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ST ScI Preprint #1363


Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission

Authors: E. Pian,1,2,3 C. M. Urry,1,3 L. Maraschi,4 G. Madejski,5 I. M. McHardy,6 A. Koratkar,1 A. Treves,7 L. Chiappetti,8 P. Grandi,9,3 R. C. Hartman,5 H. Kubo,10 C. M. Leach,6 J. E. Pesce,1 C. Imhoff,1,11 R. Thompson,1,11 A. E. Wehrle12
The gamma-ray blazar 3C 279 was monitored on a nearly daily basis with IUE, ROSAT and EGRET for three weeks between December 1992 and January 1993. During this period, the blazar was at a historical minimum at all wavelengths. Here we present the UV data obtained during the above multiwavelength campaign. A maximum UV variation of ~50% is detected, while during the same period the X-ray flux varied by no more than 13%. At the lowest UV flux level the average spectrum in the 1230-2700  interval is unusually flat for this object (<alphaUV > ~ 1). The flattening could represent the lowest energy tail of the inverse Compton component responsible for the X-ray emission, or could be due to the presence of a thermal component at ~20000 K possibly associated with an accretion disk. The presence of an accretion disk in this blazar object, likely observable only in very low states and otherwise hidden by the beamed, variable synchrotron component, would be consistent with the scenario in which the seed photons for the inverse Compton mechanism producing the gamma-rays are external to the relativistic jet. We further discuss the long term correlation of the UV flux with the X-ray and gamma-ray fluxes obtained at various epochs. All UV archival data are included in the analysis. Both the X- and gamma-ray fluxes are generally well correlated with the UV flux, approximately with square root and quadratic dependences, respectively.
Status:
Appeared in: The Astrophysical Journal

Affiliations:
1) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
2) Present address: Istituto di Tecnologie e Studio delle Radiazioni Extraterrestri, CNR, Via Gobetti 101, I-40129 Bologna, Italy
3) Guest Observer with the International Ultraviolet Explorer
4) Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milan, Italy
5) Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD 20771
6) Department of Physics, University of Southampton, Southampton SO9 5NH, UK
7) Department of Physics, University of Como, Via Lucini 3, I-22100 Como, Italy
8) Istituto di Fisica Cosmica e Tecnologie Relative, CNR, via Bassini 15, I-20133 Milan, Italy
9) Istituto di Astrofisica Spaziale, CNR, via Fosso del Cavaliere, Area di Ricerca Tor Vergata, I-00133 Rome, Italy
10) Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan
11) Infrared Processing Analysis Center, MC 100-22, Jet Propulsion Laboratory and California Institute of Technology, Pasadena, CA 91125
12) Science Programs, Computer Sciences Corp., 1100 West Street, Laurel, MD 20707

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Last updated:  10/16/2000