HESS J1943+213: a candidate extreme BL Lacertae object
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.
Cite
@article{arxiv.1103.0763,
title = {HESS J1943+213: a candidate extreme BL Lacertae object},
author = {H. E. S. S. Collaboration and : and A. Abramowski and F. Acero and F. Aharonian and A. G. Akhperjanian and G. Anton and A. Balzer and A. Barnacka and U. Barres de Almeida and A. R. Bazer-Bachi and Y. Becherini and J. Becker and B. Behera and K. Bernlöhr and A. Bochow and C. Boisson and J. Bolmont and P. Bordas and V. Borrel and J. Brucker and F. Brun and P. Brun and T. Bulik and I. Büsching and S. Carrigan and S. Casanova and M. Cerruti and P. M. Chadwick and A. Charbonnier and R. C. G. Chaves and A. Cheesebrough and L. -M. Chounet and A. C. Clapson and G. Coignet and P. Colom and J. Conrad and M. Dalton and M. K. Daniel and I. D. Davids and B. Degrange and C. Deil and H. J. Dickinson and A. Djannati-Ataï and W. Domainko and L. O'C. Drury and F. Dubois and G. Dubus and J. Dyks and M. Dyrda and K. Egberts and P. Eger and P. Espigat and L. Fallon and C. Farnier and S. Fegan and F. Feinstein and M. V. Fernandes and A. Fiasson and G. Fontaine and A. Förster and M. Füßling and Y. A. Gallant and H. Gast and L. Gérard and D. Gerbig and B. Giebels and J. F. Glicenstein and B. Glück and P. Goret and D. Göring and S. Häffner and J. D. Hague and D. Hampf and M. Hauser and S. Heinz and G. Heinzelmann and G. Henri and G. Hermann and J. A. Hinton and A. Hoffmann and W. Hofmann and P. Hofverberg and M. Holler and D. Horns and A. Jacholkowska and O. C. de Jager and C. Jahn and M. Jamrozy and I. Jung and M. A. Kastendieck and K. Katarzyński and U. Katz and S. Kaufmann and D. Keogh and D. Khangulyan and B. Khélifi and D. Klochkov and W. Kluźniak and T. Kneiske and Nu. Komin and K. Kosack and R. Kossakowski and H. Laffon and G. Lamanna and D. Lennarz and T. Lohse and A. Lopatin and C. -C. Lu and V. Marandon and A. Marcowith and J. Masbou and D. Maurin and N. Maxted and T. J. L. McComb and M. C. Medina and J. Méhault and N. Nguyen and R. Moderski and E. Moulin and C. L. Naumann and M. Naumann-Godo and M. de Naurois and D. Nedbal and D. Nekrassov and B. Nicholas and J. Niemiec and S. J. Nolan and S. Ohm and J-F. Olive and E. de Oña Wilhelmi and B. Opitz and M. Ostrowski and M. Panter and M. Paz Arribas and G. Pedaletti and G. Pelletier and P. -O. Petrucci and S. Pita and G. Pühlhofer and M. Punch and A. Quirrenbach and M. Raue and S. M. Rayner and A. Reimer and O. Reimer and M. Renaud and R. de los Reyes and F. Rieger and J. Ripken and L. Rob and S. Rosier-Lees and G. Rowell and B. Rudak and C. B. Rulten and J. Ruppel and F. Ryde and V. Sahakian and A. Santangelo and R. Schlickeiser and F. M. Schöck and A. Schönwald and A. Schulz and U. Schwanke and S. Schwarzburg and S. Schwemmer and A. Shalchi and M. Sikora and J. L. Skilton and H. Sol and G. Spengler and Ł. Stawarz and R. Steenkamp and C. Stegmann and F. Stinzing and K. Stycz and I. Sushch and A. Szostek and J. -P. Tavernet and R. Terrier and O. Tibolla and M. Tluczykont and K. Valerius and C. van Eldik and G. Vasileiadis and C. Venter and J. P. Vialle and A. Viana and P. Vincent and M. Vivier and H. J. Völk and F. Volpe and S. Vorobiov and M. Vorster and S. J. Wagner and M. Ward and A. Wierzcholska and A. Zajczyk and A. A. Zdziarski and A. Zech and H. -S. Zechlin and T. H. Burnett and A. B. Hill},
journal= {arXiv preprint arXiv:1103.0763},
year = {2016}
}
Comments
10 pages, 7 figures, in press at A&A