Speaker: Yubo Su (Cornell University)
Observational Signatures of Tertiary-Induced Binary Black Hole Mergers

Abstract: Many proposed scenarios for black hole (BH) mergers involve a tertiary companion that periodically excites an inner BH binary to extreme eccentricities via the von Zeipel-Lidov-Kozai (ZLK) effect. These eccentricity cycles enable the inner binary to merge efficiently via emission of gravitational waves during periods of high eccentricity. These scenarios often carry unique observational signatures that may be compared to the growing catalog of the binary BH mergers observed by LIGO/VIRGO. In this talk, I will present the observational signatures of two particular scenarios. First, I will discuss the dynamics of the spins of the BHs in the inner binary as they undergo regular ZLK eccentricity cycles. I will show that, under certain conditions, the BH spins upon merger preferentially lie in the orbital plane of the binary. This evolution can be understood analytically and yields a distribution of the binary effective spin parameter \chi_eff centered on zero, in line with observations. Second, I will discuss the effect of the inner binary’s mass ratio on the merger efficiency with an eccentric tertiary. Under these assumptions, I will show that inner binaries with more unequal masses merge more efficiently, sometimes substantially so. Though many uncertainties remain, this procedure produces a distribution of mass ratios in merging BHs in tension with that observed by LIGO/VIRGO.

Speaker: Ayşegül Tümer (University of Utah)
Enhancing and extending NuSTAR’s capabilities with the characterization of scattered light background: implications for observations of galaxy clusters

Abstract: Galaxy clusters are the largest gravitationally bound structures in the universe. According to large scale structure formation scenarios, they are hierarchically formed by mergers of smaller scale structures, which are the most energetic (10^65 ergs/s) processes in the universe that drive shocks and turbulence into the intracluster medium (ICM). Thermodynamical properties of the X-ray emitting ICM are sensitive probes of these dynamic activities. Although we have advanced X-ray satellites to observe these phenomena, there are caveats in interpreting their data; the most challenging one being the characterization of the background. In this talk, I will present our techniques and approaches to obtain the true data of clusters of galaxies from the X-ray mission NuSTAR, and share the process of how we deduce the real emission on a working example of the cluster Abell 3395.