Real-time Astronomy with LIGO and Virgo: Status and Prospects Erik Katsavounidis LIGO-MIT for the LIGO Scientific Collaboration and the Virgo Collaboration January 28, 2010 GWDAW14 – Rome

The path to gravitational wave astronomy In this conference: First generation individual detectors first global network First generation networks second, third generation and beyond First detections source astrophysics Actively engaging the full spectrum of electromagnetic and particle astrophysics

The S6/VSR2 paradigm LIGO and Virgo are currently (and since July 7th 2009) in their S6 and VSR2 science runs (respectively): An opportunity to improve data analysis infrastructure and organization with respect to the previous runs of the instruments A test case for the advanced detectors regime Immediate goals (on the data analysis front): Near real-time Electromagnetic (EM) follow-up of outlier events (possibly detection candidates) in order to catch the early light from astrophysical sources Rapid follow-up with gravitational-wave (GW) detectors of external triggers with the intention to provide a statement on gravitational wave emission associated with them (see talks by A. Dietz, S. Marka) Prompt detector characterization: improve instruments and ultimate scientific reach for the off-line searches by promptly identifying and hopefully fixing noise sources affecting the sensitivity of the instruments (see talks by N. Christensen, F. Robinet) Improve turn-around time of final science results and publications

Scientific rationale GW sources are reasonably likely to emit in the EM too UV/optical afterglows from supernovae/GRBs have been observed peaking on time scales of hours to days prompt X-ray outbursts, bright X-ray afterglows have been observed in connection with core-collapse supernovae, GRBs Also likely for GW sources to be nearby (so that to be detected with initial instruments), EM detection generally easier EM signatures may be missed (e.g. beaming effects, simply because not looking at the right time at the right place) Even if at the current sensitivity level, few -if any- detections are expected, the scientific payoff in case of a discovery will be tremendous reinforce GW detection provide position of the source with much reduced error circle host galaxy, distance Connecting observations from many wavelengths and GWs  understanding astrophysical processes  multi-messenger astronomy

The real-time implementation challenge Over the summer-fall 2009, the burst and binary inspiral search groups in LIGO and Virgo have put in place near real-time, O(10min), search pipelines looking for unmodeled bursts and low mass inspirals (see talk by Damir Buskulic) in S6/VSR2 Burst searches are as complete as possible and very similar to searches run “offline” Use h(t) data calibrated online (~1 min latency) and transferred from all detector sites to a single one They process 3-site data with ~10min latency, identify significant events and threshold them according to user-defined criteria Establish background in order to assess events’ significance Apply data quality criteria Provide reconstruction of the events’ sky position 500-600 CPUs are employed in order to keep up with data and within the O(10min) mark

Position reconstruction of burst sources Formal study over a broad range of simulated signals added on S5/VSR1 and S6/VSR2 instrument data (the “Position Reconstruction Challenge”) Performance varies significantly with signal-to-noise ratio (SNR), morphology, analysis parameters 5-10 degrees near threshold, 1-2 degrees for “loud” signals Position error areas hide the fact that they may be broken down to many disjoint patches

Galaxy targeting Position reconstruction error area can be further reduced if priors on the directional origin of a GW burst are assumed: known galaxy in our nearby universe, the Milky Way! Galaxy catalogs have been developed by LIGO-Virgo collaborators for the purpose of compact binary searches and the EM follow-up (Kopparapu et al. 2008, ApJ, 675, 1459; Daw, Dhillon, and White, in preparation) These catalogs give positions, as well as estimates for distances and blue luminosities, for over 50,000 galaxies out to a distance of 100 Mpc About 20% of 0.5x0.5 sq. deg. fields intersect a known galaxy within 100 Mpc

Initial partner telescopes Swift satellite mission: capable of performing multi-wavelength observations of GRBs and their aftermath. Three different telescopes record gamma-ray, X-ray, ultra-violet, and optical light UV/optical telescope: 0.4x0.4 sq. deg. FOV X-ray telescope: 0.3x0.3 sq. deg. FOV 3 Target-of-Opportunity (ToO) observations granted for Cycle 5 (April 2009-March 2010) TAROT robotic observatories in France and Chile 1.85x1.85 sq. deg. FOV follows up GRBs, carries out a supernova search QUEST in Chile 4.6x4.1 sq. deg. FOV survey telescope for supernova searches, etc. Pi of the sky 20x20 sq. deg FOV run by the U of Warsaw Signed MOUs for collaborative work (and accepted to image ~1 target/day) Awarded ToO time on the Liverpool telescope for the April 19th – June 15th time window Swift Pi of the sky TAROT

Putting it all together… Starting ~20th of December and through January 8th the first EM follow-up program took off the ground! The real-time burst search identified outlier events that were pushed all the way to obtaining images with our initial telescope partners Burst events had to meet certain significance requirements when compared with background, be localizable in the sky with decent probability and within the instruments’ FOV budget and meet basic data quality requirements Operation driven by scripts collecting events from the search methods in real-time, processing them and communicating them via e-mail to a designated and volunteered group of LIGO-Virgo collaborators Event-by-event decisions (to follow up in EM or not) could be reached typically within 30minutes Tight (and crucial) coordination with the instrument control rooms, telescope principals, LIGO-Virgo search groups altogether EM data collected and are currently being analyzed in collaboration with telescope principals Extremely fruitful exercise on numerous fronts!

Plans for the remaining of S6/VSR2 LIGO and Virgo have short and long commissioning breaks planned for most of Winter/Spring 2010, but likely to come back in triple-coincidence mode of operations in later Spring/early Summer 2010 Identify lessons-learned and address shortcomings of the first EM follow-up program Expect initial partners to continue working with us (Swift, TAROT, QUEST, Pi of the sky) Establish additional (if) telescope partners – expand in other frequencies (radio: NRAO/VLA ToO?, LOFAR and MWA ToO-style of observations) Prepare for a restart of such program that includes bursts and compact binary inspiral triggers feeding into it Challenges never stop! Understand EM backgrounds Understand role of priors assumed for gravitational-wave transient signal (e.g., origin from within known mass in the Universe or not, morphology and polarization etc)

Summary and Outlook LIGO and Virgo have completed a ~3-week long near-real time search for bursts that allowed the follow-up of outlier events in the optical and X-rays “Near-real-time” requirements for such a project have been largely met, with outlier events becoming available for EM observation within 30-60 minutes after data were collected Many lessons were learned from this exercise and a rich to-do list with more challenges in it awaits us Efforts so far to catch EM counterparts to gravitational-wave transients have been opportunistic in nature Important path-finding exercise for routine detections expected with advanced detectors in 2014-2015 and the new astronomical messenger they will bring in Need to start getting ready now: put the right software tools in place think out well how the coordinated GW-EM searches will be performed