EDP Sciences
Free access
Volume 501, Number 3, July III 2009
Page(s) 925 - 932
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361/200911814
Published online 27 May 2009
A&A 501, 925-932 (2009)
DOI: 10.1051/0004-6361/200911814

Multiwavelength periodicity study of Markarian 501

C. Rödig, T. Burkart, O. Elbracht, and F. Spanier

Lehrstuhl für Astronomie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
    e-mail: fspanier@astro.uni-wuerzburg.de

Received 9 February 2009 / Accepted 27 April 2009

Context. Active galactic nuclei (AGN) are highly variable emitters of electromagnetic waves from the radio to the gamma-ray regime. This variability may be periodic, which in turn could be the signature of a binary black hole. Systems of black holes are strong emitters of gravitational waves whose amplitude depends on the binary orbital parameters such as the component mass, the orbital semi-major-axis and eccentricity.
Aims. It is our aim to prove the existence of periodicity of the AGN Markarian 501 from several observations in different wavelengths. A simultaneous periodicity in different wavelengths provides evidence of bound binary black holes in the core of AGN.
Methods. Existing data sets from observations by Whipple, SWIFT, RXTE, and MAGIC have been analysed with the Lomb-Scargle method, the epoch-folding technique and the SigSpec software.
Results. Our analysis shows a 72-day period, which could not be seen in previous works due to the limited length of observations. This does not contradict a 23-day period that can be derived as a higher harmonic from the 72-day period.

Key words: galaxies: active -- BL Lacertae objects: individual: Mrk 501 -- X-rays: galaxies -- gamma rays: observations

© ESO 2009