A B S T R A C TWe present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2±3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ,100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0X150X05 M ( of 56 Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K 2 L H 2X5Y that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be preexisting and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.

From the peak of a gravitational microlensing high-magnification event in the A component of QSO 2237+0305, which was accurately monitored by the GLITP collaboration, we derived new information on the nature and size of the optical V -band and R-band sources in the far quasar. If the microlensing peak is caused by a microcaustic crossing, we firstly obtained that the standard accretion disk is a scenario more reliable/feasible than other usual axially symmetric models. Moreover, the standard scenario fits both the V -band and R-band observations with reduced chi-square values very close to one. Taking into account all these results, a standard accretion disk around a supermassive black hole is a good candidate to be the optical continuum main source in QSO 2237+0305. Secondly, using the standard source model and a robust upper limit on the transverse galactic velocity, we inferred that 90 per cent of the V -band and R-band luminosities are emitted from a region with radial size less than 1.2 10 −2 pc (= 3.7 10 16 cm, at 2σ confidence level).

We present V R observations of QSO 2237+0305 conducted by the GLITP collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma (Spain). The PSF fitting method and an adapted version of the ISIS subtraction method have been used to derive the V R light curves of the four components (A-D) of the quasar. The mean errors range in the intervals 0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the faintest component (D) having the largest uncertainties. We address the relatively good agreement between the A-D light curves derived using different -2filters, photometric techniques, and telescopes. The new V R light curves of component A extend the time coverage of a high magnification microlensing peak, which was discovered by the OGLE team.

CCD observations of the gravitational lens system Q0957+561A,B in the BV RI bands are presented in this paper. The observations, taken with the 82 cm IAC-80 telescope, at Teide Observatory, Spain, were made from the beginning of 1996 February to 1998 July, as part of an on-going lens monitoring program. Accurate photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component by means of DAOPHOT software. This alternative method equals and even improves the results obtained with previous techniques. The final dataset is characterized by its high degree of homogeneity as it was obtained using the same telescope and instrumentation during a period of almost 3 years. The resulting delay, obtained with a new method, the δ 2 -test, is of 425 ± 4 days, slightly higher than the value previously accepted (417 days), but concordant with the results obtained by Pelt et al.

Photometric optical data of QSO 0957+561 covering the period 1984-99 are analyzed to discern between the two values of the time delay (417 and 424 days) mostly accepted in the recent literature. The observations, performed by groups from three different institutions-Princeton University, Harvard-Smithsonian Center for Astrophysics, and Instituto de Astrofísica de Canarias-and including new unpublished 1998-9 data from the IAC80 Telescope, were obtained in five filters (V , R, I, g, and r). The different light curves have been divided into observational seasons and two restriction have been applied to better calculate the time delay: (i) points with a strange photometric behavior have been removed; and (ii) data sets without large gaps have been selected. Simulated data were generated to test several numerical methods intended to compute the time delay (∆τ AB ). The methods giving the best results-the discrete correlation function, δ-square, z-transformed discrete correlation function, and linear interpolation-were then applied to real data. A first analysis of the 23 different time delays derived from each technique shows that ∆τ AB must be into the interval 420-424 days. From our statistical study, a most probable value of ∆τ AB = 422.6 ± 0.6 days is inferred.