Mrk 766 is a rather bright (typical flux of about one milliCrab) Narrow Line Seyfert 1 galaxy at redshift 0.012, showing complex and puzzling X-ray variability (Molendi et al. 1993; Molendi & Maccacaro 1994; Page et al. 1999) on time-scales as short as 1000 sec (Leighly et al. 1996). The 1992 June ROSAT PSPC observations, discussed by Molendi & Maccacaro (1994), indicated large amplitude variations in the softest part of the spectrum (0.1-0.9 keV), while the hardest part (0.9-2 keV) was consistent with being constant. The authors suggested accretion disc emission as the origin of the variable component. Recently, Page et al. (1999) analysed spectral variability in ROSAT PSPC data collected from 1991 to 1994, reaching different conclusions: a highly variable (on time-scales as short as 5000 s) hard power law component, and a constant soft excess. The ASCA-ROSAT observation reported by Leighly et al. (1996) shows a complex and variable spectrum, with the primary power law photon index changing from 1.6 to 2 within the observation, and variable warm absorber too. The soft excess variability was anti-correlated with that of the hard component. A narrow iron K line was detected only when the source was in a high flux level.
We observed Mrk 766 with BeppoSAX to take advantage of the wide energy band of the satellite and try to better understand the origin of the spectral complexity in this source.
The paper is organized as follows: Sect. 2 describes the observation and data reduction; Sect. 3 presents the temporal, and Sect. 4 the spectral, analysis; the results are compared with the ASCA-ROSAT ones in Sect. 5, discussed in Sect. 6 and summarized in Sect. 7.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000