Very High Energy Gamma-Ray Observations of Markarian 421

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Session 11 -- Luminous AGN and QSOs
Display presentation, Monday, 30, 1994, 9:20-6:30

[11.13] Very High Energy Gamma-Ray Observations of Markarian 421

J.A.Zweerink, A.Kerrick, P.Kwok, R.C.Lamb, D.A.Lewis, G.Mohanty (ISU), J.Buckley, M.Chantell, V.Connaughton, A.C.Rovero, T.C.Weekes (CfA), D.J.Fegan, S.Fennell, J.Quinn (UC Dublin), A.M.Hillas, J.Rose, M.West (U Leeds), M.F.Cawley (St. Patrick's C), C.W.Akerlof, D.Meyer, M.Schubnell (U Mich), J.A.Gaidos, G.Sembroski, J.Wilson (Purdue U)

Markarian 421 is the closest (z=0.031), yet dimmest identified AGN observed by EGRET. As yet, it is also the only AGN to be observed at TeV energies by the Whipple Observatory imaging gamma-ray telescope. The energy spectrum of Mrk421 between 0.3 GeV and 4 TeV was previously reported to be 1.02x$10^{-11} E^{-2.06}$ photons/cm$^{2}$/s/TeV. At TeV energies, this represents a 6$\sigma$ excess above background. However, the EGRET and Whipple observations used to determine the spectrum were not taken contemporaneously. Previous EGRET and Whipple observations showed no strong evidence of variablility. In April 1994, Markarian 421 was observed with both the Whipple telescope and EGRET. The preliminary results of the Whipple observations in the energy range between 0.25 TeV and 10 TeV will be reported. Of special interest are energies above 3 TeV where the effects of intergalactic absorption from the IR background should become noticeable.

Monday program listing