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dc.contributor.authorBüsching, I.
dc.contributor.authorDe Jager, O.C.
dc.contributor.authorVenter, C.
dc.contributor.authorVorster, M.
dc.date.accessioned2012-09-05T08:23:00Z
dc.date.available2012-09-05T08:23:00Z
dc.date.issued2011
dc.identifier.citationBüsching, I. et al. 2011. HESS J1943+213: a candidate extreme BL Lacertae object. Astronomy & astrophysics, 526: Article no A49. [https://doi.org/10.1051/0004-6361/201116545]en_US
dc.identifier.issn0004-6361
dc.identifier.issn1432-0746 (Online)
dc.identifier.urihttp://hdl.handle.net/10394/7231
dc.identifier.urihttps://doi.org/10.1051/0004-6361/201116545
dc.description.abstractWe report on a newly detected point-like source, HESS J1943+213 located in the Galactic plane. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. HESS J1943+213 is detected at the significance level of 7.9 \sigma (post-trials) at RA(J2000)=19h 43m 55s +- 1s (stat) +- 1s (sys), DEC(J2000) = +21deg 18' 8" +- 17" (stat) +- 20" (sys). The source has a soft spectrum with photon index Gamma = 3.1 +- 0.3 (stat) +- 0.2 (sys) and a flux above 470 GeV of 1.3 +- 0.2 (stat) +- 0.3 (sys) x 10^{-12} cm^{-2} s^{-1}. There is no Fermi/LAT counterpart down to a flux limit of 6 x 10^{-9} cm^{-2} s^{-1} in the 0.1-100 GeV energy range (95% confidence upper limit calculated for an assumed power-law model with a photon index Gamma=2.0). The data from radio to VHE gamma-rays do not show any significant variability. We combine new H.E.S.S., Fermi/LAT and Nancay Radio Telescope observations with pre-existing non-simultaneous multi-wavelength observations of IGR J19443+2117 and discuss the likely source associations as well as the interpretation as an active galactic nucleus, a gamma-ray binary or a pulsar wind nebula. The lack of a massive stellar counterpart disfavors the binary hypothesis, while the soft VHE spectrum would be very unusual in case of a pulsar wind nebula. In addition, the distance estimates for Galactic counterparts places them outside of the Milky Way. All available observations favor an interpretation as an extreme, high-frequency peaked BL Lac object with a redshift z>0.14. This would be the first time a blazar is detected serendipitously from ground-based VHE observations, and the first VHE AGN detected in the Galactic Plane.en_US
dc.language.isoenen_US
dc.publisherEDP Sciencesen_US
dc.subjectGalaxies: active
dc.subjectBL Lacertae objects: individual: IGR J19443+2117
dc.subjectGamma rays: general
dc.titleHESS J1943+213: a candidate extreme BL Lacertae objecten_US
dc.typeArticleen_US
dc.contributor.researchID12006653 - Venter, Christo
dc.contributor.researchID12792322 - Vorster, Michael Johannes
dc.contributor.researchID13235176 - Büsching, Ingo
dc.contributor.researchID10065857 - De Jager, Ocker Cornelis


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