English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

All data available in B band for the BL Lac object MRK421 from 22publications are used to construct a historical light curve, dating back to1900. It is found that the light curve is very complicated and consists of aset of outbursts with very large duration. The brightness of MRK421 varies from11.6 magnitude to more than 16 magnitude. Analyses with Jurkevich method ofcomputing period of cyclic phenomena reveal in the light curve two kinds ofbehaviors. The first one is non-periodic with rapid, violent variations inintensity on time scales of hours to days. The second one is periodic with apossible period of $23.1\pm 1.1$ years. Another possible period of $15.3\pm0.7$ years is not very significant. We have tested the robustness of theJurkevich method. The period of about one year found in the light curves ofMRK421 and of other objects is a spurious period due to the method and theobserving window. We try to explain the period of $23.1 \pm1.1$ years under thethermal instability of a slim accretion disk around a massive black hole ofmass of $2 *10^6 M_\odot$.Comment: Tex, 14 pages, 5 Postscript figures. Accepted for publication in A&A  Supplement Serie

The long-term optical behavior of Mkn 421