Directional Limits on Persistent Gravitational Waves from Advanced LIGO’s First Observing Run

Abstract

We employ gravitational-wave radiometry to map the stochastic gravitational wave backgroundexpected from a variety of contributing mechanisms and test the assumption of isotropy using datafrom the Advanced Laser Interferometer Gravitational Wave Observatory’s (aLIGO) first observing run.We also search for persistent gravitational waves from point sources with only minimal assumptionsover the 20–1726 Hz frequency band. Finding no evidence of gravitational waves from either pointsources or a stochastic background, we set limits at 90% confidence. For broadband point sources, wereport upper limits on the gravitational wave energy flux per unit frequency in the range Fα;ΘðfÞ <ð0.1–56Þ × 10−8 erg cm−2 s−1 Hz−1ðf=25 HzÞα−1 depending on the sky location Θ and the spectralpower index α. For extended sources, we report upper limits on the fractional gravitational wave energydensity required to close the Universe of Ωðf;ΘÞ < ð0.39–7.6Þ × 10−8 sr−1ðf=25 HzÞα depending on Θand α. Directed searches for narrowband gravitational waves from astrophysically interesting objects(Scorpius X-1, Supernova 1987 A, and the Galactic Center) yield median frequency-dependent limits onstrain amplitude of h0 < ð6.7; 5.5; and 7.0Þ × 10−25, respectively, at the most sensitive detector frequenciesbetween 130–175 Hz. This represents a mean improvement of a factor of 2 across the band comparedto previous searches of this kind for these sky locations, considering the different quantities of strainconstrained in each case.