Related papers: Pulsar Timing Constraints on the Fermi Massive Bla…
The "blazar sequence" posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively small synchrotron peak frequencies, nu_peak, and that the least powerful such objects should have the highest…
In this paper we present results of a short-term optical monitoring of 13 blazars. The objects were monitored mostly in the R-band for a total of ~ 160 hours between 2006 and 2011. We study the nature of the short-term variations and show…
The combined University of Michigan Radio Astronomy Observatory (UMRAO) and Owens Valley Radio Observatory (OVRO) blazar monitoring programs at 14.5/15 GHz provide uninterrupted light curves of $\sim~46-50$ yr duration for 83 blazars,…
The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging…
In order to search for the evidence of quasi-periodic oscillation (QPO) in blazar, multicolor optical observations of the BL Lacertae object S5 0716+714 were performed from 2005 to 2012. For $I$ band on March 19 2010 with low variability…
We investigate the spectral properties of the brightest gamma-ray flares of blazars detected by the Fermi Large Area Telescope. We search for the presence of spectral breaks and measure the spectral curvature on typical time scales of a few…
We investigate the relative occurrence of radio--loud and radio-quiet quasars in the first billion years of the Universe, powered by black holes heavier than one billion solar masses. We consider the sample of high-redshfit blazars detected…
The fascination with the blazar OJ 287 stems not only from its status as a prominent candidate for a close supermassive black hole (SMBH) binary, but also because of the thermal bremsstrahlung origin proposed for its giant optical…
Pulsar timing arrays record gravitational waves from supermassive black hole binaries at two spacetime points: an Earth term, measured when the wave passes the Earth, and a pulsar term, measured when the wave passed each pulsar at an…
We propose and test a fairly simple idea that could account for the blazar sequence: all jets are launched with similar energy per baryon, independently of their power. For instance, flat-spectrum radio quasars (FSRQs), the most powerful…
Supermassive black hole binaries (SMBHs) are expected to result from galaxy mergers, and thus are natural byproducts (and probes) of hierarchical structure formation in the Universe. They are also the primary expected source of…
Almost 10 yr of $\gamma$-ray observations with the Fermi Large Area Telescope (LAT) have revealed extreme $\gamma$-ray outbursts from flat spectrum radio quasars (FSRQs), temporarily making these objects the brightest $\gamma$-ray emitters…
Supermassive black hole (SMBH) binary systems are unavoidable outcomes of galaxy mergers. Their dynamics encode information about their formation and growth, the composition of their host galactic nuclei, the evolution of galaxies, and the…
We compare the \gamma-ray light curves of the blazars, constructed with data provided by the Fermi Large Area Telescope, with flux and polarization variations in the VLBI core and bright superluminal knots obtained via monthly monitoring…
We use statistical results from a large sample of about 500 blazars, based on two surveys, the Deep X-ray Radio Blazar Survey (DXRBS), nearly complete, and the RASS-Green Bank survey (RGB), to provide new constraints on the spectral energy…
Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler…
We perform monthly total and polarized intensity imaging of a sample of $\gamma$-ray blazars (33 sources) with the Very Long Baseline Array (VLBA) at 43 GHz with the high resolution of 0.1 milliarcseconds. From Summer 2008 to October 2009…
We use simple comparisons of the optical and radio properties of the wide separation (3'' to 10'') quasar pairs to demonstrate that they are binary quasars rather than gravitational lenses. The most likely model is that all the pairs are…
Velocity offsets in the broad Balmer lines of quasars and their temporal variations serve as indirect evidence for bound supermassive black hole binaries (SBHBs) at sub-parsec separations. In this work, we test the SBHB hypothesis for 14…
A populations of stellar mass black hole binaries may exist in globular clusters. The dynamics of globular cluster evolution imply that there may be at most one black hole binary is a globular cluster. The population of binaries are…