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Exploration of the Time Domain

Exploration of the Time Domain. S. G. Djorgovski VOEvent Workshop, CACR, Caltech, April 2005. Overview. Scientific motivation and opportunity A poorly explored portion of the observable parameter space A range of exciting astrophysical phenomena Possibility of fundamental new discoveries

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Exploration of the Time Domain

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  1. Exploration of the Time Domain S. G. Djorgovski VOEvent Workshop, CACR, Caltech, April 2005

  2. Overview • Scientific motivation and opportunity • A poorly explored portion of the observable parameter space • A range of exciting astrophysical phenomena • Possibility of fundamental new discoveries • Technological advances and synoptic surveys • Pilot project using DPOSS plate overlaps • A rich phenomenology of the time-variable sky • Palomar-Quest: status and plans • Some challenges ahead

  3. Exploration of the Time Domain Thingsthat go bang! in the night… New and old. Synoptic sky surveys will require a real-time mining of massive data streams and multi-PB archives Megaflares on normal stars Optical transients

  4. Exploration of the Time Domain Thingsthat move… Quauar M. Brown et al. Sedna NEAT Tunguska

  5. A Systematic Search for Transients and Highly Variable Objects Using DPOSS Plate Overlaps B. Granett, A. Mahabal, S.G. Djorgovski, and the DPOSS Team ~ 1.5 O overlaps between adjacent plates  ~ 40% of the total survey area Baselines from days to ~ 10 yrs, typical ~ 2-4 yrs Typical limiting mags r ~ 20, using 3 bandpasses (JFN  gri) Effective Area Coverage in a “Snapshot” Survey: If texp < tburst and baseline ∆t >> tburst , then Effective Area = Useful Area  Npasses  Nfilters For DPOSS: ~ 15,000 deg2 0.4 2  3 ~ 0.9 Sky

  6. Variable Source Types of Detections Plate Flaw Transient

  7. Preliminary Spectroscopic Follow-Up (34 sources)

  8. Spectroscopic Source Identifications: 35% QSOs (1/2 radio loud) 18% CVs 18% M dwarfs 6% Earlier type stars 23% Unidentified (likely BL Lacs?)

  9. Examples of DPOSS Transients

  10. Examples of DPOSS Transients flaw asteroid

  11. DPOSS Pilot Project Conclusions: • Faint, variable sky has a very rich phenomenology • Spectroscopic follow-up will be a key bottleneck for any synoptic sky surveys • Most high-amplitude variable sources down to ~ 20 mag are QSOs (Blazars, OVVs…), CVs, and flaring late-type dwarfs, with some early-type stars • Asteroids may be a significant contaminant in a search for transients • We find many more transients (~ 103/Sky) than expected from current models for orphan afterglows. • Most of them are probably QSOs, CVs, flaring stars, and distant SNe; some may well be afterglows; and some may be new types of phenomena • The Palomar-Quest survey should provide a major new venue for the exploration of the time domain

  12. The Palomar-Quest Digital Sky Survey • The Palomar-Quest Consortium: Caltech - Yale - JPL • 50% point&shoot (NEAT, M.Brown), 50% drift scan (PQ survey) • PQ survey: a fully digital successor to the historic Palomar sky surveys; a Caltech-JPL-Yale-NCSA-… collaboration • Data rate ~ 1 TB/month; ~100 TB total; many scientific uses • VO connections and standards built in from the start; a testbed for many new IT/ VO applications

  13. The PQ Survey:A new, digital, synoptic sky surveyusing the Quest-2 112-CCD camera at the Palomar 48” Samuel Oschin telescope • A collaboration between Caltech, Yale/Indiana U., and NCSA/UIUC; plus collaborations with other groups (INAOE, LBL, JPL…); started in summer of 2003 • About 50% of the telescope time, driftscan mode • Now next-day (or month… processing  real-time • NVO connections and standards built in from start • Repeated observations, time baselines minutes to years • A science and technology precursor/testbed for the LSST and other major synoptic sky surveys in the future

  14. PQ Survey Sky Coverage • Range -25°<  < +30°, excluding the Galactic plane • Ultimately cover ~ 14,000 - 15,000 deg2 • Rate ~ 500 deg2/night in 4 bands • As of Jan’05, covered ~ 13,000 deg2 in UBRI, of which ~ 11,000 deg2 at least twice, and ~ 4,700 deg2 at least 4 times; and ~ 14,100 deg2 in rizz, of which ~ 11,600 deg2 at least twice, and ~ 4,200 deg2 at least 4 times

  15. The PQ Survey Science • Large QSO and gravitational lens survey • Tests of the concordance cosmology • Dark mattter distribution • AGN physics and evolution • High-redshift (z ~ 4 - 6.5) QSO survey • Probes of reionization and early structure formation • Exploring the time domain • Supernovae, GRBs, AGN, var. stars, optical transients • Surprizes and new phenomena? • Time baselines ranging from minutes (inter-CCD) to days, months, years (repeat scans) to decades (cross-match to DPOSS, SDSS, etc.) • Galactic structure and stellar astrophysics • Etc. etc. - think what it can do for you

  16. Palomar-Quest Data Flow P48 Catalogs Archive Image Archive Data Proc. Master Archive Target Selection Pipeline CIT SDSC Yale CIT Data Broker P200 NCSA Follow-up JPL LBL SNF

  17. PQ Survey: Recent and Upcoming Developments • Completely redoing the DRP at Caltech • Much (much!) better data cleaning • Image remapping to a standard pixel grid, to enable image coaddition and subtraction • Using the HyperAtlas technology for this • Using some TeraGrid resources • Yet to come: better object detection, classification • Next: A real-time DRP for discovery of transents and moving objects (collaborate w. JPL, M. Brown)

  18. Improved Cleaning of PQ Data

  19. Improved Depth in PQ Image Coadds PQ SDSS

  20. A Search for Low-z Supernovae C. Baltay, R. Ellis, A. Gal-Yam, S.R. Kulkarni, and the LBL SNF (Using the image subtraction technique) • Calibration of the SN Ia Hubble diagram • New standard candles from SN II • Endpoints of massive star evolution

  21. Optical Transients and Asteroids (Exploratory work; A. Mahabal, with P. Kollipara, a Caltech undergrad)

  22. Palomar-Quest Real-Time Transients Discovery System Data Flow P48 Image Archive Off-site Archives LBL SNF Other? CIT Data Broker Yale NCSA Master Archive Variables Archive CIT Next-Day Pipeline CIT Fast Pipeline Comparison Engine: Vars./Trans. Detector Website Known Variables Checker Source Classification Engine Alert Decision Engine JPL NEAT Archive Broadcast Alert Asteroid Separator Engine NVO / Multi- Off-site Archives

  23. Some Challenges Ahead • Automated, reliable, adaptive data cleaning • High volume data generators  lots of glitches • Cutting-edge systems  poor stability • High completeness / Low contamination • Must work with “solar system people” - moving objects are the major contaminant for extra-solar-system variables and transients (and vice versa?) • Automated, reliable event classification and alert decisions (need Machine Learning methods) • Sparse data from the event originator; folding in heterogeneous external data; VO connections; etc.

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