The high-energy γ-ray emission of AP Librae

• Published in: Astronomy and astrophysics (Berlin) 2015-01, Vol.573, p.A31
• Main Authors: Abramowski, A., Aharonian, F., Akhperjanian, A. G., Anton, G., Balzer, A., Bernlöhr, K., Birsin, E., Biteau, J., Bolmont, J., Bordas, P., Brun, P., Chalme-Calvet, R., Cheesebrough, A., Chrétien, M., Colafrancesco, S., Cologna, G., Cui, Y., Dalton, M., Daniel, M. K., Deil, C., deWilt, P., Dickinson, H. J., Djannati-Ataï, A., Domainko, W., Dubus, G., Dyrda, M., Edwards, T., Egberts, K., Eger, P., Farnier, C., Fegan, S., Feinstein, F., Fernandes, M. V., Fiasson, A., Förster, A., Gajdus, M., Giavitto, G., Giebels, B., Grondin, M.-H., Grudzińska, M., Häffner, S., Heinzelmann, G., Henri, G., Hervet, O., Hillert, A., Hinton, J. A., Jahn, C., Janiak, M., Katarzyński, K., Klepser, S., Komin, Nu, Kosack, K., Krayzel, F., Krüger, P. P., Lemière, A., Lemoine-Goumard, M., Lu, C.-C., Maxted, N., Meintjes, P. J., Mohamed, M., Moulin, E., de Naurois, M., Oakes, L., Ohm, S., Oya, I., Petrucci, P.-O., Peyaud, B., Poon, H., Pühlhofer, G., Reichardt, I., Reimer, A., Renaud, M., Rob, L., Rowell, G., Rudak, B., Rulten, C. B., Sahakian, V., Sanchez, D. A., Santangelo, A., Schüssler, F., Schulz, A., Schwanke, U., Schwarzburg, S., Sol, H., Spengler, G., Spies, F., Steenkamp, R., Stycz, K., Sushch, I., Tavernier, T., Terrier, R., Trichard, C., van Eldik, C., Völk, H. J., Volpe, F., Ward, M., Weitzel, Q., Willmann, P., Wouters, D., Yang, R.
• Format: Article
• Language: English
• Subjects: Astronomy; Astroparticle Physics; Astropartikelfysik; Astrophysics; BL Lacertae objects: individual: AP Librae; Emission; Flux; Fluxes; galaxies: active; gamma rays: galaxies; High Energy Astrophysical Phenomena; Light curve; Mathematical analysis; Sciences of the Universe; Spectra; Spectral energy distribution
• ISSN: 0004-6361; 1432-0746; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201321436

The γ-ray spectrum of the low-frequency-peaked BL Lac (LBL) object AP Librae is studied, following the discovery of very-high-energy (VHE; E> 100 GeV) γ-ray emission up to the TeV range by the H.E.S.S. experiment. This makes AP Librae one of the few VHE emitters of the LBL type. The measured spectrum yields a flux of (8.8 ± 1.5stat ± 1.8sys) × 10-12 cm-2 s-1 above 130 GeV and a spectral index of Γ = 2.65 ± 0.19stat ± 0.20sys. This study also makes use of Fermi-LAT  observations in the high energy (HE, E> 100 MeV) range, providing the longest continuous light curve (5 years) ever published on this source. The source underwent a flaring event between MJD 56 306–56 376 in the HE range, with a flux increase of a factor of 3.5 in the 14 day bin light curve and no significant variation in spectral shape with respect to the low-flux state. While the H.E.S.S.  and (low state) Fermi-LAT fluxes are in good agreement where they overlap, a spectral curvature between the steep VHE spectrum and the Fermi-LAT  spectrum is observed. The maximum of the γ-ray emission in the spectral energy distribution is located below the GeV energy range.