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

Time Domain Astrophysics Moving objects: Solar system, Galactic structure, exoplanets Variability 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 yr Synoptic, panoramic surveys  event discovery Rapid follow-up and multi-  keys to understanding Intrinsic Modulation along the LOS: microlensing, ISS, eclipses, variable extinction …

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.

A possible orphan afterglow  discovered serendipitously in DPOSS: an 18th mag transient associated with a 24.5 mag galaxy. At z est ~ 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 ~ afterglows down to R ~ 20 mag per sky snapshot. … But it could be something else entirely… Optical Transients in DPOSS DPOSS Keck

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

Accretion Flares From (Otherwise Quiescent) SMBHs: X-Ray Komossa et al. (Rosat) 5 candidate events, amplitude > 10 2 (quiet state could be L x ~ 0) L peak ~ erg/s, E tot ~ erg ~ M  c 2 Ultra-soft spectra, kT < 0.1 keV Tidal disruption and fallback. Expected rate ~ /galaxy/yr

Accretion Flares From (Otherwise Quiescent) SMBHs: Visible PALS-1 (Stern et al.) Possible gravitationally magnified U-band dropout (z ~ 3.3?) behind Abell 267

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

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 ~ 1.5 O overlaps between adjacent plates  ~ 40% of the total survey area Effective Area Coverage in a “Snapshot” Survey: If t exp > t burst, then Effective Area = Useful Area  N passes  N filters For DPOSS: ~ 15,000 deg 2  0.4  2  3 ~ 0.9 Sky B. Granett, A. Mahabal, S.G. Djorgovski, and the DPOSS Team Baselines from days to ~ 10 yrs, typical ~ 2-4 yrs Typical limiting mags r ~ 20, using 3 bandpasses (JFN  gri)

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 (~ 10 3 /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 P48 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: R wide VO connections and standards built in Exploration of the time domain is one of the key science goals

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

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

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

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 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