1. 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

2. 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

3. 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

4. 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

5. 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
CPUs are employed in order to keep up with data and within the O(10min) mark

6. 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

7. 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

8. 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

9. 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 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!

10. 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)

11. 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 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 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