//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21520 SUBJECT: GRB 170817A: Fermi GBM detection DATE: 17/08/17 20:00:07 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE), C. Meegan (UAH) and A. Goldstein (USRA) report on behalf of the Fermi GBM Team: "At 12:41:06.47 UT on 17 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170817A (trigger 524666471 / 170817529). The on-ground calculated location, using the GBM trigger data, is RA = 176.8, DEC = -39.8 (J2000 degrees, equivalent to 12 h 47 m, -39 d 48'), with an uncertainty of 11.6 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 91 degrees. The GRB light curve shows a weak short pulse with a duration (T90) of about 2 s (50-300 keV). The time-averaged spectrum from T0-0.512 s to 2.048 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.89 +/- 0.5 and the cutoff energy, parameterized as Epeak, is 82 +/- 21 keV The event fluence (10-1000 keV) in this time interval is (2.3 +/- 0.4)E-07 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0-0.32 s in the 8-1000 keV band is 1.9 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21540 SUBJECT: GRB 170817B: Fermi GBM detection DATE: 17/08/18 04:12:29 GMT FROM: Oliver J Roberts at USRA/NASA O.J. Roberts (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 21:47:34.43 UT on 17 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170817B (trigger 524699259 / 170817908). The on-ground calculated location, using the GBM trigger data, is RA = 83.0, DEC = +50.1, with an uncertainty of 3.7 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 initial angle from the Fermi LAT boresight to the GBM best location is 90 degrees. The GBM triggered multiple short unresolvable pulses over a total duration (T90) of 2.6 s (50-300 keV). The time-averaged spectrum from T0+0.0 to T0+2.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.87 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 1120 +/- 228 keV The event fluence (10-1000 keV) in this time interval is (4.93 +/- 0.16)E-06 erg/cm^2. The 64 ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 10.4 +/- 1.6 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21593 SUBJECT: GRB 170817B: Insight-HXMT observation DATE: 17/08/19 13:32:35 GMT FROM: Shaolin Xiong at IHEP Z. W. Li, J. Y. Liao, C. K. Li, X. B. Li, S. L. Xiong, C. Z. Liu, X. F. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, X. Ma, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: During the commissioning phase, at 2017-08-17T21:47:34.00 (T0), Insight-HXMT detected GRB 170817B (trigger ID: HEB170817908) in a routine search of the data, which was also observed by Fermi/GBM (Roberts et al. 2017, GCN 21540). The Insight-HXMT light curve consists of multiple pulses with a duration (T90) of 2.64 s measured from T0+0.40 s. The 50-ms peak rate, measured from T0+0.40 s, is 6135.4 cnts/sec. The total counts from this burst is 5353.1 counts. URL_LC: http://www.hxmt.org/images/GRB/HEB170817908_lc.jpg All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. The time-averaged spectrum from T0 to T0+3.60 s is adequately fit by a Power Law model with spectral index = -1.60 +/- 0.05. The energy fluence is (1.09 +/- 0.05)E-05 erg/cm^2 in 200 - 5000 keV in this time interval. The analysis results presented above are preliminary; final results will be published elsewhere. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org/index.php/enhome . //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22206 SUBJECT: LIGO/Virgo G298048: Brightening X-ray Emission from GW170817/GRB170817A/SSS17a DATE: 17/12/07 22:11:17 GMT FROM: Phil Evans at U of Leicester Daryl Haggard, John J. Ruan, Melania Nynka (McGill/MSI), Vicky Kalogera (Northwestern/CIERA), and Phil Evans (Leicester) report: We have performed a detailed analysis of new Chandra X-ray observations of GW170817 obtained via Chandra Director's Discretionary Time (PI: Wilkes, Program Number 18408601). The X-ray counterpart to GW170817/GRB170817A/SSS17a is clearly detected in the new observations. This program acquired two exposures of GRB170817A: (1) a 74.09 ks exposure (ObsID 20860) beginning at 2017 December 2.08 UT, approximately 108 days post-burst, and (2) a 24.74 ks exposure (ObsID 20861) beginning at 2017 December 6.45 UT, approximately 111 days post-burst. Since the two new exposures are close in time and the X-ray emission of GRB170817A is not expected to vary significantly over ~4 day timescales, we co-add the two data sets into one 98.83 ks exposure at 109.2 days post-burst. We perform spectral extractions assuming an absorbed power-law spectral model with fixed NH = 7.5e20 cm^−2 and find that the X-ray flux of GRB170817A has an absorbed flux of f(0.3−8 keV) = 1.58e−14 +/- 0.14 erg s^−1 cm^−2 (Gamma = 1.62 +/- 0.27) at 109.2 days post-burst, which corresponds to an unabsorbed luminosity of L(0.3−10 keV) = 42.5e38 +/- 3.7 erg s^−1 (see also Troja et al. GCN 22201 and Margutti et al. GCN 22203). This represents significant X-ray brightening compared to Chandra observations at 15.6 days post-burst, for which we find an absorbed flux of f(0.3−8 keV) = 0.36e−14 +/- 0.1 erg s^−1 cm^−2 (Gamma = 2.4 +/- 0.8) and an unabsorbed luminosity of L(0.3−10 keV) = 10.4e38 +/- 2.0 erg s^−1 (Haggard et al. 2017). We also examine the three previously-detected X-ray sources CXOU J130948, CXOU 130946, and the host galaxy NGC 4993. The fluxes of CXOU 130946 and the host-galaxy NGC 4993 are consistent with our previous deep Chandra observations, while CXOU J130948 appears to be variable in X-rays (Margutti et al. 2017; Haggard et al. 2017). The origin of the X-ray emission from the NS-NS coalescence GW170817/GRB170817A is an important diagnostic for all post-merger interpretations, and different scenarios predict distinct evolution in its X-ray light curve. These observations support scenarios in which the X-ray and radio emission share a common origin, i.e., the X-ray light curve is consistent with outflow models which may be either a cocoon shocked by the jet or dynamical ejecta from the merger. Further deep X-ray monitoring can place powerful constraints on the physical parameters of these models. The X-ray brightening strengthens the argument that simple top-hat jet models are not consistent with the latest observations. However, more advanced models of structured jets with off-axis viewing angles should be pursued and cannot yet be ruled out. We thank Belinda Wilkes and the Chandra scheduling, data processing, and archive teams for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22372 SUBJECT: GW170817/GRB170817A: Preliminary results of Chandra monitoring DATE: 18/01/29 20:42:49 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of a larger collaboration: The Chandra X-ray Observatory re-observed the field of GW170817 starting on January 17th, 2018, and performed five short exposures observations as part of its on-going monitoring program (PI: Wilkes). Only three of these exposures (ObsID: 20936, 20938, 20939) are currently archived and available to the public. Here we report the preliminary findings from these observations. The X-ray afterglow is detected with high significance in all the exposures at an average count rate of 0.0016 cts/s in the 0.5-8.0 keV energy band. A preliminary inspection of the hardness ratio does not show any significant spectral variation. Therefore, we perform a spectral analysis using an absorbed power-law model with absorption column fixed at the Galactic value of 7.5E20 cm^-2 and a photon index Gamma=1.575 as derived from our broadband analysis (Troja et al. 2018, arXiv:1801.06516). We derive an unabsorbed X-ray flux of (3.2 +/- 0.3)E-14 erg/cm2/s in the 0.3-10 keV energy band. The quoted error is at the 68% confidence level. This new measurement is higher than the value measured by Chandra at ~110 days (~2.5E-14 erg/cm2/s, Troja et al. 2018), and higher than the value measured by XMM-Newton at ~135 days (D'Avanzo et al., 2018). The latest measurement is consistent with a rising afterglow with F~t^0.8, although, within the errors, a slow turn-over of the X-ray light curve cannot be excluded. Further analysis is on-going. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22374 SUBJECT: GW170817/GRB170817A: Updated results from the full Chandra dataset DATE: 18/01/30 13:00:12 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of a larger collaboration: We analyzed the full set of five observations of GW170817 performed by the Chandra X-ray Observatory between January 17th and January 28th, 2018, i.e. ~153 and ~164 days after the merger. A log of observations is reported below: ObsID   Exposure [ks]     0.5-8.0 keV count rate [cts/s] 20936     31.75           0.0018 +/- 0.0002 20937     20.77           0.0014 +/- 0.0003 20938     15.86           0.0019 +/- 0.0003 20939     22.25           0.0011 +/- 0.0002 20945     14.22           0.0010 +/- 0.0003 The average net count-rate is 0.00148 +/- 0.00011 cts/s, consistent with the value of 0.00145 +/- 0.00014 observed at 110 days (Troja et al. 2018, arXiv:1801.06516). The average spectrum, obtained by coadding the five exposures, is well described by an absorbed power-law model with N_H=7.5E20 cm^-2 and photon index Gamma=1.65+/-0.16 (68% c.l.), consistent with the value derived from the broadband spectrum at earlier times (Troja et al. 2018, arXiv:1801.06516). Based on this new analysis, we estimate an unabsorbed X-ray flux of (2.6 +/- 0.3)E-14 erg/cm2/s (68% c.l.) in the 0.3-10 keV band, consistent with the X-ray flux measured at 110 days. Our results do not support the claim of a decreasing X-ray flux, as suggested by D'Avanzo et al. (2018, arXiv:1801.06164), and are consistent either with a slowly rising afterglow or a slow turn-over of the X-ray light curve expected when the afterglow reaches its peak (e.g. Lazzati et al. 2017, arXiv:1712.03237; Troja et al. 2018, arXiv:1801.06516). We note that the X-ray afterglow displays a marginal level of variability on timescales of a few days, being the count-rate from the last two exposures (20939,20945) consistently lower. The spectrum from these two observations is characterized by a photon index Gamma= 1.9 +/- 0.3 (68% c. l.), slightly softer than the value measured in the first three exposures (20936,20937, and 20938) Gamma = 1.59+/-0.17  (68% c. l.), yet consistent within the large uncertainties. The lower count-rate and soft spectral shape could be indicative of the cooling frequency entering the X-ray band, although the limited statistics prevent us to draw any firm conclusion. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22763 SUBJECT: GW170817/GRB170817A: LBT optical detection DATE: 18/06/05 14:03:37 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS), M. Cantiello (INAF-OA Abruzzo) V. Testa, D. Paris (INAF-OAR), A. Melandri, S. Covino, O. S. Salafia, P. D'Avanzo, S. Campana (INAF-OAB), L. Nicastro, E. Palazzi, F. Cusano (INAF-OAS), G. Stratta (Urbino University/INFN Firenze), R. Carini, S. Piranomonte, E. Brocato (INAF-OAR), V. D'Elia (ASDC), and M. Branchesi (GSSI) report on behalf of the GRAWITA collaboration and its partners: We observed the optical counterpart of GRB 170817A (Kienlin et al., GCN 21520) associated to GW 170817 (LVC GCN Circ. 21509, 21513) with the LBC imager mounted on the Large Binocular Telescope (Mt Graham, AZ, USA). Observations were performed in the r-sloan filter on 2018-01-23, i.e., ~160 days after the GW/GRB trigger. At the location of the optical transient (e.g., Coulter et al., GCN 21529; Adams et al., 21816) we detect the optical afterglow of GRB 170817A with magnitude r-sloan=26.2+-0.4, calibrated against Pan-STARRS field stars. Image analysis was performed after preliminary removal of an elliptical model of the underlying host galaxy from each single frame. However, some residual emission is left which contributes for ~0.2 mags to the uncertainty of the photometry. Our detection is the first one from a ground-based optical telescope. It is in agreement with a turnover/flattening in the optical light curve of GW 170817/GRB 170817A as inferred by Alexander at al. 2018 (arXiv:1805.02870) and with the overall flattening/declining temporal evolution observed in the X-ray and radio bands (D'Avanzo et al. 2018, A&A, 613 L1; Hajela et al. GCN Circ. 22692; Troja et al. GCN Circ. 22693; Dobie et al. arXiv:1803.06853; Alexander at al. 2018; arXiv:1805.02870). We acknowledge the excellent support from the LBT staff in obtaining these observations.