The Gamma-Ray Energy Spectrum of the Active Galaxy Markarian 421

Details The Gamma-Ray Energy Spectrum of the Active Galaxy Markarian 421 The Gamma-Ray Energy Spectrum of the Active Galaxy Markarian 421

Sep 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........5z&link_type=abstract

Thesis (PHD). IOWA STATE UNIVERSITY , Source DAI-B 58/03, p. 1332, Sep 1997, 95 pages.

Astronomy and Astrophysics

Astronomy

2

Crab Nebula

Scientific paper

This is a study of the very high energy gamma-ray emission from Markarian 421. The data were taken by the Whipple Observatory 10 meter imaging atmospheric Cherenkov telescope (IACT) during the 1995/96 observing season. A method of extracting energy spectra using data obtained from IACTs has been previously developed at Iowa State University. This method is reviewed in the context of finding the spectrum of the Crab Nebula, the 'standard candle' of very high energy gamma-ray astronomy. One important quantity that sets the energy scale of the Whipple 10 meter telescope is the electronic gain. This quantity has been determined by a direct measurement of the telescope electronics and by scaling previously measured values to the current observing season. Once the spectrum of the Crab Nebula during the 1995/96 observing season is found, the method is then applied to the Markarian 421 data. Of particular interest is a very intense flare observed on 7 May 1996. After the energy spectrum during the flare is found, I extend the method to investigate the high energy end of the spectrum. DeJager, Stecker and Salamon predict that the spectrum of Markarian 421 will cutoff between 1-10 TeV due to absorption by extragalactic background light. No cutoff is observed from the flare up to 6 TeV where statistics run out. Instead, the derived spectrum is more consistent with that predicted by MacMinn and Primack which gradually steepens between 0.3-10 TeV and then cuts off above 10 TeV. Energy spectra were found from the rest of the 1995/96 Markarian 421 data after dividing the data into periods of high and low emission. The low state spectrum is slightly steeper than the high state spectrum. However the difference, because of the limited number of photons collected during the low periods, is not statistically significant, being only 1.2σ.

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