Constraining the neutron star EOS in ascending-descending GW chirps and its potential implications for a stochastic GW-foreground search in O4-5

Our Universe is rife with transient sources of emission in the LVK bandwidth of sensitivity collectively contributing to a stochastic GW-foreground (SGWF). The main source for SGWF is expected to be compact binary coalescences. DNS, and possibly BH-NS mergers may feature ascending-descending chirps from merger to post-merger BH spin-down. DNS mergers may reveal delayed collapse of the initial HMNS to a BH, marked by the onset of descending chirp. This is recently observed at 5.5σ significance by a 3.7 seconds long GW170817B during GRB170817A, starting 0.92±0.08 seconds after the merger. Since the EOS of the initial HMNS is constrained by its lifetime, we propose surveying the start time of these descending GW chirps over multiple events during O4-5. As we extend our horizon distances, we explore the potential impact of such ascending-descending chirps on the SGWF.