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• Siraprapa Sanpa-arsa --- Green Bank Telescope (GBT) Radio Millisecond Pulsars Searches in Fermi unassociated LAT sources.  Abstract

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  After Fermi launched in 2008, it has revolutionized gamma-ray pulsar astronomy, by enabling the discovery of many new millisecond pulsars (MSPs). The Fermi Pulsar Search Consortium (PSC) has organized hundreds of radio observations of pulsar-like Large Area Telescope (LAT) unassociated gamma-ray sources. In about 4 years, the PSC has discovered 64 new MSPs. These new discoveries number more than all MSPs in the first 20 years (from 1982 to 2002) of MSP searching combined. Notably, among the 64 new MSPs, there are at least 13 “black widows” and 4 “redbacks” (the rare populations of eclipsing pulsar binaries). As one of the PSC radio telescopes, the Green Bank Telescope (GBT) has, outstandingly, helped uncover 35 new MSPs. By searching more Fermi unassociated sources from the LAT 1-year, 2-year and soon 3-year Point Source Catalog, the GBT will almost certainly discover additional MSPs. The newly discovered MSPs will provide more potential additions to the pulsar timing arrays (like NANOGrav) as well as improve the understanding of MSP formation and evolution.

  
  

• Andrew McCann --- VHE Emission from Gamma-ray pulsars.  Abstract

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  NASA's Fermi space telescope has provided us with a bountiful new population of gamma-ray sources following its discovery of 140 new gamma-ray pulsars. One common feature exhibited by all of these pulsars is the form of their spectral energy distribution, which can be described by a power law followed by a spectral break occurring between ~1 and ~8 GeV. The unanimity of the break energy across the entire Fermi pulsar sample suggests that the sites of acceleration and processes of gamma-ray emission are common across the different pulsar types. The common wisdom is that the break is followed by an exponential cut-off driven by radiation/reaction-limited curvature emission. The discovery of pulsed gamma rays from the Crab pulsar, the only pulsar so far detected at very high energies (E>100GeV), contradicts this "cut-off" picture. In this talk I will review, from an observational stand point, what we know about the emission of pulsars at VHE energies.

  
  

• 1 Slide:
  • Jezebel Rodriguez Garcia (pdf)
    
  • Ori Weiner (pdf)
    
  • Juliana Vievering (ppt)
    
  • Stanislav Stefanik (pdf)
    

Wed. June 4

• Björn Ahlgren --- Photospheric emission in gamma-ray bursts.  Abstract

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  This is a short review of the current status of the research on photospheric prompt emission in gamma-ray bursts (GRBs). While GRB spectra are usually fitted with Band functions, these give little understanding of the underlying emission mechanisms, which has prompted several new approaches to the problem. With the analysis of FERMI data and numerical simulations of GRB prompt emission, the aim is to be able to produce both light curves and spectral curves and to be able to fully explain the phenomenon. In this talk I will focus on models for subphospheric dissipation, in which dissipation of kinetic energy below the photosphere gives rise to spectra which can differ significantly from a simple blackbody. In particular, I will discuss how different parameters such as the Lorentz factor and the optical depth at which the dissipation occurs affect the resulting spectra. My current work involves fitting such models to data for the first time.

  
  

• Lee Yacobi --- Constraints on the hadronic content of Fermi GRBs.  Abstract

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  Recently the Fermi-LAT has detected approximately 35 GRBs with gamma ray emission above 100 GeV.  Several models have been proposed to explain this high-energy emission, including hadronic models, where photon-hadron process produces charged pions and subsequently the 100 TeV neutrinos. We are using the data from Fermi-GBM to calibrate the photon (representing electrons) energy content of the GRB jet. Given the non-detection of GRB neutrinos, we aim to put upper limits on the proton (turned pion) energy content. The same photon-hadron process that is expected to produce the charged pions and subsequently the 100 TeV neutrinos, would also generate neutral pions that decay to photons of similar energy. These high-energy photons have been hypothesized to cascade through pair production processes down to the GeV regime, where they can escape the jet and be observed by Fermi-LAT. These high-energy photons have been hypothesized to cascade through pair production processes down to the GeV regime, where they can escape the jet and be observed by Fermi-LAT. Within this scenario, we are using the observed GeV photon fluence to put another upper limit on the energy content of the protons in the jet. Within this scenario, we are using the observed GeV photon fluence to put another upper limit on the energy content of the protons in the jet.

  
  

• Henrike Fleischhack --- A template method for measuring the iron spectrum in cosmic rays with Cherenkov telescopes.  Abstract

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  The energy-dependent abundance of elements in cosmic rays is an important part of the understanding of acceleration and propagation of cosmic rays. Imaging Air Cherenkov Telescopes, used mainly in gamma ray astronomy, can measure the direct Cherenkov light emitted by heavy nuclei as well as the Cheronkov light emitted by their air showers. Thus they are sensitive to the charge of the primary particles. I will introduce a template method that can be used to reconstruct charge and energy of primary particles simultaneously. With this, we can separate heavy nuclei from lighter cosmic rays, and thus measure the abundance and spectrum of these nuclei in the range of tens to hundreds of TeV.

  
  

• 1 Slide:
  • Kimberly Zoldak
  • Ramesh Koirala
  • James Lau

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