Kunyang Li to Lead a Talk for the 2021 HEAD Frontier Virtual Seminar Series

Kunyang Li
Kunyang (Lily) Li

The next HEAD (High Energy Astrophysics Division) Frontier Seminar will be held on Friday, April 16th at 1:00pm EDT (17:00 UTC). There will be three exciting talks by early-career researchers lined up, including CRA’s own Kunyang Li.

    • The Detectability of Kiloparsec Scale Dual AGNs: The Impact of Galactic Structure and Black Hole Orbital Properties, Kunyang Li (Georgia Institute of Technology)
    • Demystifying the Prompt Emission of Gamma Ray Bursts, Tyler Parsotan (Oregon State University)
    • New Evidence for the 3.5 keV Feature in Clusters is Inconsistent with a Dark Matter Origin, Sunayana Bhargava (CEA Paris-Saclay)

    Meeting URL (via Zoom): https://aas-org.zoom.us/j/92093881225
    Date and Time: Friday, April 16th at 1:00pm EDT (17:00 UTC)
    Meeting ID: 920 9388 1225
    Find your local numberhttps://aas-org.zoom.us/u/adJipvkJWW

    The talk abstracts are available below and on HEAD main website, where you can also find links to previous talks in this seminar series (through the AAS/HEAD Youtube channel).

    The Detectability of Kiloparsec Scale Dual AGNs: The Impact of Galactic Structure and Black Hole Orbital Properties

    Kunyang Li (Georgia Institute of Technology)

    Observational searches for dual active galactic nuclei (dAGNs) at kiloparsec separations are crucial for understanding the role of galaxy mergers in the evolution of galaxies. In addition, kpc-scale dAGNs may serve as the parent population of merging massive black hole (MBH) binaries, an important source of gravitational waves. We use a semi-analytical model to describe the orbital evolution of unequal mass MBH pairs under the influence of stellar and gaseous dynamical friction in post-merger galaxies. We quantify how the detectability of approximately 40,000 kpc-scale dAGNs depends on the structure of their host galaxies and the orbital properties of the MBH pair. Our models indicate that kpc-scale dAGNs are most likely to be detected in gas-rich post-merger galaxies with smaller stellar bulges and relatively massive, rapidly rotating gas disks. The detectability is also increased in systems with MBHs of comparable masses following low eccentricity prograde orbits. In contrast, dAGNs with retrograde, low eccentricity orbits are some of the least detectable systems among our models. The dAGNs in models in which the accreting MBHs are allowed to exhibit radiative feedback are characterized by a significantly lower overall detectability. The suppression in detectability is most pronounced in gas-rich merger remnant galaxies, where radiation feedback is more likely to arise. If so, then large, relatively gas poor galaxies may be the best candidates for detecting dAGNs.

    Demystifying the Prompt Emission of Gamma Ray Bursts

    Tyler Parsotan (Oregon State University)

    Gamma Ray Bursts (GRBs) are the most powerful explosions in the universe, emitting more energy in a few seconds than our sun will emit in its entire lifetime. As a result, these explosions are excellent laboratories for exploring the interplay between matter and radiation in extreme environments. This interplay is integral to understanding astrophysical jets and the various compact objects that are thought to power GRBs. Recent advances in simulating the initial prompt emission of GRBs attempt to simulate this interplay between the jet properties and the resulting electromagnetic signature; this has resulted in various successes in reproducing observational aspects of GRBs. Here, we present the open source Monte Carlo Radiation Transfer (MCRaT) code. MCRaT propagates and Compton-scatters individual photons that have been injected into the collimated outflow in order to produce mock observed light curves, spectra, and polarization measurements from optical to gamma rays. These light curves and spectra allow us to compare our results to GRB observational data. We find excellent agreement between our mock observed GRBs and real GRB observations in terms of spectra and polarization measurements. Furthermore, we can understand the mock observations in terms of the jet structure and what real observations of GRBs can tell us about their jet structures. There are various improvements that can be made to MCRaT, but this code paves the way to connecting observed GRB radiation to the properties of the GRB jet in a way that was not previously possible.

    New Evidence for the 3.5 keV Feature in Clusters is Inconsistent with a Dark Matter Origin

    Sunayana Bhargava (University of Sussex)

    There have been several reports of a detection of an unexplained excess of X-ray emission at 3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM-Newton satellite. We explore evidence for a 3.5 keV excess in the spectra of 117 redMaPPer galaxy clusters – the largest study of its kind. In our analysis of individual spectra, we identify three systems with an excess of flux at 3.5 keV (one of which might be due to a discrete emission line). We group the remaining 114 clusters into temperature bins to search for an increase in 3.5 keV flux with temperature (a reliable proxy for halo mass) and find no evidence for a positive trend. We conclude that a 3.5 keV flux excess in our sample is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay.