Gilad Sadeh & Mudit Garg

Talk 1: Gilad Sadeh, 3:00pm - 3:30pm
Non-thermal emission following Compact Objects Mergers
Mergers of compact objects are expected to produce a highly relativistic collimated ejecta along with a quasi-spherical mildly relativistic ejecta. We model the non-thermal emission produced by the relativistic ejecta. Guided by 1D and 2D numerical calculations (that we carried out using our purposely modified relativistic hydrodynamics AMR code), we derived analytic and semi-analytic formulae describing the signal expected from collisionless shocks driven by the mildly relativistic (\gamma\beta~1) Kilonova ejecta, and by moderately relativistic (\gamma<10) outflow that is likely to dominate the emission from jetted outflows observed off-axis. Our results improve upon earlier order-of-magnitude estimates based on extrapolations of non- or ultra-relativistic results. They are thus essential for inferring constraints on the fast parts of the ejecta based on future radio & X-ray observations. Specifically, we provide an alternative explanation, different from that commonly considered in the literature, for the extensive radio & X-ray data of GW170817. Existing models consider a narrow ultra-relativistic jet and have difficulty accounting for all data. We suggest a wider-angle stratified ejecta with a lower Lorentz factor range. It is the first single-component complete numerical calculation that fits all the radio & X-ray data of this unprecedented event.

Talk 2: Mudit Garg, 3:30pm - 4:00pm
Our current understanding is that an environment – mainly consisting of gas, stars, or a third massive black hole (MBH) – is required to bring MBH binaries (MBHBs) with total mass ∼ [10^4, 10^7] MSun to near-merger from parsec separation. The final inspiral is driven by radiated gravitational waves (GWs) in near milli-Hz frequencies, which the recently adopted space-based mission LISA will observe in the 2030s up to high redshifts. Despite GWs dominating the binary evolution in the LISA band, a suitable environment can still non-negligibly speed up or slow down the binary inspiral or sustain residual initial orbital eccentricity. Using realistic data analysis techniques, I show how well LISA will measure gas-induced perturbation or initial eccentricity, together or separately. I also explore if a small eccentricity can mimic a weak gas effect and vice versa to motivate synergies between LISA and electromagnetic observations. Moreover, I show how ignoring moderate gas effects (Eddington ratio ~0.1) or eccentricity (~10^(-2.5)) biases binary parameters and violates general relativity. Lastly, I demonstrate how spin-eccentricity correlations in the LISA band can break certain degeneracies regarding formation channels. Therefore, my results have rich implications for astrophysics, data analysis, fundamental physics, and cosmology. LISA will launch in a decade, making this study exciting and valuable in unlocking the mysteries of MBHB evolution.