HESS observations and VLT spectroscopy of PG1553+113

F. Aharonian; A. G. Akhperjanian; U. De Barres Almeida; A. R. Bazer-Bachi; B. Behera; M. Beilicke; W. Benbow; K. Bernlöhr; C. Boisson; O. Bolz; V. Borrei; I. Braun; E. Brion; A. M. Brown; R. Bühler; T. Bulik; I. Büsching; T. Boutelier; S. Carrigan; P. M. Chadwick; L. M. Chounet; A. C. Clapson; G. Coignet; R. Cornils; L. Costamante; M. Dalton; B. Degrange; H. J. Dickinson; A. Djannati-Ataï; W. Domainko; L. O.C. Drury; F. Dubois; G. Dubus; J. Dyks; K. Egberts; D. Emmanoulopoulos; P. Espigat; C. Farnier; F. Feinstein; A. Fiasson; A. Förster; G. Fontaine; Seb Funk; M. Füßling; Y. A. Gallant; B. Giebels; J. F. Glicenstein; B. Glück; P. Goret; C. Hadjichristidis; D. Hauser; M. Hauser; G. Heinzelmann; G. Henri; G. Hermann; J. A. Hinton; A. Hoffmann; W. Hofmann; M. Holleran; S. Hoppe; D. Horns; A. Jacholkowska; O. C. De Jager; I. Jung; K. Katarzyński; E. Kendziorra; M. Kerschhaggl; B. Khélifi; D. Keogh; Nu Komin; K. Kosack; G. Lamanna; I. J. Latham; A. Lemière; M. Lemoine-Goumard; J. P. Lenain; T. Lohse; J. M. Martin; O. Martineau-Huynh; A. Marcowith; C. Masterson; D. Maurin; G. Maurin; T. J.L. McComb; R. Moderski; E. Moulin; M. De Naurois; D. Nedbal; S. J. Nolan; S. Ohm; J. P. Olive; E. De Oña Wilhelmi; K. J. Orford; J. L. Osborne; M. Ostrowski; M. Panter; G. Pedaletti; G. Pelletier; P. O. Petrucci; S. Pita; G. Pühlhofer; M. Punch; S. Ranchon; B. C. Raubenheimer; M. Raue; S. M. Rayner; M. Renaud; J. Ripken; L. Rob; L. Rolland; S. Rosier-Lees; G. Rowell; B. Rudak; J. Ruppel; V. Sahakian; A. Santangelo; R. Schlickeiser; F. Schöck; R. Schröder; U. Schwanke; S. Schwarzburg; S. Schwemmer; A. Shalchi; H. Sol; D. Spangler; Stawarz; R. Steenkamp; C. Stegmann; G. Superina; P. H. Tam; J. P. Tavernet; R. Terrier; C. Van Eldik; G. Vasileiadis; C. Venter; J. P. Vialle; P. Vincent; M. Vivier; H. J. Völk; F. Volpe; S. J. Wagner; M. Ward; A. A. Zdziarski; A. Zech

doi:10.1051/0004-6361:20078603

HESS observations and VLT spectroscopy of PG1553+113

F. Aharonian
, A. G. Akhperjanian
, U. De Barres Almeida
, A. R. Bazer-Bachi
, B. Behera
, M. Beilicke
, W. Benbow
, K. Bernlöhr
, C. Boisson
, O. Bolz
, V. Borrei
, I. Braun
, E. Brion
, A. M. Brown
, R. Bühler
, T. Bulik
, I. Büsching
, T. Boutelier
, S. Carrigan
, P. M. Chadwick

L. M. Chounet, A. C. Clapson, G. Coignet, R. Cornils, L. Costamante, M. Dalton, B. Degrange, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O.C. Drury, F. Dubois, G. Dubus, J. Dyks, K. Egberts, D. Emmanoulopoulos, P. Espigat, C. Farnier, F. Feinstein, A. Fiasson, A. Förster, G. Fontaine, Seb Funk, M. Füßling, Y. A. Gallant, B. Giebels, J. F. Glicenstein, B. Glück, P. Goret, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, A. Hoffmann, W. Hofmann, M. Holleran, S. Hoppe, D. Horns, A. Jacholkowska, O. C. De Jager, I. Jung, K. Katarzyński, E. Kendziorra, M. Kerschhaggl, B. Khélifi, D. Keogh, Nu Komin, K. Kosack, G. Lamanna, I. J. Latham, A. Lemière, M. Lemoine-Goumard, J. P. Lenain, T. Lohse, J. M. Martin, O. Martineau-Huynh, A. Marcowith, C. Masterson, D. Maurin, G. Maurin, T. J.L. McComb, R. Moderski, E. Moulin, M. De Naurois, D. Nedbal, S. J. Nolan, S. Ohm, J. P. Olive, E. De Oña Wilhelmi, K. J. Orford, J. L. Osborne, M. Ostrowski, M. Panter, G. Pedaletti, G. Pelletier, P. O. Petrucci, S. Pita, G. Pühlhofer, M. Punch, S. Ranchon, B. C. Raubenheimer, M. Raue, S. M. Rayner, M. Renaud, J. Ripken, L. Rob, L. Rolland, S. Rosier-Lees, G. Rowell, B. Rudak, J. Ruppel, V. Sahakian, A. Santangelo, R. Schlickeiser, F. Schöck, R. Schröder, U. Schwanke, S. Schwarzburg, S. Schwemmer, A. Shalchi, H. Sol, D. Spangler, Stawarz, R. Steenkamp, C. Stegmann, G. Superina, P. H. Tam, J. P. Tavernet, R. Terrier, C. Van Eldik, G. Vasileiadis, C. Venter, J. P. Vialle, P. Vincent, M. Vivier, H. J. Völk, F. Volpe, S. J. Wagner, M. Ward, A. A. Zdziarski, A. Zech

Max-Planck-Institut für Kernphysik
Dublin Institute for Advanced Studies
Yerevan Physics Institute
Durham University
CNRS
Landessternwarte Heidelberg
Universität Hamburg
Humboldt-Universität zu Berlin
LUTH - Laboratoire de l'Univers et de ses Theories
Institut Pierre Simon Laplace, CNRS and CEA
Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
North-West University
Ip Paris
Université Paris-Sud
Astroparticule and Cosmol APC
Laboratoire Univers et Particules de Montpellier
Friedrich-Alexander University (FAU) Erlangen-Nürnberg and Universitätsklinikum Erlangen
University of Leeds
University of Tübingen
MPG
Universités Paris VI and VII
Charles University
Jagiellonian University
University of Adelaide
Ruhr-University Bochum
University of Namibia

Résultats de recherche: Contribution à un journal › Article › Revue par des pairs

Résumé

Aims. The properties of the very high energy (VHE; E > 100 GeV) γ-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. Methods. VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System. (HESS) in 2005 and 2006. H + K (1.45-2.45 μm) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. Results. A VHE signal, ̃10 standard deviations, is detected by HESS during the 2 years of observations (24.8 h live time). The integral flux above 300 GeV is (4.6 = 0.6_stat ±0.9_syst) × 10 ^-12 cm^-2 s^-1, corresponding to ̃3.4% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured, from 225 GeV to ~1.3 TeV, and is characterized by a very soft power law (photon index of Γ = 4.5 ±0.3stat ±0.1 _syst). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.

langue originale	Anglais
Pages (de - à)	481-489
Nombre de pages	9
journal	Astronomy and Astrophysics
Volume	477
Numéro de publication	2
Les DOIs	https://doi.org/10.1051/0004-6361:20078603
état	Publié - 1 janv. 2008
Modification externe	Oui

Accès au document

10.1051/0004-6361:20078603

Contient cette citation

Aharonian, F., Akhperjanian, A. G., De Barres Almeida, U., Bazer-Bachi, A. R., Behera, B., Beilicke, M., Benbow, W., Bernlöhr, K., Boisson, C., Bolz, O., Borrei, V., Braun, I., Brion, E., Brown, A. M., Bühler, R., Bulik, T., Büsching, I., Boutelier, T., Carrigan, S., ... Zech, A. (2008). HESS observations and VLT spectroscopy of PG1553+113. Astronomy and Astrophysics, 477(2), 481-489. https://doi.org/10.1051/0004-6361:20078603

@article{b5894496fb514537b40e23350619756d,

title = "HESS observations and VLT spectroscopy of PG1553+113",

abstract = "Aims. The properties of the very high energy (VHE; E > 100 GeV) γ-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. Methods. VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System. (HESS) in 2005 and 2006. H + K (1.45-2.45 μm) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. Results. A VHE signal,{\~ }10 standard deviations, is detected by HESS during the 2 years of observations (24.8 h live time). The integral flux above 300 GeV is (4.6 = 0.6stat ±0.9syst) × 10 -12 cm-2 s-1, corresponding to{\~ }3.4\% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured, from 225 GeV to \textasciitilde{}1.3 TeV, and is characterized by a very soft power law (photon index of Γ = 4.5 ±0.3stat ±0.1 syst). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.",

keywords = "Galaxies: active, Gamma rays: observations",

author = "F. Aharonian and Akhperjanian, \{A. G.\} and \{De Barres Almeida\}, U. and Bazer-Bachi, \{A. R.\} and B. Behera and M. Beilicke and W. Benbow and K. Bernl{\"o}hr and C. Boisson and O. Bolz and V. Borrei and I. Braun and E. Brion and Brown, \{A. M.\} and R. B{\"u}hler and T. Bulik and I. B{\"u}sching and T. Boutelier and S. Carrigan and Chadwick, \{P. M.\} and Chounet, \{L. M.\} and Clapson, \{A. C.\} and G. Coignet and R. Cornils and L. Costamante and M. Dalton and B. Degrange 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 K. Egberts and D. Emmanoulopoulos and P. Espigat and C. Farnier and F. Feinstein and A. Fiasson and A. F{\"o}rster and G. Fontaine and Seb Funk and M. F{\"u}{\ss}ling and Gallant, \{Y. A.\} and B. Giebels and Glicenstein, \{J. F.\} and B. Gl{\"u}ck and P. Goret and C. Hadjichristidis and D. Hauser and M. Hauser and G. Heinzelmann and G. Henri and G. Hermann and Hinton, \{J. A.\} and A. Hoffmann and W. Hofmann and M. Holleran and S. Hoppe and D. Horns and A. Jacholkowska and \{De Jager\}, \{O. C.\} and I. Jung and K. Katarzy{\'n}ski and E. Kendziorra and M. Kerschhaggl and B. Kh{\'e}lifi and D. Keogh and Nu Komin and K. Kosack and G. Lamanna and Latham, \{I. J.\} and A. Lemi{\`e}re and M. Lemoine-Goumard and Lenain, \{J. P.\} and T. Lohse and Martin, \{J. M.\} and O. Martineau-Huynh and A. Marcowith and C. Masterson and D. Maurin and G. Maurin and McComb, \{T. J.L.\} and R. Moderski and E. Moulin and \{De Naurois\}, M. and D. Nedbal and Nolan, \{S. J.\} and S. Ohm and Olive, \{J. P.\} and \{De O{\~n}a Wilhelmi\}, E. and Orford, \{K. J.\} and Osborne, \{J. L.\} and M. Ostrowski and M. Panter and G. Pedaletti and G. Pelletier and Petrucci, \{P. O.\} and S. Pita and G. P{\"u}hlhofer and M. Punch and S. Ranchon and Raubenheimer, \{B. C.\} and M. Raue and Rayner, \{S. M.\} and M. Renaud and J. Ripken and L. Rob and L. Rolland and S. Rosier-Lees and G. Rowell and B. Rudak and J. Ruppel and V. Sahakian and A. Santangelo and R. Schlickeiser and F. Sch{\"o}ck and R. Schr{\"o}der and U. Schwanke and S. Schwarzburg and S. Schwemmer and A. Shalchi and H. Sol and D. Spangler and Stawarz and R. Steenkamp and C. Stegmann and G. Superina and Tam, \{P. H.\} and Tavernet, \{J. P.\} and R. Terrier and \{Van Eldik\}, C. and G. Vasileiadis and C. Venter and Vialle, \{J. P.\} and P. Vincent and M. Vivier and V{\"o}lk, \{H. J.\} and F. Volpe and Wagner, \{S. J.\} and M. Ward and Zdziarski, \{A. A.\} and A. Zech",

year = "2008",

month = jan,

day = "1",

doi = "10.1051/0004-6361:20078603",

language = "English",

volume = "477",

pages = "481--489",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

number = "2",

}

Aharonian, F, Akhperjanian, AG, De Barres Almeida, U, Bazer-Bachi, AR, Behera, B, Beilicke, M, Benbow, W, Bernlöhr, K, Boisson, C, Bolz, O, Borrei, V, Braun, I, Brion, E, Brown, AM, Bühler, R, Bulik, T, Büsching, I, Boutelier, T, Carrigan, S, Chadwick, PM, Chounet, LM, Clapson, AC, Coignet, G, Cornils, R, Costamante, L, Dalton, M, Degrange, B, Dickinson, HJ, Djannati-Ataï, A, Domainko, W, Drury, LOC, Dubois, F, Dubus, G, Dyks, J, Egberts, K, Emmanoulopoulos, D, Espigat, P, Farnier, C, Feinstein, F, Fiasson, A, Förster, A, Fontaine, G, Funk, S, Füßling, M, Gallant, YA, Giebels, B, Glicenstein, JF, Glück, B, Goret, P, Hadjichristidis, C, Hauser, D, Hauser, M, Heinzelmann, G, Henri, G, Hermann, G, Hinton, JA, Hoffmann, A, Hofmann, W, Holleran, M, Hoppe, S, Horns, D, Jacholkowska, A, De Jager, OC, Jung, I, Katarzyński, K, Kendziorra, E, Kerschhaggl, M, Khélifi, B, Keogh, D, Komin, N, Kosack, K, Lamanna, G, Latham, IJ, Lemière, A, Lemoine-Goumard, M, Lenain, JP, Lohse, T, Martin, JM, Martineau-Huynh, O, Marcowith, A, Masterson, C, Maurin, D, Maurin, G, McComb, TJL, Moderski, R, Moulin, E, De Naurois, M, Nedbal, D, Nolan, SJ, Ohm, S, Olive, JP, De Oña Wilhelmi, E, Orford, KJ, Osborne, JL, Ostrowski, M, Panter, M, Pedaletti, G, Pelletier, G, Petrucci, PO, Pita, S, Pühlhofer, G, Punch, M, Ranchon, S, Raubenheimer, BC, Raue, M, Rayner, SM, Renaud, M, Ripken, J, Rob, L, Rolland, L, Rosier-Lees, S, Rowell, G, Rudak, B, Ruppel, J, Sahakian, V, Santangelo, A, Schlickeiser, R, Schöck, F, Schröder, R, Schwanke, U, Schwarzburg, S, Schwemmer, S, Shalchi, A, Sol, H, Spangler, D, Stawarz, Steenkamp, R, Stegmann, C, Superina, G, Tam, PH, Tavernet, JP, Terrier, R, Van Eldik, C, Vasileiadis, G, Venter, C, Vialle, JP, Vincent, P, Vivier, M, Völk, HJ, Volpe, F, Wagner, SJ, Ward, M, Zdziarski, AA & Zech, A 2008, 'HESS observations and VLT spectroscopy of PG1553+113', Astronomy and Astrophysics, VOL. 477, Numéro 2, p. 481-489. https://doi.org/10.1051/0004-6361:20078603

TY - JOUR

T1 - HESS observations and VLT spectroscopy of PG1553+113

AU - Aharonian, F.

AU - Akhperjanian, A. G.

AU - De Barres Almeida, U.

AU - Bazer-Bachi, A. R.

AU - Behera, B.

AU - Beilicke, M.

AU - Benbow, W.

AU - Bernlöhr, K.

AU - Boisson, C.

AU - Bolz, O.

AU - Borrei, V.

AU - Braun, I.

AU - Brion, E.

AU - Brown, A. M.

AU - Bühler, R.

AU - Bulik, T.

AU - Büsching, I.

AU - Boutelier, T.

AU - Carrigan, S.

AU - Chadwick, P. M.

AU - Chounet, L. M.

AU - Clapson, A. C.

AU - Coignet, G.

AU - Cornils, R.

AU - Costamante, L.

AU - Dalton, M.

AU - Degrange, B.

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 - Egberts, K.

AU - Emmanoulopoulos, D.

AU - Espigat, P.

AU - Farnier, C.

AU - Feinstein, F.

AU - Fiasson, A.

AU - Förster, A.

AU - Fontaine, G.

AU - Funk, Seb

AU - Füßling, M.

AU - Gallant, Y. A.

AU - Giebels, B.

AU - Glicenstein, J. F.

AU - Glück, B.

AU - Goret, P.

AU - Hadjichristidis, C.

AU - Hauser, D.

AU - Hauser, M.

AU - Heinzelmann, G.

AU - Henri, G.

AU - Hermann, G.

AU - Hinton, J. A.

AU - Hoffmann, A.

AU - Hofmann, W.

AU - Holleran, M.

AU - Hoppe, S.

AU - Horns, D.

AU - Jacholkowska, A.

AU - De Jager, O. C.

AU - Jung, I.

AU - Katarzyński, K.

AU - Kendziorra, E.

AU - Kerschhaggl, M.

AU - Khélifi, B.

AU - Keogh, D.

AU - Komin, Nu

AU - Kosack, K.

AU - Lamanna, G.

AU - Latham, I. J.

AU - Lemière, A.

AU - Lemoine-Goumard, M.

AU - Lenain, J. P.

AU - Lohse, T.

AU - Martin, J. M.

AU - Martineau-Huynh, O.

AU - Marcowith, A.

AU - Masterson, C.

AU - Maurin, D.

AU - Maurin, G.

AU - McComb, T. J.L.

AU - Moderski, R.

AU - Moulin, E.

AU - De Naurois, M.

AU - Nedbal, D.

AU - Nolan, S. J.

AU - Ohm, S.

AU - Olive, J. P.

AU - De Oña Wilhelmi, E.

AU - Orford, K. J.

AU - Osborne, J. L.

AU - Ostrowski, M.

AU - Panter, M.

AU - Pedaletti, G.

AU - Pelletier, G.

AU - Petrucci, P. O.

AU - Pita, S.

AU - Pühlhofer, G.

AU - Punch, M.

AU - Ranchon, S.

AU - Raubenheimer, B. C.

AU - Raue, M.

AU - Rayner, S. M.

AU - Renaud, M.

AU - Ripken, J.

AU - Rob, L.

AU - Rolland, L.

AU - Rosier-Lees, S.

AU - Rowell, G.

AU - Rudak, B.

AU - Ruppel, J.

AU - Sahakian, V.

AU - Santangelo, A.

AU - Schlickeiser, R.

AU - Schöck, F.

AU - Schröder, R.

AU - Schwanke, U.

AU - Schwarzburg, S.

AU - Schwemmer, S.

AU - Shalchi, A.

AU - Sol, H.

AU - Spangler, D.

AU - Stawarz,

AU - Steenkamp, R.

AU - Stegmann, C.

AU - Superina, G.

AU - Tam, P. H.

AU - Tavernet, J. P.

AU - Terrier, R.

AU - Van Eldik, C.

AU - Vasileiadis, G.

AU - Venter, C.

AU - Vialle, J. P.

AU - Vincent, P.

AU - Vivier, M.

AU - Völk, H. J.

AU - Volpe, F.

AU - Wagner, S. J.

AU - Ward, M.

AU - Zdziarski, A. A.

AU - Zech, A.

PY - 2008/1/1

Y1 - 2008/1/1

N2 - Aims. The properties of the very high energy (VHE; E > 100 GeV) γ-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. Methods. VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System. (HESS) in 2005 and 2006. H + K (1.45-2.45 μm) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. Results. A VHE signal, ̃10 standard deviations, is detected by HESS during the 2 years of observations (24.8 h live time). The integral flux above 300 GeV is (4.6 = 0.6stat ±0.9syst) × 10 -12 cm-2 s-1, corresponding to ̃3.4% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured, from 225 GeV to ~1.3 TeV, and is characterized by a very soft power law (photon index of Γ = 4.5 ±0.3stat ±0.1 syst). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.

AB - Aims. The properties of the very high energy (VHE; E > 100 GeV) γ-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. Methods. VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System. (HESS) in 2005 and 2006. H + K (1.45-2.45 μm) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. Results. A VHE signal, ̃10 standard deviations, is detected by HESS during the 2 years of observations (24.8 h live time). The integral flux above 300 GeV is (4.6 = 0.6stat ±0.9syst) × 10 -12 cm-2 s-1, corresponding to ̃3.4% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured, from 225 GeV to ~1.3 TeV, and is characterized by a very soft power law (photon index of Γ = 4.5 ±0.3stat ±0.1 syst). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.

KW - Galaxies: active

KW - Gamma rays: observations

U2 - 10.1051/0004-6361:20078603

DO - 10.1051/0004-6361:20078603

M3 - Article

AN - SCOPUS:38349194505

SN - 0004-6361

VL - 477

SP - 481

EP - 489

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 2

ER -

HESS observations and VLT spectroscopy of PG1553+113

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