EM counterparts to GW sources

Detecting High-Energy counterparts with Daksha

Daksha has been designed to detect electromagnetic counterparts to gravitational wave (EMGW) sources from inspirals such as binary neutron star (BNS) and black hole neutron star (BH-NS) merger, also emissions from continuous gravitational wave sources which are pulsars. Till date there has been only one detection of EMGW i.e. the observation of GRB170817A associated with GW170817 ( Abbott 2017d) along with other electromagnetic counterparts observed from gamma-rays to radio. This event was detected by Fermi Gamma-ray Space Telescope and INTEGRAL (V. Savchenko2017). Many other instruments have missed this important event. Daksha has been designed keeping in my the lessons learned from this event. Two key features of Daksha are the higher sensitivity and all-sky coverage, thanks to which we will detect far more events than other missions. Daksha can detect GRBs , do a quick onboard localisation, obtain light curve, create coarse light curves and spectra to be broadcast globally within ∼ 1 minute of each event. This information will enable research groups across the globe to prioritise their resources and start rapid follow-up observations.

The event mode data will be down-linked on the next ground-station pass which will be used to produce improved data products. The broad spectral coverage will help obtaining better spectral components of the prompt emission. Daksha will also provide coverage of prompt emission in the soft X-rays. Daksha will also be able to measure polarization for bright sources. All bursts detected by Daksha can also be utilized for “triggered” searches in GW network data for corresponding GW signals. Our calculations show that this can give a significant boost to the number of binary neutron star events detected in GW (Bhattacharjee et al. in prep).