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Register a new userTowards micro-arcsecond spatial resolution with Air Cherenkov Telescope arrays as optical intensity interferometers
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In this poster contribution we highlight the equivalence between an Imaging Air Cherenkov Telescope (IACT) array and an Intensity Interferometer for a range of technical requirements. We touch on the differences between a Michelson and an Intensity Interferometer and give a brief overview of the current IACT arrays, their upgrades and next generation concepts (CTA, AGIS, completion 2015). The latter are foreseen to include 30-90 telescopes that will provide 400-4000 different baselines that range in length between 50m and a kilometre. Intensity interferometry with such arrays of telescopes attains 50 micro-arcseconds resolution for a limiting V magnitude of ~8.5. This technique opens the possibility of a wide range of studies, amongst others, probing the stellar surface activity and the dynamic AU scale circumstellar environment of stars in various crucial evolutionary stages. Here we discuss possibilities for using IACT arrays as optical Intensity Interferometers.
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The present generation of ground-based Very High Energy (VHE) gamma-ray observatories consist of arrays of up to four large (> 12m diameter) light collectors quite similar to those used by R. Hanbury Brown to measure stellar diameters by Intensity Interferometry in the late 60s. VHE gamma-ray observatories to be constructed over the coming decade will involve several tens of telescopes of similar or greater sizes. Used as intensity interferometers, they will provide hundreds of independent baselines. Now is the right time to re-assess the potential of intensity interferometry so that it can be taken into consideration in the design of these large facilities.
We summarize the present status of VLBI experiments at 3 mm (86 GHz), 2 mm (129-150 GHz) and 1.3 mm (215-230 GHz). We present and discuss a new 3 mm VLBI map of M87 (Virgo A), which has a spatial resolution of only approx. 20 Schwarzschild radii. We discuss recent VLBI results for SgrA* and argue in favor of new observations within an extended European mm-VLBI network, in order to search for variability. We discuss the possibilities to image the `event horizon of a super-massive black hole at wavelengths < 2mm, and conclude that the addition of large and sensitive millimetre telescopes such as CARMA, the SMA, the LMT and ALMA will be crucial for this.
The First G-APD Cherenkov Telescope (FACT) became operational at La Palma in October 2011. Since summer 2012, due to very smooth and stable operation, it is the first telescope of its kind that is routinely operated from remote, without the need for a data-taking crew on site. In addition, many standard tasks of operation are executed automatically without the need for manual interaction. Based on the experience gained so far, some alterations to improve the safety of the system are under development to allow robotic operation in the future. We present the setup and precautions used to implement remote operations and the experience gained so far, as well as the work towards robotic operation.
In this paper we describe the different software and hardware elements of a mini-telescope for the detection of cosmic rays and gamma-rays using the Cherenkov light emitted by their induced particle showers in the atmosphere. We estimate the physics reach of the standalone mini-telescope and present some results of the measurements done at the Sauverny Observatory of the University of Geneva and at the Saint-Luc Observatory, which demonstrate the ability of the telescope to observe cosmic rays with energy above about 100 TeV. Such a mini-telescope can constitute a cost-effective out-trigger array that can surround other gamma-ray telescopes or extended air showers detector arrays. Its development was born out of the desire to illustrate to students and amateurs the cosmic ray and gamma-ray detection from ground, as an example of what is done in experiments using larger telescopes. As a matter of fact, a mini-telescope can be used in outreach night events. While outreach is becoming more and more important in the scientific community to raise interest in the general public, the realisation of the mini-telescope is also a powerful way to train students on instrumentation such as photosensors, their associated electronics, acquisition software and data taking. In particular, this mini-telescope uses silicon photomultipliers (SiPM) and the dedicated ASIC, CITIROC.
Super-high spatial resolution observations in the infrared are now enabling major advances in our understanding of supermassive black hole systems at the centers of galaxies. Infrared interferometry, reaching resolutions of milliarcseconds to sub-milliarcseconds, is drastically changing our view of the central structure from a static to a very dynamic one by spatially resolving to the pc-scale. We are also starting to measure the dynamical structure of fast moving gas clouds around active supermassive black holes at a scale of less than a light year. With further improvements on resolution and sensitivity, we will be able to directly image the exact site of the black holes feedback to its host galaxy, and quantify the effect of such interaction processes. Near-future high angular resolution studies will definitely advance our mass determinations for these black holes, and we might even witness the existence of binary black hole systems at the center of galaxies.
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