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Featured researches published by M. Hess.


Physical Review D | 1999

Cosmic ray proton spectrum determined with the imaging atmospheric Cherenkov technique

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; A. S. Belgarian; K. Bernlöhr; J. J. G. Beteta; H. Bojahr; S. M. Bradbury; I. Calle; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; I. Holl; D. Horns; Alejandro Ibarra; R. Kankanyan; M. Kestel; O. Kirstein; C. Köhler

The HEGRA system of 4 imaging atmospheric Cherenkov telescopes ~IACTs! has been used to determine the flux and the spectrum of cosmic ray protons over a limited energy range around 1.5 TeV. Although the IACT system is designed for the detection of g-rays with energies above 500 GeV, it has also a large detection area of .10 6 m 2 33 msr for primary protons of energies above 1 TeV and the capability to reconstruct the primary proton energy with a reasonable accuracy DE/E of 50% near this threshold. Furthermore, the principle of stereoscopic detection of air showers permits the effective suppression of air showers induced by heavier primaries already on the trigger level, and in addition on the software level by analysis of the stereoscopic images. The combination of both capabilities permits a determination of the proton spectrum almost independently of the cosmic ray chemical composition. The accuracy of our estimate of the spectral index at 1.5 TeV is limited by systematic uncertainties and is comparable to the accuracy achieved with recent balloon and space borne experiments. In this paper we describe in detail the analysis tools, namely the detailed Monte Carlo simulation, the analysis procedure and the results. We determine the local ~i.e., in the range of 1.5‐3 TeV! differential spectral index to be g p52.7260.02stat60.15syst and obtain an integral flux above 1.5 TeV of F (.1.5 TeV)53.160.6 stat61.2syst310 22 /s sr m 2 . @S0556-2821~99!04107-7#


Astroparticle Physics | 1999

TeV γ-ray observations of the Crab and Mkn 501 during moonshine and twilight

D. Kranich; R. Mirzoyan; D. Petry; B. C. Raubenheimer; F. Aharonian; A. G. Akhperjanian; J. A. Barrio; C. Beck; K. Bernlöhr; H. Bojahr; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. Gebauer; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; A. Ibarra; R. Kankanyan; M. Kestel; O. Kirstein

Abstract TeV γ-ray signals from the Crab Nebula and Mkn 501 were detected with the HEGRA CT1 imaging Cerenkov telescope during periods when the moon was shining and during twilight. This was accomplished by lowering the high voltage supply of the photomultipliers in fixed steps up to 13%. No other adjustments were made and no filters were used. Laser runs could not establish any nonlinearity in the gain of the individual pixels, and the trigger rate was uniform over the whole camera. The energy threshold was increased by up to a factor of two, depending on the amount of HV reduction. In a series of observations lasting 11.7 hours, a signal with a 3.4σ significance was detected from the Crab. During the 1997 multiple flare episode of Mkn 501 a 26σ combined excess was recorded during 134 hours of observations under various moonshine/twilight conditions. The results show that this technique can easily be adapted to increase the exposure of a source, which is important for sources showing rapid time variability such as AGNs or GRBs. Observations can be made up to ∼ 20° angular separation from the moon and until the moon is 85% illuminated (ten to eleven days before and after new moon), as well as during 20 to 40 minutes during twilight, before the commencement of astronomical darkness.


The fourth compton symposium | 2008

Study of the temporal and spectral characteristics of TeV gamma radiation from Mkn 501 during a state of high activity by the HEGRA IACT array

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; J. J. G. Beteta; S. Bradbury; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; E. Feigl; J. Fernandez; V. Fonseca; A. Frass; B. Funk; J. Gonzalez; V. Haustein; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; I. Holl; D. Horns; R. Kankanian; O. Kirstein; C. Köhler; A. Konopelko; H. Kornmayer

During the period March-April 1997, a high flux level of TeV γ-rays was observed from Mkn 501, using the HEGRA stereoscopic system of four imaging atmospheric Cherenkov telescopes (IACTs). The almost background-free detection of γ-rays with a rate exceeding in average 100 h−1, coupled with good energy resolution of the instrument ⩽25% allowed a study of the flux variation on time scales between 5 min and days, and measurements of the differential energy spectrum of the source for selected periods. Here we briefly discuss the results of observations with emphasis on the measurements of temporal and spectral characteristics of the source at 3 subsequent periods in April when the average flux of the source showed a remarkable increase of the flux from about one to eight times the flux observed from the Crab Nebula.


Nuclear Physics B - Proceedings Supplements | 1999

Cherenkov light based measurement of extensive air showers around the knee with the HEGRA experiment

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; A. S. Belgarian; K. Bernlöhr; H. Bojahr; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; J. Fernandez; V. Fonseca; J.C. Gonzales; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; R. Kankanyan; M. Kestel; O. Kirstein; C. Köhler; A. Konopelko; H. Kornmayer; D. Kranich; H. Krawczynski

Data of the wide angle atmospheric Cherenkov light detector array AIROBICC and the scintillator matrix of the HEGRA air shower detector complex are combined to determine the energy spectrum and coarse composition of charged cosmic rays in the energy interval from 300 TeV to 10 PeV.


Astronomy and Astrophysics | 1999

The time averaged TeV energy spectrum of Mkn 501 of the extraordinary 1997 outburst as measured with the stereoscopic Cherenkov telescope system of HEGRA

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; H. Bojahr; I. Calle; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; A. Ibarra; R. Kankanyan; J. Kettler; C. Köhler; A. Konopelko; H. Kornmeyer; M. Kestel; D. Kranich; H. Krawczynski


Astronomy and Astrophysics | 1998

THE TEMPORAL CHARACTERISTICS OF THE TEV GAMMA-RADIATION FROM MKN 501 IN 1997. I. DATA FROM THE STEREOSCOPIC IMAGING ATMOSPHERIC CHERENKOV TELESCOPE SY STEM OF HEGRA

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; H. Bojahr; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; V. Fonseca; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; Alejandro Ibarra; R. Kankanyan; O. Kirstein; C. Köhler; A. Konopelkol; H. Kornmeyer; D. Kranich; H. Krawczynski; H. Lampeitl; A. Lindner; E. Lorenz


Astronomy and Astrophysics | 1999

OBSERVATIONS OF MKN 421 DURING 1997 AND 1998 IN THE ENERGY RANGE ABOVE 500GEV WITH THE HEGRA STEREOSCOPIC CHERENKOV TELESCOPE SYSTEM

F. Aharonian; A. G. Akhperjanian; M. Andronache; J. A. Barrio; K. Bernlöhr; H. Bojahr; I. Calle; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. C. Gonzalez; N. Götting; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; A. Ibarra; R. Kankanyan; J. Kettler; C. Köhler; A. Konopelko; H. Kornmeyer; M. Kestel


Astronomy and Astrophysics | 1999

THE TEMPORAL CHARACTERISTICS OF THE TEV GAMMA -EMISSION FROM MKN 501 IN 1997. II, RESULTS FROM HEGRA CT1 AND CT2

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; H. Bojahr; I. Calle; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. Gebauer; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; Alejandro Ibarra; R. Kankanyan; M. Kestel; C. Kirstein; C. Köhler; H. Kornmayer; D. Kranich; H. Krawczynski


Astronomy and Astrophysics | 1999

Phase-resolved TeV gamma-ray characteristics of the Crab and Geminga pulsars

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; H. Bojahr; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; S. Denninghoff; V. Fonseca; J. C. Gonzalez; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; H. Hohl; D. Horns; Alejandro Ibarra; R. Kankanyan; M. Kestel; O. Kirstein; C. Köhler; A. Konopelko; H. Kornmeyer; D. Kranich; H. Krawczynski; H. Lampeitl


Astronomy and Astrophysics | 1997

MEASUREMENT OF THE FLUX, SPECTRUM, AND VARIABILITY OF TEV GAMMA -RAYS FROMMKN 501 DURING A STATE OF HIGH ACTIVITY

F. Aharonian; A. G. Akhperjanian; J. A. Barrio; K. Bernlöhr; J. J. G. Beteta; S. M. Bradbury; J. L. Contreras; J. Cortina; A. Daum; T. Deckers; E. Feigl; J. Fernandez; V. Fonseca; A. Frass; B. Funk; J. C. Gonzalez; V. Haustein; G. Heinzelmann; M. Hemberger; G. Hermann; M. Hess; A. Heusler; W. Hofmann; I. Holl; D. Horns; R. Kankanian; O. Kirstein; C. Köhler; A. Konopelko; H. Kornmayer

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A. Daum

Karlsruhe Institute of Technology

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V. Fonseca

Complutense University of Madrid

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J. L. Contreras

Complutense University of Madrid

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