Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011

A. Abramowski; F. Aharonian; F. Ait Benkhali; A. G. Akhperjanian; E. Angüner; G. Anton; S. Balenderan; A. Balzer; A. Barnacka; Y. Becherini; J. Becker Tjus; K. Bernlöhr; E. Birsin; E. Bissaldi; J. Biteau; M. Böttcher; C. Boisson; J. Bolmont; P. Bordas; J. Brucker; F. Brun; P. Brun; T. Bulik; S. Carrigan; S. Casanova; M. Cerruti; P. M. Chadwick; R. Chalme-Calvet; R. C G Chaves; A. Cheesebrough; M. Chrétien; S. Colafrancesco; G. Cologna; J. Conrad; C. Couturier; Y. Cui; M. Dalton; M. K. Daniel; I. D. Davids; B. Degrange; C. Deil; P. Dewilt; H. J. Dickinson; A. Djannati-Ataï; W. Domainko; L. O C Drury; G. Dubus; K. Dutson; J. Dyks; M. Dyrda; T. Edwards; K. Egberts; P. Eger; P. Espigat; C. Farnier; S. Fegan; F. Feinstein; M. V. Fernandes; D. Fernandez; A. Fiasson; G. Fontaine; A. Förster; M. Füßling; M. Gajdus; Y. A. Gallant; T. Garrigoux; G. Giavitto; B. Giebels; J. F. Glicenstein; M. H. Grondin; M. Grudzińska; S. Häffner; J. Hahn; J. Harris; G. Heinzelmann; G. Henri; G. Hermann; O. Hervet; A. Hillert; J. A. Hinton; W. Hofmann; P. Hofverberg; M. Holler; D. Horns; A. Jacholkowska; C. Jahn; M. Jamrozy; M. Janiak; F. Jankowsky; I. Jung; M. A. Kastendieck; K. Katarzyński; U. Katz; S. Kaufmann; B. Khélifi; M. Kieffer; S. Klepser; D. Klochkov; W. Kluåniak; T. Kneiske; D. Kolitzus; Nu Komin; K. Kosack; S. Krakau; F. Krayzel; P. P. Krüger; H. Laffon; G. Lamanna; J. Lefaucheur; A. Lemière; M. Lemoine-Goumard; J. P. Lenain; D. Lennarz; T. Lohse; A. Lopatin; C. C. Lu; V. Marandon; A. Marcowith; R. Marx; G. Maurin; N. Maxted; M. Mayer; T. J L McComb; J. Méhault; P. J. Meintjes; U. Menzler; M. Meyer; R. Moderski; M. Mohamed; E. Moulin; T. Murach; C. L. Naumann; M. De Naurois; J. Niemiec; S. J. Nolan; L. Oakes; S. Ohm; E. De Oña Wilhelmi; B. Opitz; M. Ostrowski; I. Oya; M. Panter; R. D. Parsons; M. Paz Arribas; N. W. Pekeur; G. Pelletier; J. Perez; P. O. Petrucci; B. Peyaud; S. Pita; H. Poon; G. Pühlhofer; M. Punch; A. Quirrenbach; S. Raab; M. Raue; A. Reimer; O. Reimer; M. Renaud; R. De Los Reyes; F. Rieger; L. Rob; C. Romoli; S. Rosier-Lees; G. Rowell; B. Rudak; C. B. Rulten; V. Sahakian; D. A. Sanchez; A. Santangelo; R. Schlickeiser; F. Schüssler; A. Schulz; U. Schwanke; S. Schwarzburg; S. Schwemmer; H. Sol; G. Spengler; F. Spies; Å Stawarz; R. Steenkamp; C. Stegmann; F. Stinzing; K. Stycz; I. Sushch; A. Szostek; J. P. Tavernet; T. Tavernier; A. M. Taylor; R. Terrier; M. Tluczykont; C. Trichard; K. Valerius; C. Van Eldik; B. Van Soelen; G. Vasileiadis; C. Venter; A. Viana; P. Vincent; H. J. Völk; F. Volpe; M. Vorster; T. Vuillaume; S. J. Wagner; P. Wagner; M. Ward; M. Weidinger; Q. Weitzel; R. White; A. Wierzcholska; P. Willmann; A. Wörnlein; D. Wouters; V. Zabalza; M. Zacharias; A. Zajczyk; A. A. Zdziarski; A. Zech; H. S. Zechlin

doi:10.1051/0004-6361/201322897

Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011

A. Abramowski, F. Aharonian, F. Ait Benkhali, A. G. Akhperjanian, E. Angüner, G. Anton, S. Balenderan, A. Balzer, A. Barnacka, Y. Becherini, J. Becker Tjus, K. Bernlöhr, E. Birsin, E. Bissaldi, J. Biteau, M. Böttcher, C. Boisson, J. Bolmont, P. Bordas, J. BruckerF. Brun, P. Brun, T. Bulik, S. Carrigan, S. Casanova, M. Cerruti, P. M. Chadwick, R. Chalme-Calvet, R. C G Chaves, A. Cheesebrough, M. Chrétien, S. Colafrancesco, G. Cologna, J. Conrad, C. Couturier, Y. Cui, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, P. Dewilt, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O C Drury, G. Dubus, K. Dutson, J. Dyks, M. Dyrda, T. Edwards, K. Egberts, P. Eger, P. Espigat, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, D. Fernandez, A. Fiasson, G. Fontaine, A. Förster, M. Füßling, M. Gajdus, Y. A. Gallant, T. Garrigoux, G. Giavitto, B. Giebels, J. F. Glicenstein, M. H. Grondin, M. Grudzińska, S. Häffner, J. Hahn, J. Harris, G. Heinzelmann, G. Henri, G. Hermann, O. Hervet, A. Hillert, J. A. Hinton, W. Hofmann, P. Hofverberg, M. Holler, D. Horns, A. Jacholkowska, C. Jahn, M. Jamrozy, M. Janiak, F. Jankowsky, I. Jung, M. A. Kastendieck, K. Katarzyński, U. Katz, S. Kaufmann, B. Khélifi, M. Kieffer, S. Klepser, D. Klochkov, W. Kluåniak, T. Kneiske, D. Kolitzus, Nu Komin, K. Kosack, S. Krakau, F. Krayzel, P. P. Krüger, H. Laffon, G. Lamanna, J. Lefaucheur, A. Lemière, M. Lemoine-Goumard, J. P. Lenain, D. Lennarz, T. Lohse, A. Lopatin, C. C. Lu, V. Marandon, A. Marcowith, R. Marx, G. Maurin, N. Maxted, M. Mayer, T. J L McComb, J. Méhault, P. J. Meintjes, U. Menzler, M. Meyer, R. Moderski, M. Mohamed, E. Moulin, T. Murach, C. L. Naumann, M. De Naurois, J. Niemiec, S. J. Nolan, L. Oakes, S. Ohm, E. De Oña Wilhelmi, B. Opitz, M. Ostrowski, I. Oya, M. Panter, R. D. Parsons, M. Paz Arribas, N. W. Pekeur, G. Pelletier, J. Perez, P. O. Petrucci, B. Peyaud, S. Pita, H. Poon, G. Pühlhofer, M. Punch, A. Quirrenbach, S. Raab, M. Raue, A. Reimer, O. Reimer, M. Renaud, R. De Los Reyes, F. Rieger, L. Rob, C. Romoli, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, V. Sahakian, D. A. Sanchez, A. Santangelo, R. Schlickeiser, F. Schüssler, A. Schulz, U. Schwanke, S. Schwarzburg, S. Schwemmer, H. Sol, G. Spengler, F. Spies, Å Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, K. Stycz, I. Sushch, A. Szostek, J. P. Tavernet, T. Tavernier, A. M. Taylor, R. Terrier, M. Tluczykont, C. Trichard, K. Valerius, C. Van Eldik, B. Van Soelen, G. Vasileiadis, C. Venter, A. Viana, P. Vincent, H. J. Völk, F. Volpe, M. Vorster, T. Vuillaume, S. J. Wagner, P. Wagner, M. Ward, M. Weidinger, Q. Weitzel, R. White, A. Wierzcholska, P. Willmann, A. Wörnlein, D. Wouters, V. Zabalza, M. Zacharias, A. Zajczyk, A. A. Zdziarski, A. Zech, H. S. Zechlin

Physics and Astronomy (Twin Cities)

Research output: Contribution to journal › Article › peer-review

15 Scopus citations

Abstract

Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters. Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their γ-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented. Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale. Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects. Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN. Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).

Original language	English (US)
Article number	A9
Journal	Astronomy and Astrophysics
Volume	564
DOIs	https://doi.org/10.1051/0004-6361/201322897
State	Published - Apr 2014

Bibliographical note

Funding Information:
The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support of the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the French Ministry for Research, the CNRS-IN2P3 and the Astroparticle Interdisciplinary Programme of the CNRS, the UK Science and Technology Facilities Council (STFC), the IPNP of the Charles University, the Czech Science Foundation, the Polish Ministry of Science and Higher Education, the South African Department of Science and Technology and National Research Foundation, and by the University of Namibia. We appreciate the excellent work of the technical support staff in Berlin, Durham, Hamburg, Heidelberg, Palaiseau, Paris, Saclay, and in Namibia in the construction and operation of the equipment. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France.

Keywords

Galaxies: active
Gamma rays: galaxies

Publisher link

10.1051/0004-6361/201322897

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Abramowski, A., Aharonian, F., Ait Benkhali, F., Akhperjanian, A. G., Angüner, E., Anton, G., Balenderan, S., Balzer, A., Barnacka, A., Becherini, Y., Becker Tjus, J., Bernlöhr, K., Birsin, E., Bissaldi, E., Biteau, J., Böttcher, M., Boisson, C., Bolmont, J., Bordas, P., ... Zechlin, H. S. (2014). Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011. Astronomy and Astrophysics, 564, Article A9. https://doi.org/10.1051/0004-6361/201322897

Abramowski, A, Aharonian, F, Ait Benkhali, F, Akhperjanian, AG, Angüner, E, Anton, G, Balenderan, S, Balzer, A, Barnacka, A, Becherini, Y, Becker Tjus, J, Bernlöhr, K, Birsin, E, Bissaldi, E, Biteau, J, Böttcher, M, Boisson, C, Bolmont, J, Bordas, P, Brucker, J, Brun, F, Brun, P, Bulik, T, Carrigan, S, Casanova, S, Cerruti, M, Chadwick, PM, Chalme-Calvet, R, Chaves, RCG, Cheesebrough, A, Chrétien, M, Colafrancesco, S, Cologna, G, Conrad, J, Couturier, C, Cui, Y, Dalton, M, Daniel, MK, Davids, ID, Degrange, B, Deil, C, Dewilt, P, Dickinson, HJ, Djannati-Ataï, A, Domainko, W, Drury, LOC, Dubus, G, Dutson, K, Dyks, J, Dyrda, M, Edwards, T, Egberts, K, Eger, P, Espigat, P, Farnier, C, Fegan, S, Feinstein, F, Fernandes, MV, Fernandez, D, Fiasson, A, Fontaine, G, Förster, A, Füßling, M, Gajdus, M, Gallant, YA, Garrigoux, T, Giavitto, G, Giebels, B, Glicenstein, JF, Grondin, MH, Grudzińska, M, Häffner, S, Hahn, J, Harris, J, Heinzelmann, G, Henri, G, Hermann, G, Hervet, O, Hillert, A, Hinton, JA, Hofmann, W, Hofverberg, P, Holler, M, Horns, D, Jacholkowska, A, Jahn, C, Jamrozy, M, Janiak, M, Jankowsky, F, Jung, I, Kastendieck, MA, Katarzyński, K, Katz, U, Kaufmann, S, Khélifi, B, Kieffer, M, Klepser, S, Klochkov, D, Kluåniak, W, Kneiske, T, Kolitzus, D, Komin, N, Kosack, K, Krakau, S, Krayzel, F, Krüger, PP, Laffon, H, Lamanna, G, Lefaucheur, J, Lemière, A, Lemoine-Goumard, M, Lenain, JP, Lennarz, D, Lohse, T, Lopatin, A, Lu, CC, Marandon, V, Marcowith, A, Marx, R, Maurin, G, Maxted, N, Mayer, M, McComb, TJL, Méhault, J, Meintjes, PJ, Menzler, U, Meyer, M, Moderski, R, Mohamed, M, Moulin, E, Murach, T, Naumann, CL, De Naurois, M, Niemiec, J, Nolan, SJ, Oakes, L, Ohm, S, De Oña Wilhelmi, E, Opitz, B, Ostrowski, M, Oya, I, Panter, M, Parsons, RD, Paz Arribas, M, Pekeur, NW, Pelletier, G, Perez, J, Petrucci, PO, Peyaud, B, Pita, S, Poon, H, Pühlhofer, G, Punch, M, Quirrenbach, A, Raab, S, Raue, M, Reimer, A, Reimer, O, Renaud, M, De Los Reyes, R, Rieger, F, Rob, L, Romoli, C, Rosier-Lees, S, Rowell, G, Rudak, B, Rulten, CB, Sahakian, V, Sanchez, DA, Santangelo, A, Schlickeiser, R, Schüssler, F, Schulz, A, Schwanke, U, Schwarzburg, S, Schwemmer, S, Sol, H, Spengler, G, Spies, F, Stawarz, Å, Steenkamp, R, Stegmann, C, Stinzing, F, Stycz, K, Sushch, I, Szostek, A, Tavernet, JP, Tavernier, T, Taylor, AM, Terrier, R, Tluczykont, M, Trichard, C, Valerius, K, Van Eldik, C, Van Soelen, B, Vasileiadis, G, Venter, C, Viana, A, Vincent, P, Völk, HJ, Volpe, F, Vorster, M, Vuillaume, T, Wagner, SJ, Wagner, P, Ward, M, Weidinger, M, Weitzel, Q, White, R, Wierzcholska, A, Willmann, P, Wörnlein, A, Wouters, D, Zabalza, V, Zacharias, M, Zajczyk, A, Zdziarski, AA, Zech, A & Zechlin, HS 2014, 'Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011', Astronomy and Astrophysics, vol. 564, A9. https://doi.org/10.1051/0004-6361/201322897

@article{5dce0b750aa642cb86f3806d6e9e35e3,

title = "Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011",

abstract = "Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters. Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their γ-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented. Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale. Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects. Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN. Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).",

keywords = "Galaxies: active, Gamma rays: galaxies",

author = "A. Abramowski and F. Aharonian and {Ait Benkhali}, F. and Akhperjanian, {A. G.} and E. Ang{\"u}ner and G. Anton and S. Balenderan and A. Balzer and A. Barnacka and Y. Becherini and {Becker Tjus}, J. and K. Bernl{\"o}hr and E. Birsin and E. Bissaldi and J. Biteau and M. B{\"o}ttcher and C. Boisson and J. Bolmont and P. Bordas and J. Brucker and F. Brun and P. Brun and T. Bulik and S. Carrigan and S. Casanova and M. Cerruti and Chadwick, {P. M.} and R. Chalme-Calvet and Chaves, {R. C G} and A. Cheesebrough and M. Chr{\'e}tien and S. Colafrancesco and G. Cologna and J. Conrad and C. Couturier and Y. Cui and M. Dalton and Daniel, {M. K.} and Davids, {I. D.} and B. Degrange and C. Deil and P. Dewilt and Dickinson, {H. J.} and A. Djannati-Ata{\"i} and W. Domainko and Drury, {L. O C} and G. Dubus and K. Dutson and J. Dyks and M. Dyrda and T. Edwards and K. Egberts and P. Eger and P. Espigat and C. Farnier and S. Fegan and F. Feinstein and Fernandes, {M. V.} and D. Fernandez and A. Fiasson and G. Fontaine and A. F{\"o}rster and M. F{\"u}{\ss}ling and M. Gajdus and Gallant, {Y. A.} and T. Garrigoux and G. Giavitto and B. Giebels and Glicenstein, {J. F.} and Grondin, {M. H.} and M. Grudzi{\'n}ska and S. H{\"a}ffner and J. Hahn and J. Harris and G. Heinzelmann and G. Henri and G. Hermann and O. Hervet and A. Hillert and Hinton, {J. A.} and W. Hofmann and P. Hofverberg and M. Holler and D. Horns and A. Jacholkowska and C. Jahn and M. Jamrozy and M. Janiak and F. Jankowsky and I. Jung and Kastendieck, {M. A.} and K. Katarzy{\'n}ski and U. Katz and S. Kaufmann and B. Kh{\'e}lifi and M. Kieffer and S. Klepser and D. Klochkov and W. Klu{\aa}niak and T. Kneiske and D. Kolitzus and Nu Komin and K. Kosack and S. Krakau and F. Krayzel and Kr{\"u}ger, {P. P.} and H. Laffon and G. Lamanna and J. Lefaucheur and A. Lemi{\`e}re and M. Lemoine-Goumard and Lenain, {J. P.} and D. Lennarz and T. Lohse and A. Lopatin and Lu, {C. C.} and V. Marandon and A. Marcowith and R. Marx and G. Maurin and N. Maxted and M. Mayer and McComb, {T. J L} and J. M{\'e}hault and Meintjes, {P. J.} and U. Menzler and M. Meyer and R. Moderski and M. Mohamed and E. Moulin and T. Murach and Naumann, {C. L.} and {De Naurois}, M. and J. Niemiec and Nolan, {S. J.} and L. Oakes and S. Ohm and {De O{\~n}a Wilhelmi}, E. and B. Opitz and M. Ostrowski and I. Oya and M. Panter and Parsons, {R. D.} and {Paz Arribas}, M. and Pekeur, {N. W.} and G. Pelletier and J. Perez and Petrucci, {P. O.} and B. Peyaud and S. Pita and H. Poon and G. P{\"u}hlhofer and M. Punch and A. Quirrenbach and S. Raab and M. Raue and A. Reimer and O. Reimer and M. Renaud and {De Los Reyes}, R. and F. Rieger and L. Rob and C. Romoli and S. Rosier-Lees and G. Rowell and B. Rudak and Rulten, {C. B.} and V. Sahakian and Sanchez, {D. A.} and A. Santangelo and R. Schlickeiser and F. Sch{\"u}ssler and A. Schulz and U. Schwanke and S. Schwarzburg and S. Schwemmer and H. Sol and G. Spengler and F. Spies and {\AA} Stawarz and R. Steenkamp and C. Stegmann and F. Stinzing and K. Stycz and I. Sushch and A. Szostek and Tavernet, {J. P.} and T. Tavernier and Taylor, {A. M.} and R. Terrier and M. Tluczykont and C. Trichard and K. Valerius and {Van Eldik}, C. and {Van Soelen}, B. and G. Vasileiadis and C. Venter and A. Viana and P. Vincent and V{\"o}lk, {H. J.} and F. Volpe and M. Vorster and T. Vuillaume and Wagner, {S. J.} and P. Wagner and M. Ward and M. Weidinger and Q. Weitzel and R. White and A. Wierzcholska and P. Willmann and A. W{\"o}rnlein and D. Wouters and V. Zabalza and M. Zacharias and A. Zajczyk and Zdziarski, {A. A.} and A. Zech and Zechlin, {H. S.}",

note = "Funding Information: The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support of the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the French Ministry for Research, the CNRS-IN2P3 and the Astroparticle Interdisciplinary Programme of the CNRS, the UK Science and Technology Facilities Council (STFC), the IPNP of the Charles University, the Czech Science Foundation, the Polish Ministry of Science and Higher Education, the South African Department of Science and Technology and National Research Foundation, and by the University of Namibia. We appreciate the excellent work of the technical support staff in Berlin, Durham, Hamburg, Heidelberg, Palaiseau, Paris, Saclay, and in Namibia in the construction and operation of the equipment. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France.",

year = "2014",

month = apr,

doi = "10.1051/0004-6361/201322897",

language = "English (US)",

volume = "564",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

TY - JOUR

T1 - Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011

AU - Abramowski, A.

AU - Aharonian, F.

AU - Ait Benkhali, F.

AU - Akhperjanian, A. G.

AU - Angüner, E.

AU - Anton, G.

AU - Balenderan, S.

AU - Balzer, A.

AU - Barnacka, A.

AU - Becherini, Y.

AU - Becker Tjus, J.

AU - Bernlöhr, K.

AU - Birsin, E.

AU - Bissaldi, E.

AU - Biteau, J.

AU - Böttcher, M.

AU - Boisson, C.

AU - Bolmont, J.

AU - Bordas, P.

AU - Brucker, J.

AU - Brun, F.

AU - Brun, P.

AU - Bulik, T.

AU - Carrigan, S.

AU - Casanova, S.

AU - Cerruti, M.

AU - Chadwick, P. M.

AU - Chalme-Calvet, R.

AU - Chaves, R. C G

AU - Cheesebrough, A.

AU - Chrétien, M.

AU - Colafrancesco, S.

AU - Cologna, G.

AU - Conrad, J.

AU - Couturier, C.

AU - Cui, Y.

AU - Dalton, M.

AU - Daniel, M. K.

AU - Davids, I. D.

AU - Degrange, B.

AU - Deil, C.

AU - Dewilt, P.

AU - Dickinson, H. J.

AU - Djannati-Ataï, A.

AU - Domainko, W.

AU - Drury, L. O C

AU - Dubus, G.

AU - Dutson, K.

AU - Dyks, J.

AU - Dyrda, M.

AU - Edwards, T.

AU - Egberts, K.

AU - Eger, P.

AU - Espigat, P.

AU - Farnier, C.

AU - Fegan, S.

AU - Feinstein, F.

AU - Fernandes, M. V.

AU - Fernandez, D.

AU - Fiasson, A.

AU - Fontaine, G.

AU - Förster, A.

AU - Füßling, M.

AU - Gajdus, M.

AU - Gallant, Y. A.

AU - Garrigoux, T.

AU - Giavitto, G.

AU - Giebels, B.

AU - Glicenstein, J. F.

AU - Grondin, M. H.

AU - Grudzińska, M.

AU - Häffner, S.

AU - Hahn, J.

AU - Harris, J.

AU - Heinzelmann, G.

AU - Henri, G.

AU - Hermann, G.

AU - Hervet, O.

AU - Hillert, A.

AU - Hinton, J. A.

AU - Hofmann, W.

AU - Hofverberg, P.

AU - Holler, M.

AU - Horns, D.

AU - Jacholkowska, A.

AU - Jahn, C.

AU - Jamrozy, M.

AU - Janiak, M.

AU - Jankowsky, F.

AU - Jung, I.

AU - Kastendieck, M. A.

AU - Katarzyński, K.

AU - Katz, U.

AU - Kaufmann, S.

AU - Khélifi, B.

AU - Kieffer, M.

AU - Klepser, S.

AU - Klochkov, D.

AU - Kluåniak, W.

AU - Kneiske, T.

AU - Kolitzus, D.

AU - Komin, Nu

AU - Kosack, K.

AU - Krakau, S.

AU - Krayzel, F.

AU - Krüger, P. P.

AU - Laffon, H.

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N1 - Funding Information: The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support of the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the French Ministry for Research, the CNRS-IN2P3 and the Astroparticle Interdisciplinary Programme of the CNRS, the UK Science and Technology Facilities Council (STFC), the IPNP of the Charles University, the Czech Science Foundation, the Polish Ministry of Science and Higher Education, the South African Department of Science and Technology and National Research Foundation, and by the University of Namibia. We appreciate the excellent work of the technical support staff in Berlin, Durham, Hamburg, Heidelberg, Palaiseau, Paris, Saclay, and in Namibia in the construction and operation of the equipment. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France.

PY - 2014/4

Y1 - 2014/4

N2 - Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters. Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their γ-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented. Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale. Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects. Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN. Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).

AB - Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters. Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their γ-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented. Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale. Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects. Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN. Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).

KW - Galaxies: active

KW - Gamma rays: galaxies

UR - http://www.scopus.com/inward/record.url?scp=84897468203&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84897468203&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201322897

DO - 10.1051/0004-6361/201322897

M3 - Article

AN - SCOPUS:84897468203

SN - 0004-6361

VL - 564

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A9

ER -

Flux upper limits for 47 AGN observed with H.E.S.S. in 2004 - 2011

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