1.  of the Sky
Innovative approach to GRB optical counterparts and other short optical transients detection
Study of astrophysical phenomena with time scale from seconds to months
K. Malek2), L.W. Piotrowski3), M. Biskup3), M. Cwiok3), W. Dominik3), G.Kasprowicz4), M. Kwiatkowski4), A. Majczyna1), L. Mankiewicz2), M. Molak4), K. Nawrocki1),
K. Pozniak4), R. Romaniuk4), D. Rybka1), P. Sitek1), M. Sokolowski1), J. Uzycki4), G. Wrochna1), M. Zaremba4), A.F. Zarnecki3)
1) Soltan Institute for Nuclear Studies; 2) Center for Theoretical Physics, Polish Academy of Sciences; 3) Institute of Experimantal Physics, Warsaw University; 4) Warsaw University of Technology
Special thanks to prof. B. Paczynski (Princeton University) and G. Pojmanski (Warsaw University) and all staff of the Las Campanas Observatory.
We present an innovative approach to the GRB optical counterparts observations, which ought to overcome one of the main obstacles
towards deeper understanding of GRB phenomenon: only a few observations in the very early stage of the burst. The “ of the Sky”
introduces the idea of constant, high time resolution, large sky area monitoring. Efficient data stream reduction algorithms were
created, to allow optical transient detections not depending on GRB satellites.
FULL SYSTEM CAPABILITIES
first data: fall 2007
optical counterparts observations after, during and even prior to GRB
flare star detection
variable and novae star observations
other short time-scale astrophysical phenomena detection possibilities
FULL SYSTEM (under construction)
2 matrices of 16 CCD cameras, 2000x2000 pixels, lenses: Canon EF f=85mm, f/d=1.2, matrices outlied by ~50 km, working in coincidence
FoV: 16 × 20o×20o = 2 steradians:
more than Swift BAT FoV equal to GLAST FoV
limiting mag.: 13.5m (1 frame 10s), 15m (coadded frames)
NEW APPROACH
constant large sky area monitoring
none or even negative time delay w.r.t. to satellite GRB triggers
self-triggering capabilities
high time resolution
PROTOTYPE
2 CCD, 2000x2000 pixels each, lenses: Zeiss , f=85mm, f/d=1.2,
FoV: 21o×21o, angular resolution: 36''
limiting mag.: 11-13m (1 frame 10s), 13-14m (20 frames)
FIRST RESULTS (from prototype)
Search for GRB optical counterparts:
165 GCN alerts received (>7.2004):
- 5 apparatus off clouds below horizon
- 81 daytime outside FoV inside FoV
limits 9m – 14.3m published:
GRB , , , , , , , ,
limits during the burst: GRB A, GRB
Search for optical flashes:
~132 flashes < 10s detected (may be flashing satellites)
8 flashes >10s detected (including flare of CN Leo)
Full system (rendering)
Prototype working at Las Campanas,
Chile, since
Modes of observation
The prototype system works autonomously, according to schedule, which could be changed via Internet:
follows SWIFT or Integral FoV
independently detects optical flashes in real time (self-triggering)
performs dedicated observations of interesting objects (eg. blasars, quasars, novae) in spare-time
twice a night makes a full sky survey (2x40 min)
instantaneously follows satellite alerts distributed by GCN
Outburst of CN Leo flare star, automatically detected by “ of the sky” on-line flash detection algorithm. Star was not visible in our range before its outburst, thus it well simulates expected behavior of GRB optical counterpart.
IS  RANGE SUFFICIENT?
Our knowledge about early brightness is weak, for most optical counterparts were observed long after GRB. How to estimate how many of them will be in “ of the Sky” range?
On-line data stream reduction
3000 frames/night, 1 frame = 8 MB -> 25 GB/night
(full system: 32x25 GB = 800 GB/night)
algorithms inspired by particle physics – multilevel trigger
Level 1 – very fast and simple single pixel analysis
Level 2 – sophisticated object analysis
This figure show events reduction ratio for several nights. Level 1 consists of very fast and simple cuts mainly for eliminating constant stars and apparatus effects. Coincidence performed between Level 1 and Level 2 mainly eliminates cosmic radiation effects. Level 2 is designed to eliminate real objects, like satellites, planes, meteors and stars not reduced by Level 1, that are not in our field of interest.
Results of extrapolation of 45 best early lightcurves (<5000s) to 30 s after GRB. The average brightness, not filter corrected, is. 15.7m. (data from GRBlog).
Maximal GRB optical counterpart brightness in the first 100 s after GRB, for 39 bursts. The average brightness is 15.9m (data from GRBlog).
Both the extrapolation and the real maximal magnitudo show, that we should be able to see close to one half of the GRB optical counterparts (during night, on our hemisphere). That is very optimistic!