Gamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS2155-304 and PG1553+113

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dc.citation.doi10.1051/0004-6361/201629427en_ZA
dc.contributor.authorChen, A.
dc.contributor.authorColafrancesco, S.
dc.contributor.authorJingo, M.
dc.contributor.authorKomin, Nu.
dc.contributor.authorShafi, N.
dc.contributor.authorAbdalla, H.
dc.contributor.authorAbramowski, A.
dc.contributor.authorAharonian, F.
dc.contributor.authorAit Benkhali, F.
dc.contributor.authorAkhperjanian, A. G.
dc.contributor.authorAndersson, T.
dc.contributor.authorAngüner, E. O.
dc.contributor.authorArrieta, M.
dc.contributor.authorAubert, P.
dc.contributor.authorBackes, M.
dc.contributor.authorBalzer, A.
dc.contributor.authorBarnard, M.
dc.contributor.authorBecherini, Y.
dc.contributor.authorBecker Tjus, J.
dc.contributor.authorBerge, D.
dc.contributor.authorBernhard, S.
dc.date.accessioned2018-02-06T14:41:58Z
dc.date.available2018-02-06T14:41:58Z
dc.date.issued2017-04
dc.description.abstractContext. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV for small zenith angle observations. Such an extension of the instrument's energy range is particularly beneficial for studies of active galactic nuclei with soft spectra, as expected for those at a redshift ≥0.5. The high-frequency peaked BL Lac objects PKS 2155-304 (z = 0:116) and PG 1553+113 (0:43 < z < 0:58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Aims. The aims of this work are twofold: to demonstrate the monoscopic analysis of CT5 data with a low energy threshold, and to obtain accurate measurements of the spectral energy distributions (SED) of PKS 2155-304 and PG 1553+113 near their SED peaks at energies 100 GeV. Methods. Multiple observational campaigns of PKS 2155-304 and PG 1553+113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument (CT1'5). A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis. Results. Using the data from CT5, the energy spectra of PKS 2155-304 and PG 1553+113 were reconstructed down to conservative threshold energies of 80 GeV for PKS 2155-304, which transits near zenith, and 110 GeV for the more northern PG 1553+113. The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5.0φ statistical preference for non-zero curvature for PKS 2155-304 and 4.5φ for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi-LAT spectrum of PKS 2155-304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.en_ZA
dc.description.librarianEM2018en_ZA
dc.identifier.citationAbdalla, H., Chen, A., and Colafrancesco, S. et al. 2017. Gamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS2155-304 and PG1553+113. ASTRONOMY & ASTROPHYSICS 600, Article number A89.en_ZA
dc.identifier.issn0004-6361 (Print)
dc.identifier.issn1432-0746 (Online)
dc.identifier.urihttps://hdl.handle.net/10539/23785
dc.journal.titleASTRONOMY & ASTROPHYSICSen_ZA
dc.journal.volume600en_ZA
dc.language.isoenen_ZA
dc.publisherEDP Sciencesen_ZA
dc.rights© ESO 2017en_ZA
dc.subjectAbsorption spectroscopyen_ZA
dc.subjectGalaxiesen_ZA
dc.subjectSpectroscopyen_ZA
dc.subjectTelescopesen_ZA
dc.subjectUncertainty analysisen_ZA
dc.subjectBL Lacertae objects: individual: PG 1553+113en_ZA
dc.subjectBL Lacertae objects: individual: PKS 2155-304en_ZA
dc.subjectGalaxies: activeen_ZA
dc.subjectGamma rays: galaxiesen_ZA
dc.subjectActive galactic nucleien_ZA
dc.subjectBL Lacertae objectsen_ZA
dc.subjectExtragalactic background lighten_ZA
dc.subjectSpectral energy distributionen_ZA
dc.subjectSystematic uncertaintiesen_ZA
dc.subjectGamma raysen_ZA
dc.titleGamma-ray blazar spectra with H.E.S.S. II mono analysis: The case of PKS2155-304 and PG1553+113en_ZA
dc.typeArticleen_ZA
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