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2007A&A...473L..25A - Astronomy and Astrophysics, volume 473, L25-28 (2007/10-3)

Discovery of VHE γ-rays from the distant BL Lacertae 1ES0347-121.

AHARONIAN F., AKHPERJANIAN A.G., BARRES DE ALMEIDA U., BAZER-BACHI A.R., BEHERA B., BEILICKE M., BENBOW W., BERNLOEHR K., BOISSON C., BOLZ O., BORREL V., BRAUN I., BRION E., BROWN A.M., BUEHLER R., BULIK T., BUESCHING I., BOUTELIER T., CARRIGAN S., CHADWICK P.M., CHOUNET L.-M., CLAPSON A.C., COIGNET G., CORNILS R., COSTAMANTE L., DALTON M., DEGRANGE B., DICKINSON H.J., DJANNATI-ATAIE A., DOMAINKO W., DRURY L.O'C., DUBOIS F., DUBUS G., DYKS J., EGBERTS K., EMMANOULOPOULOS D., ESPIGAT P., FARNIER C., FEINSTEIN F., FIASSON A., FOERSTER A., FONTAINE G., FUNK SEB., FUESSLING M., GALLANT Y.A., GIEBELS B., GLICENSTEIN J.F., GLUECK B., GORET P., HADJICHRISTIDIS C., HAUSER D., HAUSER M., HEINZELMANN G., HENRI G., HERMANN G., HINTON J.A., HOFFMANN A., HOFMANN W., HOLLERAN M., HOPPE S., HORNS D., JACHOLKOWSKA A., DE JAGER O.C., JUNG I., KATARZYNSKI K., KENDZIORRA E., KERSCHHAGGL M., KHELIFI B., KEOGH D., KOMIN N., KOSACK K., LAMANNA G., LATHAM I.J., LEMIERE A., LEMOINE-GOUMARD M., LENAIN J.-P., LOHSE T., MARTIN J.M., MARTINEAU-HUYNH O., MARCOWITH A., MASTERSON C., MAURIN D., MAURIN G., McCOMB T.J.L., MODERSKI R., MOULIN E., DE NAUROIS M., NEDBAL D., NOLAN S.J., OHM S., OLIVE J.-P., DE ONA WILHELMI E., ORFORD K.J., OSBORNE J.L., OSTROWSKI M., PANTER M., PEDALETTI G., PELLETIER G., PETRUCCI P.-O., PITA S., PUEHLHOFER G., PUNCH M., RANCHON S., RAUBENHEIMER B.C., RAUE M., RAYNER S.M., RENAUD M., RIPKEN J., ROB L., ROLLAND L., ROSIER-LEES S., ROWELL G., RUDAK B., RUPPEL J., SAHAKIAN V., SANTANGELO A., SCHLICKEISER R., SCHOECK F., SCHROEDER R., SCHWANKE U., SCHWARZBURG S., SCHWEMMER S., SHALCHI A., SOL H., SPANGLER D., STAWARZ L., STEENKAMP R., STEGMANN C., SUPERINA G., TAM P.H., TAVERNET J.-P., TERRIER R., VAN ELDIK C., VASILEIADIS G., VENTER C., VIALLE J.P., VINCENT P., VIVIER M., VOELK H.J., VOLPE F., WAGNER S.J., WARD M., ZDZIARSKI A.A. and ZECH A.

Abstract (from CDS):

Our aim is to study the production mechanism for very-high-energy (VHE; >100GeV) γ-rays in distant active galactic nuclei (AGN) and use the observed VHE spectrum to derive limits on the Extragalactic Background Light (EBL). We also want to determine physical quantities through the modeling of the object's broad-band spectral energy distribution (SED). VHE observations (∼25h live time) of the BL Lac 1ES0347-121 (redshift z=0.188) were conducted with the High Energy Stereoscopic System (HESS) between August and December 2006. Contemporaneous X-ray and UV/optical observations from the SWIFT satellite are used to interpret the SED of the source in terms of a synchrotron self Compton (SSC) model. An excess of 327 events, corresponding to a statistical significance of 10.1 standard deviations, is detected from 1ES0347-121. Its photon spectrum, ranging from ∼250GeV to ∼3TeV, is well described by a power law with a photon index of Γ=3.10±0.23stat±0.10sys. The integral flux above 250GeV corresponds to ∼2% of the flux of the Crab Nebula above the same threshold. No VHE flux variability is detected within the data set. Constraints on the EBL density at optical to near-infrared wavelengths derived from the photon spectrum of 1ES0347-121 are close to the strongest limits derived previously. The strong EBL limits confirm earlier findings, that the EBL density in the near-infrared is close to the lower limits from source counts. This implies that the universe is more transparent to VHE γ-rays than previously believed. An SSC model provides a reasonable description of the contemporaneous SED.

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Journal keyword(s): galaxies: BL Lacertae objects: individual: 1ES0347-121 - gamma rays: observations - cosmology: diffuse radiation - galaxies: BL Lacertae objects: general - galaxies: active

Simbad objects: 3

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