Exploration of the Time Domain A New Old

Exploration of the Time Domain: A New Old Frontier S. G. Djorgovski (Caltech) 2 nd Zwicky Workshop, Berkeley, May 25, 2005

Time Domain Astrophysics • Moving objects: Solar system, Galactic structure, exoplanets • Variability Intrinsic Modulation along the LOS: microlensing, ISS, eclipses, variable extinction … Physical causes of intrinsic variability: – – – Evolution (structural changes etc. ), generally long time scales Internal processes, e. g. , turbulence inside stars Accretion / collapse, protostars to CVs to GRBs to QSOs Thermonuclear explosions Magnetic field reconnections, e. g. , stellar flares Line of sight changes (rotation, jet wiggles…) Variability is known on time scales from ms to 1010 yr Synoptic, panoramic surveys event discovery Rapid follow-up and multi- keys to understanding

Intrinsically Variable Phenomena • Things we know about: – Stars: oscillations, noise, activity cycles, atmospheric phenomena (flares, etc. ), eclipses, explosions (SNe, GRBs), accretion (CVs, novae), spinning beams (pulsars, SS 433, …) – AGN: accretion power spectrum, beaming phenomena • Things we see, but don’t really understand: – Faint fast transients – Archival OTs – Megaflares on normal stars • Things we expect to see, and maybe we do: – Breakout shocks of Type II SNe – SMBH loss cone accretion events – BH mergers (LIGO, LISA? ), QSO formation…? • Things as yet unknown and/or unexpected: – Manifestations of ETCs? (SETF? )

Flaring M Dwarfs (a vermin of the synoptic sky surveys? ) Lynx OT (Catalina Sky Survey) SDSS Counterpart

Megaflares From Normal (? ) Stars An example from DPOSS: A normal, main-sequence star which underwent an outburst by a factor of > 300. There is some anecdotal evidence for such megaflares in normal stars (Schaefer). The cause(s), duration, and frequency of these outbursts is currently unknown.

Optical Transients in DPOSS A possible orphan afterglow discovered serendipitously in DPOSS: an 18 th mag transient associated with a 24. 5 mag galaxy. At zest ~ 1, the observed brightness is ~ 100 times that of a SN at the peak. How many do we expect to see? Depending on the beaming factors, there should be ~ 10 - 100 afterglows down to R ~ 20 mag per sky snapshot. … But it could be something else entirely… Keck

Faint, Fast Transients (Tyson et al. ) Some flaring M-stars, some extragalactic, … A heterogeneous population!

Accretion Flares From (Otherwise Quiescent) SMBHs: X-Ray Tidal disruption and fallback. Expected rate ~ 10 -4 /galaxy/yr Komossa et al. (Rosat) 5 candidate events, amplitude > 102 (quiet state could be Lx ~ 0) Lpeak ~ 1044 erg/s, Etot ~ 1050 erg ~ 10 -4 M c 2 Ultra-soft spectra, k. T < 0. 1 ke. V

Accretion Flares From (Otherwise Quiescent) SMBHs: Visible PALS-1 (Stern et al. ) Possible gravitationally magnified U-band dropout (z ~ 3. 3? ) behind Abell 267

Accretion Flares From (Otherwise Quiescent) SMBHs: Visible Totani et al. , SUBARU Variable sources in the centers of apparently normal galaxies at z ~ few tenths Low-L AGN? L ~ 10 -2 Lhost

Accretion Flares From Our Galaxy’s Own Central Black Hole? A. Ghez et al.

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 deg 2 0. 4 2 3 ~ 0. 9 Sky

DPOSS Plate Overlap Survey: High-Amplitude (non-OT) Variables Spectroscopic Source Identifications: 35% QSOs (1/2 radio loud) 18% CVs 18% M dwarfs 6% Earlier type stars 23% Unidentified (likely BL Lacs? )

Examples of DPOSS Transients

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 Digital Sky Survey • • Using a 112 -CCD camera on the P 48 50% P&S, 50% DS (the PQ survey) A Caltech-JPL-Yale-… collaboration Data rate ~ 1 TB/month; ~100 TB total; ~ 10 TB of DS already in hand DS: ~ 500 deg 2 / night in up to 4 filters, down to ~ 21 mag per pass DS: multiple passes over ~ 15, 000 deg 2, time baselines minutes to years (decades) DS: UBRI and rizz filters; PS: Rwide VO connections and standards built in • Exploration of the time domain is one of the key science goals

PQ 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

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

P 48 Palomar-Quest Real-Time Transients Discovery System Data Flow Image Archive CIT Data Broker Off-site Archives LBL SNF Yale Other? NCSA CIT Next-Day Pipeline CIT Fast Pipeline JPL NEAT Archive Comparison Engine: Vars. /Trans. Detector Asteroid Separator Engine Known Variables Checker Master Archive Variables Archive Website Source Classification Engine NVO / Multi- Off-site Archives Alert Decision Engine Broadcast Alert

Some Challenges Ahead • Automated, reliable, adaptive data cleaning – High volume data generators lots of glitches – Cutting-edge systems poor stability • High completeness / Low contamination • Integrate event discovery and (multi- ) follow-up • 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.

Dumkopfs! I already said it all back in 1935…

PQ Survey Sky Coverage • Range -25°< < +30°, excluding the Galactic plane • Ultimately cover ~ 14, 000 - 15, 000 deg 2 • Rate ~ 500 deg 2/night in 4 bands • As of Jan’ 05, covered ~ 13, 000 deg 2 in UBRI, of which ~ 11, 000 deg 2 at least twice, and ~ 4, 700 deg 2 at least 4 times; and ~ 14, 100 deg 2 in rizz, of which ~ 11, 600 deg 2 at least twice, and ~ 4, 200 deg 2 at least 4 times

Overview • Discoveries are often made through a systematic exploration of observable parameter space, e. g. , the Time Domain – A poorly explored portion of the observable parameter space at any (also , GW) and at many time scales – A range of exciting astrophysical phenomena – Possibility of fundamental new discoveries • Some things that go bang in the night – Known, expected, unknown/unexpected • A pilot project using DPOSS plate overlaps – A rich phenomenology of the time-variable sky • Palomar-Quest survey: status and plans