Discovery of Strongly-lensed Gravitational Waves – Implications for the LSST Observing Strategy. (arXiv:1902.05140v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Smith_G/0/1/0/all/0/1">Graham P. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robertson_A/0/1/0/all/0/1">Andrew Robertson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bianconi_M/0/1/0/all/0/1">Matteo Bianconi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jauzac_M/0/1/0/all/0/1">Mathilde Jauzac</a> (on behalf of the LSST Strong Lensing Science Collaboration and the Gravitationally Lensed Gravitational Wave Hunters)
LSST’s wide-field of view and sensitivity will revolutionize studies of the
transient sky by finding extraordinary numbers of new transients every night.
The recent discovery of a kilonova counterpart to LIGO/Virgo’s first detection
of gravitational waves (GWs) from a double neutron star (NS-NS) merger also
creates an exciting opportunity for LSST to offer a Target of Opportunity (ToO)
mode of observing. We have been exploring the possibility of detecting strongly
lensed GWs, that would enable new tests of GR, extend multi-messenger astronomy
out to $zgtrsim1$, and deliver a new class of sub-millisecond precision
time-delay constraints on lens mass distributions. We forecast that the rate of
detection of lensed NS-NS mergers in the 2020s will be $sim0.1$ per Earth
year, that the typical source will be at $zsimeq2$, and that the
multiply-imaged kilonova counterpart will have a magnitude of ${rm
AB}simeq25.4$ in $g/r/i$-band filters – i.e. fainter than the sensitivity of a
single LSST WFD visit. We therefore advocate (1) creating a flexible and
efficient Target of Opportunity programme within the LSST observing strategy
that is capable of discovering sources fainter than single-visit depth, and (2)
surveying the entire observable extragalactic sky as rapidly as possible in the
WFD survey. The latter will enable a very broad range of early science that
relies on wide survey area for detection of large samples of objects and/or
maximizing the fraction of sky over which reference imaging is available. For
example, it will enable prompt discovery of a uniform and all-sky sample of
galaxy/group/cluster-scale lenses that will underpin LSST strong-lensing
science. This white paper complements submissions from DESC, SLSC, and TVSSC,
that discuss kilonova, GW, and strong lensing.
LSST’s wide-field of view and sensitivity will revolutionize studies of the
transient sky by finding extraordinary numbers of new transients every night.
The recent discovery of a kilonova counterpart to LIGO/Virgo’s first detection
of gravitational waves (GWs) from a double neutron star (NS-NS) merger also
creates an exciting opportunity for LSST to offer a Target of Opportunity (ToO)
mode of observing. We have been exploring the possibility of detecting strongly
lensed GWs, that would enable new tests of GR, extend multi-messenger astronomy
out to $zgtrsim1$, and deliver a new class of sub-millisecond precision
time-delay constraints on lens mass distributions. We forecast that the rate of
detection of lensed NS-NS mergers in the 2020s will be $sim0.1$ per Earth
year, that the typical source will be at $zsimeq2$, and that the
multiply-imaged kilonova counterpart will have a magnitude of ${rm
AB}simeq25.4$ in $g/r/i$-band filters – i.e. fainter than the sensitivity of a
single LSST WFD visit. We therefore advocate (1) creating a flexible and
efficient Target of Opportunity programme within the LSST observing strategy
that is capable of discovering sources fainter than single-visit depth, and (2)
surveying the entire observable extragalactic sky as rapidly as possible in the
WFD survey. The latter will enable a very broad range of early science that
relies on wide survey area for detection of large samples of objects and/or
maximizing the fraction of sky over which reference imaging is available. For
example, it will enable prompt discovery of a uniform and all-sky sample of
galaxy/group/cluster-scale lenses that will underpin LSST strong-lensing
science. This white paper complements submissions from DESC, SLSC, and TVSSC,
that discuss kilonova, GW, and strong lensing.
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