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 R13: Fermi-HAWC-VERITASFocus
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Sponsoring Units: DAP Chair: Udara Abeysekara, University of Utah Room: 250F |
Monday, April 18, 2016 10:45AM - 10:57AM |
R13.00001: TeV Gamma-Ray Observations of Geminga with HAWC Hao Zhou Geminga is a radio-quiet pulsar that was first detected at GeV energies. Its pulsations were first discovered in X-rays. It is one of the closest middle-aged pulsars at approximately 250 parsecs from Earth. The Geminga pulsar is one of the brightest sources in the GeV sky but there is no unambiguous evidence for the existence of a pulsar wind nebula at GeV energies. Milagro reported an extended TeV source spatially consistent with Geminga, but IACT observations using standard analysis techniques have only provided upper limits. Geminga has been interpreted as a nearby cosmic-ray accelerator, which would possibly explain the observed multi-GeV positron excess. TeV observations of Geminga are crucial to test this interpretation. The High Altitude Water Cherenkov (HAWC) Observatory, located at 4100 m above see level in central Mexico, is sensitive to gamma rays between 100 GeV and 100 TeV. Thanks to its large field of view of 2 steradians, HAWC has a good sensitivity to extended sources. We will present the preliminary results for TeV gamma-ray emission from Geminga from HAWC data. Spectral and morphological analyses are on-going with a growing data set. [Preview Abstract] |
Monday, April 18, 2016 10:57AM - 11:09AM |
R13.00002: VERITAS Observations of the Cygnus Region of the Galaxy Ralph Bird The Cygnus region is a very active region of our Galaxy, with many sources of GeV and TeV gamma-ray emission, such as supernova remnants, pulsar wind nebulae, high mass X-ray binaries and massive star clusters. A detailed study of the Cygnus region can give insight into the processes of particle acceleration in astrophysical sources. VERITAS is an array of four 12-meter diameter imaging atmospheric Cherenkov telescopes located at Mt. Hopkins, AZ, USA. From 2007 through 2012 nearly 300 hours of data was gathered in the Cygnus region, covering 67 to 83 degrees Galactic longitude and -2 to 5 degrees in Galactic latitude. An update of the Fermi-LAT and VERITAS analysis of this region is presented. In particular we examine the source and hotspot regions within the Milagro dataset covering this region and the comparison between these objects in the three different instruments. [Preview Abstract] |
Monday, April 18, 2016 11:09AM - 11:21AM |
R13.00003: Scrutinizing the gamma-ray sky for dark matter subhalos Daniel Nieto Castano Galactic dark matter subhalos are promising targets for dark matter searches in the gamma-ray band. Unlike other more conventional targets, like dwarf spheroidal galaxies, galaxy clusters, or the Galactic Center and Halo, the locations of these hypothetical sources remain unknown. Under the assumption of a self-annihilating dark matter particle of mass above 100 GeV, dark matter subhalos may emerge in the gamma-ray sky as sources without counterpart at longer wavelengths. Gamma-ray instruments mapping large fractions of the sky, like the LAT on board the {\em Fermi} satellite and the HAWC observatory, are well suited to pinpoint the locations of these sources, while imaging atmospheric Cherenkov telescopes like VERITAS offer the possibility of deeper follow-up observations for a better spectral characterization. We elaborate on the synergy between the before-mentioned instruments regarding searches for dark matter subhalos and present the results of VERITAS observations on an intriguing dark matter subhalo candidate from the Fermi-LAT Second Point Source Catalog. [Preview Abstract] |
Monday, April 18, 2016 11:21AM - 11:33AM |
R13.00004: Gamma-ray Monitoring of Active Galactic Nuclei with HAWC Robert Lauer Active Galactic Nuclei (AGN) are extra-galactic sources that can exhibit extreme flux variability over a wide range of wavelengths. TeV gamma rays have been observed from about 60 AGN and can help to diagnose emission models and to study cosmic features like extra-galactic background light or inter-galactic magnetic fields. The High Altitude Water Cherenkov (HAWC) observatory is a new extensive air shower array that can complement the pointed TeV observations of imaging air Cherenkov telescopes. HAWC is optimized for studying gamma rays with energies between 100 GeV and 100 TeV and has an instantaneous field of view of \textasciitilde 2 sr and a duty cycle \textgreater 95{\%} that allow us to scan 2/3 of the sky every day. By performing an unbiased monitoring of TeV emissions of AGN over most of the northern and part of the southern sky, HAWC can provide crucial information and trigger follow-up observations in collaborations with pointed TeV instruments. Furthermore, HAWC coverage of AGN is complementary to that provided by the Fermi satellite at lower energies. In this contribution, we will present HAWC flux light curves of TeV gamma rays from various sources, notably the bright AGN Markarian 421 and Markarian 501, and highlight recent results from multi-wavelengths and multi-instrument studies. [Preview Abstract] |
Monday, April 18, 2016 11:33AM - 11:45AM |
R13.00005: The Gamma-ray opacity of the Universe: New Results and Future Outlook Marco Ajello The extragalactic background light comprises the emission from all stars and accreting compact objects in the observable Universe. Gamma-ray telescopes have the capabilities of probing the density of the EBL via the detection of the attenuation that the EBL leaves in the spectra of cosmic gamma-ray sources. Here we will report on past and future measurements of the EBL using Fermi and on the potential synergy between Fermi, HAWC and VERITAS and how that can be harvested to produce a coherent picture of the EBL and of its evolution with cosmic time. [Preview Abstract] |
Monday, April 18, 2016 11:45AM - 11:57AM |
R13.00006: Probing the Extragalactic Background Light in the Fermi-VERITAS-HAWC Era Elisa Pueschel The observed spectra of active galactic nuclei carry the imprint of gamma-ray interactions with the extragalactic background light (EBL). As gamma rays from an extragalactic source travel to the observer, pair production on the EBL plays a role in reprocessing the photons to lower energies, obscuring the intrinsic source spectrum. An overview of recent EBL constraints, which use blazar spectral measurements to constrain the EBL’s spectral energy distribution, will be presented. Prospects for future EBL measurements capitalizing on the synergy between the Fermi-LAT, VERITAS and HAWC instruments will be discussed. [Preview Abstract] |
Monday, April 18, 2016 11:57AM - 12:33PM |
R13.00007: New Opportunities and Challenges in Gamma Ray Astrophysics Invited Speaker: Roger Blandford Recent, exciting discoveries by LIGO, IceCube and the Parkes Radio Telescope together with an increasingly sophisticated program of multi-wavelength monitoring of the established cosmic transients, present fresh opportunities and challenges to gamma ray observatories.Their large etendue and microsecond timing make them key steps along the path to source identification and modeling. Highly variable, relativistic sources point to the need for new mechanisms through which electromagnetic energy can be rapidly converted into gamma rays, a process called, generically, magnetoluminescence. [Preview Abstract] |
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