1 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 LSST + Tony Tyson UC Davis LSST Chief Scientist

LSST Wide-Fast-Deep survey A survey of 37 billion objects in space and time Each sky patch will be visited over 800 times: 30 trillion measurements A survey of 37 billion objects in space and time Each sky patch will be visited over 800 times: 30 trillion measurements arXiv:

3 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Six Filters

A uniform sky survey ~90% of time will be spent on a uniform survey: every 3-4 nights, the whole observable sky will be scanned twice per night after 10 years, half of the sky will be imaged about 1000 times (in 6 bandpasses, ugrizy): a digital color movie of the sky ~100 PB of data: about 2.5 million 3.2 Gpix images (visits), enabling measurements for 37 billion objects LSST in one sentence: An optical/near-IR survey of half the sky in ugrizy bands to r~27.5 (36 nJy) based on ~825 visits over a 10-year period: deep wide fast. LSST will collect about 2.5 million visits. Each visit results in a 3.2 Gpix image of 9.6 sq.deg. Visit: basic unit for data taking; baseline assumes a total exposure time per visit of 30 sec, split into two back-to-back exposures of 15 sec each

5 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Sky Coverage

6 Hot-Wiring the Transient Universe Santa Barbara CA May 12, LSST Observing Cadence Detection of transients announced within 60 seconds. Expect: 1-10 million alerts per night, “thousands worthy of followup!” “thousands worthy of followup!” MAIN SURVEY (deep-wide-fast) Deep Wide Survey: 18,000 square degrees to a uniform depth of u: 26.1 g: 27.4 r: 27.5 i: 26.8 z: 26.1 y: 24.9 u: 26.1 g: 27.4 r: 27.5 i: 26.8 z: 26.1 y: pairs of 15 second exposures (to r~24.5 mag) per visit - visit the same position again within ~1 hour with another pair of exposures - number of visits per night: 850 (~8,000 sq. deg) MINI SURVEYS (deep drilling) 10% of time: ~30 selected fields (~300 sq. deg) Continuous 15 sec exposures: ~1hour/night Continuous 15 sec exposures: ~1hour/night LSST “guaranteed” fields: CDFS, COSMOS, ES1 and XMM-LSS Co-observing? Co-observing?

7 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Petascale Computing, Gbps Networks The computing cluster at the LSST Archive at NCSA will run the processing pipelines. Single-user, single-application data center Commodity computing clusters. Distributed file system for scaling and hierarchical storage Local-attached, shared-nothing storage when high bandwidth needed Long Haul Networks to transport data from Chile to the U.S. 2x100 Gbps from Summit to La Serena (new fiber) 2x40 Gbps for La Serena to Champaign, IL (path diverse, existing fiber) Archive Site and U.S. Data Access Center NCSA, Champaign, IL Archive Site and U.S. Data Access Center NCSA, Champaign, IL Base Site and Chilean Data Access Center La Serena, Chile Base Site and Chilean Data Access Center La Serena, Chile

8 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Database and Science User Interface Massively parallel, distributed, fault-tolerant relational database. To be built on existing, robust, well- understood, technologies (MySQL and xrootd) Commodity hardware, open source Advanced prototype in existence (qserv) Science User Interface to enable the access to and analysis of LSST data Web and machine interfaces to LSST databases Visualization and analysis capabilities

9 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 LSST From the User’s Perspective − A stream of ~1-10 million time-domain events per night, detected and transmitted to event distribution networks within 60 seconds of observation. − A catalog of orbits for ~6 million bodies in the Solar System. − A catalog of ~37 billion objects (20B galaxies, 17B stars), ~7 trillion observations (“sources”), and ~30 trillion measurements (“forced sources”), produced annually, accessible through online databases. − Deep co-added images. − Services and computing resources at the Data Access Centers to enable user-specified custom processing and analysis. − Software and APIs enabling development of analysis codes. Level 3 Level 1 Level 2

10 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 High Data Quality − System designed for maximum data quality – Nightly full system calibration – Real time correction for atmosphere transmission – CCD detector and camera ghosting artifacts known and included in event detection algorithm – Full pixel data distribution used in detection significance – Automated data quality assessment at multiple levels − Designed to enable use cases requiring rapid detection and follow-up – Will subtract each incoming image against a deep template constructed from prior observations of the same spot, and detect sources on the difference image – New PSF objects appearing between 15 sec exposures can yield ~30 sec time resolution – Significant sources defined in full context of known imaging artifacts and measured noise – Below, this will be called “detection” or “detected sources” – Goal: object detections in alerts and catalogs will be real, not system artifacts − Position, flux, and shape will be measured for each detection – Shape measurement will include characterization of trailing (assisting detection of NEOs) More Information: LSST Data Products Definition Document; (note: this document is updated approximately annually)

11 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 LSST Services in Support of Level 1 − Forced Photometry (“Precovery”) Service – Automatically perform and make available forced photometry at the position of all newly detected sources, on imaging acquired over the preceding 30 days – On request, for a limited number of positions perform and make available forced photometry on all imaging overlapping that position – Turnaround on a ~day timescale. − Alert generation service – Package and transmit all alerts to community-supported alert distribution networks − Limited end-user alert stream subscription and filtering service – Individuals will be able to subscribe to receive a small (~20) number of alerts per visit, filtered based on user-specified criteria – Limited functionality: no classification, not planning to cross-match to external catalogs, etc. – We expect the community will provide sophisticated event brokers with classification engines, cross-match capabilities to other catalogs, etc. More Information: LSST DPDD;

What is a “true transient”? “True transients” are those that can reach photometric variability of at least 1 mag/hr. This definition rejects most common variable stars (an M dwarf burst might qualify), and also rejects SNe. It is most certainly not a perfect definition but it does select transients where LSST latency of only 60 sec will represent major new science opportunities

Optical “X” Modes  Transient discovery via co-observing >30 sec timescales  Follow-up research longer timescale multi-wavelength investigations of new phenomena

PTF burst 40 days before SN 14

15 One LSST unique contribution: t < t 0 information LSST will have the time history of 37 billion objects in the database. Transient phenomena may exhibit precursor activity: 1.Use as Bayesian prior in classification post-alert 2.Treat as part of the “light curve.” 27 th –> 24 th mag. 3.Catch interesting objects on their way up. Issue pre-alerts.

16 Gravitational lens time delayed flares Above: predicted abundances of LSST lensed quasars (left) and supernovae (right, divided by type).

Alert Rate In ten minutes time the LSST transient pipeline is likely to issue ~10,000 alerts at 5σ. While most of these will be moving objects, perhaps several thousand will be flaring objects or bursts. Possibly new kinds of objects! Clearly any followup requires high purity samples. What is needed then is highly trusted event classification. FAST 17

18 Automated discovery Data exploration This is required also for automated Data Quality Assessment

19 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Need automated classification broker

20 Deep Lens Survey

Summary 1) Sources detected in difference images (DIASources) will be measured and reported in 60 sec (baseline: as a VOEvent stream). Users will be able to filter this stream (of the order millions of DIAsources per night, including variable stars, SNe, asteroids, and “everything else”). 2) LSST will deliver a toolbox, and this will be done on a fixed schedule and budget. The more we can gain from other surveys and groups outside the formal project boundaries, the better this toolbox will be, for everyone. LSST Project invites community members with relevant expertise to help optimize the project-led development. The critical period for data broker development is prior to first light (say, two years earlier, which is 2017), and thus we have only about 2 years!

22 Hot-Wiring the Transient Universe Santa Barbara CA May 12, 2015 Project Timeline

23 LSST Data Products: ls.st / dpdd lsst.org

24 Three classes of LSST+ spectroscopy 1.Calibration samples for quantities that can be derived from photometric data: photometric redshifts for galaxies, photometric metallicity for stars 2.Supplemental data that cannot be obtained from LSST data: radial velocity, emission and absorption line strengths 3.Identification spectra for transient, weird and unusual objects (SNe, GRB followup, high-z quasars, brown dwarfs) + Co-Observing!