Upgrade of Iqueye, a novel photon-counting photometer for the ESO New Technology Telescope

Iqueye is a novel extremely high speed photon-counting photometer for the European Southern Observatory New Technology Telescope in La Silla (Chile). Iqueye collects the light from the telescope through a few arcsec aperture, and splits it along four independent channels, each feeding a single photon avalanche diode. The produced count pulses are collected by a time-to-digital converter board and suitably time-tagged. Thanks to a rubidium oscillator and a GPS receiver, an absolute rms timing accuracy better than 0.5 ns during one-hour observations can be achieved by postprocessing the data. The system can sustain a count rate of up to 8 MHz uninterruptedly for an entire night of observation. After the first run in January 2009, some improvements have been evidenced and realized: a more practical mechanical structure, a better optimization of the optical design, an additional filter wheel per each channel, a fifth photon counting detector for monitoring the sky, a more interactive interface software. The updated Iqueye has been tested in December 2009, and the obtained results showed still better performance. As an example, the light curves of visible pulsars down to the 25th visible magnitude have been obtained in a few hours of observation.