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 platesArchival 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 platesSuitable 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 possibleHowever, the access to the data is still difficult, but: Recently, efforts to digitize the platesUse of scanners, powerful computers and innovative software allows the effective data evaluation for the first time

Optical Transients of Optical Transients of Astrophysical OriginAstrophysical 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 Optical Transients - very large amplitude AGN flaresAGN flares

> 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)

Example of results from extended analyses on archival sky patrol plates

Optical Transient Optical Transient Analyses - OT in Analyses - OT in

Triangulum, Sonneberg Triangulum, Sonneberg Astrograph Plate, 6 mag Astrograph Plate, 6 mag

above plate limitabove plate limit

the searches for the searches for analogous OTs are analogous OTs are

difficult since the plates difficult since the plates contains typically 10 000 contains typically 10 000

- 100 000 star images- 100 000 star images

Sonneberg Observatory Plate Archive: 270 000 Sonneberg Observatory Plate Archive: 270 000 plates 1928 - 200plates 1928 - 20022, largest European plate , largest European plate

collectioncollection

History: evaluation of archival History: evaluation of archival plates by eye estimationplates by eye estimation

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

Eye estimation can however still yields valuable results:

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 short-living 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

Obloha.jpgObloha.jpg

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 Astronomical plates - our contributioncontribution

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 … continueOur 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.

Obloha.jpg

Digitized Schmidt plate, TLS Tautenburg, lim mag 20, field M92. Newly detected variable objects with light amplitude > 2

mag are indicated

UKSTU PlatesUKSTU 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 UKSTUOur projects at the UKSTU 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 1313.2-3259 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....