Aims. Metis is the first solar coronagraph designed for a space mission and is capable of performing simultaneous imaging of the off-limb solar corona in both visible and UV light. The observations obtained with Metis aboard the Solar Orbiter ESA-NASA observatory will enable us to diagnose, with unprecedented temporal coverage and spatial resolution, the structures and dynamics of the full corona in a square field of view (FoV) of ±2.9 • in width, with an inner circular FoV at 1.6 • , thus spanning the solar atmosphere from 1.7 R to about 9 R , owing to the eccentricity of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter mission profile, Metis will be able to observe the solar corona from a close (0.28 AU, at the closest perihelion) vantage point, achieving increasing out-of-ecliptic views with the increase of the orbit inclination over time. Moreover, observations near perihelion, during the phase of lower rotational velocity of the solar surface relative to the spacecraft, allow longer-term studies of the off-limb coronal features, thus finally disentangling their intrinsic evolution from effects due to solar rotation. Methods. Thanks to a novel occultation design and a combination of a UV interference coating of the mirrors and a spectral bandpass filter, Metis images the solar corona simultaneously in the visible light band, between 580 and 640 nm, and in the UV H i Lyman-α line at 121.6 nm. The visible light channel also includes a broadband polarimeter able to observe the linearly polarised component of the K corona. The coronal images in both the UV H i Lyman-α and polarised visible light are obtained at high spatial resolution with a spatial scale down to about 2000 km and 15000 km at perihelion, in the cases of the visible and UV light, respectively. A temporal resolution down to 1 second can be achieved when observing coronal fluctuations in visible light. Results. The Metis measurements, obtained from different latitudes, will allow for complete characterisation of the main physical parameters and dynamics of the electron and neutral hydrogen/proton plasma components of the corona in the region where the solar wind undergoes the acceleration process and where the onset and initial propagation of coronal mass ejections (CMEs) take place. The near-Sun multi-wavelength coronal imaging performed with Metis, combined with the unique opportunities offered by the Solar Orbiter mission, can effectively address crucial issues of solar physics such as: the origin and heating/acceleration of the fast and slow solar wind streams; the origin, acceleration, and transport of the solar energetic particles; and the transient ejection of coronal mass and its evolution in the inner heliosphere, thus significantly improving our understanding of the region connecting the Sun to the heliosphere and of the processes generating and driving the solar wind and coronal mass ejections. Conclusions. This paper presents the scientific objectives and requirements, the overall optical design of the Metis instrument, t...

We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as '2013a') followed by a much brighter outburst ('2013b') three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN 2010mc and (in 2012) SN 2009ip. The absolute magnitude reached by LSQ13zm during 2013a (M R = −14.87±0.25 mag) is comparable with those of supernova impostors, while that of the 2013b event (M R = −18.46 ± 0.21 mag) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20000 km s −1 . The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Luminous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy.

Context. A new extremely high speed photon-counting photometer, Iqueye, has been installed and tested at the New Technology Telescope, in La Silla. Aims. This instrument is the second prototype of a "quantum" photometer being developed for future Extremely Large Telescopes of 30-50 m aperture. Methods. Iqueye divides the telescope aperture into four portions, each feeding a single photon avalanche diode. The counts from the four channels are collected by a time-to-digital converter board, where each photon is appropriately time-tagged. Owing to a rubidium oscillator and a GPS receiver, an absolute rms timing accuracy better than 0.5 ns during one-hour observations is achieved. The system can sustain a count rate of up to 8 MHz uninterruptedly for an entire night of observation. Results. During five nights of observations, the system performed smoothly, and the observations of optical pulsar calibration targets provided excellent results.

The Crab nebula pulsar was observed in 2009 January and December with a novel very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we computed accurate phase coherent timing solutions for the two observing runs and over the entire year 2009. Our statistical uncertainty on the determination of the phase of the main pulse and the rotational period of the pulsar for short (a few days) time intervals are ≈ 1 µs and ∼0.5 ps, respectively. Comparison with the Jodrell Bank radio ephemerides shows that the optical pulse leads the radio one by ∼ 240 µs in January and ∼ 160 µs in December, in agreement with a number of other measurements performed after 1996. A third-order polynomial fit adequately describes the spin-down for the 2009 January plus December optical observations. The phase noise is consistent with being Gaussian distributed with a dispersion σ of ≈ 15 µs in most observations, in agreement with theoretical expectations for photon noise-induced phase variability.

Context. We observed the Crab pulsar in October 2008 at the Copernico Telescope in Asiago -Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum Eye), which has the best temporal resolution and accuracy ever achieved in the optical domain (hundreds of picoseconds). Aims. Our goal was to perform a detailed analysis of the optical period and phase drift of the main peak of the Crab pulsar and compare it with the Jodrell Bank ephemerides. Methods. We determined the position of the main peak using the steepest zero of the cross-correlation function between the pulsar signal and an accurate optical template. Results. The pulsar rotational period and period derivative have been measured with great accuracy using observations covering only a two day time interval. The error on the period is 1.7 ps, limited only by the statistical uncertainty. Both the rotational frequency and its first derivative agree with those from the Jodrell Bank radio ephemerides archive. We also found evidence that the optical peak precedes the radio peak by ∼230 μs. The distribution of phase residuals of the whole dataset is slightly more scattered than that of a synthetic signal generated as a sequence of pulses distributed in time with the probability proportional to the pulse shape. Conclusions. The counting statistics and quality of the data allowed us to determine the pulsar period and period derivative with great accuracy in two days only. The time of arrival of the optical peak of the Crab pulsar precedes the radio peak in agreement with what was recently reported in the literature. The distribution of the phase residuals can be approximated with a Gaussian and is consistent with being completely caused by photon noise (for the best data sets).