Multi-Messenger GW and EM astronomyGianluca M Guidi

Università di Urbino – INFN Firenzefor the LIGO Scientific Collaboration and Virgo Collaboration

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GW-EM Multi-Messenger:why?

● Advanced detectors will most probably directly detect GW in the near future.

● Among GW sources are the most violent phenomena in the universe: compact binary coalescences (CBC) – BNS, NSBH, BBH – supernovae, neutron stars ..

● Some of them should emit in EM; current observations and theoretical predictions links these phenomena to GRBs, kilonovae, Soft Gamma Ray repeaters, etc

EM observations following up GW detection, and vice versa, will help to elucidate the nature of the sources and permit to study a same phenomena with the most complete set of observations possible until now.

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Results from previous runs: Ex-triggered searches

Exclusion distance for 69 short GRBsPRL 113 (2014) 011102

GRB 051103 in M81 Astrophys. J. 755 (2012) 2

● GW off-line observations triggered by external observatories

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Results from previous runs EM follow-up of GW triggers

● GW trigger → EM follow-up → Image analysis

The gravitational wave skymap for event G19377 – a fake signal - ApJS 211 (2014) 7;

Sky maps and locations imaged by Swift while following up the January event.ApJS 203 (2012) 28

Astron Astrophys 539 (2012) A124; Astron Astrophys 541 (2012) A155

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The present and the future: Creating the GW-EM network for EM follow-up

● LIGO and Virgo engaged in 2014 in a coordination program to create a large network of EM facilities which could perform follow-up of GW triggers

● Two open calls for proposals to sign MoU with LVC http://www.ligo.org/scientists/GWEMalerts.php

– Large participation: 70 signed a MoU

– The network covers all observable EM wavelengths and include the major telescopes on Earth along with 10 space observatories

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The present and the future: Creating the GW-EM network for EM follow-up

● How do we collaborate ? → Data and information sharing:

– All parties will share information with all PARTNERS in the follow-up program through a dedicated communication network.

– LIGO and VIRGO will communicate the detected GW candidate events in the form of alerts.

– For each follow-up observation made by XXXXX, XXXXX will share the coordinates of the observations that have been made as soon as practical and within 12 hours of the observingTime. …..

– XXXXX is encouraged to share data analysis results in the form of a list of plausible candidates, or other relevant findings, or a non-detection statement as promptly as possible.

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EM followup The big picture

● From GW to EM observers through DA and validation

Courtesy of P Shawhan

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EM followupGraceDB: a GW-events DB

● Coincident GW triggers found by a CBC (gstlal, MBTA) or Burst (cWB) pipeline, with their characterisics, skymaps, DQ are stored in a dedicated DB which can be accessed by the EM partners.

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EM followupGraceDB: a GW-events DB

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EM followupChallenges : expected rate

● We expect initially a low number of detections and a loose sky localization

ArXiv:1304.0670http://dx.doi.org/10.1088/0004-637X/804/2/114

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EM followupChallenges : sky localization

M1 = 1.4 M

o; M

2 = 1.2 M

o

FAR = 3.772e-14 Hz

● We can reconstruct the source location but, generally, with large area probability-density sky-maps

– Simulated example of a BNS signal recovered by gstlal in O1-like data

http://www.ligo.org/scientists/first2yearsSinger et al, ApJ, 795, 105Reed Essick et al. 2015 ApJ 800 81

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EM followupChallenges : sky localization

Example for a simulated BBH signal recovered by cWB

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EM followupChallenges : sky localization

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EM followup GW alerts and their structure

● Alerts will be shared between LVC and their EM partners

….. after a GW event found by a CBC or Burst search

Preliminary alert VOEvent_0:

We have found a significant event!

(we give instruments, FAR, type and time)

3-5 min

Initial alert VOEvent_1

The event has passed Data Quality checks

Rapid Localization Skymaps are produced

(chirp mass, max distance; peak frequency, duration, ...)

5-10 min

Update alerts VOEvent_2, 3, ...

Revised skymaps, refined FAR ….hours

Retractio

n V

OE

vent notice

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EM followupEvent significance

● We measure the significance of an event E with its False Alarm Rate, i.e. the (expected number of noise events) per sec with a ranking statistic value (~SNR) higher than the one of E

● In O1 (14 Sep 15 – 13 Dec 15) we propose to set a FAR threshold so that we expect ~1 CBC alert and ~1 Burst alert per calendar month

– We will generate alerts for ~6 false event candidates, plus however the real event candidates that are loud enough to pass the FAR threshold too

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EM followupGW vs EM vs GW-EM Analysis

● Detection of a GW signal can be unrelated from the existence of an EM counterpart

● LVC with their EM partners will possibly perform separate analysis in the search of GW and EM counterparts.

● However, joint analysis of GW and EM candidates could happen and increase the significance of a discover

– EM followup could be crucial for verifying or interpreting the GW event

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GRB triggered search

● GCN alerts → GW analysis

● Different types of analysis at different latencies:

Low latency, medium latency and “Archival” searches:

– RAVEN pipeline matches up low-latency GW triggers with GCN;

– Launches deep coherent searches in minutes; answer in ~hours

– Run same deep search pipelines, include all GRBs

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GRB triggered searchThe big picture

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Conclusions

● We have set up several searches apt to exploit the multimessenger nature of the GW sources

● The field is still young: we have a lot to test and learn!

● Let us see what comes out from O1 …