Prospects and challenges in the electromagnetic follow-up of LIGO-Virgo gravitational wave transients

Abstract

The kilometer-scale ground based gravitational wave (GW) detectors, LIGO and Virgo, are being upgraded to their advanced configurations. We expect the two LIGO observatories to undertake a 3 month science run in 2015 with a limited sensitivity. Virgo should come online in 2016, and join LIGO for a 6 month science run. Through a sequence of science runs and commissioning periods, the final sensitivity should be reached by ∼ 2019. LIGO and Virgo are expected to deliver the first direct detection of gravitational wave transients in the next few years. Most of the known sources of GWs targeted by LIGO and Virgo will likely be luminous in the electromagnetic (EM) spectrum as well. Compact binary coalescences are thought to be progenitors of short gamma-ray bursts, while long gamma-ray bursts are likely to be associated with core collapse supernova. A joint detection of gravitational and EM radiation may help confirm these associations, and expand our understanding of those astrophysical systems. Due to the transient nature, a search for the EM counterparts to GW events should be done with the shortest latency. In this paper we describe the EM follow-up program of Advanced LIGO and Virgo, from the search for GWs to the production of sky maps. Furthermore, we quantify the expected sky localization errors in the first two years of operation of the advanced detectors network. INTRODUCTIONThe advanced version of the ground based gravitational wave observatories LIGO 1 will start collecting data in 2015, followed shortly after by Advanced Virgo.2 Through a sequence of commissioning periods, they will reach their design sensitivity at the end of this decade, when they will probe a volume of the Universe a factor of 10 3 larger than the initial detectors. The Japanese detector KAGRA, 3 and LIGO-India 4 are also expected to join this global network in the early 2020s, further increasing the sensitivity, and dramatically improving sky localization of gravitational wave (GW) sources. Ground based detectors are thus expected to make the first direct detection of gravitational radiation, and start gravitational wave astronomy.Beside the obvious interest that a direct GW detection deserves on its own, there is much interest in the possibility of joint electromagnetic -gravitational detections. In fact GW detectors target several classes of astrophysical sources, some of which are also expected to be luminous in the electromagnetic (EM) spectrum. 5-8The most promising sources of GWs are compact binary systems (CBC) consisting of neutron stars and/or black holes, which are also the best theoretically understood. Loss of energy through gravitational wave emission makes the orbit to shrink (inspiral phase), until the two objects merge to form a single black hole. This releases the excess of energy "ringing-down" to equilibrium. The inspiral part can be described well using Post-Newtonian theory (see.9 for a review), while effective one body (EOB) models 10 and Inspiral-Merger-Ringdown (IMR) phenomenological models 11 can descr...