Multi-wavelength observations of H 2356-309

AIMS: The properties of the broad-band emission from the high-frequency peaked BL Lac H 2356-309 (z=0.165) are investigated. METHODS: Very High Energy (VHE; E > 100 GeV) observations of H 2356-309 were performed with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Simultaneous optical/UV and X-ray observations were made with the XMM-Newton satellite on June 12/13 and June 14/15, 2005. NRT radio observations were also contemporaneously performed in 2005. ATOM optical monitoring observations were also made in 2007. RESULTS: A strong VHE signal, ~13 sigma total, was detected by HESS after the four years HESS observations (116.8 hrs live time). The integral flux above 240 GeV is I(>240 GeV) = (3.06 +- 0.26 {stat} +- 0.61 {syst}) x 10^{-12} cm^{-2} s^{-1}, corresponding to ~1.6% of the flux observed from the Crab Nebula. A time-averaged energy spectrum is measured from 200 GeV to 2 TeV and is characterized by a power law (photon index of Gamma = 3.06 +- 0.15 {stat} +- 0.10 {syst}). Significant small-amplitude variations in the VHE flux from H 2356-309 are seen on time scales of months and years, but not on shorter time scales. No evidence for any variations in the VHE spectral slope are found within these data. The XMM-Newton X-ray measurements show a historically low X-ray state, characterized by a hard, broken-power-law spectrum on both nights. CONCLUSIONS: The broad-band spectral energy distribution (SED) of the blazar can be adequately fit using a simple one-zone synchrotron self-Compton (SSC) model. In the SSC scenario, higher VHE fluxes could be expected in the future since the observed X-ray flux is at a historically low level.

A. R. Bazer-Bachi | K. J. Orford | M. V. Fernandes | M. C. Medina | Nicolas Produit | T. Bulik | G. Anton | J. Conrad | U. Katz | E. Moulin | T. Lohse | T. Mccomb | M. Kerschhaggl | W. Domainko | C. Deil | W. Benbow | S. Rosier-Lees | A. Quirrenbach | J. Olive | C. Venter | M. Raue | F. Dubois | S. Ohm | C. Stegmann | I. Davids | W. Hofmann | M. Hauser | G. Fontaine | R. Schlickeiser | B. Degrange | L. Chounet | F. Aharonian | D. Horns | Y. Gallant | S. Fegan | K. Kosack | Y. Becherini | F. Feinstein | P. Goret | M. Naumann-Godo | A. Santangelo | L. Drury | S. Gabici | S. Wagner | M. Sikora | J. Ruppel | M. Vivier | C. Farnier | K. Valerius | D. Khangulyan | L. Stawarz | H. Dickinson | J. Ripken | B. Opitz | M. Ward | J. Tavernet | M. Panter | B. Behera | C. Boisson | J. Bolmont | P. Brun | R. Buehler | M. Daniel | M. Naurois | G. Dubus | J. Dyks | M. Dyrda | K. Egberts | P. Eger | A. Fiasson | L. Gérard | B. Giebels | J. Glicenstein | G. Henri | G. Hermann | P. Hofverberg | A. Jacholkowska | I. Jung | K. Katarzyński | B. Khélifi | W. Kluźniak | N. Komin | R. Kossakowski | G. Lamanna | J. Lenain | A. Marcowith | R. Moderski | D. Nedbal | J. Niemiec | S. Nolan | M. Ostrowski | M. P. Arribas | G. Pedaletti | P. Petrucci | S. Pita | M. Punch | O. Reimer | M. Renaud | F. Rieger | L. Rob | B. Rudak | C. Rulten | F. Ryde | V. Sahakian | U. Schwanke | S. Schwarzburg | S. Schwemmer | H. Sol | R. Steenkamp | F. Stinzing | A. Szóstek | R. Terrier | O. Tibolla | M. Tluczykont | C. Eldik | G. Vasileiadis | J. Vialle | A. Viana | P. Vincent | S. Vorobiov | A. Zdziarski | A. Zech | L. Costamante | V. Borrel | H. Voelk | D. Gerbig | G. Puehlhofer | G. Rowell | F. Brun | R. Chaves | A. Djannati-Atai | V. Marandon | P. Chadwick | I. Sushch | S. Kaufmann | J. Hinton | E. Wilhelmi | F. Acero | S. Heinz | M. Fuessling | B. Nicholas | R. Reyes | A. Akhperjanian | A. Bochow | J. Brucker | T. Boutelier | A. Charbonnier | A. Cheesebrough | A. Clapson | M. Dalton | P. Espigat | G. Heinzelmann | A. Hoffmann | S. Hoppe | C. Jahn | D. Keogh | D. Klochkov | T. Kneiske | J. Masbou | D. Maurin | J. Méhault | D. Nekrassov | G. Pelletier | B. Raubenheimer | S. Rayner | A. Shalchi | J. Skilton | P. Tam | L. Venter | F. Volpe | L. Fallon | D. Hampf | H. Zechlin | M. Holleran | O. D. Jager | I. Buesching | C. Lu | H. C. A. Abramowski | F. Schoeck | N. Nguyen | U. D. Almeida | A. Foerster | K. Bernloehr | K. Bernloehr | B. Glueck | D. Goering | A. Schoenwald | J. Conrad | M. Arribas | C.-C. Lu | S. Wagner | K. Orford

[1]  E. Striani,et al.  FERMI LARGE AREA TELESCOPE FIRST SOURCE CATALOG , 2010 .

[2]  Gino Tosti,et al.  FERMI OBSERVATIONS OF TeV-SELECTED ACTIVE GALACTIC NUCLEI , 2009 .

[3]  et al,et al.  Fermi observations of TeV-selected AGN , 2009, 0910.4881.

[4]  Robert P. Johnson,et al.  BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY , 2009, 0902.1559.

[5]  U. Padova,et al.  Extragalactic optical-infrared background radiation, its time evolution and the cosmic photon-photon opacity , 2008, 0805.1841.

[6]  G. Theureau,et al.  Kinematics of the Local Universe. XIII. 21-cm line measurements of 452 galaxies with the Nançay radiotelescope, JHK Tully-Fisher relation, and preliminary maps of the peculiar velocity field , 2006, astro-ph/0611626.

[7]  A. R. Bazer-Bachi,et al.  A low level of extragalactic background light as revealed by γ-rays from blazars , 2005, Nature.

[8]  Stsci,et al.  Observational Gamma-ray Cosmology , 2005, astro-ph/0502177.

[9]  P. Giommi,et al.  The Sedentary Survey of Extreme High Energy Peaked BL Lacs. II. The Catalog and Spectral Properties , 2004, astro-ph/0411093.

[10]  M. Hauser,et al.  ATOM - an Automatic Telescope for Optical Monitoring , 2004 .

[11]  M. Giavalisco,et al.  APJ, ACCEPTED Preprint typeset using L ATEX style emulateapj v. 11/12/01 NEAR-INFRARED OBSERVATIONS OF BL LACERTAE HOST GALAXIES , 2003 .

[12]  L. Costamante,et al.  TeV candidate BL Lac objects , 2001, astro-ph/0112201.

[13]  P. Giommi,et al.  Extreme synchrotron BL Lac objects , 2001, astro-ph/0103343.

[14]  H. Sol,et al.  The multifrequency emission of Mrk 501 From radio to TeV gamma-rays , 2001 .

[15]  R. McCray,et al.  Astrophysical Journal, in press Preprint typeset using L ATEX style emulateapj v. 26/01/00 ON THE ABSORPTION OF X-RAYS IN THE INTERSTELLAR MEDIUM , 2000 .

[16]  D. Calzetti,et al.  The Hubble Space Telescope Survey of BL Lacertae Objects. IV. Infrared Imaging of Host Galaxies , 2000, astro-ph/0006306.

[17]  J. E. Pesce,et al.  The Hubble Space Telescope Survey of BL Lacertae Objects. II. Host Galaxies , 1999, astro-ph/9911109.

[18]  R. Cousins,et al.  A Unified Approach to the Classical Statistical Analysis of Small Signals , 1997, physics/9711021.

[19]  D. A. Verner,et al.  Atomic data for astrophysics. II. New analytic fits for photoionization cross sections of atoms and ions , 1996 .

[20]  Takashi Ichikawa,et al.  GALAXY COLORS IN VARIOUS PHOTOMETRIC BAND SYSTEMS , 1995 .

[21]  J. E. O'Donnell R(sub nu)-dependent optical and near-ultraviolet extinction , 1994 .

[22]  R. Falomo On the galaxy surrounding the BL Lac object H2356 - 309 , 1991 .

[23]  J. Mathis,et al.  The relationship between infrared, optical, and ultraviolet extinction , 1989 .

[24]  K. Wood,et al.  The HEAO A-1 X-Ray Source Catalog (Wood+, 1984) , 1984 .

[25]  Ti-Pei Li,et al.  Analysis methods for results in gamma-ray astronomy , 1983 .

[26]  H. Tananbaum,et al.  The fourth Uhuru catalog of X-ray sources. , 1978 .

[27]  R. Gould,et al.  Opacity of the Universe to High-Energy Photons , 1966 .