MASTER prompt and follow-up GRB observations

There are the results of gamma-ray bursts observations obtained using the MASTER robotic telescope in 2007 - 2009. We observed 20 error-boxes of gamma-ray bursts this period.The limits on their optical brightnesses have been derived. There are 5 prompt observations among them, obtained at our very wide field cameras. Also we present the results of the earliest observations of the optical emission of the gamma-ray bursts GRB 050824 and GRB 060926.


Introduction
The construction of robotic telescopes, which not only automatically acquire but also automatically process images and choose observing strategies, is rather new and vigorously developing area in modern astronomy.MASTER (Mobile Astronomy System of Telescope Robots, http://observ.pereplet.ru) is the first and still unique robotic telescope system in Russia, began to be created through the efforts of scientists at the Sternberg Astronomical Institute of Moscow State University and the Moscow "Optika" Association in 2002, and continues to be developed to the present MASTER-NET (Lipunov [1,2,3]).
MASTER is dedicated to observation and detection of optical transients on time scales of seconds to days.The emphasis is on gamma-ray bursts (GRBs), the most powerful explosions in our Universe.A special program package for image reduction in real time has been created,making it possible not only to carry out astrometry and photometry of a frame, but to recognize objects not contained in astronomical catalogs: supernovae, new asteroids, optical transients, and so forth.This software let us open several supernovae SN2008gy, SN 2006ak, SN2005ee, SN 2005bv).We observed 20 error boxes of gamma-ray bursts in 2007-2009 y.y.The results of them are presented.There are 5 prompt observations, obtained by our very wide field cameras (VWFC) during last half-year after we mount these cameras in Kislovodsk and Irkutsk in autumn 2009.

MASTER system
Now MASTER system has 4 bases: near Moscow, near Kislovodsk, near Irkutsk and near Ekaterinburg (Lipunov [3]).We have far observatories only a year and a half, and of about 5 years we observed only from Moscow telescope system, that are in village near Domodedovo airport.This small distances from Moscow State University let us design, test and modify robot system, repair possible technical fault and write reduction software without state financial support.But minus is very bad weather condition near megapolis (less than 70 nights per yr and most of them are in summer white nights)).But we observed several tens error boxes during 5 years (HETE and Swift epochs) and in most of them our observations were the earliest (Lipunov [2]).
MASTER characteristics (Lipunov [3]) are closest to the american ROTSE-III system [4] (http://www.rotse.net).MASTER differs in its larger field of view and the presence of several telescopes on a single axis, which makes us possible to obtain images at several different wavelengths simultaneously, that was realized in MASTER-Ural observations.
So as up to 2008 year most of GRB observations were at MASTER-Moscow system, there are the following characters of it.
The main telescope (355 mm diameter) takes images in white light, and is the main search element of the system.An Apogee Alta U16 (4096 × 4096 pixels) is installed on it, making it possible to obtain images in a six square degree field.In addition, MASTER has a very-wide-field camera (50 • × 60 • ) that covered the field of view of the HETE orbiting gamma-ray telescope, made it possible to obtain simultaneous observations with HETE to 9 m using a separate automated scheme.This widefield equipment enables searches only for bright, transient objects.Now we have very wide field cameras at Kislovodsk on the Mountain Solar Station of the Main Astronomical Observatory in Pulkovo, making it possible to continuously monitor a 420-square-degree field of sky to 13m in a five second exposure.Such cameras are now in Irkutsk.
The Kislovodsk, Domodedovo, Ural and Irkutsk systems are connected via the Internet, and are able to respond to the detection of uncataloged objects (optical transients) within several tens of seconds (including processing time).The results of observations using the MASTER network will be reported separately.
All MASTER system are able to operate in a fully automated regime: automatically, based on the ephemeredes (sunset) and the presence of satisfactory weather conditions (the control computer is continuously attached to a weather sensor), the roofs (above the main mount and wide-field camera) are opened, the telescopes are pointed at bright stars and pointing corrections introduced, and, depending on the seeing, it then either goes into a standby regime or begins a survey of the sky using a specialized, fully automated programme.
Thus, observations are conducted in two regimes: survey and "alert" (e.g.observations of the locations of gamma-ray bursts based on coordinates obtained).In the former case, the main telescopes automatically takes three frames of an arbitrary region in succession, with exposures from 30 to 60 s, moves to a neighboring region 2 • away and carries out the same procedure, and so on, repeating a given set of three frames every 40-50 min.This makes it possible to avoid artefacts in the data processing, and to locate moving objects.
The alert regime is supported by a continuous connection between the control computer and the GCN international gamma-ray burst (GRB) network (http://gcn.gsfc.nasa.gov).After detection of a GRB by a space gamma-ray observatory SWIFT, Konus-Wind, FERMI etc.), the telescope obtains the coordinates of the burst region (coordinate error box), automatically points to this direction, obtains an image of this region, reduces this image, and identifies all objects not present in the computer catalogs.If a GRB is detected during the day, its coordinates are included in the observing program for the next night.
A special program package for image reduction in real time has been created,making it possible not only to carry out astrometry and photometry of a frame, but to recognize objects not contained in astronomical catalogs: supernovae, new asteroids, optical transients, and so forth.Over the entire time observations have been obtained on the MASTER system (see the results of 2002-2006 observations in [1, 2, 5]), images have been obtained for almost 100 GRB error boxes at this moment.In a half cases, these observations were the first in the world.

GRB observations
During 2007-2009 years we observed 20 GRB.The results of our prompt and followup observations are in Table 1.Kislovodsk and Irkutsk VWFC had different cameras during 2007 and 2008 year, so there are V and R bands in second column of the table.We have unfiltered images from these cameras, but they are closest to V and R bands, and we calibrated using TICHO catalogue (Gorbovskoy, [25]).
There were 5 prompt observations by very wide field cameras in Irkutsk and Kislovodsk stations during last half-year (after mounting several VWFC there): GRB090424, GRB090328B, GRB090320B, GRB090305B, GRB081130B.There were no optical candidate found at reducted images and we give the optical limits for GRBs.
We also calculate the ratio of optical to gamma fluence (Gorbovskoy [25]) for GRB.

Conclusions
We presented the results of last years GRB observations obtained on the MASTER robotic telescope, which is the only telescope of its kind in Russia.These results include 5 prompt observations of GRB in 2008 and 2009yy., follow-up observations of 15 another GRB in 2007-2009, and the first observations of optical emission from the gamma-ray bursts GRB 050824 and GRB 060926.Our data together with observations made later yield a brightness-variation law for GRB 050824 of t −0.55±0.05 .Our experience of two years of operation of the MASTER wide-field robotic telescope has demonstrated its unique capabilities.We hope, that new MASTER telescopes at Kislovodsk and Ural stations, and also new Irkutsk and Blagoveschwnsk systems, that are made now, will justify our hopes.If such systems could be installed at suitable sites at various hour angles across Russia, they would provide unique information via continuous monitoring of both the near and distant cosmos.