ap-6-11.dvi Acta Polytechnica Vol. 51 No. 6/2011 Pi of the Sky Telescopes in Spain and Chile M. Siudek, T. Batsch, A. J. Castro-Tirado, H. Czyrkowski, M. Cwiok, R. Dabrowski, M. Jeĺınek, G. Kasprowicz, A. Majcher, A. Majczyna, K. Malek, L. Mankiewicz, K. Nawrocki, R. Opiela, L. W. Piotrowski, M. Sokolowski, R. Wawrzaszek, G. Wrochna, M. Zaremba, A. F. Żarnecki Abstract Pi of the Sky is a system of robotic telescopes designed for observations of short timescale astrophysical phenomena, e.g. prompt optical GRB emissions. The apparatus is designed to monitor a large fraction of the sky with 12–13m range and time resolution of the order of 1–10 seconds. In October 2010 the first unit of the new Pi of the Sky detector system was successfully installed in the INTA El Arenosillo Test Centre in Spain. We also moved our prototype detector from Las Campanas Observatory to San Pedro de Atacama Observatory in March 2011. The status and performance of both detectors is presented. Keywords: Gamma Ray Burst (GRB), prompt optical emissions, optical flashes, nova stars, variable stars, robotic telescopes. 1 Introduction Piof theSky [4] is a robotic telescopedesigned for ob- servations of short timescale astrophysical phenom- ena, especially for prompt optical counterparts of Gamma Ray Bursts (GRBs). Other scientific goals include searching for nova and supernova stars and monitoring interesting objects such as blasars, AGNs or variable stars. The apparatus design allows us to monitor a large fraction of the sky with good range and time resolution. The Pi of the Sky project in- volves scientists, engineers and students from lead- ing Polish academic and research units: the An- drzej Soltan Institute for Nuclear Studies, the Cen- ter for Theoretical Physics (Polish Academy of Sci- ence), the Institute ofExperimentalPhysics (Faculty of Physics, University of Warsaw), Warsaw Univer- sity of Technology and the Space Research Center (Polish Academy of Science). The detector was designed mainly to search and observe prompt optical counterparts of GRBs dur- ing or even before gamma emission. To manage this goal it is necessary to develop advanced and fully automatic software for real-time data analysis and identification of flashes [2]. The standard approach assumes reaction to satellite alerts distributed by the Gamma Ray Burst Coordinates Network (GCN) [1] andmoving the telescope to the target as fast as pos- sible. This approach does not allow us to observe an optical emission from the source exactly at the mo- ment of or before theGRBexplosion,which is crucial for understanding the nature of GRBs. Pi of the Sky applies an innovative solution,which assumes contin- uous observationof a largepart of the sky to increase thepossibilityof catchingaGRBandaself-triggering system to detect flashes. The observations of the fa- mous “naked-eye” GRB080318B have confirmed the usefulness of this strategy. 2 The prototype Tests of hardware and softwarewere performed with a prototype, which is just a small version of the fi- nal detector. The prototype is equipped with two custom-designed 442A 2048 × 2048 CCD cameras equipped with Canon telephoto lenses with focal length f =85 cm, f /d =1.2 and covering a 20◦ ×20◦ field of view. Thepixel size is 15×15 μm2, which cor- responds to 36 arcsec in the sky. The CCD is cooled with a two-stagePeltiermodule up to 40 degrees be- low the ambient temperature. Both cameras observe the samefieldof viewwith a time resolutionof 10 sec- onds. The limiting magnitude for a single frame is 12m and rises to 13.5m for a frame stacked from 20 exposures. This rather short magnitude range is de- termined by the system design and by the observa- tional strategy. All observations are made in white light and no filter is used, except for an IR-cut fil- ter in order to minimize the sky background. Since May 2009 we have had a Bessel-Johnson R-band fil- ter installed on one of the cameras in order to facil- itate absolute calibration of the measurements. The prototypeworked at the Las CampanasObservatory (LCO) in Chile from June 2004 till the end of 2009 (see Figure 1). In 2008 the prototype automatically recognized and observed the prompt optical emission from the famous “naked-eye” GRB080319B. These spectacular observations confirm the efficiency of the 64 Acta Polytechnica Vol. 51 No. 6/2011 flash recognition algorithms and the usefulness of the observational strategy. Fig. 1: Pi of the Sky prototype (left) located at the Las Campanas Observatory (right) 2.1 Moving the prototype from LCO to SPdA In March 2011 the prototype was moved from LCO and installed in the San Pedro de Atacama Obser- vatory (SPdA) (see Figure 2). The new location is situated approximately 740 km north of the previ- ous location and about 2400 meters above sea level. Thanks to the shorter distance to the equator, the observed part of the sky is larger than that at LCO. The new site was selected because of the good and stable weather conditions. The sky is clear or al- most clear for more than 80 % of the night. In 2010 there were 309 observing nights. The SPdA hosts several robotic telescopes, e.g. the 40 cm tele- scope from the Institute of Astrophysics of Andalu- sia, the 40 cm telescope used for exoplanet work on behalf of the Microfun project, and a variety of “tourist” telescopes. The observatory is coordi- natedbyAlainMaury,whoprovides support, general maintenance and improvements for these telescopes. AlainMaury’sweather stationalsoprovides real-time information about weather conditions. Fig. 2: Pi of the Sky prototype (left) located in the new dome at SPdA (right) 3 New detector unit in Spain The prototype is only a small version of the final de- tector. In October 2010 the first unit of the Pi of the Sky detector system was successfully installed in the INTA El Arenosillo test centre in Mazagón near Huelva, Spain, on the coast of the Atlantic Ocean. The final system consists of 4 CCD cameras on one specially designed equatorial mount (see Figure 3). The custom-designed cameras are an improved ver- sion of the cameras developed for the prototype sys- tem operational in Chile. Cameras with STA0820 2k × 2k CCD chips are equipped with EF Canon lenses with a focal length f = 85 mm (f /d = 1.2) and together cover a 40◦ ×40◦ field of view. Fig. 3: New Pi of the Sky unit located in Spain 3.1 Observation mode The custom-designed equatorial mount located in Spain is an improved version of the mount devel- oped by G. Pojmanski for the prototype system op- erational in Chile. The original design was scaled up to hold 4 cameras and, thanks to the mechanism for deflecting the cameras (see Figure 4), it enableswork in two operation modes: • Common-target (DEEP), when all cameras point at the same object • Side-by-side (WIDE), with cameras covering ad- jacent fields (see Figure 5). Fig. 4: Mount design with 2 CCD cameras (prototype in Chile)(left) and for 4 CCD cameras (newdetector unit in Spain) (right) Fig. 5: Two modes: side-by-side (left) and common tar- get (right) 65 Acta Polytechnica Vol. 51 No. 6/2011 With harmonic drives, encoders and control so- lutions based on Ethernet and the industrial CAN standard, the newdesign of the telescopemount pro- vides much better pointing accuracy and a shorter reaction time than the prototype. 4 The ultimate system The full Pi of the Sky systemwill consist of two sites equipped with 12 custom-designed CCD cameras on 3 equatorial mounts each, separated by a distance of about 100 km. The first new unit has already been installed near Huelva, and we are planning to install the second site near Malaga (see Figure 6). Pairs of cameras will work in coincidence and will observe the same field of view. The system is designed to identify and remove the reflections from the satel- lites by the parallax and eliminate cosmic rays by analyzing the coincidence onboth cameras. Thiswill significantly improve our real-time flash recognition algorithms, while a test performed by the prototype revealed that the most common background sources are flashes due to cosmic rays and near-Earth flashes from Sun light reflections from satellites. The whole system will be capable of continuous observations of about two steradians of the sky, which roughly cor- responds to the field of view of the BAT instrument on board the Swift satellite [3]. The final systemwill largely allow the elimination of time for re-pointing the telescope to the coordinates from GCN and the dead time for decision process and signal propaga- tion from the satellite to GCN and from GCN to a ground-based telescopes. Fig. 6: Scheme of the final system 5 Summary The prototype working in the period 2004–2009 in the Las Campanas Observatory was successfully moved and installed in the San Pedro de Atacama Observatory (SPdA) inMarch2011. InOctober 2010 we managed to install the first unit of the new Pi of the Sky detector system in the INTA El Arenosillo TestCentre inSpain. BothPi of the Sky instruments operate in the fully autonomous mode, practically without any human supervision and search for short timescale astrophysical phenomena. Acknowledgement We are very grateful to G. Pojmanski for access to the ASAS dome and for sharing his experience with us. We would like to thank the staff of the LasCam- panas Observatory, San Pedro de Atacama Obser- vatory and the BOOTES-1 station at ESAt/INTA- CEDEAinElArenosillo (Mazagón,Huelva) for their help during the installation and maintenance of our detector. This workwas financed by the PolishMin- istry of Science and Higher Education in 2009–2011 as a research project. References [1] Barthelmy, S. D., et al.: The GRB Coordinates Network (GCN): a Status Report, Gamma-Ray Bursts, AIP conference proceedings, 428, p. 99, 1997. [2] Burd, A., et al.: Pi of the Sky – all-sky, real-time search for fast optical transients,NewAstronomy, 10 (5), 2005, 409–416. [3] Gehrels, N., et al.: The Gamma Ray Burst Mis- sion, ApJ, 611, p. 1005–1020, 2004. [4] Malek, K., et al.: Pi of the Sky Detector, Ad- vances in Astronomy 2010, 2010, 194946. Malgorzata Siudek Katarzyna Malek Lech Mankiewicz Rafal Opiela Center forTheoreticalPhysics of thePolishAcademy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland Tadeusz Batsch Ariel Majcher Agnieszka Majczyna Krzysztof Nawrocki Marcin Sokolowski Grzegorz Wrochna The Andrzej Soltan Institute for Nuclear Studies Hoza 69, 00-681 Warsaw, Poland Alberto J. Castro-Tirado Martin Jeĺınek Instituto de Astrofiśica de Andalućia CSIC Glorieta de la Astronomía s/n E-18080Granada, Spain Henryk Czyrkowski Mikolaj Cwiok Ryszard Dabrowski Lech W. Piotrowski 66 Acta Polytechnica Vol. 51 No. 6/2011 Aleksander F. Żarnecki Faculty of Physics University of Warsaw Hoza 69, 00-681 Warsaw, Poland Grzegorz Kasprowicz Institute of Electronic Systems Warsaw University of Technology Nowowiejska 15/19, 00-665 Warsaw, Poland Roman Wawrzaszek SpaceResearchCenter of the PolishAcademy of Sci- ences Bartycka 18A, 00-716Warsaw, Poland Marcin Zaremba Faculty of Physics Warsaw University of Technology Koszykowa 75, 00-662 Warsaw, Poland 67