Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability

• For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

Experimental/ gamma-ray sources (astronomical)

Seyfert galaxies

X-ray sources (astronomical)/ Seyfert 1 galaxy

short-timescale variability

multiwavelength observations

multiwavelength continuum variability

spectral energy distribution

AD 1993 12

peak historical brightness

X-ray variability

UV variability

optical variability

soft gamma-ray energies

AGN monitoring campaigns

UV fluctuation power spectra

periodicity/ A9850R Active and peculiar galaxies A9870Q Cosmic X-ray sources A9870R Cosmic gamma-ray sources A9850G Radiation and spectra of galaxies A9580J Photographic region astronomical observations A9580M Space ultraviolet astronomical observations A9580N X-ray astronomical observations A9580Q gamma-ray and cosmic ray observations/ NGC 4151

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