In the faint short gamma-ray burst sGRB 170817A followed by the gravitational waves (GWs) from a merger of two neutron stars (NSs) GW170817, the spectral peak energy is too high to explain only by canonical off-axis emission. We investigate the off-axis appearance of an sGRB prompt emission scattered by a cocoon, which is produced through the jet–merger–ejecta interaction, with either subrelativistic or mildly relativistic velocities. We show that the observed properties of sGRB 170817A, in particular the high peak energy, can be consistently explained by the Thomson-scattered emission with a typical sGRB jet, together with its canonical off-axis emission, supporting that an NS–NS merger is the origin of sGRBs. The scattering occurs at ≲1010–1012 cm not far from the central engine, implying the photospheric or internal shock origin of the sGRB prompt emission. The boundary between the jet and cocoon is sharp, which could be probed by future observations of off-axis afterglows. The scattering model predicts a distribution of the spectral peak energy that is similar to the observed one but with a cutoff around ∼MeV energy and its correlations with the luminosity, duration, and time lag from GWs, providing a way to distinguish it from alternative models. Scattered Short Gamma-Ray Bursts as Electromagnetic Counterparts to Gravitational Waves and Implications of GW170817 and GRB 170817A - IOPscience The American Astronomical Society (AAS) , established in 1899 and based in Washington, DC, is the major organization of professional astronomers in North America. Its membership of about 7,000 individuals also includes physicists, mathematicians, geologists, engineers, and others whose research and educational interests lie within the broad spectrum of subjects comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe. The following article is Free article Scattered Short Gamma-Ray Bursts as Electromagnetic Counterparts to Gravitational Waves and Implications of GW170817 and GRB 170817A Shota Kisaka , Kunihito Ioka , Kazumi Kashiyama , and Takashi Nakamura Published 2018 October 29 • © 2018. The American Astronomical Society. All rights reserved. The Astrophysical Journal , Volume 867 , Number 1 Citation Shota Kisaka et al 2018 ApJ 867 39 DOI 10.3847/1538-4357/aae30a PDF Opens in a new tab. ePub You need an eReader or compatible software to experience the benefits of the ePub3 file format . Kunihito Ioka AFFILIATIONS Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan; kunihito.ioka@yukawa.kyoto-u.ac.jp EMAIL kunihito.ioka@yukawa.kyoto-u.ac.jp https://orcid.org/0000-0002-3517-1956 Kazumi Kashiyama AFFILIATIONS Department of Physics, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan; kashiyama@phys.s.u-tokyo.ac.jp Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033, Japan EMAIL kashiyama@phys.s.u-tokyo.ac.jp https://orcid.org/0000-0003-4299-8799 Takashi Nakamura AFFILIATIONS Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan; kunihito.ioka@yukawa.kyoto-u.ac.jp Department of Physics, Kyoto University, Kyoto 606-8502, Japan; nakamura.takashi.57a@st.kyoto-u.ac.jp EMAIL nakamura.takashi.57a@st.kyoto-u.ac.jp Notes Article metrics 1210 Total downloads 0 Video abstract views Permissions Get permission to re-use this article Share this article Article information Dates Received 2017 November 10 Revised 2018 September 13 Accepted 2018 September 18 Published 2018 October 29 Keywords binaries (including multiple): close ; gamma-ray burst: general ; gravitational waves ; scattering Journal RSS Create or edit your corridor alerts Corridor alerts Receive alerts on all new research papers in American Astronomical Society ( A A S ) journals as soon as they are published. Select your desired journals and corridors below. You will need to select a minimum of one corridor. Corridors Journals Please note, The Planetary Science Journal (PSJ) does not currently use the corridors. Create alert What are corridors? 0004-637X/867/1/39 Abstract In the faint short gamma-ray burst sGRB 170817A followed by the gravitational waves (GWs) from a merger of two neutron stars (NSs) GW170817, the spectral peak energy is too high to explain only by canonical off-axis emission. Introduction On 2017 August 17, gravitational waves (GWs) from a merger of two neutron stars (NSs) were finally discovered by the Laser Interferometer Gravitational-Wave Observatory (LIGO), along with Virgo, and dubbed as GW170817 (Abbott et al. 2017c ). The Fermi Gamma-ray Burst Monitor ( Fermi /GBM) and INTEGRAL also detected a short (duration ∼2 s) gamma-ray burst sGRB 170817A ∼1.7 s after the GWs ceased (Abbott et al. 2017b ; Goldstein et al. 2017 ; Savchenko et al. 2017 ). Follow-up observations involving more than 3000 people identified the counterparts across the electromagnetic (EM) wavelengths (Abbott et al. In Section 3.3 , we again emphasize that the scattering model generally predicts the spectral peak energy E p to be similar to the on-axis value if E p  ≲ MeV. Finally, we apply the scattering model to GRB 170817A/GW170817 and discuss the implications in Section 4 . In Section 5 , we discuss the constraints from the observations such as afterglow emission. We present the summary and Since the scattered fraction is proportional to the beaming angle ∼1/Γ j as in Equation ( 4 ), the scattered luminosity L sc could be enhanced. The time lag of the scattered emission behind the GW signal is given by where t j is the time of the jet launch after the merger, and t br is the timescale for the jet breakout from the merger ejecta. 7 The last term in Equation ( 8 ) is the delay time of a single pulse caused by the curvature effect of the emission surface at the scatter-starting radius r scbr , in the case of .

On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is 5.0 x 10(exp -8). We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of (+1.74 +/- 0.05) s between GRB170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between -3 x 10(exp-16) times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar