Gamma-ray Burst 180809A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN NOTICE
  

  TITLE:           GCN/MAXI NOTICE
  NOTICE_DATE:     Thu 09 Aug 18 12:00:46 UT
  NOTICE_TYPE:     MAXI Unknown Source Position
  EVENT_ID_NUM:    339385460
  EVENT_RA:        297.95d {+19h 51m 47s} (J2000),
                   298.25d {+19h 53m 00s} (current),
                   297.14d {+19h 48m 33s} (1950)
  EVENT_DEC:       -34.63d {-34d 37' 36"} (J2000),
                   -34.58d {-34d 34' 41"} (current),
                   -34.76d {-34d 45' 20"} (1950)
  EVENT_ERROR:     1.0 [deg radius, stat+sys, 90% containment]
  EVENT_FLUX:      2015.0 +- 0.0 [mCrab]
  EVENT_DATE:      18339 TJD;   221 DOY;   18/08/09
  EVENT_TIME:      41905.00 SOD {11:38:25.00} UT
  EVENT_TSCALE:    1day
  EVENT_EBAND:     Low, 2-4 keV
  SUN_POSTN:       139.32d {+09h 17m 16s}  +15.78d {+15d 46' 48"}
  SUN_DIST:        153.34 [deg] 
  MOON_POSTN:      111.12d {+07h 24m 30s}  +20.64d {+20d 38' 38"}
  MOON_DIST:       164.71 [deg] 
  MOON_ILLUM:      6 [%]
  GAL_COORDS:        5.75,-26.73 [deg] galactic lon,lat of the burst (or transient)        
  ECL_COORDS:      293.36,-13.43 [deg] ecliptic lon,lat of the burst (or transient)
  COMMENTS:        MAXI Unknown Source Position. GRB or unknown X-ray Transient.
  

• GCN NOTICE
  

   
  TITLE:           GCN/MAXI NOTICE
  NOTICE_DATE:     Thu 09 Aug 18 12:08:36 UT
  NOTICE_TYPE:     MAXI Unknown Source Position
  EVENT_ID_NUM:    339385460
  EVENT_RA:        297.79d {+19h 51m 10s} (J2000),
                   298.09d {+19h 52m 23s} (current),
                   296.98d {+19h 47m 55s} (1950)
  EVENT_DEC:       -34.66d {-34d 39' 45"} (J2000),
                   -34.61d {-34d 36' 51"} (current),
                   -34.79d {-34d 47' 26"} (1950)
  EVENT_ERROR:     1.0 [deg radius, stat+sys, 90% containment]
  EVENT_FLUX:      890.0 +- 0.0 [mCrab]
  EVENT_DATE:      18339 TJD;   221 DOY;   18/08/09
  EVENT_TIME:      41905.00 SOD {11:38:25.00} UT
  EVENT_TSCALE:    1day
  EVENT_EBAND:     Low, 2-4 keV
  SUN_POSTN:       139.32d {+09h 17m 17s}  +15.78d {+15d 46' 42"}
  SUN_DIST:        153.22 [deg] 
  MOON_POSTN:      111.21d {+07h 24m 51s}  +20.64d {+20d 38' 20"}
  MOON_DIST:       164.76 [deg] 
  MOON_ILLUM:      6 [%]
  GAL_COORDS:        5.67,-26.61 [deg] galactic lon,lat of the burst (or transient)        
  ECL_COORDS:      293.22,-13.44 [deg] ecliptic lon,lat of the burst (or transient)      
  COMMENTS:        MAXI Unknown Source Position. GRB or unknown X-ray Transient.
  

• GCN Circular #23103
  F. Yatabe, S. Nakahira, T. Mihara, Y. Takao, M. Matsuoka (RIKEN), M. Serino, T. Sakamoto, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), H. Negoro, M. Nakajima, A. Sakamaki, W. Maruyama (Nihon U.), 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 (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 11:38:25 UT on 9 August 2018. Assuming that the source flux was constant over the transit, we obtain the source position at
  (R.A., Dec) = (297.793 deg, -34.663 deg) = (19 51 10, -34 39 46) (J2000)
  with a 90% C.L. statistical error of 0.09 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 890 +- 57 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy,we obtain a rectangular error box for the transient source with the following corners:

  (R.A., Dec) = (297.202, -33.964) deg = (19 48 48, -33 57 49) (J2000)
  (R.A., Dec) = (297.086, -34.046) deg = (19 48 20, -34 02 46) (J2000)
  (R.A., Dec) = (298.358, -35.535) deg = (19 53 25, -35 32 04) (J2000)
  (R.A., Dec) = (298.475, -35.451) deg = (19 53 54, -35 27 03) (J2000)
  

  There was no significant excess flux in the previous transit at UT 10:05 with an upper limit of 20 mCrab.
• GCN Circular #23104
  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 180809A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00072
  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 #23106
  V. D'Elia (SSDC), S.L. Gibson (U. Leicester), Z. Liu (NAOC / U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.P. Osborne (U. Leicester) 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 180809A (Yatabe et al. GCN Circ. 23103) in a series of observations tiled on the sky. The total exposure time is 777 s, distributed over 6 tiles; the maximum exposure at a single sky location was 898 s. The data were collected between T0+13.7 ks and T0+22.0 ks, and are entirely in Photon Counting (PC) mode.
  An uncatalogued X-ray source is detected and is above the RASS limit, and is therefore likely the GRB afterglow. Using 731 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 = 297.90271, -34.78546 which is equivalent to:

  RA (J2000): 19h 51m 36.65s
  Dec(J2000): -34d 47' 07.6"
  

  with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position is 9.1 arcmin from the MAXI position. The light curve is currently consistent with a constant source of mean count rate 2.2e-01 ct/sec. A power-law fit gives an index of 0.3 (+/-0.9). More data are necessary to determine potential fading.
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.4 (+0.7, -0.6). The best-fitting absorption column is 8.4 (+5.4, -3.8) x 10^21 cm^-2, in excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (8.2 x 10^-11) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     8.4 (+5.4, -3.8) x 10^21 cm^-2
  Galactic foreground: 1.2 x 10^21 cm^-2
  Excess significance: 3.1 sigma
  Photon index:	     2.4 (+0.7, -0.6)
  

  The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020814. The results of the full analysis of the tiled XRT observations are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00072.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #23107
  A.K.H. Kong (NTHU, Taiwan) reports
  We observed the field of GRB 180809A (Yatabe et al. GCN 23103) with the T30 0.51m telescope of iTelescope.Net in Siding Spring, Australia. The observation was done with a luminance filter (400-700 nm) beginning at 2018-08-09 12:51:14 UT (73 min after the trigger) for 300 sec. At the position of the proposed X-ray afterglow (D'Elia et al. GCN 23106), we do not detect any optical emission with a detection limit of about 20 mag by comparing with the Gaia DR2 catalogue.
• GCN Circular #23117
  S. Ricciarini (U of Florence), 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), A. V. Penacchioni, P. S. Marrocchesi (U of Siena) and the CALET collaboration:
  The GRB 180809A (MAXI/GSC detection: Yatabe et al., GCN Circ. 23103; Fermi-GBM trigger #555507497) was detected in ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data near the MAXI trigger time at T0=11:38:25 UT on 9 August 2018. The burst signal was seen by all CGBM detectors.
  The burst light curve shows a weak pulse which starts at T-15.1 sec and ends at T-4.2 sec. The T90 and the T50 durations measured by the SGM data are 10.0 +- 1.6 sec and 5.0 +- 1.6 sec (40-1000 keV), respectively.
  The ground processed light curve is available at
  http://cgbm.calet.jp/cgbm_trigger/ground/1217849910/
  The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
• GCN Circular #23118
  E. Bissaldi (Politecnico & INFN Bari) reports on behalf of the Fermi GBM Team:
  "At 11:38:12.08 UT on 9 August 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180809A (trigger 555507497 / 180809485), which was also detected by MAXI/GSC (Yatabe et al. 2018, GCN 23103) and Swift/XRT (D'Elia et al. 2018, GCN 23106). The GBM on-ground location is consistent with the Swift position.
  The angle from the Fermi LAT boresight at the GBM trigger time is 60 degrees.
  The GBM light curve consists of multiple emission episodes with a duration (T90) of about 220 s (50-300 keV). The time-averaged spectrum of the main emission episode from T0-5 s to T0+15 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.37 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 620 +/- 230 keV.
  The event fluence (10-1000 keV) in this time interval is (6.8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.2 s in the 10-1000 keV band is 4.0 +/- 0.3 ph/s/cm^2.
  The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
• GCN Circular #23141
  V. D'Elia (SSDC) reports on behalf of the Swift/XRT team:
  Swift performed a second visit to the field of the MAXI-detected burst GRB 180809A (Yatabe et al. GCN Circ. 23103). The XRT data comprise 3700 s of exposure time, acquired ~5 days after the GRB trigger and entirely in PC mode.
  No excess is found at the position of the candidate afterglow reported by D'Elia et al. (GCN Circ. 23106), down to a three sigma upper limit of ~4E-3 cts/s, corresponding to a 0.3-10 keV observed flux of ~1E-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). We thus conclude that the source reported by D'Elia et al. (GCN Circ. 23106) was indeed the X-ray counterpart of the MAXI GRB 180809A.
  This circular is an official product of the Swift/XRT team