Monitoring the Gamma-ray Sky through 4.5 Years of Fermi LAT Flare Advocate Service

The Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides for a quick look and review of the gamma-ray sky observed daily by the Fermi Large Area Telescope (LAT). The FA-GSW service provides alerts and communicates to the external scientific community potentially new gamma-ray sources, interesting transients and source flares. A weekly digest containing the highlights about the variable LAT gamma-ray sky at E>100 MeV is published in the web ("Fermi Sky Blog"). Other news items are occasionally posted through the Fermi multiwavelength mailing list, Astronomer's Telegrams (ATels) and Gamma-ray Coordination Network notes (GCNs). From July 2008 to January 2013 about 230 ATels and some GCNs have been published by the Fermi LAT Collaboration, more than 40 target of opportunity observing programs have been triggered by the LAT Collaboration and performed though the Swift satellite, and individual observing alerts have been addressed to ground-based Cherenkov telescopes. This is helping the Fermi mission to catch opportunities offered by the variable high-energy sky, increasing the rate of simultaneous multifrequency observations and the level of international scientific cooperation.Comment: 2012 Fermi Symposium proceedings - eConf C121028. 4 pages, 4 figures. Submitted on behalf of the Fermi LAT collaboratio

Time-domain behavior of blazar OJ 287 and the binary supermassive black hole conjecture

The proper understanding of blazar variability at the various electromagnetic spectral bands is one goal of multifrequency astrophysics. In this frame a peculiar and controversial phenomenology is the periodicity, postulated for long-term radio or optical flux light curves of about a dozen of blazars. The well-known BL Lac object OJ 287 (PKS 0851+202, S3 0851+20, PG 0851+202, z = 0.306) is not only a high-variable, peculiar, extragalactic source with hints for approximatively cyclical optical outbursts, but it also represents a case of substantial intensive and extensive (longterm) multifrequency observations. This rich database allow us a deeper analysis based on a wide range of variability timescales with some recent results that are highlighted here