Quasar Variability

PKS2349Together with Dr. Željko Ivezić I am conducting quasar variability studies. Quasars are active galaxies, that is those where a  big, kiloparsec in size,  relativistic jet  of charged particles,  is ejected from the central region surrounding a supermassive black hole in the center. Almost every galaxy underwent a quasar phase at some  stage of their evolution.  I use two samples of Quasars for this research, both located in a small patch of the sky around the celestial equator called Stripe 82 : one from  the Sloan Digital Sky Survey (SDSS) and another from the  Catalina Real-time Transient Survey (CRTS). The SDSS Stripe 82 sample of quasars has previously been modelled by Chelsea McLeod  (eg. MacLeod at al. 2012, MacLeod et al. 2011 , MacLeod et al. 2010 ), employing the mathematical formulation of the Damped Random Walk.  The CRTS survey is still ongoing, and the products of the survey can be found here. It does not use filters – the photometry is calibrated to the V-band *zeropoint*, but do not apply color corrections that would convert their magnitudes to true V-band magnitudes. (B. Sesar, priv. comm.). The SDSS Survey has subsequent Data Releases (DR). My research uses the SDSS DR7, which is calibrated in u,g,r,i,z filters.   The CRTS Quasar sample has 7931  objects, whereas the SDSS Quasar sample has 9258 objects.

We aim to probe whether short-scale variability on timescale 54 days in rest frame (as found by Graham et al. 2014) also shows a signal in SDSS as well as CRTS data. The Graham et al. 54 days time scale in rest frame corresponds to 152 days in observers frame. Therefore, Stripe 82 SDSS and CRTS sampling ought be able to uncover evidence for such short time scales.

We processed the CRTS data with FORTRAN code of Chris Kochanek ( Ohio State University) (Kozlowski et al 2010, ApJ, 708, 927).  to show their behavior.  The results were presented on the 225th American Astronomical Society meeting in Seattle  (see the poster).

Using CRTS lightcurves for stars and quasars I also conduct research on their structure function: below are plotted the CRTS quasars and the stars (preliminary results). Those show that the claim for variability of CRTS quasars is supported by evidence from the data, since stars (blue and red points) do not show that behavior.  SF_both_200_bins_17

 

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