Pi of the Sky system of robotic telescopes Ł. Obara1, T. Batsch2, H. Czyrkowski1, A. Ćwiek2, M. Ćwiok1, R. Dąbrowski1, G. Kasprowicz3, A. Majcher2, K. Małek2, L. Mankiewicz4, K. Nawrocki2, R. Opiela4, L. W. Piotrowski1,5, M. Siudek4, M. Sokołowski2,6,7, R. Wawrzaszek8, G. Wrochna2, M. Zaremba1, A. F. Żarnecki1 1) Faculty of Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland 2) National Centre for Nuclear Research, Hoza 69, 00-681 Warsaw, Poland 3) Institute of Electronic Systems, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warsaw, Poland 4) Centre for Theoretical Physics of the Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 5) RIKEN, 2-1 Hirosawa, 351-0198 Wako, Saitama, Japan 6) International Centre for Radio Astronomy Research - Curtin University, GPO Box U1987, Perth, WA 6845, Australia 7) ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) 8) Space Research Center of the Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland Pi of the Sky is a system of wide field of view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical GRB emission. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m −13m range and time resolution of the order of 1−10 seconds. System design and observation strategy were successfully tested with a prototype detector operational in 2004-2009 at Las Campanas Observatory, Chile, and moved to San Pedro de Atacama Observatory in March 2011. In October 2010 the first unit of the final Pi of the Sky detector system, with 4 CCD cameras, was successfully installed in the INTA El Arenosillo Test Centre in Spain. The system was completed with three more units (12 CCD cameras) installed on a new platform in INTA in July 2013, resulting in a total coverage of about 6 000 square degrees. 2004 BL86 During its closest approach, at night from 26 to 27 January 2015, the asteroid 2004 BL86 was merely 1.2 mln km (about 3 times Earth-Moon distance) from Earth and reached luminosity about 9m. We performed observations of the asteroid from our south observatory in San Pedro de Atacama, where it was visible during the whole night. Below is an image of the asteroid passing the M44 open cluster in Cancer (is in the middle of the frames). The frame is an average of 5 consecutive 10 s frames. Asteroid position was reconstructed on over 500 images covering more than 3 hours of observations. Dedicated tools were used for automatic determination of asteroid trajectory. Fig 1. Four detector unit installed in 2013 in the INTA El Arenosillo test centre in Mazagón near Huelva, Spain. Each detector unit in Spain: - four cameras on equatorial mount, - field of view 40ox40o (WIDE mode) or 20ox20o (DEEP mode), - UV – IR cut filters, Fig 2. Dome at San Pedro de Atacama, Chile, where the prototype unit was moved from Las Campanas Observatory in March 2011. Prototype in Chile: - two cameras on equatorial mount, - field of view 20ox20o, - one camera has an R filter (Johnson-Bessel) installed, Fig. 5. Pi of the Sky image of 2004 BL86 asteroid (indicated by an arrow in the main image and by circle on the magnified section) passing M44 on January 26, 2015. Artificial colors. Future plans To extend our observation capabilities we are currently working on the design of the new „Pi of the Sky Plus” telescope. Fast parallactic mount, with maximum speed of up to 30 per second, absolute pointing precision of about 20", and load of up to 100 kg will allow us to use 4 lenses with f = 296 mm and 180 mm aperture (see Fig. 6). - Canon photolenses, f = 85 mm, f/d = 1.2, - matrix size 2048x2048 pixels, - pixel size 15x15 μm2 (36”). Selected results GRB 080319B On March 19th 2008, at 6:12:49 UT automatic algorithms of the Pi of the Sky prototype system detected a new object in the sky. A few seconds later an alert from GCN arrived - the Swift satellite detected an extremely luminous GRB, which will be refered to as GRB080319B. Also in optical band its brightness was greater than all bursts observed until then. At the maximum it was as bright as 5.3m. Fig. 6. Design of the new „Pi of the Sky Plus” telescope. Satellite observations Fig. 3. Optical lightcurve of GRB 080319B. Pi of the Sky telescopes can also measure geostationary and low orbit satellites, as well as space debris. As a part of preparations for the dedicated measurements with the „Pi of the Sky Plus” telescope, we performed test observations with Pi of the Sky telescope in INTA, with f = 200 mm (f/d = 1.8) lenses. One of the collected images is presented in Fig. 7. Geostationary satellites can be easily identified as point-like objects (indicated by green circles) on the image taken without sky tracking (Earth rotation compensation). The optical light curve reconstructed from Pi of the Sky data is shown in figure 3. The most curious was, that luminosity measured by Pi of the Sky was over 10,000 times greater, than luminosity extrapolated from gamma to optical band. This shows, that optical emission is caused by different mechanism than emission in gamma rays. DG CVn outburst Red dwarf star located at a distance of about 18 pc underwent an eruption on 23rd April 2014 21:07:08 UT and was detected by SWIFT satellite as well as Pi of the Sky and BOOTES robotic telescopes. The event was also observed later with big telescopes (CAHA, GTC, BTA). Pi of the Sky observation compared with SWIFT results showed that the hard X-ray emission was delayed by about 50 s with respect to the prompt optical emission (first flare) from DG Cvn. This effect can be explained by the chromospheric evaporation scenario (Neupert, 1968). Fig. 6. Test image from dedicated observations with f = 200 mm (f/d = 1.8) Canon photolenses, taken with Pi of the Sky telescope in Spain. Geostationary satellites are indicated by green circles. Acknowledgments This work has been partially financed by the Polish Ministry of Science and Higher Education in 2009-2014 as a research project and by POLISH-SWISS ASTRO PROJECT cofound under the Swiss programm of cooperation with new member states of European Union. Fig. 4a: Optical light curve from the PI (from T0 − 150 s onwards); 4b: Swift/BAT light curve in the 15–25 keV energy range (i.e. hard X-rays). The time (in seconds) is measured with respect to the BAT trigger time (T0)