The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999

F. Aharonian; A. Akhperjanian; J. Barrio; K. Bernlöhr; H. Börst; H. Bojahr; O. Bolz; J. Contreras; J. Cortina; S. Denninghoff; V. Fonseca; J. Gonzalez; N. Götting; G. Heinzelmann; G. Hermann; A. Heusler; W. Hofmann; D. Horns; C. Iserlohe; A. Ibarra; I. Jung; R. Kankanyan; M. Kestel; J. Kettler; A. Kohnle; A. Konopelko; H. Kornmeyer; D. Kranich; H. Krawczynski; H. Lampeitl; E. Lorenz; F. Lucarelli; N. Magnussen; O. Mang; H. Meyer; R. Mirzoyan; A. Moralejo; L. Padilla; M. Panter; R. Plaga; A. Plyasheshnikov; J. Prahl; G. Pühlhofer; A. Röhring; W. Rhode; G. P. Rowell; V. Sahakian; M. Samorski; M. Schilling; F. Schröder; M. Siems; W. Stamm; M. Tluczykont; H. Völk; C. Wiedner; W. Wittek

doi:10.1086/318321

The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999

F. Aharonian
, A. Akhperjanian
, J. Barrio
, K. Bernlöhr
, H. Börst
, H. Bojahr
, O. Bolz
, J. Contreras
, J. Cortina
, S. Denninghoff
, V. Fonseca
, J. Gonzalez
, N. Götting
, G. Heinzelmann
, G. Hermann
, A. Heusler
, W. Hofmann
, D. Horns
, C. Iserlohe
, A. Ibarra

I. Jung, R. Kankanyan, M. Kestel, J. Kettler, A. Kohnle, A. Konopelko, H. Kornmeyer, D. Kranich, H. Krawczynski, H. Lampeitl, E. Lorenz, F. Lucarelli, N. Magnussen, O. Mang, H. Meyer, R. Mirzoyan, A. Moralejo, L. Padilla, M. Panter, R. Plaga, A. Plyasheshnikov, J. Prahl, G. Pühlhofer, A. Röhring, W. Rhode, G. P. Rowell, V. Sahakian, M. Samorski, M. Schilling, F. Schröder, M. Siems, W. Stamm, M. Tluczykont, H. Völk, C. Wiedner, W. Wittek

Research output: Contribution to journal › Review article › peer-review

50 Scopus citations

Abstract

During 1997, the BL Lac object Mrk 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission character-istics of the source in the subsequent years of 1998 and 1999 as measured with the stereoscopic Cheren-kov telescope system of the High-Energy Gamma-Ray Astronomy (HEGRA; La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A data set of 122 observation hours with the HEGRA telescope system makes it possible to assess for the first time the Mrk 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Exclud-ing the data of a strong flare, we find evidence that the 1998-1999 low-flux spectrum is substantially softer (by 0.44 ±O.l_stat in spectral index) than the 1997 time-averaged spectrum. The 500 GeV to ≃10 TeV energy spectrum can well be described by a power-law model with exponential cutoff: dN/dE ∝ E^-α exp (-E/E₀), with α = 2.31 ± 0.22_stat and E₀ = 5.1(_-2.3^+7.8)_stat TeV. Within statistical accuracy, a pure power-law model also gives an acceptable fit to the data: dN/dE ∝ E ^-Γ, with Γ = 2.76 ±0.08_stat. After presenting the 1998-1999 TeV characteristics of the source, we discuss the implications of the results.

Original language	English
Pages (from-to)	898-902
Number of pages	5
Journal	Astrophysical Journal
Volume	546
Issue number	2 PART 1
DOIs	https://doi.org/10.1086/318321
State	Published - Jan 10 2001

Keywords

BL Lacertae objects: individual (Markarian 501)
Galaxies: jets
Gamma rays : observations

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10.1086/318321

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Aharonian, F., Akhperjanian, A., Barrio, J., Bernlöhr, K., Börst, H., Bojahr, H., Bolz, O., Contreras, J., Cortina, J., Denninghoff, S., Fonseca, V., Gonzalez, J., Götting, N., Heinzelmann, G., Hermann, G., Heusler, A., Hofmann, W., Horns, D., Iserlohe, C., ... Wittek, W. (2001). The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999. Astrophysical Journal, 546(2 PART 1), 898-902. https://doi.org/10.1086/318321

@article{771472645ddf45408e8a34e555487c35,

title = "The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999",

abstract = "During 1997, the BL Lac object Mrk 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission character-istics of the source in the subsequent years of 1998 and 1999 as measured with the stereoscopic Cheren-kov telescope system of the High-Energy Gamma-Ray Astronomy (HEGRA; La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A data set of 122 observation hours with the HEGRA telescope system makes it possible to assess for the first time the Mrk 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Exclud-ing the data of a strong flare, we find evidence that the 1998-1999 low-flux spectrum is substantially softer (by 0.44 ±O.lstat in spectral index) than the 1997 time-averaged spectrum. The 500 GeV to ≃10 TeV energy spectrum can well be described by a power-law model with exponential cutoff: dN/dE ∝ E-α exp (-E/E0), with α = 2.31 ± 0.22stat and E0 = 5.1(-2.3+7.8)stat TeV. Within statistical accuracy, a pure power-law model also gives an acceptable fit to the data: dN/dE ∝ E -Γ, with Γ = 2.76 ±0.08stat. After presenting the 1998-1999 TeV characteristics of the source, we discuss the implications of the results.",

keywords = "BL Lacertae objects: individual (Markarian 501), Galaxies: jets, Gamma rays : observations",

author = "F. Aharonian and A. Akhperjanian and J. Barrio and K. Bernl{\"o}hr and H. B{\"o}rst and H. Bojahr and O. Bolz and J. Contreras and J. Cortina and S. Denninghoff and V. Fonseca and J. Gonzalez and N. G{\"o}tting and G. Heinzelmann and G. Hermann and A. Heusler and W. Hofmann and D. Horns and C. Iserlohe and A. Ibarra and I. Jung and R. Kankanyan and M. Kestel and J. Kettler and A. Kohnle and A. Konopelko and H. Kornmeyer and D. Kranich and H. Krawczynski and H. Lampeitl and E. Lorenz and F. Lucarelli and N. Magnussen and O. Mang and H. Meyer and R. Mirzoyan and A. Moralejo and L. Padilla and M. Panter and R. Plaga and A. Plyasheshnikov and J. Prahl and G. P{\"u}hlhofer and A. R{\"o}hring and W. Rhode and Rowell, \{G. P.\} and V. Sahakian and M. Samorski and M. Schilling and F. Schr{\"o}der and M. Siems and W. Stamm and M. Tluczykont and H. V{\"o}lk and C. Wiedner and W. Wittek",

year = "2001",

month = jan,

day = "10",

doi = "10.1086/318321",

language = "English",

volume = "546",

pages = "898--902",

journal = "Astrophysical Journal",

issn = "0004-637X",

number = "2 PART 1",

}

Aharonian, F, Akhperjanian, A, Barrio, J, Bernlöhr, K, Börst, H, Bojahr, H, Bolz, O, Contreras, J, Cortina, J, Denninghoff, S, Fonseca, V, Gonzalez, J, Götting, N, Heinzelmann, G, Hermann, G, Heusler, A, Hofmann, W, Horns, D, Iserlohe, C, Ibarra, A, Jung, I, Kankanyan, R, Kestel, M, Kettler, J, Kohnle, A, Konopelko, A, Kornmeyer, H, Kranich, D, Krawczynski, H, Lampeitl, H, Lorenz, E, Lucarelli, F, Magnussen, N, Mang, O, Meyer, H, Mirzoyan, R, Moralejo, A, Padilla, L, Panter, M, Plaga, R, Plyasheshnikov, A, Prahl, J, Pühlhofer, G, Röhring, A, Rhode, W, Rowell, GP, Sahakian, V, Samorski, M, Schilling, M, Schröder, F, Siems, M, Stamm, W, Tluczykont, M, Völk, H, Wiedner, C & Wittek, W 2001, 'The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999', Astrophysical Journal, vol. 546, no. 2 PART 1, pp. 898-902. https://doi.org/10.1086/318321

TY - JOUR

T1 - The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999

AU - Aharonian, F.

AU - Akhperjanian, A.

AU - Barrio, J.

AU - Bernlöhr, K.

AU - Börst, H.

AU - Bojahr, H.

AU - Bolz, O.

AU - Contreras, J.

AU - Cortina, J.

AU - Denninghoff, S.

AU - Fonseca, V.

AU - Gonzalez, J.

AU - Götting, N.

AU - Heinzelmann, G.

AU - Hermann, G.

AU - Heusler, A.

AU - Hofmann, W.

AU - Horns, D.

AU - Iserlohe, C.

AU - Ibarra, A.

AU - Jung, I.

AU - Kankanyan, R.

AU - Kestel, M.

AU - Kettler, J.

AU - Kohnle, A.

AU - Konopelko, A.

AU - Kornmeyer, H.

AU - Kranich, D.

AU - Krawczynski, H.

AU - Lampeitl, H.

AU - Lorenz, E.

AU - Lucarelli, F.

AU - Magnussen, N.

AU - Mang, O.

AU - Meyer, H.

AU - Mirzoyan, R.

AU - Moralejo, A.

AU - Padilla, L.

AU - Panter, M.

AU - Plaga, R.

AU - Plyasheshnikov, A.

AU - Prahl, J.

AU - Pühlhofer, G.

AU - Röhring, A.

AU - Rhode, W.

AU - Rowell, G. P.

AU - Sahakian, V.

AU - Samorski, M.

AU - Schilling, M.

AU - Schröder, F.

AU - Siems, M.

AU - Stamm, W.

AU - Tluczykont, M.

AU - Völk, H.

AU - Wiedner, C.

AU - Wittek, W.

PY - 2001/1/10

Y1 - 2001/1/10

N2 - During 1997, the BL Lac object Mrk 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission character-istics of the source in the subsequent years of 1998 and 1999 as measured with the stereoscopic Cheren-kov telescope system of the High-Energy Gamma-Ray Astronomy (HEGRA; La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A data set of 122 observation hours with the HEGRA telescope system makes it possible to assess for the first time the Mrk 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Exclud-ing the data of a strong flare, we find evidence that the 1998-1999 low-flux spectrum is substantially softer (by 0.44 ±O.lstat in spectral index) than the 1997 time-averaged spectrum. The 500 GeV to ≃10 TeV energy spectrum can well be described by a power-law model with exponential cutoff: dN/dE ∝ E-α exp (-E/E0), with α = 2.31 ± 0.22stat and E0 = 5.1(-2.3+7.8)stat TeV. Within statistical accuracy, a pure power-law model also gives an acceptable fit to the data: dN/dE ∝ E -Γ, with Γ = 2.76 ±0.08stat. After presenting the 1998-1999 TeV characteristics of the source, we discuss the implications of the results.

AB - During 1997, the BL Lac object Mrk 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission character-istics of the source in the subsequent years of 1998 and 1999 as measured with the stereoscopic Cheren-kov telescope system of the High-Energy Gamma-Ray Astronomy (HEGRA; La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A data set of 122 observation hours with the HEGRA telescope system makes it possible to assess for the first time the Mrk 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Exclud-ing the data of a strong flare, we find evidence that the 1998-1999 low-flux spectrum is substantially softer (by 0.44 ±O.lstat in spectral index) than the 1997 time-averaged spectrum. The 500 GeV to ≃10 TeV energy spectrum can well be described by a power-law model with exponential cutoff: dN/dE ∝ E-α exp (-E/E0), with α = 2.31 ± 0.22stat and E0 = 5.1(-2.3+7.8)stat TeV. Within statistical accuracy, a pure power-law model also gives an acceptable fit to the data: dN/dE ∝ E -Γ, with Γ = 2.76 ±0.08stat. After presenting the 1998-1999 TeV characteristics of the source, we discuss the implications of the results.

KW - BL Lacertae objects: individual (Markarian 501)

KW - Galaxies: jets

KW - Gamma rays : observations

UR - https://www.scopus.com/pages/publications/0035835112

U2 - 10.1086/318321

DO - 10.1086/318321

M3 - Review article

AN - SCOPUS:0035835112

SN - 0004-637X

VL - 546

SP - 898

EP - 902

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2 PART 1

ER -

The TeV energy spectrum of Markarian 501 measured with the stereoscopic telescope system of HEGRA during 1998 and 1999

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