Engineering topics

Kerrick, A. D.

Publications and source records attributed to Kerrick, A. D..

3 records

NASA NTRS1995

Upper Limits on TeV Gamma-Ray Emission from Active Galactic Nuclei

The results of a search for TeV gamma-ray emission from 35 active galactic nuclei (AGNS) using the Whipple Observatory High Resolution Atmospheric Cerenkov Camera are reported. Fifteen of these objects have been detected at GeV energies by the EGRET experiment on the Compton Gamma Ray Observatory. None of the 35 objects gave a signal at the 3 sigma level; Mrk 421 remains the only AGN detected at TeV energies. The absence of a TeV signal may imply a change in the primary source spectrum and/or the effect of absorption by pair production on intergalactic infrared photons.

Kerrick, A. D.↗

NASA NTRS1995

An upper limit to the infrared background from observations of TeV gamma rays

An upper bound to the energy density of infrared background radiation is derived from considering the effect of gamma-gamma interactions on the observed TeV gamma-ray spectrum of the active galaxy Markarian 421. This upper bound proves to be the most restrictive for the wavelength range of 10-12 micrometers. These constraints are presently limited by the uncertainty of extrapolating the source spectrum from 5 to 500 GeV. Observations in the regime less than 100 GeV would significantly improve these limits, allowing for a wide range of IR production models to be constrained.

Biller, S. D.↗

NASA NTRS1995

Outburst of TeV photons from Markarian 421

Markarian 421, an active galactic nucleus (AGN) of the BL Lacertae type, is the closest Energetic Gamma Ray Experiment Telescope (EGRET)-detected AGN. It has been monitored by the Whipple Observatory very high energy gamma-ray telescope since its discovery at TeV energies, for approximately 90 nights, totaling 130 hours of observation. Observations from 1993 December 23 to 1994 May 10 showed an average sourve flux only half that of its 1992 discovery level. However, observations on 1994 May 14 and 15 show an increase in flux above this quiescent level by a factor of approximately 10. The timescale of this increase provides the best geometric constraint on the extent of TeV photon emission regions within AGNs. The observation of the high TeV flux occurred 1 day prior to the observation by ASCA of a very high 2-10 keV X-ray flux. This strong TeV outburst is reminiscent of the behavior seen for the stronger 100 MeV-GeV EGRET sources (e.g. 3C 279) but was not anticipated in view of the fact that the six EGRET observations of Mrk 421 from 1991 June to 1993 July showed no evidence for variability.

Kerrick, A. D.↗