Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session M18: Active Galactic Nuclei |
Hide Abstracts |
Sponsoring Units: DAP Chair: Robert Lauer, University of New Mexico Room: 251F |
Sunday, April 17, 2016 3:30PM - 3:42PM |
M18.00001: Probing the magnetic field structure in Sgr~A${}^*$ on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations Roman Gold, Jonathan McKinney, Michael Johnson, Sheperd Doeleman Accreting black holes (BHs) are at the core of relativistic astrophysics as messengers of the strong-field regime of General Relativity and prime targets of several observational campaigns, including imaging the black hole shadow in SagA* and M87 with the Event Horizon Telescope. I will present results from general-relativistic, polarized radiatiative transfer models for the inner accretion flow in Sgr A*. The models use time dependent, global GRMHD simulations of hot accretion flows including standard-and-normal-evolution (SANE) and magnetically arrested disks (MAD). I present comparisons of these synthetic data sets to the most recent observations with the Event Horizon Telescope and show how the data distinguishes the models and probes the magnetic field structure. [Preview Abstract] |
Sunday, April 17, 2016 3:42PM - 3:54PM |
M18.00002: Small Seed Black Hole Growth in Various Accretion Regimes Hannalore J. Gerling-Dunsmore, Philip F. Hopkins Observational evidence indicates a population of super massive black holes (SMBHs) ($\sim10^9 - 10^{10} M_{\odot}$) formed within 1 Gyr after the Big Bang. One proposed means of SMBH formation is accretion onto small seed black holes (BHs) ($\sim100 M_{\odot}$). However, the existence of SMBHs within 1 Gyr requires rapid growth, but conventional models of accretion fail to grow the seed BHs quickly enough. Super Eddington accretion ($\dot{M} > \dot{M}_{Eddington}$) may aid in improving growth efficiency. We study small seed BH growth via accretion in 3D, using the magneto-hydrodynamics+gravity code GIZMO. In particular, we consider a BH in a high density turbulent star-forming cloud, and ask whether or not the BH can capture sufficient gas to grow rapidly. We consider both Eddington-limited and super Eddington regimes, and resolve physics on scales from 0.1 pc to 1 kpc while including detailed models for stellar feedback physics, including stellar winds, supernovae, radiation pressure, and photo-ionization. We present results on the viability of different small seed BHs growing into SMBH candidates. [Preview Abstract] |
Sunday, April 17, 2016 3:54PM - 4:06PM |
M18.00003: Exceptional X-ray Weak Quasars and Their Implications for Accretion Flows, Winds, and Broad Line Regions William Brandt, Bin Luo, Patrick Hall, Jianfeng Wu Actively accreting supermassive black holes (SMBHs) are found, nearly universally, to create luminous X-ray emission. However, there are apparent X-ray weak exceptions to this rule that are now providing novel insights, including many weak-line quasars (WLQs). We have been systematically studying such X-ray weak quasars with Chandra observations and near-infrared spectroscopy, and I will report results on their remarkable properties and describe implications for models of the accretion disk/corona, quasar winds, and emission-line formation. We have found evidence that many of these WLQs have geometrically thick inner accretion disks, likely due to high Eddington ratios, that shield the high-ionization broad line region from the relevant ionizing continuum. This basic model can explain, in a unified manner, the weak lines and diverse X-ray properties of WLQs. Such shielding may, more generally, play a significant role in shaping the broad distributions of quasar emission-line equivalent widths and blueshifts. An expectation of our model is that WLQs should be more common at high redshift, and they may serve as a signature of rapid SMBH growth at early cosmic times. I will end by discussing some promising ongoing studies that are extending these ideas. [Preview Abstract] |
Sunday, April 17, 2016 4:06PM - 4:18PM |
M18.00004: Spectacular variability of gamma-ray emission in blazar 3C279 during the large outburst in June 2015 Grzegorz Madejski, Masaaki Hayashida, Katsuaki Asano, David Thompson, Krzysztof Nalewajko, Marek Sikora The most luminous celestial extragalactic sources of persistent gamma-ray emission are active galaxies with relativistic jets pointing towards the observer. Those are commonly called blazars, and Flat Spectrum Radio Quasar 3C 279 has been one of the brightest gamma-ray blazars in the sky. In Dec. 2013, April 2014, and June 2015 it showed powerful outbursts with the gamma-ray flux at $E > 100$ MeV higher than 1e-5 ph/cm$^2$/s, measured by the Fermi-LAT gamma-ray detector. The Dec. 2013 outburst showed an unusually hard power-law gamma-ray spectrum (photon index $\sim$1.7), and an asymmetric light curve profile with a few-hour time scale variability. The June 2015 outburst was extreme, with a record-breaking $E > 100$ MeV flux of 4e-5 ph/cm$^2$/s, more than $10\times$ higher than the average gamma-ray flux of the Crab Nebula. The high flux prompted a Fermi-LAT Target of Opportunity pointing observation. The increase of exposure and the very high flux state of the source allowed us to resolve the gamma-ray flux on a sub-orbital time scales, revealing variability on time scales of tens of minutes. Here, we present the observational results of those outbursts from 3C279 with a focus on detailed analysis of the 2015 June outburst. [Preview Abstract] |
Sunday, April 17, 2016 4:18PM - 4:30PM |
M18.00005: ABSTRACT MOVED TO T1.058 |
Sunday, April 17, 2016 4:30PM - 4:42PM |
M18.00006: ABSTRACT WITHDRAWN |
Sunday, April 17, 2016 4:42PM - 4:54PM |
M18.00007: Highlights of recent results from the VERITAS Active Galactic Nuclei Observing Program Udara Abeysekara Active Galactic Nuclei (AGN) are the dominant class of the Very High Energy (VHE) gamma-ray sources. The VERITAS Observatory dedicates about 430 hr/year of dark time and 200 hr/year of observations under moonlight, on the AGN observing program. VERITAS is located at the Fred Lawrence Whipple Observatory near Tucson, Arizona, and is sensitive to gamma rays with energies between of 85 GeV and 30 TeV. VERITAS became fully operational in 2007, and has since then detected 34 very high energy (VHE) AGN. The majority of the detected galaxies are blazars, in addition to a few radio galaxies. The VHE emission mechanism, and the location of the VHE emission zone of AGN are still poorly understood. Detailed observations of VHE AGN are necessary for understanding these uncertainties. AGN are plausible source candidates for ultra-high-energy cosmic rays and astrophysical neutrinos. VHE gamma-rays from AGN can also be used as probes to place limits on extragalactic background light density. This presentation will report the most recent results from the VERITAS AGN program including newly discovered AGN, and VHE flares of known TeV AGN. [Preview Abstract] |
Sunday, April 17, 2016 4:54PM - 5:06PM |
M18.00008: Statistical Detection of Flaring Blazars with HAWC Thomas Weisgarber The High Altitude Water Cherenkov (HAWC) Observatory monitors gamma-ray blazars and other sources with unprecedented sensitivity for a TeV survey instrument. Due to its high duty cycle, HAWC facilitates unbiased studies of the flaring rates of blazars at the highest energies. We will describe a technique to search for sub-threshold events in the HAWC data in order to identify new transient sources and place limits on the flaring rates of known sources. We will also present initial results from a search of HAWC data using this method. [Preview Abstract] |
Sunday, April 17, 2016 5:06PM - 5:18PM |
M18.00009: Detection and Rapid Notification of Flaring Sources with HAWC Ian Wisher We will present a method for rapid detection and notification of flaring states of blazars using the High Altitude Water Cherenkov (HAWC) Observatory. The HAWC detector is an extensive air shower instrument with a high duty cycle, large field of view, and extraordinary sensitivity to TeV gamma rays. This allows HAWC to perform unbiased monitoring of a large number of different sources for flaring states and catch rare events. Once a flaring state is detected, rapid notifications can be sent to other observatories to facilitate follow-up observations and multi-wavelength measurements. In addition to presenting the sensitivity of the method, we will also present results from a search for blazar flares with HAWC data taken to date. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700