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HESS J1943+213: a candidate extreme BL Lacertae object

A. Abramowski Fabio Acero 1 F. Aharonian A. G. Akhperjanian G. Anton Agnès Balzer A. Barnacka 2 U. Barres de Almeida A. R. Bazer-Bachi 3 Y. Becherini 4, 5 J. Becker B. Behera K. Bernlöhr A. Bochow C. Boisson 6 J. Bolmont 7 P. Bordas V. Borrel 3 J. Brucker F. Brun 4 P. Brun 2 T. Bulik I. Büsching S. Carrigan S. Casanova M. Cerruti 6 P. M. Chadwick A. Charbonnier 7 R. C. G. Chaves A. Cheesebrough L. -M. Chounet 4 A. C. Clapson G. Coignet 8 P. Colom 9 J. Conrad M. Dalton M. K. Daniel I. D. Davids B. Degrange 4 C. Deil H. J. Dickinson A. Djannati-Ataï 10 W. Domainko L. O'C. Drury F. Dubois 8 G. Dubus 11 J. Dyks M. Dyrda K. Egberts P. Eger P. Espigat 5 L. Fallon C. Farnier 1 S. Fegan 4 F. Feinstein 1 M. V. Fernandes A. Fiasson 8 G. Fontaine 4 A. Förster M. Füßling Y. A. Gallant 1 H. Gast L. Gérard 5 D. Gerbig B. Giebels 4 J. F. Glicenstein 2 B. Glück P. Goret 2 D. Göring S. Häffner J. D. Hague D. Hampf M. Hauser S. Heinz G. Heinzelmann G. Henri 11 G. Hermann J. A. Hinton A. Hoffmann W. Hofmann P. Hofverberg M. Holler D. Horns A. Jacholkowska 7 O. C. de Jager C. Jahn M. Jamrozy I. Jung M. A. Kastendieck K. Katarzyński U. Katz S. Kaufmann D. Keogh D. Khangulyan B. Khélifi 4 D. Klochkov W. Kluźniak T. Kneiske Nu. Komin 8 K. Kosack 2 R. Kossakowski 8 H. Laffon 4 G. Lamanna 8 D. Lennarz T. Lohse A. Lopatin C. -C. Lu V. Marandon 5 A. Marcowith 1 J. Masbou 8 D. Maurin 7 N. Maxted T. J. L. Mccomb M. C. Medina 2 J. Méhault 1 N. Nguyen R. Moderski Emmanuel Moulin 2 C. L. Naumann 7 M. Naumann-Godo 2 M. de Naurois 4 D. Nedbal D. Nekrassov B. Nicholas J. Niemiec S. J. Nolan S. Ohm J-F. Olive 3 E. de Oña Wilhelmi B. Opitz M. Ostrowski M. Panter M. Paz Arribas G. Pedaletti G. Pelletier 11 P. -O. Petrucci 11 S. Pita 5 G. Pühlhofer M. Punch 5 A. Quirrenbach M. Raue S. M. Rayner A. Reimer O. Reimer M. Renaud 1 R. de Los Reyes F. Rieger J. Ripken L. Rob S. Rosier-Lees 8 G. Rowell B. Rudak C. B. Rulten J. Ruppel F. Ryde V. Sahakian A. Santangelo R. Schlickeiser F. M. Schöck A. Schönwald A. Schulz U. Schwanke S. Schwarzburg S. Schwemmer A. Shalchi M. Sikora J. L. Skilton H. Sol 6 G. Spengler \l. Stawarz R. Steenkamp C. Stegmann F. Stinzing K. Stycz I. Sushch A. Szostek 11 J. -P. Tavernet 7 R. Terrier 5 O. Tibolla M. Tluczykont K. Valerius C. van Eldik G. Vasileiadis 1 C. Venter J. P. Vialle 8 A. Viana 2 P. Vincent 7 M. Vivier 2 H. J. Völk F. Volpe S. Vorobiov 1 M. Vorster S. J. Wagner M. Ward A. Wierzcholska A. Zajczyk A. A. Zdziarski A. Zech 6 H. -S. Zechlin T. H. Burnett A. B. Hill
1 LPTA - Laboratoire de Physique Théorique et Astroparticules
2 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
3 CESR - Centre d'étude spatiale des rayonnements
4 LLR - Laboratoire Leprince-Ringuet
5 APC (UMR_7164) - AstroParticule et Cosmologie
6 LUTH (UMR_8102) - Laboratoire Univers et Théories
7 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
8 LAPP - Laboratoire d'Annecy de Physique des Particules
9 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
10 APC - AHE - APC - Astrophysique des Hautes Energies
APC (UMR_7164) - AstroParticule et Cosmologie, Dipartimento di Astronomia, Universita degli Studi di Bologna
11 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
Abstract : 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 \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.
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Submitted on : Tuesday, March 29, 2011 - 9:52:11 AM
Last modification on : Thursday, January 7, 2021 - 5:56:02 PM

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A. Abramowski, Fabio Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, et al.. HESS J1943+213: a candidate extreme BL Lacertae object. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 529, pp.A49. ⟨10.1051/0004-6361/201116545⟩. ⟨in2p3-00580720⟩

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