//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21761 SUBJECT: GRB 170830A: MAXI/GSC detection DATE: 17/08/30 05:53:04 GMT FROM: H. Negoro at Nihon U. T. Yoneyama (Osaka U.), S. Nakahira (RIKEN), S. Sugita (Tokyo Tech), T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN), H. Negoro, M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), N. Kawai, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, (Osaka U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki, H. Kawai (Chuo U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.) GRB 170830A: MAXI/GSC detection The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at UT 03:15:29 UT on 2017 August 30. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (267.244 deg, -2.000 deg) = (17 48 58, -02 00 00) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.09 deg and 0.05 deg, respectively. The roll angle of long axis from the north direction is 41.0 deg counterclockwise. We estimated a rectangular error box for the transient source with the following corners: (266.590, -1.392) deg = (17 46 21, -01 23 31) (J2000) (266.518, -1.475) deg = (17 46 04, -01 28 30) (J2000) (267.633, -2.210) deg = (17 50 31, -02 12 36) (J2000) (267.637, -2.281) deg = (17 50 32, -02 16 50) (J2000). There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 1330 +- 75 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at UT 01:42 and in the next transit at UT 04:48 with an upper limit of 20 mCrab for each. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21764 SUBJECT: GRB 170830A: iTelescope optical observations DATE: 17/08/30 09:48:50 GMT FROM: Denis Denisenko at SAI MSU D. Denisenko (Sternberg Astronomical Institute, Moscow State University) reports: MAXI/GSC error box of GRB 170830A (T. Yoneyama et al., GCN 21761) was observed remotely by iTelescope.Net T32 instrument (0.43-m f/6.8 reflector + FLI Proline 16803 CCD) in Siding Spring, Australia, at 08:55-08:58 UT on 2017 Aug. 30 (5.7 hours after the trigger time). The telescope was centered at R.A. = 17 48 20, Decl. = -01 50 00 with a 43'x43' field of view covering the entire rectangular error box by MAXI/GSC. Observations were performed at the zenith distance of 31 degree, only 18 deg from the waxing Moon (phase 0.60). Visual inspection of the combined image (3x60-sec unfiltered exposures) against 1991-06-15 DSS Red plate shows no optical transient to the 3-sigma upper limit of 18.5m (calibrated against USNO-B1.0 Red magnitudes). In particular, there is no new object in the vicinity of the unidentified ROSAT X-ray source 1RXS J174835.3-014843 which falls inside the gamma-ray burst error box. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21773 SUBJECT: GRB 170830A: Astrosat CZTI detection DATE: 17/08/31 13:22:08 GMT FROM: Vidushi Sharma at IUCAA V. Bhalerao (IITB), V. Sharma and D. Bhattacharya (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data showed clear detection of GRB 170830A (MAXI/GSC detection: Yoneyama T. et al., GCN Circ. 21761) in the 40-200 keV energy range. The light curve shows multiple peaks of emission with the strongest peak at 03:14:00 UT, ~89 s before the MAXI/GSC trigger. The measured peak count rate is 66.3 counts/sec above the background in combined data of four quadrants, with a total of 91.4 counts. The local mean background count rate was 395.1 counts/sec. Using cumulative rates, we measure a T90 of 57.6 secs. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21776 SUBJECT: GRB 170830A: Fermi GBM observation DATE: 17/08/31 17:04:28 GMT FROM: Elisabetta Bissaldi at U.Innsbruk/IAPP M. Stanbro (UAH), E. Bissaldi (Politecnico & INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 03:14:01.95 UT on 30 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170830A (trigger 525755646 / 170830135). This trigger is likely associated with the transient source reported by MAXI/GSC (Yoneyama et al., GCN 21761), which was also detected by AstroSat (Bhalerao et al., GCN 21773). The on-ground calculated location, using the GBM trigger data, is RA = 275.9, DEC = -4.0, with an uncertainty of 2.6 degrees (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 angle from the Fermi LAT boresight at the GBM trigger time is 100 degrees. The GBM light curve shows two peaks with a duration (T90) of about 110 s (50-300 keV). The time-averaged spectrum from T0 to T0+92 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.54 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 180 +/- 40 keV. The event fluence (10-1000 keV) in this time interval is (4.20 +/- 0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0 in the 10-1000 keV band is 4.6 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."