Aims. We present the characteristics and some early scientific results of the first instrument at the Large Binocular Telescope (LBT), the Large Binocular Camera (LBC). Each LBT telescope unit will be equipped with similar prime focus cameras. The blue channel is optimized for imaging in the UV − B bands and the red channel for imaging in the VRIz bands. The corrected field-of-view of each camera is approximately 30 arcmin in diameter, and the chip area is equivalent to a 23 × 23 arcmin 2 field. In this paper we also present the commissioning results of the blue channel. Methods. The scientific and technical performance of the blue channel was assessed by measurement of the astrometric distortion, flat fielding, ghosts, and photometric calibrations. These measurements were then used as input to a data reduction pipeline applied to science commissioning data. Results. The measurements completed during commissioning show that the technical performance of the blue channel is in agreement with original expectations. Since the red camera is very similar to the blue one we expect similar performance from the commissioning that will be performed in the following months in binocular configuration. Using deep UV image, acquired during the commissioning of the blue camera, we derived faint UV galaxy-counts in a ∼500 sq. arcmin sky area to U(Vega) = 26.5. These galaxy counts imply that the blue camera is the most powerful UV imager presently available and in the near future in terms of depth and extent of the field-of-view. We emphasize the potential of the blue camera to increase the robustness of the UGR multicolour selection of Lyman break galaxies at redshift z ∼ 3.

Aims. With an observed and rest-frame duration of <2 s and <0.5 s, respectively, GRB 090426 could be classified as a short GRB. The prompt detection, both from space and ground-based telescopes, of a bright optical counterpart to this GRB offered a unique opportunity to complete a detailed study. Methods. Based on an extensive ground-based observational campaign, we obtained the spectrum of the optical afterglow of GRB 090426, measuring its redshift and obtaining information about the medium in which the event took place. We completed follow-up observations of the afterglow optical light curve down to the brightness level of the host galaxy that we firmly identified and studied. We also retrieved and analyzed all the available high-energy data of this event, and compared the results with our findings in the optical. This represents one of the most detailed studies of a short-duration event presented so far. Results. The time properties qualify GRB 090426 as a short burst. In this case, its redshift of z = 2.61 would be the highest yet found for a GRB of this class. On the other hand, the spectral and energy properties are more similar to those of long bursts. LBT late-time deep imaging identifies a star-forming galaxy at a redshift consistent with that of the GRB. The afterglow lies within the light of its host and shows evidence of local absorption.

Context. The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H i ionizing background at z 3. Aims. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at λ ≤ 912 Å rest-frame and those which are able to reach the CGM/IGM, not being absorbed by the neutral hydrogen or by the dust of the galaxy's ISM. Methods. We have used ultra-deep U-band imaging (U = 30.2mag at 1σ) by LBC/LBT in the CANDELS/GOODS-North field, as well as deep imaging in COSMOS and EGS fields, in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 ≤ z ≤ 3.40 to faint magnitude limits (L = 0.2L * , or equivalently M 1500 ∼ −19). The narrow redshift range implies that the LBC U-band filter samples exclusively the λ ≤ 912 Å rest-frame wavelengths. Results. We have measured through stacks a stringent upper limit (<1.7% at 1σ) for the relative escape fraction of H i ionizing photons from bright galaxies (L > L * ), while for the faint population (L = 0.2L * ) the limit to the escape fraction is 10%. We have computed the contribution of star-forming galaxies to the observed UV background at z ∼ 3 and we have found that it is not enough to keep the Universe ionized at these redshifts, unless their escape fraction increases significantly (≥ 10%) at low luminosities (M 1500 ≥ −19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental to measure the Lyman continuum escape fraction down to faint magnitudes (M 1500 ∼ −16) which are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.

We present the first deep color-magnitude diagram of the Canes Venatici I (CVn I) dwarf galaxy from observations with the wide-field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVn I: it harbors an old (տ10 Gyr), metal-poor ( ), and spatially extended population along with a much younger [Fe/H] ∼ Ϫ2.0 (∼1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by pc to the east of the galaxy center. The data suggest that this young population, which represents ϩ40 64 Ϫ20 ∼3%-5% of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found in a recent spectroscopic survey. CVn I therefore follows the behavior of the other remote MW dwarf spheroidals, which all contain intermediate-age and/or young populations: a complex star formation history is possible in extremely low mass galaxies.

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light. Spectroscopic observations are also discussed. Using as a distance calibrator the Type Ia SN 2000E, which occurred some months later in the same galaxy, and fitting a blackbody law to the photometric data we obtain a maximum bolometric luminosity for SN 1999el of ∼ 10 44 erg s −1 . In general, the photometric properties of SN 1999el are very similar to those of SN 1998S, a bright and well studied Type IIn SN, showing a fast decline in all observed bands similar to those of Type II-L SNe. The differences with SN 1998S are analyzed and ascribed to the differences in a pre-existing circumstellar envelope in which dust was already present at the moment of the SN outburst. We infer that light echoes may play a possibly -2significant role in affecting the observed properties of the light curves, although improved theoretical models are needed to account for the data. We conclude that mass loss in the progenitor RG stars is episodic and occurs in an asymmetric way. This implies that collapsing massive stars appear as normal Type II SN if this occurs far from major mass loss episodes, whereas they appear as Type IIn SNe if a large mass loss episode is in progress.Subject headings: supernovae: general -supernovae: individual (SN 1999el)galaxies: individual (NGC 6951) -infrared:stars 1 Based on observations collected with the AZT-24 telescope (Campo Imperatore, Italy), the 1.8-m telescope of the Osservatorio Astronomico di Padova (Asiago, Italy), the TNT telescope operated by the Osservatorio Astronomico di Collurania-Teramo (Teramo, Italy), the Italian National Telescope TNG (La Palma, Canary Islands, Spain), the 1-m telescope of the Observatorio Astronómico Nacional (Tonantzintla, Mexico), the 2.1-m telescope of the Guillermo Haro Observatory (Cananea, Mexico).

We present optical (UBV RI) and near-infrared (JHK) photometry, along with optical spectra, of the Type Ia supernova SN 2000E in the spiral galaxy NGC 6951. It was discovered by the staff of the Teramo Observatory during the monitoring of the SN 1999el. The observations span a time interval of 234 days in the optical and 134 days in the near-infrared (starting ∼ 16 days and ∼ 7 days before maximum B light, respectively). Optical spectra are available from 6 days before maximum B light to 122 days after it. The photometric behavior of SN 2000E is remarkably similar to that of SN 1991T and SN 1992bc: it exhibits a ∆m 15 (B) = 0.94, thus being classifiable as a slow-declining Type Ia SN and showing the distinctive features of such a class of objects both in the visible and in the near-infrared. Spectroscopically, SN 2000E appears as a "normal" Type Ia supernova, like SN 1990N. We could constrain reddening [E(B − V ) ∼ 0.5

Context. Deep multicolour surveys are the main tool for exploring the formation and evolution of the very faint galaxies that are beyond the spectroscopic limit of present technology. The photometric properties of these faint galaxies are usually compared with current renditions of semianalytical models to provide constraints on the detailed treatment of the fundamental physical processes involved in galaxy formation and evolution, namely the mass assembly and the star formation. Aims. Galaxy counts over large sky areas in the 360 nm near-UV band are particularly difficult to obtain given the low efficiency of near-UV instrumentation, even at 8 m class telescopes. Observing in the near-UV bands can provide a first assessment of the distribution of star formation activity in distant (up to z ∼ 3) galaxies. A relatively large instrumental field of view helps to minimize the biases caused by cosmic variance. Methods. We obtained deep images in the 360 nm U band provided by the blue channel of the Large Binocular Camera at the prime focus of the Large Binocular Telescope. Over an area of 0.4 sq. deg., we derived the galaxy number counts down to U = 27 in the Vega system (corresponding to U = 27.86 in the AB system) at a completeness level of 30% reaching the faintest current limit for this wavelength and sky area. Results. The shape of the galaxy number counts in the U band can be described by a double power-law, the bright side being consistent with the shape of shallower surveys of comparable or greater areas. The slope bends over significantly at U > 23.5 ensuring the convergence of the contribution by star-forming galaxies to the extragalactic background light in the near-UV band to a value that is more than 70% of the most recent upper limits derived for this band. We jointly compared our near-UV and K band counts collected from the literature with a few selected hierarchical CDM models, concentrating on specific critical issues in the physical description of the galaxy formation and evolution.

This paper describes the results obtained so far with AquEYE, a single photon counting, fixed aperture photometer for the Asiago 182 cm telescope. AquEYE has been conceived as a prototype of a truly ‘quantum’ photometer for future Extremely Large Telescopes of 30–50 m aperture. This prototype is characterized by four independent channels equipped with single photon avalanche diodes (SPADs) as detectors. The counts from the four channels are acquired by a TDC board which has a nominal 25 ps time tagging capability. Taking into account the 35 ps jitter in the SPAD itself, the overall precision of the time tags is of the order of 50 ps. The internal oscillator is locked to an external rubidium clock; a GPS pulse per second is collected by the TDC itself to obtain a UTC reference. The maximum photon count rate which the present system can sustain is 12 MHz