C. Germanà

Iqueye, a single photon-counting photometer applied to the ESO new technology telescope

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 optical light curve of the LMC pulsar B0540-69 in 2009

This paper reports a detailed analysis of the optical light curve of PSR B0540-69, the second brightest pulsar in the visible band, obtained in 2009 (Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a raising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms respectively. Our new values of spin frequencies allow to extend by 3.5 years the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications on the braking index and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed around 1700 years.

The Crab pulsar seen with AquEYE at Asiago Cima Ekar observatory

We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed AquEYE (the Asiago Quantum Eye), was mounted in 2008 at the 182 cm Copernicus Observatory in Asiago. AquEYE observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal.

The optical light curve of the Large Magellanic Cloud pulsar B0540−69 in 2009

This paper reports a detailed analysis of the optical light curve of PSR B0540-69, the second brightest pulsar in the visible band, obtained in 2009 (Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a raising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms respectively. Our new values of spin frequencies allow to extend by 3.5 years the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications on the braking index and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed around 1700 years.

Timing of optical pulsars with two high time resolution photometers at Asiago and NTT

We have built two single photon very high speed photometers (Aqueye for the Asiago 1.8m telescope and Iqueye for the 3.5m ESO NTT) as prototypes of a ‘quantum’ photometer for the European Extremely Large Telescope (E‐ELT) The two photometers are the most accurate ‘time machines’ available to optical astronomy. Under the control of a GPS receiver and a Rubidium clock, the arrival time of each detected photon is referenced to UTC with a precision better than 500 picoseconds, continuously for hours of data acquisition. Light curves for three optical pulsars (Crab, B0540‐69, Vela) will be reported. Results from simultaneous observations of the Crab pulsar with the Jodrell Bank RadioTelescope will also be reported.

The optical light curve of the Large Magellanic Cloud pulsar B0540−69 in 2009: The optical light curve of the PSR B0540−69

This paper reports a detailed analysis of the optical light curve of PSR B0540-69, the second brightest pulsar in the visible band, obtained in 2009 (Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a raising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms respectively. Our new values of spin frequencies allow to extend by 3.5 years the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications on the braking index and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed around 1700 years.

Crab Pulsar Observations with AquEYE

As is well known, the Crab pulsar displays a light curve with a characteristic double peak profile having a period of 33 milliseconds. Its pulse profile has been extensively monitored by several authors; it is also used for testing high‐speed photon counters. We have studied the optical light curve of the Crab pulsar by means of a novel photon counting instrument, that has the capability to provide data with exceptionally high temporal resolution and time tagging accuracy of each incoming photon.

Very fast photon counting photometers for astronomical applications: IquEYE for the ESO 3.5m New Technology Telescope

Almost all astronomical instruments detect and analyze the first order spatial and/or temporal coherence properties of the photon stream coming from celestial sources. Additional information might be hidden in the second and higher order coherence terms, as shown long ago by Hanbury-Brown and Twiss with the Narrabri Intensity Interferometer. The future Extremely Large Telescopes and in particular the 42 m telescope of the European Southern Observatory (ESO) could provide the high photon flux needed to extract this additional information. To put these expectations (which we had already developed at the conceptual level in the QuantEYE study for the 100 m OverWhelmingly Large Telescope to experimental test in the real astronomical environment, we realized a small prototype (Aqueye) for the Asiago 182 cm telescope. This instrument is the fastest photon counting photometer ever built. It has 4 parallel channels operating simultaneously, feeding 4 Single Photon-Avalanche Diodes (SPADs), with the ability to push the time tagging capabilities below the nano-second region for hours of continuous operation. Aqueye has been extensively used to acquire photons from a variety of variable stars, in particular from the pulsar in the Crab Nebula. Following this successful realization, a larger version, named Iqueye, has been built for the 3.5 m New Technology Telescope (NTT) of ESO. Iqueye follows the same optical solution of dividing the telescope pupil in 4 sub-pupils, imaged on new generation SPADs having useful diameters of 100 micrometers, time jitter less than 50 picoseconds and dark-count noise less than 50 counts/second. The spectral efficiency of the system peaks in the visible region of the spectrum. Iqueye operated very successfully at the NTT in January 2009. The present paper describes the main features of the two photometers and present some of the astronomical results already obtained.

Detecting Rapid optical Variability in X‐ray Binaries with OWL

A new generation instrument performing photon‐counting at submillisecond timescales in the optical domain is under study for extremely large collecting area telescopes (such as OWL). In this paper we report results from a preliminary theoretical investigation on the possibility of detecting high frequency (kHz) variability of X‐ray binaries in the optical band with such an instrument. We calculated the visual magnitude that a source should have in order for a high frequency QPO to be observable in the optical band with a very large collecting area telescope (100 m diameter). The model computes the optical‐through‐X‐ray spectrum emitted by the accretion disk and the donor star, taking irradiation into account. The most promising sources for the detection of rapid variability in the optical band turn out to be Black Hole Soft X‐ray Transients.