The most intense monitoring observations yet made in the optical and near-infrared wave bands were carried out for Seyfert 1 galaxies NGC 5548, NGC 4051, NGC 3227, and NGC 7469 by the MAGNUM telescope, and clear timedelayed responses of the K-band flux variations to the V-band flux variations were found for all of these galaxies. Their H À K color temperatures of 1500-1800 K, estimated from their observed flux variation gradients, support a view that the bulk of the K flux should originate in the thermal radiation of hot dust surrounding the central engine and that the lag time should correspond to light-travel distance between them. Cross-correlation analysis measures their lag times to be 47-53 (NGC 5548), 11-18 (NGC 4051), about 20 (NGC 3227), and 65-87 (NGC 7469) days. The lag times are tightly correlated with the optical luminosities, as expected from dust reverberation (Át / L 0:5 ), while weakly with the central virial masses, which suggests that the inner radii of the dust tori around active nuclei have oneto-one correspondences with their central luminosities. In the lag time versus central luminosity diagram, the K-band lag times place an upper boundary on the similar lag times of broad emission lines in the literature, which not only supports the unified scheme of AGNs but also implies a physical transition from the BLR out to the dust torus that encircles the BLR. Correlated short-term V-band and X-ray flux variations in NGC 5548 are also found with a delay of 1 or 2 days, indicating the thermal reprocessing of X-ray emission by the central accretion flow.

We present the results of a dust reverberation survey for 17 nearby Seyfert 1 galaxies, which provides the largest homogeneous data collection for the radius of the innermost dust torus. A delayed response of the K-band light curve after the V -band light curve was found for all targets, and 49 measurements of lag times between the flux variation of the dust emission in the K band and that of the optical continuum emission in the V band were obtained by the cross-correlation function analysis and also by an alternative method for estimating the maximum likelihood lag. The lag times strongly correlated with the optical luminosity in the luminosity range of M V = −16 to −22 mag, and the regression analysis was performed to obtain the correlation log ∆t (days) = −2.11 − 0.2M V assuming ∆t ∝ L 0.5 , which was theoretically expected. We discuss the possible origins of the intrinsic scatter of the dust lag-luminosity correlation, which was estimated to be approximately 0.13 dex, and we find that the difference of internal extinction and delayed response of changes in lag times to the flux variations could have partly contributed to intrinsic scatter. However, we could not detect any systematic change of the correlation with the subclass of the Seyfert type or the Eddington ratio. Finally, we compare the dust reverberation radius with the near-infrared interferometric radius of the dust torus and the reverberation radius of broad Balmer emission lines. The interferometric radius in the K band was found to be systematically larger than the dust reverberation radius in the same band by about a factor of two, which could be interpreted by the difference between the flux-weighted radius and the response-weighted radius of the innermost dust torus. The reverberation radius of the broad Balmer emission lines was found to be systematically smaller than the dust reverberation radius by about a factor of 4-5, which strongly supports the unified scheme of the Seyfert type of active galactic nuclei (AGNs). Moreover, we examined the radius-luminosity correlations for the hard X-ray (14-195 keV) and the [O IV]λ25.89 µm emission-line luminosities, which would be applicable for obscured AGNs.

We present new data for five under-luminous type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) is analyzed together with similar objects studied in the past. All of them show a flat light curve plateau lasting about 100 days, an under luminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P-Cygni lines. A velocity of the ejected material below 10 3 km s −1 is inferred from measurements at the end of the plateau. The 56 Ni masses ejected in the explosion are very small ( 10 −2 M ⊙ ). We investigate the correlations among 56 Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy (2003), according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56 Ni. We propose that these faint objects represent the low luminosity tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modeling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core-collapse of intermediate mass stars, in the mass range 10-15 M ⊙ .

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the "hypernova" SN 1997ef. However, its kinetic energy [∼ ergs] and 51 (4-10) # 10 the mass ejected (2.5-5) are smaller, resulting in a faster evolving light curve. The SN synthesized M , ∼0.07 of 56 Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be M , used to define a hypernova, whose defining character, namely very broad spectral features, is the result of high kinetic energy. The likely main-sequence mass of the progenitor star was [20][21][22][23][24][25] , which is also lower than M , that of both hypernovae SN 1997ef and SN 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by the summer of 2002, are necessary to confirm these values.

The light curves of 'hypernovae', i.e. very energetic supernovae with E 51 ≡ E/10 51 ergs ∼ > 5 − 10 are characterized at epochs of a few months by a phase of linear decline. Classical, onedimensional explosion models fail to simultaneously reproduce the light curve near peak and at the linear decline phase. The evolution of these light curves may however be explained by a simple model consisting of two concentric components. The outer component is responsible for the early part of the light curve and for the broad absorption features observed in the early spectra of hypernovae, similar to the one-dimensional models. In addition, a very dense inner component is added, which reproduces the linear decline phase in the observed magnitude-versus-time relation for SNe 1998bw, 1997ef, and 2002ap. This simple approach does contain one of the main features of jet-driven, asymmetric explosion models, namely the presence of a dense core. Although the total masses and energies derived with the two-component model are similar to those obtained in previous studies which also adopted spherical symmetry, this study suggests that the ejecta are aspherical, and thus the real energies and masses may deviate from those derived assuming spherical symmetry. The supernovae which were modeled are divided into two groups, according to the prominence of the inner component: the inner component of SN 1997ef is denser and more 56 Ni-rich, relative to the outer component, than the corresponding inner components of SNe 1998bw and 2002ap. These latter objects have a similar inner-to-outer component ratio, although they have very different global values of mass and energy.