Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L09: Astrophysical TransientsLive
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Sponsoring Units: DAP Chair: Grant Mathews, Notre Dame |
Sunday, April 18, 2021 3:45PM - 3:57PM Live |
L09.00001: Fast Radio Bursts and the Milky Way Nayab Gohar, Chris Flynn Fast Radio Bursts (FRBs) are highly energetic transient events, with durations of order of microseconds to milliseconds, recently shown to lie at cosmological distances. Recently, an FRB-like event was seen from the Milky Way magnetar SGR 1935+2154 by CHIME and STARE2, radio telescopes that have ongoing FRB search programs. Finding further events like that from SGR1935+2154 from other magnetars in the Milky Way will be strongly affected by the turbulent interstellar medium, their intrinsic energy distribution and to some extent their spatial locations within the plane of the Milky Way disk. Here, we examine searches for more such FRB-like events, using two models for the distribution of electrons in the ISM in order to estimate the dispersion measure and pulse scattering of mock events, and a range of models for the spatial distribution and luminosity functions, evaluating what fraction of FRB-like events in the Milky Way could be detected by all-sky experiments such as STARE2. In all the models examined, only a fraction of burst events is detectable, mainly due to the scattering effects of the ISM. A similar experiment to STARE2, operating in the Southern Hemisphere, could increase the detection rate significantly. [Preview Abstract] |
Sunday, April 18, 2021 3:57PM - 4:09PM Live |
L09.00002: Searching for Lensed Fast Radio Bursts with CHIME/FRB Calvin Leung, Zarif Kader, Matt Dobbs, Kiyoshi Masui Gravitational lensing of fast radio bursts (FRBs) on timescales of nanoseconds to milliseconds is sensitive to the presence of massive bodies up to $100 M_{\odot}$--including brown dwarves, rogue stars, and exotic objects like MACHOs or primordial black holes. The CHIME telescope, a widefield low-frequency radio interferometer operating over the frequency range of 400-800 MHz, detects several FRBs every day, and I will describe the status of our search for a lensed FRB. Our coherent time-domain search uses data from the CHIME/FRB baseband system and a procedure similar to geodetic VLBI cross-correlation. This allows us to resolve images with $10^{-8}$ to $10^{-1}$ second lensing delays, and disentangles intrinsic FRB morphology from genuine multipath propagation induced by a lens. [Preview Abstract] |
Sunday, April 18, 2021 4:09PM - 4:21PM Live |
L09.00003: Relativistic Stream Collisions in Tidal Disruption Events Gauri Batra, Wenbin Lu, Sterl Phinney In a tidal disruption event (TDE), a star approaching a black hole is torn apart by the black hole's tidal force, resulting in the squeezing of the star to form a stream of tidally disrupted material. Some of this material is bound and keeps orbiting the black hole while some is unbound and escapes. To understand the outcome of TDEs, it is crucial to find where the bound stream intersects itself since intersection can lead to potentially observable shocks, accretion disks and secondary outflows. We compute the intersection points for a Schwarzschild (non-spinning) black hole and a Kerr (spinning) black hole, first for the equatorial case where the stream lies in a plane and then for the general case where the stream evolution is in three dimensions. We numerically integrate the geodesic equations of motion to find the path of the stream and discuss the algorithm used to find the region of self-intersection. This algorithm takes into account various aspects of the model including stream thickness and energy distribution of the stream material. As a result, we obtain the dependence of the self-intersection region on multiple parameters such as angular momentum, black hole spin, and stream thickness. [Preview Abstract] |
Sunday, April 18, 2021 4:21PM - 4:33PM Live |
L09.00004: The Distribution of Inclinations of TDEs by Kerr Black Holes Michael Kesden, Thomas DeMastri A tidal disruption event (TDE) occurs when a star wanders close enough to a supermassive black hole (SBH) for its tidal fields to overwhelm the star's self gravity. Some of the resulting stellar debris can be accreted by the SBH to power a bright electromagnetic flare. The orbital angular momentum of the tidally disrupted star will generally be inclined with respect to the SBH spin which may have several observational consequences for the resulting TDE including delayed circularization and accretion of the tidal debris, (2) quasi-periodic oscillations of emission for the accretion disk, and (3) varying energy available to power luminous emission. We calculate, as a function of SBH mass and spin, the distribution of TDE inclinations which results from a complicated interplay between spin-dependent tidal forces, the spin-dependent threshold for direct capture by the event horizon, and two-body stellar relaxation. We find that the inclination distribution is biased towards prograde inclinations in the full loss-cone limit at low SBH masses, flips towards a retrograde bias at intermediate SBH masses where the stronger tidal forces on retrograde orbits dominate, and then returns to a strong prograde bias at higher masses where all retrograde orbits lead to direct capture. [Preview Abstract] |
Sunday, April 18, 2021 4:33PM - 4:45PM Live |
L09.00005: More than Meets the Eye: The Evolution of Gamma-ray Burst Jets, and its Effect on the High Redshift Star Formation Rate. Nicole Lloyd-Ronning, Aycin Aykutalp, Jarrett Johnson, Valeria U. Hurtado, Chiara Ceccobello There is tantalizing evidence that the jets launched from gamma-ray bursts are narrower (more tightly collimated) at higher redshifts. This has important implications not only for the physics of the jet launch itself, but also on estimates of the high redshift star formation rate. We present observational evidence for anti-correlation between gamma-ray burst jet opening angle and redshift, discuss the potential physical mechanisms responsible for this correlation, and - finally - provide estimates of the high redshift star formation rate accounting for this important effect. [Preview Abstract] |
Sunday, April 18, 2021 4:45PM - 4:57PM Live |
L09.00006: A Probabilistic Approach to Estimating the Unknown Redshifts of BATSE Catalog Long-duration Gamma-Ray Bursts Joshua Osborne, Amir Shahmoradi, Robert Nemiroff Gamma-Ray Bursts (GRBs) are some of the most energetic explosions in the universe, releasing energies on the order of 10$^{\mathrm{52}}$ ergs, within a fraction of a second to minutes in the form of gamma rays. To understand the intrinsic properties of these bursts we must first determine the distance at which these bursts occur using what is known as the cosmological redshift. Here we present a purely probabilistic approach to estimating the redshifts of 1366 Long-duration GRBs (LGRBs) as observed by the Burst And Transient Source Experiment (BATSE). This is accomplished through a careful selection and modeling of the 5-dimensional space of redshift and the four intrinsic prompt gamma-ray emission properties: the isotropic 1024ms peak luminosity (L$_{\mathrm{iso}})$, the total isotropic emission (E$_{\mathrm{iso}})$, the spectral peak energy (E$_{\mathrm{pz}})$, as well as the intrinsic duration (T$_{\mathrm{90z}})$, while simultaneously taking into account the affects of the detector mechanism of BATSE and sample incompleteness in our dataset. We make two fundamental assumptions in our work: \textbf{1.} LGRBs trace, either exactly or closely, the Cosmic Star Formation Rate and \textbf{2.} the joint 4-dimensional distribution of the aforementioned prompt gamma-ray emission properties are well-described by a multivariate log-normal distribution. The results of our work are vastly different from those of other works, likely due to the affects of the detector threshold and sample-incompleteness on shaping the previous phenomenologically-proposed high-energy correlations in the literature. [Preview Abstract] |
Sunday, April 18, 2021 4:57PM - 5:09PM Live |
L09.00007: Extragalactic Magnetar Giant Flares are a Source of Gamma-Ray Bursts Eric Burns Cosmological gamma-ray bursts (GRBs) are flashes of high-energy radiation from the distant universe. They are known to arise from two distinct progenitor channels: short GRBs predominantly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called Magnetar Giant Flares (MGFs). Three have been observed from the Milky Way and its satellite galaxies and they have long been suspected to contribute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of 4 local (<5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment to nearby star-forming galaxies, their rise time and isotropic energy release are independently inconsistent with the larger short GRB population at >99.9\% confidence. These properties, the host galaxies, and non-detection in gravitational waves all point to an extragalactic MGF origin. Despite the small sample, the volumetric rates place MGFs as the dominant gamma-ray transient detected from extragalactic sources. These rates imply that some magnetars produce multiple MGFs, providing a source of repe [Preview Abstract] |
Sunday, April 18, 2021 5:09PM - 5:21PM Live |
L09.00008: Search for Nearby Neutron Star Mergers via Radio Flares Kyung-hwan Lee, Imre Bartos, George Privon, Jonah rose, Paul Torrey The multi-messenger discovery of the neutron star merger GW170817 showed that nearby mergers may be common. However, this merger probably would have not been identified as nearby without its gravitational wave detection, raising the possibility that other nearby events may be hiding in plain sight. A possibility to uncover such nearby mergers from the past to search for their radio emission that can last for decades. Here we discuss the possibility that the radio transient FIRST J1419$+$3940, first observed in 1993 and still detectable, could have originated from a neutron star merger. I will show that its observed radio light curve is well reproduced by a merger model with astrophysically expected parameters. I will discuss clues that could differentiate the transient's neutron star merger origin from the alternative explanation---the afterglow of an off-axis long gamma-ray burst. Existing radio surveys likely already recorded multiple radio flares, informing us of the origin and properties of neutrons tar mergers and their role in the nucleosynthesis of the heaviest elements in the Universe. [Preview Abstract] |
Sunday, April 18, 2021 5:21PM - 5:33PM Live |
L09.00009: A numerical approach to the Klein-Nishina corrections of radiative cooling in relativistic outflows Jesús Rueda-Becerril In relativistic outflows like those seen in blazars, GRBs or PWNe, it is highly probable that ultrarelativistic particles interact with photons in their environment through scattering, known as inverse Compton. The classical regime of such scattering is known as the Thomson regime, characterized for efficiently cooling particles. If the energy of the charged particle is smaller than the energy of the interacting photon, the scattering process enters into the so-called Klein-Nishina (KN) regime. Thomson regime cooling predicts a soft high-energy end of particle energy distributions. However, observations have dropped that some sources show hard spectral indices at high frequencies. This has led to think that maybe particles are not being cooled down efficiently. Asymptotic approximations of the Klein-Nishina regime have been formulated in the last decades in order to account for these corrections in the distribution of particles responsible for the observed spectrum of high energy sources. In this work we present a numerical approach of the KN corrections to particle radiative cooling, and apply it to astrophysical scenarios like GRBs. We show the observational implications by showing the multi-wavelength spectra and light curves of these objects. [Preview Abstract] |
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