INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational-wave Event GW170817

Abstract

We report the e INTernational Gamma-ray Astrophysics Laboratory (INTEGRAL) detection of the short gamma-ray burst GRB 170817A (discovered by Fermi-GBM) with a signal-to-noise ratio of 4.6, and, for the first time, its association with the gravitational waves (GWs) from binary neutron star (BNS) merging event GW170817 detected by the LIGO and Virgo observatories. The significance of association between the gamma-ray burst observed by INTEGRAL and GW170817 is 3.2 σ, while the association between the Fermi-GBM and INTEGRAL detections is 4.2 σ. GRB 170817A was detected by the SPI-ACS instrument about 2 s after the end of the gravitational wave event. We measure a fluence of (1.4 ± 0.4 ± 0.6)×10 −7 erg cm −2 ) (75-2000 keV), where, respectively, the statistical error is given at the 1 σ confidence level, and the systematic error corresponds to the uncertainty in the spectral model and instrument response.We also report on the pointed follow-up observations carried out by INTEGRAL, starting 19.5 h after the event, and lasting for 5.4 days. We provide a stringent upper limit on any electromagnetic signal in a very broad energy range, from 3 keV to 8 MeV, constraining the soft gamma-ray afterglow flux to < 7.1×10 −11 erg cm −2 s −1 (80-300 keV).Exploiting the unique capabilities of INTEGRAL, we constrained the gamma-ray line emission from radioactive decays that are expected to be the principal source of the energy behind a kilonova event following a BNS coalescence. Finally, we put a stringent upper limit on any delayed bursting activity, for example from a newly formed magnetar.

GRB 170817A Associated with GW170817: Multi-frequency Observations and Modeling of Prompt Gamma-Ray Emission

“…Using the conversion factor, we derive F = (1.8 ± 0.4) × 10 −7 erg cm −2 in the (75, 1000) keV range for GRB 170817A. This value is in agreement with one estimated in Savchenko et al (2017a) using a more complex method.…”

“…GRB 170817A PROMPT GAMMA-RAY DATA ANALYSIS 3.1. SPI-ACS/INTEGRAL The description of GRB 170817A INTEGRAL observations and detailed analysis of the burst based on IN-TEGRAL data are presented in Savchenko et al (2017a). We performed a basic analysis of the SPI AntiCoincidence Shield (SPI-ACS) data with a slightly different method to classify the burst and to estimate its energetics, and then compare our results with those of Fig.…”

The Polarizations of Gravitational Waves

“…Finally, let us mention that Einstein-aether theory is highly constrained by various experimental observations, especially the speed bound derived from GW170817 and GRB 170817A [5,[43][44][45]. Apart from this speed bound and the absence of the gravitational Cherenkov radiation, there are constraints from the observations of pulsars (such as the post-Newtonian parameters, |α 1 | < 4 × 10 −5 [65] and |α 2 | < 2 × 10 −9 [66,67] …”

“…Since the observation of GW170817 and GRB 170817A [5,43,44], many alternative theories of gravity have been highly constrained by the speed bound of the GW [45],…”

Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes

“…On 2017 August 17 12:41:06, about 2 s after the GW detection, the Gamma-ray Burst Monitor (GBM) instrument on board the Fermi satellite independently detected a short gamma-ray burst, labelled as GRB 170817A (Connaughton et al 2017;Goldstein et al 2017a;Goldstein et al 2017b;von Kienlin et al 2017). The INTErnational Gamma-Ray Astrophysics Laboratory (IN-TEGRAL) also detected GRB 170817A (Savchenko et al 2017a;Savchenko et al 2017b), providing unique information especially when the data were combined with those obtained with Fermi (Abbott et al 2017b). The close temporal coincidence of the gamma-ray burst and GW event made it a compelling target for follow-up observations at other wavelengths.…”