Date of Award
Masters of Science (Research)
Applied Physics and Instrumentation
Results from imaging and spectral surveys at radio wavelengths indicate that radio quiet quasars (RQQs) may have accretion-fuelled Super Massive Black Holes (SMBH) as their so-called central engines, similar to those hypothesised for radio loud quasars (RLQs). Recent evidence suggests that some RQQs may also harbour weak jets. Rapid optical variability is a common property of most RLQs with compact radio cores, flat radio spectra, and extended linear features emanating from the core and is linked to the presence of a powerful relativistically boosted jet. We present the results of a 3 year monitoring campaign of sixteen RQQs displaying evidence of compact cores and flat or inverted radio spectra. The objective of the campaign is to search for rapid optical variability. The observations were carried out mainly in the V-band for most of the sample. PG 16344-706 and E1821-f643 have been observed extensively in V, R, and B bands. Differential photometry is carried out using IRAF routines to calculate instrumental magnitudes. For differential photometry all of the suitable reference stars available on the CCD frame containing the RQQ are used. This is a novel approach which we believe leads to the best estimate of the quasar lightcurve.
We find that in most cases the photometric accuracy attainable lies between ~ 40-50 millimag, based on the analysis of the scatter in the reference stars. This provides the most accurate (though conservative) estimate of the uncertainty in our observations. We also find that the errors calculated by IRAF routines are underestimated at least by a factor of 1.5. We also point out that instrumental effects can lead to spurious variability of « 50-80 millimag at these short timescales. We find no evidence for variability within a given night for any of our sources. We find evidence of marginal variability from night-to-night in PG0003-fl99 of 30 millimag. We find that the lack of observed ROV in our RQQ sample doesn’t necessarily imply the lack of a weak jet but that the contrast effects in the optical (where the flux is dominated largely by the luminous accretion disk in RQQs) may prevent us from detecting rapid variations that may arise in a weak jet given the limit of the photometric accuracy attained.
Uppal, Meenakshi, "Rapid Optical Variability in Radio-Quiet Quasars" (1999). Theses [online].
Available at: https://sword.cit.ie/allthe/125