Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...421...34m&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 421, no. 1, p. 34-45
Astronomy and Astrophysics
Astrophysics
41
Active Galactic Nuclei, Balmer Series, Galaxies, Quasars, Spectrum Analysis, Amplitudes, Astrophysics, Comparison, Spectrophotometers, Variations
Scientific paper
We have monitored spectrophotometrically a subsample (28) of the Palomar-Green Bright Quasar Sample for 2 years in order to test for correlations between continuum and emission-line variations and to determine the timescales relevant to mapping the broad-line regions of high-luminosity active galactic nuclei (AGNs). Half of the quasars showed optical continuum variations with amplitudes in the range 20-75%. The rise and fall time for the continuum variations is typically 0.5-2 years. In most of the objects with continuum variations, we detect correlated variations in the broad H-alpha and H-beta emission lines. The amplitude of the line variations is usually 2-4 times smaller than the optical continuum fluctuations. We present light curves and analyze spectra for six of the variable quasars with 1000-10,000 A luminosity in the range 0.3-4 x 1045 ergs/s. In four of these objects the lines respond to the continuum variations with a lag that is smaller than or comparable to our typical sampling interval (a few months). Although continued monitoring is required to confirm these results and increase their accuracy, the present evidence indicates that quasars with the above luminosities have broad-line regions smaller than about 1 1t-yr. Two of the quasars monitored show no detectable line variations despite relatively large-amplitude continuum changes. This could be a stronger manifestation of the low-amplitude line-response phenomenon we observe in the other quasars.
Jannuzi Buell Tomasson
Kaspi Shai
Maoz Dan
Netzer Hagai
Smith Paul S.
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