Discovery of variable VHE γ -ray emission from the binary system 1FGL J1018.6-5856

A. Abramowski, F. Aharonian, F. Ait Benkhali, A. G. Akhperjanian, E. O. Angüner, M. Backes, A. Balzer, Y. Becherini, J. Becker Tjus, D. Berge, S. Bernhard, K. Bernlöhr, E. Birsin, R. Blackwell, M. Böttcher, C. Boisson, J. Bolmont, P. Bordas, J. Bregeon, F. BrunP. Brun, M. Bryan, T. Bulik, J. Carr, S. Casanova, N. Chakraborty, R. Chalme-Calvet, R. C G Chaves, A. Chen, M. Chrétien, S. Colafrancesco, G. Cologna, J. Conrad, C. Couturier, Y. Cui, I. D. Davids, B. Degrange, C. Deil, P. Dewilt, A. Djannati-Ataï, W. Domainko, A. Donath, L. O C Drury, G. Dubus, K. Dutson, J. Dyks, M. Dyrda, T. Edwards, K. Egberts, P. Eger, J. P. Ernenwein, P. Espigat, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, D. Fernandez, A. Fiasson, G. Fontaine, A. Förster, M. Füßling, S. Gabici, M. Gajdus, Y. A. Gallant, T. Garrigoux, G. Giavitto, B. Giebels, J. F. Glicenstein, D. Gottschall, A. Goyal, M. H. Grondin, M. Grudzińska, D. Hadasch, S. Häffner, J. Hahn, J. Hawkes, G. Heinzelmann, G. Henri, G. Hermann, O. Hervet, A. Hillert, J. A. Hinton, W. Hofmann, P. Hofverberg, C. Hoischen, M. Holler, D. Horns, A. Ivascenko, A. Jacholkowska, C. Jahn, M. Jamrozy, M. Janiak, F. Jankowsky, I. Jung-Richardt, M. A. Kastendieck, K. Katarzyński, U. Katz, D. Kerszberg, B. Khélifi, M. Kieffer, S. Klepser, D. Klochkov, W. Kluźniak, D. Kolitzus, Nu Komin, K. Kosack, S. Krakau, F. Krayzel, P. P. Krüger, H. Laffon, G. Lamanna, J. Lau, J. Lefaucheur, V. Lefranc, A. Lemière, M. Lemoine-Goumard, J. P. Lenain, T. Lohse, A. Lopatin, C. C. Lu, R. Lui, V. Marandon, A. Marcowith, C. Mariaud, R. Marx, G. Maurin, N. Maxted, M. Mayer, P. J. Meintjes, U. Menzler, M. Meyer, A. M W Mitchell, R. Moderski, M. Mohamed, K. Morå, E. Moulin, T. Murach, M. De Naurois, J. Niemiec, L. Oakes, H. Odaka, S. Öttl, 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, P. O. Petrucci, B. Peyaud, S. Pita, H. Poon, H. Prokoph, G. Pühlhofer, M. Punch, A. Quirrenbach, S. Raab, I. Reichardt, A. Reimer, O. Reimer, M. Renaud, R. De Los Reyes, F. Rieger, C. Romoli, S. Rosier-Lees, G. Rowell, B. Rudak, C. B. Rulten, V. Sahakian, D. Salek, D. A. Sanchez, A. Santangelo, M. Sasaki, R. Schlickeiser, F. Schüssler, A. Schulz, U. Schwanke, S. Schwemmer, A. S. Seyffert, R. Simoni, H. Sol, F. Spanier, G. Spengler, F. Spies, [No Value] Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, K. Stycz, I. Sushch, J. P. Tavernet, T. Tavernier, A. M. Taylor, R. Terrier, M. Tluczykont, C. Trichard, K. Valerius, J. Van Der Walt, C. Van Eldik, B. Van Soelen, G. Vasileiadis, J. Veh, C. Venter, A. Viana, P. Vincent, J. Vink, F. Voisin, H. J. Völk, T. Vuillaume, S. J. Wagner, P. Wagner, R. M. Wagner, M. Weidinger, Q. Weitzel, R. White, A. Wierzcholska, P. Willmann, A. Wörnlein, D. Wouters, R. Yang, V. Zabalza, D. Zaborov, M. Zacharias, A. A. Zdziarski, A. Zech, F. Zefi, N. Zywucka

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Abstract

Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018-589 A that is coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9σ and the detection of variability (χ2/ν of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy γ-ray binary detected by Fermi-LAT and also confirms the point-like source as a new VHE binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index Γ = 2.20 ± 0.14stat ± 0.2sys. Emission is detected up to ∼20 TeV. The mean differential flux level is (2.9 ± 0.4) × 10-13 TeV-1 cm-2 s-1 at 1 TeV, equivalent to ∼1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of Nσ> 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ ≲ 1 at 300 GeV).

Original languageEnglish (US)
Article numberA131
JournalAstronomy and Astrophysics
Volume577
DOIs
StatePublished - May 1 2015

Bibliographical note

Publisher Copyright:
© 2015 ESO.

Keywords

  • Acceleration of particles
  • Gamma rays: stars
  • Radiation mechanisms: non-thermal
  • Stars: individual: 1FGL J1018.6-5856
  • X-rays: binaries

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