HESS J1943+213: a candidate extreme BL Lacertae object
Creators: name: Collaboration, H. E. S. S.
name: :
name: Abramowski, A.
name: Acero, F.
name: Aharonian, F.
name: Akhperjanian, A. G.
name: Anton, G.
name: Balzer, A.
name: Barnacka, A.
name: de Almeida, U. Barres
name: Bazer-Bachi, A. R.
name: Becherini, Y.
name: Becker, J.
name: Behera, B.
name: Bernlöhr, K.
name: Bochow, A.
name: Boisson, C.
name: Bolmont, J.
name: Bordas, P.
name: Borrel, V.
name: Brucker, J.
name: Brun, F.
name: Brun, P.
name: Bulik, T.
name: Büsching, I.
name: Carrigan, S.
name: Casanova, S.
name: Cerruti, M.
name: Chadwick, P. M.
name: Charbonnier, A.
name: Chaves, R. C. G.
name: Cheesebrough, A.
name: Chounet, L. -M.
name: Clapson, A. C.
name: Coignet, G.
name: Colom, P.
name: Conrad, J.
name: Dalton, M.
name: Daniel, M. K.
name: Davids, I. D.
name: Degrange, B.
name: Deil, C.
name: Dickinson, H. J.
name: Djannati-Ataï, A.
name: Domainko, W.
name: Drury, L. O'C.
name: Dubois, F.
name: Dubus, G.
name: Dyks, J.
name: Dyrda, M.
name: Egberts, K.
name: Eger, P.
name: Espigat, P.
name: Fallon, L.
name: Farnier, C.
name: Fegan, S.
name: Feinstein, F.
name: Fernandes, M. V.
name: Fiasson, A.
name: Fontaine, G.
name: Förster, A.
name: Füßling, M.
name: Gallant, Y. A.
name: Gast, H.
name: Gérard, L.
name: Gerbig, D.
name: Giebels, B.
name: Glicenstein, J. F.
name: Glück, B.
name: Goret, P.
name: Göring, D.
name: Häffner, S.
name: Hague, J. D.
name: Hampf, D.
name: Hauser, M.
name: Heinz, S.
name: Heinzelmann, G.
name: Henri, G.
name: Hermann, G.
name: Hinton, J. A.
name: Hoffmann, A.
name: Hofmann, W.
name: Hofverberg, P.
name: Holler, M.
name: Horns, D.
name: Jacholkowska, A.
name: de Jager, O. C.
name: Jahn, C.
name: Jamrozy, M.
name: Jung, I.
name: Kastendieck, M. A.
name: Katarzyński, K.
name: Katz, U.
name: Kaufmann, S.
name: Keogh, D.
name: Khangulyan, D.
name: Khélifi, B.
name: Klochkov, D.
name: Kluźniak, W.
name: Kneiske, T.
name: Komin, Nu.
name: Kosack, K.
name: Kossakowski, R.
name: Laffon, H.
name: Lamanna, G.
name: Lennarz, D.
name: Lohse, T.
name: Lopatin, A.
name: Lu, C. -C.
name: Marandon, V.
name: Marcowith, A.
name: Masbou, J.
name: Maurin, D.
name: Maxted, N.
name: McComb, T. J. L.
name: Medina, M. C.
name: Méhault, J.
name: Nguyen, N.
name: Moderski, R.
name: Moulin, E.
name: Naumann, C. L.
name: Naumann-Godo, M.
name: de Naurois, M.
name: Nedbal, D.
name: Nekrassov, D.
name: Nicholas, B.
name: Niemiec, J.
name: Nolan, S. J.
name: Ohm, S.
name: Olive, J-F.
name: Wilhelmi, E. de Oña
name: Opitz, B.
name: Ostrowski, M.
name: Panter, M.
name: Arribas, M. Paz
name: Pedaletti, G.
name: Pelletier, G.
name: Petrucci, P. -O.
name: Pita, S.
name: Pühlhofer, G.
name: Punch, M.
name: Quirrenbach, A.
name: Raue, M.
name: Rayner, S. M.
name: Reimer, A.
name: Reimer, O.
name: Renaud, M.
name: Reyes, R. de los
name: Rieger, F.
name: Ripken, J.
name: Rob, L.
name: Rosier-Lees, S.
name: Rowell, G.
name: Rudak, B.
name: Rulten, C. B.
name: Ruppel, J.
name: Ryde, F.
name: Sahakian, V.
name: Santangelo, A.
name: Schlickeiser, R.
name: Schöck, F. M.
name: Schönwald, A.
name: Schulz, A.
name: Schwanke, U.
name: Schwarzburg, S.
name: Schwemmer, S.
name: Shalchi, A.
name: Sikora, M.
name: Skilton, J. L.
name: Sol, H.
name: Spengler, G.
name: Stawarz, Ł.
name: Steenkamp, R.
name: Stegmann, C.
name: Stinzing, F.
name: Stycz, K.
name: Sushch, I.
name: Szostek, A.
name: Tavernet, J. -P.
name: Terrier, R.
name: Tibolla, O.
name: Tluczykont, M.
name: Valerius, K.
name: van Eldik, C.
name: Vasileiadis, G.
name: Venter, C.
name: Vialle, J. P.
name: Viana, A.
name: Vincent, P.
name: Vivier, M.
name: Völk, H. J.
name: Volpe, F.
name: Vorobiov, S.
name: Vorster, M.
name: Wagner, S. J.
name: Ward, M.
name: Wierzcholska, A.
name: Zajczyk, A.
name: Zdziarski, A. A.
name: Zech, A.
name: Zechlin, H. -S.
name: Burnett, T. H.
name: Hill, A. B.
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We 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 σ(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&gt;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.
description: 10 pages, 7 figures, in press at A&amp;A