Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. I. An 8 month campaign of monitoring NGC 5548 with IUE
Por:
Clavel J., Reichert G.A., Alloin D., Crenshaw D.M., Kriss G., Krolik J.H., Malkan M.A., Netzer H., Peterson B.M., Wamsteker W., Altamore A., Baribaud T., Barr P., Beck S., Binette L., Bromage G.E., Brosch N., Diaz A.I., Filippenko A.V., Fricke K., Gaskell C.M., Giommi P., Glass I.S., Gondhalekar P., Hackney R.L., Halpern J.P., Hutter D.J., Jörsäter S., Kinney A.L., Kollatschny W., Koratkar A., Korista K.T., Laor A., Lasota J.P., Leibowitz E., Maoz D., Martin P.G., Mazeh T., Meurs E.J.A., Nair A.D., O'Brien P., Pelat D., Perez E., Perola G.C., Ptak R.L., Rodriguez-Pascual P., Rosenblatt E.I., Sadun A.C., Santos-Lleo M., Shaw R.A., Smith P.S., Stirpe G.M., Stoner R., Sun W.H., Ulrich M.-H., Van Groningen E., Zheng W.
Publicada:
1 ene 1991
Resumen:
We present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties - continuum shape, line ratios - are not unusual for type I Seyfert galaxies, but it was found to be strongly variable. The ultraviolet continuum flux and broad emission line fluxes varied significantly, going through three large maxima and three deep minima. The ratio of maximum to minimum flux was ?4.5 for the continuum at 1350 Å, and the continuum was significantly bluer when it was brighter. The high-ionization emission lines showed the strongest variations, with N v ?1240 and He II ?1640 exhibiting maximum-to-minimum flux ratios as high as those of the continuum. Intermediate-ionization lines, including Lyo? ?1216, C IV 1549, and C III] ?1909, had maximum-to-minimum amplitudes of ?2, and Mg II ?2798, the lowest ionization line, exhibited the smallest amplitude fluctuations, ? 1.3. The great majority of all variations were well resolved in time. Apart from Mg II ?2798, the emission-line variations correlate extremely well with those of the 1350 Å continuum if allowance is made for a systematic delay, lending qualitative support to the view that photoionization by the nuclear continuum is responsible for driving the emission lines. The delay of a given line seems to depend on the degree of ionization of its species. The He II ?1640 and N V ?1240 features exhibit the shortest delay, ?t ? 4-10 days, while the Ly? ?1216 and C IV ?1549 lines yield 8-16 days. The Si IV + O IV] ?1402 feature and the C III] ?1909 line exhibit significantly larger delays, between 12 and 34 days. In the case of Mg II ?2798, the cross-correlation is broad and shallow, so that the delay is only loosely constrained, ?t ? 34-72 days.
Filiaciones:
Clavel J.:
ESA IUE Observatory, P.O. Box 50727, 28080 Madrid, Spain
Reichert G.A.:
Astronomy Program, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States
Alloin D.:
Observatoire de Paris, 92195 Meudon Principal Cedex, France
Crenshaw D.M.:
Astronomy Program, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States
Kriss G.:
Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218, United States
Krolik J.H.:
Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218, United States
Malkan M.A.:
University of California, Department of Astronomy, Los Angeles, CA 90024-1562, United States
Netzer H.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Peterson B.M.:
Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210, United States
Wamsteker W.:
ESA IUE Observatory, P.O. Box 50727, 28080 Madrid, Spain
Altamore A.:
Ist. Astron. dell'Università, Via Lancisi 29, I-00161 Rome, Italy
Baribaud T.:
Observatoire de Paris, 92195 Meudon Principal Cedex, France
Barr P.:
EXOSAT Observatory, Astrophysics Division of ESA, ESTEC, Postbus 299, 2200-AG Noordwijk, Netherlands
Beck S.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Binette L.:
CITA, McLennan Laboratories, University of Toronto, 60 St. George Street, Toronto, Ont. M5S 1A1, Canada
Bromage G.E.:
Astrophysics Group, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 OQX, United Kingdom
Brosch N.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Diaz A.I.:
Depto. de Fis. Teórica, C-XI, Universidad Autónoma, Cantoblanco, 28049 - Madrid, Spain
Filippenko A.V.:
Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720, United States
Fricke K.:
Universitätssternwarte, Geismarlandstrasse 11, D-3400 Göttingen, Germany
Gaskell C.M.:
University of Michigan, Astronomy Department, Dennison Building, Ann Arbor, MI 48109-1090, United States
Giommi P.:
EXOSAT Observatory, Astrophysics Division of ESA, ESTEC, Postbus 299, 2200-AG Noordwijk, Netherlands
Glass I.S.:
S. African Astronomical Observatory, P.O. Box 9, Observatory, 7935, South Africa
Gondhalekar P.:
Astrophysics Group, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 OQX, United Kingdom
Hackney R.L.:
Western Kentucky University, Department of Physics and Astronomy, Bowling Green, KY 42101, United States
Halpern J.P.:
Columbia University, Department of Physics, 538 West 120th Street, New York, NY 10027, United States
Hutter D.J.:
Astronomy Program, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States
Jörsäter S.:
ESA STECF, Karl-Schwarzschild-Strasse 2, D-8046 Garching-bei-München, Germany
Kinney A.L.:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, United States
Kollatschny W.:
Universitätssternwarte, Geismarlandstrasse 11, D-3400 Göttingen, Germany
Koratkar A.:
University of Michigan, Astronomy Department, Dennison Building, Ann Arbor, MI 48109-1090, United States
Korista K.T.:
Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210, United States
Laor A.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Lasota J.P.:
Observatoire de Paris, 92195 Meudon Principal Cedex, France
Leibowitz E.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Maoz D.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Martin P.G.:
CITA, McLennan Laboratories, University of Toronto, 60 St. George Street, Toronto, Ont. M5S 1A1, Canada
Mazeh T.:
Sch. Phys. Astron. and Wise Observ., Tel-Aviv University, Tel Aviv 69978, Israel
Meurs E.J.A.:
Max-Planck-Inst. F. E., Giessenbachstrasse, D-80416 Garching-bei-München, Germany
Nair A.D.:
Bowling Green State University, Physics and Astronomy Department, Bowling Green, OH 43403, United States
O'Brien P.:
Department of Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
Pelat D.:
Observatoire de Paris, 92195 Meudon Principal Cedex, France
Perez E.:
Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
Perola G.C.:
Ist. Astron. dell'Università, Via Lancisi 29, I-00161 Rome, Italy
Ptak R.L.:
Bowling Green State University, Physics and Astronomy Department, Bowling Green, OH 43403, United States
Rodriguez-Pascual P.:
Instituto de Astronomia, Universidad Complutense, 28040 Madrid 3, Spain
Rosenblatt E.I.:
Univ. of California at San Diego, CASS, Code C-01 1, San Diego, CA 92093, United States
Sadun A.C.:
Bradley Observatory, Agnes Scott College, Decatur, GA 30030, United States
Santos-Lleo M.:
Instituto de Astronomia, Universidad Complutense, 28040 Madrid 3, Spain
Shaw R.A.:
Astronomy Program, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States
Smith P.S.:
Steward Observatory, University of Arizona, Tucson, AZ 85721, United States
Stirpe G.M.:
Osservatorio Astronomico di Bologna, Via Zamboni 33, I-40126 Bologna, Italy
Stoner R.:
Bowling Green State University, Physics and Astronomy Department, Bowling Green, OH 43403, United States
Sun W.H.:
Lab. for Astronomy and Solar Physics, NASA/GSFC, Greenbelt, MD 20771, United States
Ulrich M.-H.:
European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-8046 Garching-bei-München, Germany
Van Groningen E.:
Uppsala Astronomical Observatory, Box 515, S-75120 Uppsala, Sweden
Zheng W.:
University of Alabama, Department of Physics and Astronomy, Tuscaloosa, AL 35487-0324, United States
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