HESS J1943+213: A candidate extreme BL Lacertae object

A. Abramowski; F. Acero; F. Aharonian; A. G. Akhperjanian; G. Anton; A. Balzer; A. Barnacka; U. Barres De Almeida; A. R. Bazer-Bachi; Y. Becherini; J. Becker; B. Behera; K. Bernlöhr; A. Bochow; C. Boisson; J. Bolmont; P. Bordas; V. Borrel; J. Brucker; F. Brun; P. Brun; T. Bulik; I. Büsching; S. Carrigan; S. Casanova; M. Cerruti; P. M. Chadwick; A. Charbonnier; R. C G Chaves; A. Cheesebrough; L. M. Chounet; A. C. Clapson; G. Coignet; P. Colom; J. Conrad; M. Dalton; M. K. Daniel; I. D. Davids; B. Degrange; C. Deil; H. J. Dickinson; A. Djannati-Ataï; W. Domainko; L. O C Drury; F. Dubois; G. Dubus; J. Dyks; M. Dyrda; K. Egberts; P. Eger; P. Espigat; L. Fallon; C. Farnier; S. Fegan; F. Feinstein; M. V. Fernandes; A. Fiasson; G. Fontaine; A. Förster; M. Füßling; Y. A. Gallant; H. Gast; L. Gérard; D. Gerbig; B. Giebels; J. F. Glicenstein; B. Glück; P. Goret; D. Göring; S. Häffner; J. D. Hague; D. Hampf; M. Hauser; S. Heinz; G. Heinzelmann; G. Henri; G. Hermann; J. A. Hinton; A. Hoffmann; W. Hofmann; P. Hofverberg; M. Holler; D. Horns; A. Jacholkowska; 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; D. Klochkov; W. Kluźniak; T. Kneiske; Nu Komin; K. Kosack; R. Kossakowski; H. Laffon; G. Lamanna; D. Lennarz; T. Lohse; A. Lopatin; C. C. Lu; V. Marandon; A. Marcowith; J. Masbou; D. Maurin; N. Maxted; T. J L McComb; M. C. Medina; J. Méhault; N. Nguyen; R. Moderski; E. Moulin; C. L. Naumann; M. Naumann-Godo; M. De Naurois; D. Nedbal; D. Nekrassov; B. Nicholas; J. Niemiec; S. J. Nolan; S. Ohm; J. F. Olive; E. De Oña Wilhelmi; B. Opitz; M. Ostrowski; M. Panter; M. Paz Arribas; G. Pedaletti; G. Pelletier; P. O. Petrucci; S. Pita; G. Pühlhofer; M. Punch; A. Quirrenbach; M. Raue; S. M. Rayner; A. Reimer; O. Reimer; M. Renaud; R. De Los Reyes; F. Rieger; J. Ripken; L. Rob; S. Rosier-Lees; 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; G. Spengler; L. Stawarz; R. Steenkamp; C. Stegmann; F. Stinzing; K. Stycz; I. Sushch; A. Szostek; J. P. Tavernet; R. Terrier; O. Tibolla; M. Tluczykont; K. Valerius; C. Van Eldik; G. Vasileiadis; C. Venter; J. P. Vialle; A. Viana; P. Vincent; M. Vivier; H. J. Völk; F. Volpe; S. Vorobiov; M. Vorster; S. J. Wagner; M. Ward; A. Wierzcholska; A. Zajczyk; A. A. Zdziarski; A. Zech; H. S. Zechlin; T. H. Burnett; A. B. Hill

doi:10.1051/0004-6361/201116545

HESS J1943+213: A candidate extreme BL Lacertae object

A. Abramowski, F. Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, A. Balzer, A. Barnacka, U. Barres De Almeida, A. R. Bazer-Bachi, Y. Becherini, J. Becker, B. Behera, K. Bernlöhr, A. Bochow, C. Boisson, J. Bolmont, P. Bordas, V. Borrel, J. Brucker, F. BrunP. Brun, T. Bulik, I. Büsching, S. Carrigan, S. Casanova, M. Cerruti, P. M. Chadwick, A. Charbonnier, R. C G Chaves, A. Cheesebrough, L. M. Chounet, A. C. Clapson, G. Coignet, P. Colom, J. Conrad, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O C Drury, F. Dubois, G. Dubus, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, C. Farnier, S. Fegan, F. Feinstein, M. V. Fernandes, A. Fiasson, G. Fontaine, A. Förster, M. Füßling, Y. A. Gallant, H. Gast, L. Gérard, D. Gerbig, B. Giebels, J. F. Glicenstein, B. Glück, P. Goret, D. Göring, S. Häffner, J. D. Hague, D. Hampf, M. Hauser, S. Heinz, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, A. Hoffmann, W. Hofmann, P. Hofverberg, M. Holler, D. Horns, A. Jacholkowska, 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, D. Klochkov, W. Kluźniak, T. Kneiske, Nu Komin, K. Kosack, R. Kossakowski, H. Laffon, G. Lamanna, D. Lennarz, T. Lohse, A. Lopatin, C. C. Lu, V. Marandon, A. Marcowith, J. Masbou, D. Maurin, N. Maxted, T. J L McComb, M. C. Medina, J. Méhault, N. Nguyen, R. Moderski, E. Moulin, C. L. Naumann, M. Naumann-Godo, M. De Naurois, D. Nedbal, D. Nekrassov, B. Nicholas, J. Niemiec, S. J. Nolan, S. Ohm, J. F. Olive, E. De Oña Wilhelmi, B. Opitz, M. Ostrowski, M. Panter, M. Paz Arribas, G. Pedaletti, G. Pelletier, P. O. Petrucci, S. Pita, G. Pühlhofer, M. Punch, A. Quirrenbach, M. Raue, S. M. Rayner, A. Reimer, O. Reimer, M. Renaud, R. De Los Reyes, F. Rieger, J. Ripken, L. Rob, S. Rosier-Lees, 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, G. Spengler, L. Stawarz, R. Steenkamp, C. Stegmann, F. Stinzing, K. Stycz, I. Sushch, A. Szostek, J. P. Tavernet, R. Terrier, O. Tibolla, M. Tluczykont, K. Valerius, C. Van Eldik, G. Vasileiadis, C. Venter, J. P. Vialle, A. Viana, P. Vincent, M. Vivier, H. J. Völk, F. Volpe, S. Vorobiov, M. Vorster, S. J. Wagner, M. Ward, A. Wierzcholska, A. Zajczyk, A. A. Zdziarski, A. Zech, H. S. Zechlin, T. H. Burnett, A. B. Hill

Physics and Astronomy (Twin Cities)

Research output: Contribution to journal › Article › peer-review

31 Scopus citations

Abstract

Context. The H.E.S.S. Cherenkov telescope array has been surveying the Galactic plane for new VHE (>100 GeV) gamma-ray sources. Aims. We report on a newly detected point-like source, HESS J1943+213. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. Methods. We combine new H.E.S.S., Fermi/LAT and Nançay 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. Results. HESS J1943+213 is detected at the significance level of 7.9σ (post-trials) at RA(J2000)= 19 ^h43^m55^s ± 1^s _stat ± 1^s _say, Dec(J2000)= +21° 18'8" ± 17"_stat ± 20"_sys. The source has a soft spectrum with photon index Γ = 3.1 ± 0.3_stat ± 0.2_sys and a flux above 470 GeV of (1.3 ± 0.2_stat ± 0.3_sys) × 10^-12 cm^-2 s ^-1. There is no Fermi/LAT counterpart down to a flux limit of 6 × 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 Γ = 2.0). The data from radio to VHE gamma-rays do not show any significant variability. Conclusions. 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.

Original language	English (US)
Article number	A49
Journal	Astronomy and Astrophysics
Volume	529
DOIs	https://doi.org/10.1051/0004-6361/201116545
State	Published - 2011

Keywords

galaxies: active
gamma rays: general

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10.1051/0004-6361/201116545

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Abramowski, A., Acero, F., Aharonian, F., Akhperjanian, A. G., Anton, G., Balzer, A., Barnacka, A., Barres De Almeida, U., Bazer-Bachi, A. R., Becherini, Y., Becker, J., Behera, B., Bernlöhr, K., Bochow, A., Boisson, C., Bolmont, J., Bordas, P., Borrel, V., Brucker, J., ... Hill, A. B. (2011). HESS J1943+213: A candidate extreme BL Lacertae object. Astronomy and Astrophysics, 529, Article A49. https://doi.org/10.1051/0004-6361/201116545

Abramowski, A, Acero, F, Aharonian, F, Akhperjanian, AG, Anton, G, Balzer, A, Barnacka, A, Barres De Almeida, U, Bazer-Bachi, AR, Becherini, Y, Becker, J, Behera, B, Bernlöhr, K, Bochow, A, Boisson, C, Bolmont, J, Bordas, P, Borrel, V, Brucker, J, Brun, F, Brun, P, Bulik, T, Büsching, I, Carrigan, S, Casanova, S, Cerruti, M, Chadwick, PM, Charbonnier, A, Chaves, RCG, Cheesebrough, A, Chounet, LM, Clapson, AC, Coignet, G, Colom, P, Conrad, J, Dalton, M, Daniel, MK, Davids, ID, Degrange, B, Deil, C, Dickinson, HJ, Djannati-Ataï, A, Domainko, W, Drury, LOC, Dubois, F, Dubus, G, Dyks, J, Dyrda, M, Egberts, K, Eger, P, Espigat, P, Fallon, L, Farnier, C, Fegan, S, Feinstein, F, Fernandes, MV, Fiasson, A, Fontaine, G, Förster, A, Füßling, M, Gallant, YA, Gast, H, Gérard, L, Gerbig, D, Giebels, B, Glicenstein, JF, Glück, B, Goret, P, Göring, D, Häffner, S, Hague, JD, Hampf, D, Hauser, M, Heinz, S, Heinzelmann, G, Henri, G, Hermann, G, Hinton, JA, Hoffmann, A, Hofmann, W, Hofverberg, P, Holler, M, Horns, D, Jacholkowska, A, De Jager, OC, Jahn, C, Jamrozy, M, Jung, I, Kastendieck, MA, Katarzyński, K, Katz, U, Kaufmann, S, Keogh, D, Khangulyan, D, Khélifi, B, Klochkov, D, Kluźniak, W, Kneiske, T, Komin, N, Kosack, K, Kossakowski, R, Laffon, H, Lamanna, G, Lennarz, D, Lohse, T, Lopatin, A, Lu, CC, Marandon, V, Marcowith, A, Masbou, J, Maurin, D, Maxted, N, McComb, TJL, Medina, MC, Méhault, J, Nguyen, N, Moderski, R, Moulin, E, Naumann, CL, Naumann-Godo, M, De Naurois, M, Nedbal, D, Nekrassov, D, Nicholas, B, Niemiec, J, Nolan, SJ, Ohm, S, Olive, JF, De Oña Wilhelmi, E, Opitz, B, Ostrowski, M, Panter, M, Paz Arribas, M, Pedaletti, G, Pelletier, G, Petrucci, PO, Pita, S, Pühlhofer, G, Punch, M, Quirrenbach, A, Raue, M, Rayner, SM, Reimer, A, Reimer, O, Renaud, M, De Los Reyes, R, Rieger, F, Ripken, J, Rob, L, Rosier-Lees, S, Rowell, G, Rudak, B, Rulten, CB, Ruppel, J, Ryde, F, Sahakian, V, Santangelo, A, Schlickeiser, R, Schöck, FM, Schönwald, A, Schulz, A, Schwanke, U, Schwarzburg, S, Schwemmer, S, Shalchi, A, Sikora, M, Skilton, JL, Sol, H, Spengler, G, Stawarz, L, Steenkamp, R, Stegmann, C, Stinzing, F, Stycz, K, Sushch, I, Szostek, A, Tavernet, JP, Terrier, R, Tibolla, O, Tluczykont, M, Valerius, K, Van Eldik, C, Vasileiadis, G, Venter, C, Vialle, JP, Viana, A, Vincent, P, Vivier, M, Völk, HJ, Volpe, F, Vorobiov, S, Vorster, M, Wagner, SJ, Ward, M, Wierzcholska, A, Zajczyk, A, Zdziarski, AA, Zech, A, Zechlin, HS, Burnett, TH & Hill, AB 2011, 'HESS J1943+213: A candidate extreme BL Lacertae object', Astronomy and Astrophysics, vol. 529, A49. https://doi.org/10.1051/0004-6361/201116545

@article{3e88ef8b96f04b88852e8081f5307b26,

title = "HESS J1943+213: A candidate extreme BL Lacertae object",

abstract = "Context. The H.E.S.S. Cherenkov telescope array has been surveying the Galactic plane for new VHE (>100 GeV) gamma-ray sources. Aims. We report on a newly detected point-like source, HESS J1943+213. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. Methods. We combine new H.E.S.S., Fermi/LAT and Nan{\c c}ay 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. Results. HESS J1943+213 is detected at the significance level of 7.9σ (post-trials) at RA(J2000)= 19 h43m55s ± 1s stat ± 1s say, Dec(J2000)= +21° 18'8{"} ± 17{"}stat ± 20{"}sys. The source has a soft spectrum with photon index Γ = 3.1 ± 0.3stat ± 0.2sys and a flux above 470 GeV of (1.3 ± 0.2stat ± 0.3sys) × 10-12 cm-2 s -1. There is no Fermi/LAT counterpart down to a flux limit of 6 × 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 Γ = 2.0). The data from radio to VHE gamma-rays do not show any significant variability. Conclusions. 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.",

keywords = "galaxies: active, gamma rays: general",

author = "A. Abramowski and F. Acero and F. Aharonian and Akhperjanian, {A. G.} and G. Anton and A. Balzer and A. Barnacka and {Barres De Almeida}, U. and Bazer-Bachi, {A. R.} and Y. Becherini and J. Becker and B. Behera and K. Bernl{\"o}hr 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. B{\"u}sching and S. Carrigan and S. Casanova and M. Cerruti and Chadwick, {P. M.} and A. Charbonnier and Chaves, {R. C G} and A. Cheesebrough and Chounet, {L. M.} and Clapson, {A. C.} and G. Coignet and P. Colom and J. Conrad and M. Dalton and Daniel, {M. K.} and Davids, {I. D.} and B. Degrange and C. Deil and Dickinson, {H. J.} and A. Djannati-Ata{\"i} and W. Domainko and Drury, {L. O C} 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 Fernandes, {M. V.} and A. Fiasson and G. Fontaine and A. F{\"o}rster and M. F{\"u}{\ss}ling and Gallant, {Y. A.} and H. Gast and L. G{\'e}rard and D. Gerbig and B. Giebels and Glicenstein, {J. F.} and B. Gl{\"u}ck and P. Goret and D. G{\"o}ring and S. H{\"a}ffner and Hague, {J. D.} and D. Hampf and M. Hauser and S. Heinz and G. Heinzelmann and G. Henri and G. Hermann and Hinton, {J. A.} and A. Hoffmann and W. Hofmann and P. Hofverberg and M. Holler and D. Horns and A. Jacholkowska and {De Jager}, {O. C.} and C. Jahn and M. Jamrozy and I. Jung and Kastendieck, {M. A.} and K. Katarzy{\'n}ski and U. Katz and S. Kaufmann and D. Keogh and D. Khangulyan and B. Kh{\'e}lifi and D. Klochkov and W. Klu{\'z}niak 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 Lu, {C. C.} and V. Marandon and A. Marcowith and J. Masbou and D. Maurin and N. Maxted and McComb, {T. J L} and Medina, {M. C.} and J. M{\'e}hault and N. Nguyen and R. Moderski and E. Moulin and Naumann, {C. L.} and M. Naumann-Godo and {De Naurois}, M. and D. Nedbal and D. Nekrassov and B. Nicholas and J. Niemiec and Nolan, {S. J.} and S. Ohm and Olive, {J. F.} and {De O{\~n}a Wilhelmi}, E. and B. Opitz and M. Ostrowski and M. Panter and {Paz Arribas}, M. and G. Pedaletti and G. Pelletier and Petrucci, {P. O.} and S. Pita and G. P{\"u}hlhofer and M. Punch and A. Quirrenbach and M. Raue and Rayner, {S. M.} and A. Reimer and O. Reimer and M. Renaud and {De Los Reyes}, R. and F. Rieger and J. Ripken and L. Rob and S. Rosier-Lees and G. Rowell and B. Rudak and Rulten, {C. B.} and J. Ruppel and F. Ryde and V. Sahakian and A. Santangelo and R. Schlickeiser and Sch{\"o}ck, {F. M.} and A. Sch{\"o}nwald and A. Schulz and U. Schwanke and S. Schwarzburg and S. Schwemmer and A. Shalchi and M. Sikora and Skilton, {J. L.} and H. Sol and G. Spengler and L. Stawarz and R. Steenkamp and C. Stegmann and F. Stinzing and K. Stycz and I. Sushch and A. Szostek and Tavernet, {J. P.} and R. Terrier and O. Tibolla and M. Tluczykont and K. Valerius and {Van Eldik}, C. and G. Vasileiadis and C. Venter and Vialle, {J. P.} and A. Viana and P. Vincent and M. Vivier and V{\"o}lk, {H. J.} and F. Volpe and S. Vorobiov and M. Vorster and Wagner, {S. J.} and M. Ward and A. Wierzcholska and A. Zajczyk and Zdziarski, {A. A.} and A. Zech and Zechlin, {H. S.} and Burnett, {T. H.} and Hill, {A. B.}",

year = "2011",

doi = "10.1051/0004-6361/201116545",

language = "English (US)",

volume = "529",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

TY - JOUR

T1 - HESS J1943+213

T2 - A candidate extreme BL Lacertae object

AU - Abramowski, A.

AU - Acero, F.

AU - Aharonian, F.

AU - Akhperjanian, A. G.

AU - Anton, G.

AU - Balzer, A.

AU - Barnacka, A.

AU - Barres De Almeida, U.

AU - Bazer-Bachi, A. R.

AU - Becherini, Y.

AU - Becker, J.

AU - Behera, B.

AU - Bernlöhr, K.

AU - Bochow, A.

AU - Boisson, C.

AU - Bolmont, J.

AU - Bordas, P.

AU - Borrel, V.

AU - Brucker, J.

AU - Brun, F.

AU - Brun, P.

AU - Bulik, T.

AU - Büsching, I.

AU - Carrigan, S.

AU - Casanova, S.

AU - Cerruti, M.

AU - Chadwick, P. M.

AU - Charbonnier, A.

AU - Chaves, R. C G

AU - Cheesebrough, A.

AU - Chounet, L. M.

AU - Clapson, A. C.

AU - Coignet, G.

AU - Colom, P.

AU - Conrad, J.

AU - Dalton, M.

AU - Daniel, M. K.

AU - Davids, I. D.

AU - Degrange, B.

AU - Deil, C.

AU - Dickinson, H. J.

AU - Djannati-Ataï, A.

AU - Domainko, W.

AU - Drury, L. O C

AU - Dubois, F.

AU - Dubus, G.

AU - Dyks, J.

AU - Dyrda, M.

AU - Egberts, K.

AU - Eger, P.

AU - Espigat, P.

AU - Fallon, L.

AU - Farnier, C.

AU - Fegan, S.

AU - Feinstein, F.

AU - Fernandes, M. V.

AU - Fiasson, A.

AU - Fontaine, G.

AU - Förster, A.

AU - Füßling, M.

AU - Gallant, Y. A.

AU - Gast, H.

AU - Gérard, L.

AU - Gerbig, D.

AU - Giebels, B.

AU - Glicenstein, J. F.

AU - Glück, B.

AU - Goret, P.

AU - Göring, D.

AU - Häffner, S.

AU - Hague, J. D.

AU - Hampf, D.

AU - Hauser, M.

AU - Heinz, S.

AU - Heinzelmann, G.

AU - Henri, G.

AU - Hermann, G.

AU - Hinton, J. A.

AU - Hoffmann, A.

AU - Hofmann, W.

AU - Hofverberg, P.

AU - Holler, M.

AU - Horns, D.

AU - Jacholkowska, A.

AU - De Jager, O. C.

AU - Jahn, C.

AU - Jamrozy, M.

AU - Jung, I.

AU - Kastendieck, M. A.

AU - Katarzyński, K.

AU - Katz, U.

AU - Kaufmann, S.

AU - Keogh, D.

AU - Khangulyan, D.

AU - Khélifi, B.

AU - Klochkov, D.

AU - Kluźniak, W.

AU - Kneiske, T.

AU - Komin, Nu

AU - Kosack, K.

AU - Kossakowski, R.

AU - Laffon, H.

AU - Lamanna, G.

AU - Lennarz, D.

AU - Lohse, T.

AU - Lopatin, A.

AU - Lu, C. C.

AU - Marandon, V.

AU - Marcowith, A.

AU - Masbou, J.

AU - Maurin, D.

AU - Maxted, N.

AU - McComb, T. J L

AU - Medina, M. C.

AU - Méhault, J.

AU - Nguyen, N.

AU - Moderski, R.

AU - Moulin, E.

AU - Naumann, C. L.

AU - Naumann-Godo, M.

AU - De Naurois, M.

AU - Nedbal, D.

AU - Nekrassov, D.

AU - Nicholas, B.

AU - Niemiec, J.

AU - Nolan, S. J.

AU - Ohm, S.

AU - Olive, J. F.

AU - De Oña Wilhelmi, E.

AU - Opitz, B.

AU - Ostrowski, M.

AU - Panter, M.

AU - Paz Arribas, M.

AU - Pedaletti, G.

AU - Pelletier, G.

AU - Petrucci, P. O.

AU - Pita, S.

AU - Pühlhofer, G.

AU - Punch, M.

AU - Quirrenbach, A.

AU - Raue, M.

AU - Rayner, S. M.

AU - Reimer, A.

AU - Reimer, O.

AU - Renaud, M.

AU - De Los Reyes, R.

AU - Rieger, F.

AU - Ripken, J.

AU - Rob, L.

AU - Rosier-Lees, S.

AU - Rowell, G.

AU - Rudak, B.

AU - Rulten, C. B.

AU - Ruppel, J.

AU - Ryde, F.

AU - Sahakian, V.

AU - Santangelo, A.

AU - Schlickeiser, R.

AU - Schöck, F. M.

AU - Schönwald, A.

AU - Schulz, A.

AU - Schwanke, U.

AU - Schwarzburg, S.

AU - Schwemmer, S.

AU - Shalchi, A.

AU - Sikora, M.

AU - Skilton, J. L.

AU - Sol, H.

AU - Spengler, G.

AU - Stawarz, L.

AU - Steenkamp, R.

AU - Stegmann, C.

AU - Stinzing, F.

AU - Stycz, K.

AU - Sushch, I.

AU - Szostek, A.

AU - Tavernet, J. P.

AU - Terrier, R.

AU - Tibolla, O.

AU - Tluczykont, M.

AU - Valerius, K.

AU - Van Eldik, C.

AU - Vasileiadis, G.

AU - Venter, C.

AU - Vialle, J. P.

AU - Viana, A.

AU - Vincent, P.

AU - Vivier, M.

AU - Völk, H. J.

AU - Volpe, F.

AU - Vorobiov, S.

AU - Vorster, M.

AU - Wagner, S. J.

AU - Ward, M.

AU - Wierzcholska, A.

AU - Zajczyk, A.

AU - Zdziarski, A. A.

AU - Zech, A.

AU - Zechlin, H. S.

AU - Burnett, T. H.

AU - Hill, A. B.

PY - 2011

Y1 - 2011

N2 - Context. The H.E.S.S. Cherenkov telescope array has been surveying the Galactic plane for new VHE (>100 GeV) gamma-ray sources. Aims. We report on a newly detected point-like source, HESS J1943+213. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. Methods. We combine new H.E.S.S., Fermi/LAT and Nançay 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. Results. HESS J1943+213 is detected at the significance level of 7.9σ (post-trials) at RA(J2000)= 19 h43m55s ± 1s stat ± 1s say, Dec(J2000)= +21° 18'8" ± 17"stat ± 20"sys. The source has a soft spectrum with photon index Γ = 3.1 ± 0.3stat ± 0.2sys and a flux above 470 GeV of (1.3 ± 0.2stat ± 0.3sys) × 10-12 cm-2 s -1. There is no Fermi/LAT counterpart down to a flux limit of 6 × 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 Γ = 2.0). The data from radio to VHE gamma-rays do not show any significant variability. Conclusions. 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.

AB - Context. The H.E.S.S. Cherenkov telescope array has been surveying the Galactic plane for new VHE (>100 GeV) gamma-ray sources. Aims. We report on a newly detected point-like source, HESS J1943+213. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. Methods. We combine new H.E.S.S., Fermi/LAT and Nançay 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. Results. HESS J1943+213 is detected at the significance level of 7.9σ (post-trials) at RA(J2000)= 19 h43m55s ± 1s stat ± 1s say, Dec(J2000)= +21° 18'8" ± 17"stat ± 20"sys. The source has a soft spectrum with photon index Γ = 3.1 ± 0.3stat ± 0.2sys and a flux above 470 GeV of (1.3 ± 0.2stat ± 0.3sys) × 10-12 cm-2 s -1. There is no Fermi/LAT counterpart down to a flux limit of 6 × 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 Γ = 2.0). The data from radio to VHE gamma-rays do not show any significant variability. Conclusions. 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.

KW - galaxies: active

KW - gamma rays: general

UR - http://www.scopus.com/inward/record.url?scp=79953211908&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79953211908&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201116545

DO - 10.1051/0004-6361/201116545

M3 - Article

AN - SCOPUS:79953211908

SN - 0004-6361

VL - 529

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A49

ER -

HESS J1943+213: A candidate extreme BL Lacertae object

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