%0 Journal Article
%T Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-5856
%A H. E. S. S. Collaboration
%A :
%A A. Abramowski
%A F. Aharonian
%A F. Ait Benkhali
%A A. G. Akhperjanian
%A E. O. Ang¨¹ner
%A M. Backes
%A A. Balzer
%A Y. Becherini
%A J. Becker Tjus
%A D. Berge
%A S. Bernhard
%A K. Bernl£¿hr
%A E. Birsin
%A R. Blackwell
%A M. B£¿ttcher
%A C. Boisson
%A J. Bolmont
%A P. Bordas
%A J. Bregeon
%A F. Brun
%A P. Brun
%A M. Bryan
%A T. Bulik
%A J. Carr
%A S. Casanova
%A N. Chakraborty
%A R. Chalme-Calvet
%A R. C. G. Chaves
%A A. Chen
%A M. Chr¨¦tien
%A S. Colafrancesco
%A G. Cologna
%A J. Conrad
%A C. Couturier
%A Y. Cui
%A I. D. Davids
%A B. Degrange
%A C. Deil
%A P. deWilt
%A A. Djannati-Ata£¿
%A W. Domainko
%A A. Donath
%A L. O'C. Drury
%A G. Dubus
%A K. Dutson
%A J. Dyks
%A M. Dyrda
%A T. Edwards
%A K. Egberts
%A P. Eger
%A J. -P. Ernenwein
%A P. Espigat
%A C. Farnier
%A S. Fegan
%A F. Feinstein
%A M. V. Fernandes
%A D. Fernandez
%A A. Fiasson
%A G. Fontaine
%A A. F£¿rster
%A M. F¨¹£¿ling
%A S. Gabici
%A M. Gajdus
%A Y. A. Gallant
%A T. Garrigoux
%A G. Giavitto
%A B. Giebels
%A J. F. Glicenstein
%A D. Gottschall
%A A. Goyal
%A M. -H. Grondin
%A M. Grudzi¨½ska
%A D. Hadasch
%A S. H£¿ffner
%A J. Hahn
%A J. Hawkes
%A G. Heinzelmann
%A G. Henri
%A G. Hermann
%A O. Hervet
%A A. Hillert
%A J. A. Hinton
%A W. Hofmann
%A P. Hofverberg
%A C. Hoischen
%A M. Holler
%A D. Horns
%A A. Ivascenko
%A A. Jacholkowska
%A C. Jahn
%A M. Jamrozy
%A M. Janiak
%A F. Jankowsky
%A I. Jung-Richardt
%A M. A. Kastendieck
%A K. Katarzy¨½ski
%A U. Katz
%A D. Kerszberg
%A B. Kh¨¦lifi
%A M. Kieffer
%A S. Klepser
%A D. Klochkov
%A W. Klu£¿niak
%A D. Kolitzus
%A Nu. Komin
%A K. Kosack
%A S. Krakau
%A F. Krayzel
%A P. P. Kr¨¹ger
%A H. Laffon
%A G. Lamanna
%A J. Lau
%A J. Lefaucheur
%A V. Lefranc
%A A. Lemi¨¨re
%A M. Lemoine-Goumard
%A J. -P. Lenain
%A T. Lohse
%A A. Lopatin
%A C. -C. Lu
%A R. Lui
%A V. Marandon
%A A. Marcowith
%A C. Mariaud
%A R. Marx
%A G. Maurin
%J Physics
%D 2015
%I arXiv
%R 10.1051/0004-6361/201525699
%X Re-observations with the H.E.S.S. telescope array of the very-high-energy (VHE) source HESS J1018-589 A coincident with the Fermi-LAT $\gamma$-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9$\sigma$, and the detection of variability ($\chi^2$/$\nu$ of 238.3/155) in the emitted $\gamma$-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy $\gamma$-ray binary detected by Fermi-LAT, and also confirms the point-like source as a new very-high-energy binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index $\Gamma = 2.20 \pm 0.14_{\rm stat} \pm 0.2_{\rm sys}$. Emission is detected up to ~20 TeV. The mean differential flux level is $(2.9 \pm 0.4)\times10^{-13}$ 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 lightcurve. When folded on the orbital period of 16.58 days, the rebinned lightcurve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the H.E.S.S. phaseogram to a constant flux provides evidence of periodicity at the level of 3$\sigma$. The shape of the VHE phaseogram and measured spectrum suggest a low inclination, low eccentricity system with a modest impact from VHE $\gamma$-ray absorption due to pair production ($\tau$ < 1 at 300 GeV).
%U http://arxiv.org/abs/1503.02711v1