The Very High Energy Gamma-Ray Spectra of AGN

Martin Schroedter

T.C.Weekes, Thesis Advisor

Department of Physics, 

The University of Arizona

September 2004 

Astronomy and Astrophysics, v.423, p.415-419 (2004).

arXiv:astro-ph/0405513

Abstract:  A reanalysis of data taken on the Cygnus region in 1989-90 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032+4130 source reported by the Crimean Astrophysical Observatory and published by the HEGRA Collaboration. The significance at the a priori HEGRA position is 3.3σ. The peak signal was found at RA = 20h32m, Dec = +41^o33'. This is 0.6^o north of Cygnus X-3 which was the original target of the observations. The flux level (12% of the level of the Crab Nebula) is intermediate between the two later observations and suggests that the TeV source is variable.

The Astrophysical Journal, Volume 610, Issue 1, pp. 156-160.
 

Abstract:  We present results from observations taken with the Whipple 10 m very high energy γ-ray telescope with maximal sensitivity at 400 GeV during 39 hr between 2000 and 2003 in the direction of the giant radio galaxy M87. Using the entire data set, we derive a 99% confidence level upper limit on the flux of γ-ray emission above 400 GeV from M87 to be <=6.9×10-12 cm-2 s-1. This suggests variability at the 90% confidence level when compared to the flux measured by the HEGRA collaboration in 1999 if the differential spectrum is steeper than a power law of index 3.75. Our search for a correlation between the Rossi X-Ray Timing Explorer all-sky monitor observation and a potential γ-ray signal is inconclusive.

The Astrophysical Journal, Volume 608, Issue 2, pp. L97-L100.

arXiv:astro-ph/0403422

Abstract:  We report a possible detection of TeV gamma rays from the Galactic center by the Whipple 10 m gamma-ray telescope. Twenty-six hours of data were taken over an extended period from 1995 through 2003 resulting in a total significance of 3.7 σ. The measured excess corresponds to an integral flux of 1.6×10-8+/-0.5×10^-8 (stat)+/-0.3×10^-8 (sys) photons m^-2 s^-1 above an energy of 2.8 TeV, roughly 40% of the flux from the Crab Nebula at this energy. The 95% confidence region has an angular extent of about 15' and includes the position of Sgr A*. The detection is consistent with a point source and shows no evidence of variability.