GROWTH on S190426c. II. Real-Time Search for a Counterpart to the Probable Neutron Star-Black Hole Merger using an Automated Difference Imaging Pipeline for DECam. (arXiv:1905.06980v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Goldstein_D/0/1/0/all/0/1">Daniel A. Goldstein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Andreoni_I/0/1/0/all/0/1">Igor Andreoni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nugent_P/0/1/0/all/0/1">Peter E. Nugent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasliwal_M/0/1/0/all/0/1">Mansi M. Kasliwal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coughlin_M/0/1/0/all/0/1">Michael W. Coughlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anand_S/0/1/0/all/0/1">Shreya Anand</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bloom_J/0/1/0/all/0/1">Joshua S. Bloom</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martinez_Palomera_J/0/1/0/all/0/1">Jorge Martínez-Palomera</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_K/0/1/0/all/0/1">Keming Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ahumada_T/0/1/0/all/0/1">Tomás Ahumada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bagdasaryan_A/0/1/0/all/0/1">Ashot Bagdasaryan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cooke_J/0/1/0/all/0/1">Jeff Cooke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+De_K/0/1/0/all/0/1">Kishalay De</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Duev_D/0/1/0/all/0/1">Dmitry A. Duev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fremling_U/0/1/0/all/0/1">U. Christoffer Fremling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gatkine_P/0/1/0/all/0/1">Pradip Gatkine</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Matthew Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ofek_E/0/1/0/all/0/1">Eran O. Ofek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Singer_L/0/1/0/all/0/1">Leo P. Singer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yan_L/0/1/0/all/0/1">Lin Yan</a>
The discovery of a transient kilonova following the gravitational-wave event
GW170817 highlighted the critical need for coordinated rapid and wide-field
observations, inference, and follow-up across the electromagnetic spectrum. In
the Southern hemisphere, the Dark Energy Camera (DECam) on the Blanco 4-m
telescope is well-suited to this task, as it is able to cover wide-fields
quickly while still achieving the depths required to find kilonovae like the
one accompanying GW170817 to $sim$500 Mpc, the binary neutron star horizon
distance for current generation of LIGO/Virgo collaboration (LVC)
interferometers. Here, as part of the multi-facility followup by the Global
Relay of Observatories Watching Transients Happen (GROWTH) collaboration, we
describe the observations and automated data movement, data reduction,
candidate discovery, and vetting pipeline of our target-of-opportunity DECam
observations of S190426c, the first possible neutron star–black hole merger
detected via gravitational waves. Starting 7.5hr after S190426c, over 11.28,hr
of observations, we imaged an area of 525,deg$^2$ ($r$-band) and 437,deg$^2$
($z$-band); this was 16.3% of the total original localization probability and
nearly all of the probability density visible from the Southern hemisphere. The
machine-learning based pipeline was optimized for fast turnaround, delivering
transient candidates for human vetting within 17 minutes, on average, of
shutter closure. We reported nine promising counterpart candidates 2.5 hours
before the end of our observations. Our observations yielded no detection of a
bona fide counterpart to $m_z = 22.5$ and $m_r = 22.9$ at the 5$sigma$ level
of significance, consistent with the refined LVC positioning. We view these
observations and rapid inferencing as an important real-world test for this
novel end-to-end wide-field pipeline.
The discovery of a transient kilonova following the gravitational-wave event
GW170817 highlighted the critical need for coordinated rapid and wide-field
observations, inference, and follow-up across the electromagnetic spectrum. In
the Southern hemisphere, the Dark Energy Camera (DECam) on the Blanco 4-m
telescope is well-suited to this task, as it is able to cover wide-fields
quickly while still achieving the depths required to find kilonovae like the
one accompanying GW170817 to $sim$500 Mpc, the binary neutron star horizon
distance for current generation of LIGO/Virgo collaboration (LVC)
interferometers. Here, as part of the multi-facility followup by the Global
Relay of Observatories Watching Transients Happen (GROWTH) collaboration, we
describe the observations and automated data movement, data reduction,
candidate discovery, and vetting pipeline of our target-of-opportunity DECam
observations of S190426c, the first possible neutron star–black hole merger
detected via gravitational waves. Starting 7.5hr after S190426c, over 11.28,hr
of observations, we imaged an area of 525,deg$^2$ ($r$-band) and 437,deg$^2$
($z$-band); this was 16.3% of the total original localization probability and
nearly all of the probability density visible from the Southern hemisphere. The
machine-learning based pipeline was optimized for fast turnaround, delivering
transient candidates for human vetting within 17 minutes, on average, of
shutter closure. We reported nine promising counterpart candidates 2.5 hours
before the end of our observations. Our observations yielded no detection of a
bona fide counterpart to $m_z = 22.5$ and $m_r = 22.9$ at the 5$sigma$ level
of significance, consistent with the refined LVC positioning. We view these
observations and rapid inferencing as an important real-world test for this
novel end-to-end wide-field pipeline.
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