Quasi-simultaneous observations of BL Lac object MRK 501 in X-ray, UV, visible, IR, and radio frequencies

Y. Kondo, D. M. Worrall, R. F. Mushotzky, R. L. Hackney, K. R. H. Hackney, J. B. Oke, H. K. C. Yee, G. Neugebauer, K. Matthews, P. A. Feldman, R. L. Brown

Research output: Contribution to journalArticle (Academic Journal)peer-review


Observations in the X-ray, UV, visible, IR and radio regions of the BL Lac object Mrk 501 made over the course of two months are reported. The measurements were made with the A2 experiment on HEAO 1 (X-ray), the SWP and LWR cameras on IUE (UV), the 5-m Hale telescope (visible), the 2.5-m telescope at Mount Wilson (IR), the NRAO 92-m radio telescope at Green Bank (4750 MHz) and the 46-m radio telescope at the Algonquin Observatory (10275 and 10650 MHz). The quasi-simultaneously observed spectral slope is found to be positive and continuous from the X-ray to the UV, but to gradually flatten and possibly turn down from the mid-UV to the visible; the optical-radio emission cannot be accounted for by a single power law. The total spectrum is shown to be compatible with a synchrotron self-Compton emission mechanism, while the spectrum from the visible to the X-ray is consistent with synchrotron radiation or inverse-Compton scattering by a hot thermal electron cloud. The continuity of the spectrum from the UV to the X-ray is noted to imply a total luminosity greater than previous estimates by a factor of 3-4.
Original languageEnglish
Pages (from-to)690-699
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 1 Feb 1981


  • Bl Lacertae Objects
  • Infrared Astronomy
  • Radio Spectra
  • Ultraviolet Astronomy
  • Visible Spectrum
  • X Ray Sources
  • Heao 1
  • Spectral Energy Distribution
  • Synchrotron Radiation
  • Ultraviolet Spectra
  • X Ray Spectra


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