Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session G3: Extragalactic Gamma-Ray Sources |
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Sponsoring Units: DAP Chair: Brenda Dingus, Los Alamos National Laboratory Room: Thurgood Marshall South |
Sunday, February 14, 2010 8:30AM - 9:06AM |
G3.00001: Highlights from Fermi Gamma-Ray Space Telescope observations of Gamma-Ray Bursts Invited Speaker: The Fermi Gamma-Ray Space Telescope has more than doubled the number of Gamma-Ray Bursts (GRBs) detected at high energies ($>100\;$MeV) within its first year of operation. Thanks to the very wide energy range covered by Fermi's Gamma-ray Burst Monitor (GBM; $8\;$keV to $40\;$MeV) and Large Area Telescope (LAT; $25\;$MeV to $>300\;$GeV) it has measured the prompt GRB emission spectrum over an unprecedentedly large energy range (from $\sim 8\;$keV to $\sim 30\;$GeV). I will present highlights from Fermi GRB observations focusing mainly on the prompt emission phase. Interesting new observations will be discussed along with some of their possible implications, including: (i) What can we learn from the Fermi-LAT GRB detection rate, (ii) A limit on the variation of the speed of light with photon energy (for the first time beyond the Planck scale for a linear energy dependence from direct time of arrival measurements), (iii) Lower-limits on the bulk Lorentz factor of the GRB outflow (of $\sim 1000$ for the brightest Fermi LAT GRBs), (iv) The detection (or in other cases, lack thereof) of a distinct spectral component at high (and sometimes also at low) energies, and possible implications for the prompt GRB emission mechanism, (v) The later onset (and longer duration) of the high-energy emission ($>100\;$MeV) compared to the low-energy ($< 1\;$MeV) emission that is seen in most Fermi-LAT GRBs. [Preview Abstract] |
Sunday, February 14, 2010 9:06AM - 9:42AM |
G3.00002: Multiwavelength observations of Fermi blazars Invited Speaker: Multiwavelength observations of blazars have entered a new era with the launch and successful operation of the Fermi Gamma-ray Space Telescope. With concurrent monitoring programs spanning decades of energies from radio through gamma-rays, the characteristic double-peaked spectral energy distribution (SED) of blazars can be observed evolving on timescales from days to months (and ultimately to years). The low energy peak of the SED is well understood as synchrotron emission from electrons accelerated in a relativistic jet; however, the source of the high-energy emission is as yet poorly understood with multiple models often able to fit a given single-epoch SED. With both spectral and time-variability information available for a large number of sources, physical models for gamma-ray emission can be more effectively constrained. I will discuss recent and ongoing observations of blazars with Fermi, associated multiwavelength campaigns, and theoretical implications of these observations. [Preview Abstract] |
Sunday, February 14, 2010 9:42AM - 10:18AM |
G3.00003: TeV Observation of Extragalactic Gamma-Ray Sources Invited Speaker: The recent years have brought incredible progress observing the gamma-ray sky above 100\,GeV. One of the reasons is that Cherenkov telescopes such as H.E.S.S., MAGIC, and VERITAS have come online with ten times higher sensitivity in comparison to their predecessors and with an expanded energy range. These improvements resulted in a jump in the number of detected extragalactic sources, which now also includes two starburst galaxies, the first non-blazars in the extragalactic VHE sky. Furthermore, variability can and has been observed down to timescales of a few minutes in the some of the strongest sources. Correlation studies with other wavelengths have continued to prove to be a powerful tool and in some cases provided interesting constraints on the origin of the gamma-rays and their emission mechanisms. Gamma-rays from extragalactic objects also provide insight into some questions in cosmology. I will review the recent progress that has been made by observations of the extragalactic sky with imaging atmospheric Cherenkov telescopes. [Preview Abstract] |
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