = (37.429, 7.302) deg = (02 29 42, +07 18 07) (J2000)
  (R.A., Dec) = (37.165, 6.998) deg = (02 28 39, +06 59 52) (J2000)
  (R.A., Dec) = (39.010, 5.456) deg = (02 36 02, +05 27 21) (J2000)
  (R.A., Dec) = (39.274, 5.760) deg = (02 37 05, +05 45 35) (J2000) .
  

  There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 162 +- 26 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at UT 02:35 and in the next transit at 05:41 UT with an upper limit of 20 mCrab for each.
• GCN Circular #23258
  V. Lipunov, E. Gorbovskoy, D. Vlasenko, N.Tiurina, V.Kornilov, A.Kuznetsov, V.Chazov, I. Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, Lomonosov Moscow State University,SAI
  A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory
  D. Buckley, South African Astronomical Observatory (SAAO)
  R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias (IAC)
  R. Podesta, F. Podesta, C. Lopez, C.Francile Observatorio Astronomico Felix Aguilar (OAFA)
  H.Levato, Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)
  O. Gres, N.M.Budnev , Yu.Ishmuhametova Irkutsk State University (ISU)
  A. Gabovich, V. Yurkov, Yu. Sergienko Blagoveschensk Educational State University (BSPU)
  MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was starting survey on the MAXI GRB180923.17 error-box (ra=02 33 12 dec=+06 18 02 r=1) 2777 sec after notice time and 7954 sec after trigger time at 2018-09-23 06:21:04 UT. The 5-sigma upper limit on our first (60s exposure) set is about 17.9 mag
  No OT detected.
  The galacitc latitude b = 0 deg.
  The observations made on zenit distance = 39 deg.The moon (97 % bright part) is 42 deg. above the horizon. The distance between moon and object is 59 The sun altitude is -48.6 deg. The object can be observed till sunrise at 2018-09-23 10:25:33 .
  The cover map is availavle at http://observ.pereplet.ru/images/GRB180923A_cover_map.png
  Only for MASTER-team:
  The OT candidate available here https://200.123.254.238:49004//master2/trans.php?wh=transients.coord2000@%27%3C%2838.3d%2C6.30056d%29%2C2d%3E%27%3A%3Ascircle+and+transients.datetime%3E%3D%272018-09-23+04%3A08%3A30%27&class=9&t2=MAXI+GRB180923.17+optical+counterpart+candidate
  The full information about this GRB180923.17 available here https://200.123.254.238:49004//master2/grb.php?not=2018-09-23+05%3A34%3A46.484065&sat=MAXI&gcrd=%2838.3d%2C6.30056d%29&eb=1&trig=2018-09-23+04%3A08%3A30&n=GRB180923.17
  The message may be cited.
  
• GCN Circular #23259
  A. V. Penacchioni, A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita, Y. Kawakubo, A. Tezuka, S. Matsukawa, H. Onozawa, T. Ito, H. Morita, Y. Sone (AGU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena) and the CALET collaboration:
  The MAXI GRB 180923A (Maruyama et al., GCN Circ. 23257) was detected in ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data near the MAXI/GSC trigger time at T0=04:08:25 UT on 23 September 2018. The burst signal was seen by all CGBM detectors.
  The burst light curve shows a multi-peaked structure which starts at T-18 sec and ends at T+107 sec. The T90 and the T50 durations measured by the SGM data are 122 +- 15 sec and 95 +- 58 sec (40-1000 keV), respectively. The significant emission is seen only below ~100 keV.
  The ground processed light curve is available at
  http://cgbm.calet.jp/cgbm_trigger/ground/1221710834/
  The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
• GCN Circular #23263
  O.J. Roberts (USRA) and C. Meegan (UAH) and report on behalf of the Fermi GBM Team:
  "At 22:20:30.53 UT on 23 September 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180923A (trigger 559434035 / 180923931). The on-ground calculated location, using the GBM trigger data, is
  RA, Dec = 310.6, -0.7 (J2000 degrees)
  with an uncertainty of 1.0 degree (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 initial angle from the Fermi LAT boresight to the best location is 86 degrees.
  The GBM light curve shows/consists of two bright peaks with a duration (T90) of about 8.2 s (50-300 keV). The time-averaged spectrum from T0+0 s to T0+8.9 s is best fit by a Band function with Epeak = 44.5 +/- 0.5, alpha index = -0.77 +/- 0.03 and beta index = -3.02 +/- 0.05.
  The event fluence (10-1000 keV) in this time interval is (1.880 +/- 0.003)E-05 erg/cm^2. The 1s peak photon flux measured starting from T0+4.0 s in the 10-1000 keV band is 53 +/- 1 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #23269
  A.Kozlova, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline on behalf of the Konus-Wind team, report:
  The long-duration GRB 180923A localized by MAXI/GSC (Maruyama et al., GCN 23257) and observed by CALET (GBM: Penacchioni et al., GCN 23259) was detected by Konus-Wind (KW) in the waiting mode.
  The burst light curve shows two episodes, started at ~T0(MAXI)-19 s with a total duration of ~ 127 s.
  As observed by KW, the burst had a fluence of 5.42(-0.65,+1.26)x10^-6 erg/cm2 and a 2.944-s peak flux, measured from ~T0(MAXI)+93.3 s, of 3.47(-0.92,+1.15)x10^-7 erg/cm2/s (both in the 20 - 1000 keV energy range).
  Modeling the KW 3-channel time-integrated spectrum (from ~T0(MAXI)-18.6 s to ~T0(MAXI)+108 s) by a simple power-law model yields a power law index of -2.2(-0.2,+0.2), chi2=0.2/1 dof.
  The KW light curve of this burst is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB180923A
  All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary.