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SPECTRAL MONITORING OF NGC 5548 IN 1996 -- 2004
A.N. Burenkov 1 , A.I. Shapovalova 1 , N.G. Bochkarev 2 , V.H. Chavushyan 3 , S. Collin 4 , V.T.
Doroshenko 2 , L. PopoviÒc 5 , N. Borisov 1 , L. Carrasco 3 , D. IliÒc 6 , J.R. Valdes 3 , V.V.
Vlasuyk 1 , V.E. Zhdanova 2
1 Special Astrophysical Observatory of RAS, Nizhnij Arkhyz, 369167, Russia
2 Sternberg Astronomical Institute, University of Moscow, Universitetskij Prospect 13,
Moscow 119899, Russia
3 Instituto Nacional de AstrofÒÐsica, Optica y ElectrÒonica, Apartado Postal 51. C.P. 72000.
Puebla, Pue., MÒexico
4 LUTH, Observatoire de Paris, Section de Meudon, Place Janssen, 92195, Meudon, France
5 Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia
6 Department of Astronomy, Faculty of Mathematics, University of Belgrade, Studentski
trg 16, 11000 Belgrade, Serbia
We present results of a spectral monitoring program of the Seyfert galaxy NGC 5548 with
the 6m and 1m telescopes of SAO (Russia) and with the 2.1m telescope of Guillermo
Haro Observatory at Cananea, MÒexico. Spectra were obtained with longíslit spectrograph,
covering the spectral range #(4000--7500) Ú A with a (4.5--15) Ú A resolution. We found that:
-- Both the flux in the lines and continuum gradually decreased, reaching minimum
values during MayíJune 2002. In the minimum state, the wings of H# and H# became
extremely weak, corresponding to a Sy1.8 type, not to a Sy1, as observed previously when
the nucleus was brighter.
-- When the line profiles were decomposed into variable and constant components, the
variable broad component is well correlated with the continuum variation. It consists of
a double peaked structure with radial velocities of # ‘1000 km/s relative to the narrow
component. A constant component, whose presence is independent of the continuum flux
variations, shows only narrow emission lines. The mean, rms, and the averaged over years,
observed and di#erence line profiles of H# and H# reveal the same double peaked structure
at the same velocities. The relative intensity of these peaks changes with time. During 1996,
the red peak was the brightest, while in 1998--2002, the blue peak became the brighter one.
Their radial velocities vary in the range #500--1200 km/s.
-- In 2000--2002 a distinct third peak appeared in the red wing of H# and H# line
profiles. The radial velocity of this feature decreased between 2000 and 2002: by the
observed profiles, from # +(2500--2600) km/s to # +2000 km/s and it is clearly seen on
the di#erence profiles.
-- The fluxes of various parts of the line profiles are well correlated with each other and
also with the continuum flux. The blue and red parts of the line profiles at the same radial
velocities vary in an almost identical manner.
-- Our results favor the formation of the broad Balmer lines in a turbulent accretion
disc with large and moving ``optically thick'' inhomogeneities, capable of reprocessing the
central source continuum.
We made an attempt to investigate the variability of physical parameters in the BLR
of NGC 5548 using the Boltzmann plot method given by PopoviÒc (2003). We applied the
method on the broad Balmer lines, and found that variability seen in lines is also present in
the electron temperature (T). We found that the average T for the considered period was
# 10000K, and that it varies from 6000K (in 2002) till 15000K (in 1998). This variation

correlates with the optical continuum flux (r = 0.85) and may indicate existence of an
accretion disk in the BLR of NGC 5548. We found that Partial Local Thermodynamical
Equilibrium approximation is valid for at least one part of the BLR of NGC 5548.
The detailed discussion of these results is done in our papers (Shapovalova at al. 2004;
PopoviÒc et al. 2005).
Acknowledgements. This work was supported by grants from CONACYT 39560íF (Mexí
ico), RFBR 06í02í16843 (Russia) and the Ministry of Science and Environment Protection
of Serbia.
References
PopoviÒc L. ß
C.: ApJ, 2003, 599, 140.
PopoviÒc L. ß
C. et al.: Astroíph/0511676, 2005 (in press).
Shapovalova A. I. et al.: 2004, A&A, 422, 925.