Astronomy Tea Talk
Speaker 1: Joheen Chakraborty
Title: Quasi-Periodic Eruptions: the first electromagnetic counterparts to EMRIs?
Abstract:
Quasi-Periodic Eruptions (QPEs) are a newly discovered class of recurring X-ray transient originating from supermassive black holes (SMBHs) in nearby, low-mass galaxy nuclei. They are thought to be the first observed counterparts to extreme mass-ratio inspirals (EMRIs). Since their serendipitous discovery in 2019, about ten QPE sources have been discovered: the population thus far exhibits recurrence times of ~2.5-100 hours and peak luminosities of ~1e42-44 erg/s, and growing observational evidence links them to the compact accretion flows formed in the aftermath of Tidal Disruption Events (TDEs). Recent theory and modeling efforts suggest QPEs may arise from interactions between a stellar-mass orbiter and the accretion disk around an SMBH; if confirmed, QPEs carry exciting implications for upcoming space-based millihertz gravitational wave detectors (e.g. LISA) which are expected to directly detect EMRIs with a hugely uncertain rate. In this talk, I will give an overview of QPE discoveries and observations, with an emphasis on recent work testing EMRI models with timing and spectroscopy (Chakraborty+24,25a,b). I will conclude with a discussion of future prospects and what we may learn by studying QPEs.
Speaker 2: Dr. Andrea Gokus
Title: Hunting High-Redshift Blazars: Insights from X-Ray and Gamma-Ray Observations
Abstract:
Active galactic nuclei with jets pointed toward our line of sight are called blazars. Due to their extreme variability and high-energy emission, these objects serve as ideal laboratories for probing the most energetic processes in the Universe. Their high luminosities allow us to detect them across cosmic time, enabling studies of black hole growth and galaxy evolution from the early Universe to the present.
To measure the power of these jets and assess their influence on their host galaxies, data in both the X-ray and gamma-ray regimes are crucial. In particular, NuSTAR provides valuable contributions by covering a much broader energy range than most currently active X-ray missions, offering significantly improved constraints for the rising part of the high-energy emission component (typically attributed to Inverse Compton emission).
I will present results from my search for gamma-ray emission from high-redshift ( z > 3) blazars, leveraging their transient nature, as well as preliminary findings from an ongoing campaign to investigate the hard X-ray emission of high-redshift blazar candidates identified with eROSITA.