Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session H7: Extragalactic Astronomy and Gamma Ray Bursts |
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Sponsoring Units: DAP Chair: Elizabeth Hays, NASA Goddard Space Flight Center Room: Embassy D |
Sunday, April 1, 2012 10:45AM - 10:57AM |
H7.00001: Rapid TeV Gamma-Ray Variability of Active Galactic Nuclei: the Case of BL Lacertae Wei Cui Gamma-ray emitting active galactic nuclei (AGN) are characterized by variability on a wide range of timescales across nearly the entire electromagnetic spectrum. This is an indication of the dominant role that the jet plays in radiation production. The variability provides a valuable tool to study, in a relatively model-independent way, the emission processes and geometry as well as the energetics of the jet in AGN. Here, we present the discovery of a rapid TeV gamma-ray flare from BL Lacertae with VERITAS. It is the first low-frequency peaked BL Lac object that shows the phenomenon. We discuss the implications of the observation. [Preview Abstract] |
Sunday, April 1, 2012 10:57AM - 11:09AM |
H7.00002: The Impact of Gamma-ray Halos on the Angular Anisotropy of the Extragalactic Gamma-ray Background Tonia Venters, Vasiliki Pavlidou The study of the development of electromagnetic cascades in intergalactic magnetic fields (IGMF) serves as a robust probe into the strength and structure of these magnetic fields. Charged particles in electromagnetic cascades are deflected by magnetic fields giving rise to gamma-ray halos around extragalactic sources of VHE gamma rays (e.g., BL Lacertae-type objects). Such gamma-ray halos can have a profound impact on the intensity and angular properties of the contribution of extragalactic VHE sources to the extragalactic gamma-ray background (EGB) as measured by the Fermi-LAT at GeV energies. We demonstrate the impact of the deflection of cascades by the IGMF on the collective spectrum of extragalactic VHE sources, as well as the impact on the angular anisotropy of the EGB as a function of energy. [Preview Abstract] |
Sunday, April 1, 2012 11:09AM - 11:21AM |
H7.00003: Radio continuum emission and HI gas accretion in the NGC 5903/5898 compact group of galaxies Paul Wiita, Gopal Krishna, Mukul Mhaskey We investigate the nature of the multi-component radio continuum and HI emission associated with the nearby galaxy group comprised of two dominant ellipticals, NGC 5898 and NGC 5903 and a dwarf lenticular ESO514-G003. Striking new details of radio emission come from the ongoing TIFR.GMRT.SKY.SURVEY (TGSS) which provides images with a resolution of $\sim 24^{\prime \prime} \times 18^{\prime \prime}$ and rms noise of 5 mJy at 150 MHz. Previous observations of this compact triplet include images at higher frequencies of the radio continuum as well as huge HI trails originating from the vicinity of NGC 5903. The TGSS 150 MHz image has revealed a large asymmetric radio halo around NGC 5903 and also established that the dwarf SO galaxy ESO514$-$G003 is the host to a previously known bright double radio source. The radio emission from NGC 5903 is found to have a very steep radio spectrum ($\alpha \sim -1.5$) and to envelope a network of radio continuum filaments bearing a spatial relationship to the HI trails. Both its radio loud members are also the only galaxies that are seen to be connected to an HI filament. This correlation is consistent with the premise that cold gas accretion is of prime importance for triggering powerful jet activity in the nuclei of early-type galaxies. [Preview Abstract] |
Sunday, April 1, 2012 11:21AM - 11:33AM |
H7.00004: Stellar-mass compact object evolution from the deepest X-ray surveys of the extragalactic Universe Ann Hornschemeier, Bret Lehmer The ever-increasing depth of X-ray surveys raises the possibility of detecting extremely X-ray faint source populations, including the X-ray faint early-type galaxy population. Such a population of galaxies presents the opportunity to study the long-term evolution of low-mass X-ray binary (LMXB) populations. To this end, we have assembled a sample of $\sim 400$ low-luminosity early-type galaxies over $0.05 < z < 1.2$ in the three deep {\it Chandra} surveys (the CDF-S, E-CDF-S and CDF-N). Even with the 4~Ms {Chandra} Deep Field coverage currently available, the deepest survey of the extragalactic sky ever conducted at X-ray wavelengths, the vast majority of these galaxies ($>90$\%) are undetected, so our work relies heavily on stacking analysis. We compare our observational constraints with new theoretical models and discuss possibilities for future deep X-ray observations. [Preview Abstract] |
Sunday, April 1, 2012 11:33AM - 11:45AM |
H7.00005: Fermi Observations of Gamma-ray Bursts Julie McEnery The Fermi Gamma-ray Space Telescope, launched in June 2008, is a satellite based observatory to study the high energy gamma-ray sky. With their wide fields of view and enormous energy ranges, the two instruments on Fermi are especially well suited to the study of gamma-ray bursts - the brightest explosions in the Universe. The Gamma-ray Burst Monitor (GBM), with a $>$9 steradian field of view, is the most prolific detector of GRB currently in orbit and provides coverage from 8 keV to 40 MeV. The Large Area Telescope (LAT), also with a large ($>$2 steradian) field of view, provides ground-breaking high energy observations from 20 MeV to over 300 GeV. In this talk, I will describe the somewhat unexpected results revealed by Fermi observations of gamma-ray bursts and discuss how these have impacted our understanding of these exotic objects. [Preview Abstract] |
Sunday, April 1, 2012 11:45AM - 11:57AM |
H7.00006: Prospects for GRB detection with the HAWC scaler system Andreas Tepe, Ignacio Taboada HAWC, the High Altitude Water Cherenkov observatory, is a high energy cosmic gamma-ray detector. It is currently under construction at Sierra Negra in Mexico. Due to its very high duty cycle, the large effective area and extended sky coverage, HAWC is an ideal detector for transient gamma-ray emission. Gamma-ray burst (GRB) spectra are well known up to GeV energies. The HAWC scaler DAQ has a significant effective area down to 10GeV and is an excellent complementary system to existing detectors. This talk will demonstrate the prospects of the HAWC detector to detect GRBs and evaluate spectral their parameters at high energies. [Preview Abstract] |
Sunday, April 1, 2012 11:57AM - 12:09PM |
H7.00007: Recent Results from Gamma-ray-burst Neutrino Searches in IceCube Nathan Whitehorn IceCube, a cubic kilometer neutrino detector located in glacial ice at the South Pole, has recently become the first neutrino telescope with a sensitivity below the TeV-PeV neutrino flux predicted from gamma-ray bursts if GRBs are responsible for the observed extragalactic cosmic-ray flux. These neutrinos are produced in interactions between the accelerated cosmic ray protons and the photons present in the burst fireball, allowing neutrino observations to directly constrain or confirm proton acceleration in these sources. Recent results from searches for this flux using the IceCube detector will be presented, as well as implications of this result for cosmic-ray acceleration in GRBs and prospects for future searches. [Preview Abstract] |
Sunday, April 1, 2012 12:09PM - 12:21PM |
H7.00008: Probing cosmic baryons with X-ray spectroscopy of GRB afterglows Dieter Hartmann, Chryssa Kouveliotou, Jan-Willem den Herder, Luigi Piro, David Burrows, Takaya Ohashi Gamma-Ray Bursts (GRBs) provide a unique probe of the cosmic history of baryons from the first stars to the present epoch. Reconstructing the cosmic history of metals is a key observational challenge, which we plan to address with high resolution X-ray measurement. We also characterize the chemical composition of gas in clusters of galaxies and the Warm-Hot Intragalactic Medium (WHIM). Cluster measurements will take advantage of wide field of view telescopes. These goals can be fulfilled with a medium-size mission, proposed to ESA and NASA by an international consortium. The latest incarnation proposed to ESA is ORIGIN, which evolved from the EDGE and Xenia mission profiles and builds upon those previous concepts. The mission utilizes fast and autonomous satellite re-pointing following the detection of a GRB (this requires a sensitive hard X-ray detector with a large field of view) and a wide-field imaging spectrometer in the soft X-ray band. This measures the emission and absorption lines in hot and cold gas, providing diagnostics of temperature, ionization state, dynamics and abundances in clusters beyond their vir [Preview Abstract] |
Sunday, April 1, 2012 12:21PM - 12:33PM |
H7.00009: An New Analysis of Sloan Digital Sky Survey (SDSS) Data Alexander Mayer An analysis of SDSS data is presented, which challenges key assumptions underlying the standard cosmological model. In particular, easily-reproduced, statistically-significant empirical data for the theta-z relationship, the redshift-magnitude relationship and the AGN redshift-population density relationship are presented. These data do not conform with canonical predictions based on the Hubble expansion; they instead confirm a set of three interrelated predictive equations, which are based on a temporal relativistic interpretation of the cosmological redshift. [Preview Abstract] |
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