Transcript Rene Hudec and Lukas Hudec

The Novel Method for Identifying
Fast Optical Transients
The Application of Multi-Exposure Plates
for OT/GRBs analyses
René Hudec1 and Lukáš Hudec2
1 ASTRONOMICAL INSTITUTE, CZ-251 65 ONDREJOV, CZECH REPUBLIC
2 Department of Informatics, FACULTY OF MATHEMATICS AND PHYSICS, CHARLES
UNIVERSITY, PRAGUE, CZECH REPUBLIC
Archival sky patrol plates
There
are more than 3 millions archival plates
in the world, lim mag up to 23, > 5 x 5 deg in
most cases .... Ondrejov has 110 000 plates
Suitable for dense long-term photometry (up
to 100 years, up to 2000 points, up to 23 mag)
Suitable to detect rare events - years od
CONTINUOUS monitoring easily possible
However, the access to the data is still difficult,
but:
Recently, efforts to digitize the plates
Use of scanners, powerful computers and
innovative software allows the effective data
evaluation for the first time
Optical Transients of
Astrophysical Origin

OTs and OAs of Gamma Ray Bursts including Orphans (seen only in optical)
 flares on blazars and AGNs - up to 10 mag
amplitudes revealed by extended plate
analyses
 stellar OTs such as stellar flares, CVs flares
etc.
 OTs of unclear origin (observational
reports)
Optical Transients - very large amplitude
AGN flares
Example of results from
extended analyses on
archival sky patrol plates
> 10 mag amplitude optical
flare from a faint AGN, HCO
plate
Flares on faint AGNs - up to more than 10 mag
amplitudes revealed by extended plate analyses
(up to 3 years of continuous monitoring time
analysed)
Optical Transient
Analyses - OT in
Triangulum, Sonneberg
Astrograph Plate, 6 mag
above plate limit
the searches for
analogous OTs are
difficult since the plates
contains typically 10 000
- 100 000 star images
Sonneberg Observatory Plate Archive: 270 000
plates 1928 - 2002, largest European plate
collection
History: evaluation of archival
plates by eye estimation
Eye estimation can however
still yields valuable results:
Experienced person can provide
measurements with precision
analogous to plate photometers
and CCD scanning
The method is quick and suitable
for evaluation of one selected
object on many plates where
digitization is less effective
New:
The digitisation of the astronomical plates, the
novel software and the use of powerful
computers allow the automated data mining
and scientific evaluation of the plates for the
first time
Interface between astronomy and informatics
We report on the novel method how to
identify brief optical transients (OTs) on sky
archival plates.
This method does not require identification
of all objects and their comparison with the
catalogue, but rely solely on the information
included in the particular plate itself.
If we look for optical prompt emission (including
orphans) from GRBs, we need to look for shortliving transient phenomena lasting minutes.
However, on long-exposed deep images and plates,
it is very difficult to look for brief transients since
the OT image is hidden by typically tens to hundreds
of thousands stellar images with similar appearance.
The methods of comparing plates and/or
comparison with catalogues is still not very effective
and reliable.
Here we propose novel method using multiply exposed
astronomical plates and based solely on the information in
the plate itself. Such plates are available in various sky plate
archives, e,g. at the Royal Observatory Brussels.
These plates contains several (typically 2 to 10) identical star
field images on the same plate.
This means, each star inside the FOV of the telescope, is
represented several times.
Such plates have been obtained by mutiple exposures on the
same plate with tiny shifts between the exposures
It is very difficult to find transient objects on these
plates by classical methods.
However, using digitisation, and dedicated novel
software programs, it is relatively easy, effective and
reliable to identify the OT candidates.
Program by informatics student L. Hudec:
Program input: scanned multiple exposure plates
from the Royal Observatory Brussels - ESO Schmidt
(and analogous plates)
Typical
ROB
ESO
multiple
exposure
plate,
scanned
binned, 1
from 4
pixels
read out
Example of
OT found:
duration less
than 30 min
real object 2 images
fast OT and
moving
object
(asteroid)
Example of
fast OT
found duration less
than 5
minutes
The first results of the application of the novel software
program on multiply exposed plates are very promising.
At moment, the program identifies objects showing
deviations regarding to normal star constant images.
Then the human inspection is required to discard the
obvious defects. This is easy and fast. Typically 1 OT
candidate remains after the procedure for 1 plate.
The examples shown are for binned plates (1 from 4
pixels read out) to accelerate the computing process.
The final program will use non-binned data.
•Excellent example how the valuable information
obtained in archival astronomical plates can be accessed
and scientifically used
•Such analyses are possible only based on plate
digitisation, novel software and powerful computers
•Analogous procedures can be applied also for trailed star
images, spectral plates with objective prisma, etc. searches for objects with strange spectra, spectral
emission lines, rapid light changes etc.
•Collaboration with informatics students
All Sky Photographic
Monitoring - central
part of a scanned plate
Directed by the
Ondrejov Observatory
Still in operation
12 stations
lim mag 12
9 x 12 cm photographic
plates
High quality
photographic scanner
available
Real time optical data for
GRBs - Digitized Ondrejov
All Sky Plate
The area of the
GRB000926 on the plates
of the EN network.
Simultaneous optical
image, lim magnitude 8.
The position of the GRB is
indicated by a circle. The
image contains airplane
trails/lights.
Important coinstraints on
the prompt optical emission
of GRBs
Scanned Sonneberg Sky Patrol Plate - small part. The full plate has 30 x
30 degrees, lim mag 14.5, V and B plates are taken simultaneously.Time
coverage is 74 years.
Sonneberg
Photographic
Sky Patrol
Digitized
Plate - 1/4
shown here
i.e. 15 x 15
deg the full
plate has 30 x
30 deg
Lim mag 14.5
Scanned with
the HISS
scanner 12
microns
resolution
All Sky CCD Camera, Sonneberg Observatory, 7K x 4K CCD and
f/3.5 FE lens. Lim mag 10 in 1 min integration time.
Astronomical plates - our
contribution

Development of software for automated
evaluation of Sonneberg Sky Patrol Plates
 Software to detect and to classify variable
objects on Schmidt plates (Tautenburg)
 Search for faint variable and flaring objects
on digitized UKSTU plates (lim mag 23)
 Participation on the European Plate Centre
Project in Brussel
Our contribution … continue

automated evaluation of digitised plates:
spectral, trailed, multiple images,....
THE SOFTWARE DEVELOPMENT
So far, the data recorded on archival plates were accessible only by special
procedures. The recent wide digitisation of plate collections offers significantly easier
access by computers. However, there is still a gap between the digitised archive and
the scientific use. Special software is required to fill this gap.
We have developed new algorithms to access data on digitised plates. The new
algorithm is based on the flood method. This method, applied to the digitised
photographic plates, is able to reveal the star images for further analyses. This method
has been tested on a set of digitised Sonneberg Sky Patrol plates with very promising
results if compared with other methods. The flood method is based on a similar idea
as the watershed method and is reasonably simple and quick.
Digitized Schmidt plate, TLS Tautenburg, lim mag 20, field M92.
Newly detected variable objects with light amplitude > 2 mag are
indicated
UKSTU Plates






faint limits, 19 - 23
FOV 40 sq. degrees
various colors/filters
spectral plates down to
mag 18
18 000 plates over 30
years
Unfortunately end of
operation in 2001
Our projects at the UKSTU



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
Analyses on digitized UKSTU plates, focusing on
densely populated time periods and in different
filtres
Independent searches for optical afterglows of
GRBs
Statistics and classification of faint variable stars
No realiable statistics of variable stars is available
yet below mag 18!
Long-term evolution of selected faint sources such
as XTE J2123-058, XTE J1550-564, RXJ 1313.23259 etc.
Another possible analogous
informatics works:
•comparison of scanned plates - identical fields
•the same for all-sky images
•automated generating of ligh curves of all objects
on the plates - for typically 1000 plates, the same
field, different times
•spectral plates - objective prisma
•trailed plates - stars as long trails - flares, dips
•a lot of work for informatics students....