We present the result of searches for gravitational waves from 200 pulsars using data from the first observing run of the Advanced LIGO detectors. We find no significant evidence for a gravitational-wave signal from any of these pulsars, but we are able to set the most constraining upper limits yet on their gravitational-wave amplitudes and ellipticities. For eight of these pulsars, our upper limits give bounds that are improvements over the indirect spin-down limit values. For another 32, we are within a factor of 10 of the spin-down limit, and it is likely that some of these will be reachable in future runs of the advanced detector. Taken as a whole, these new results improve on previous limits by more than a factor of two.

We report on an all-sky search for periodic gravitational waves in the frequency band 20-475 Hz and with a frequency time derivative in the range of ½−1.0; þ0.1 × 10 −8 Hz=s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our galaxy. This search uses the data from Advanced LIGO's first observational run, O1. No periodic gravitational wave signals were observed, and upper limits were placed on their strengths. The lowest upper limits on worst-case (linearly polarized) strain amplitude h 0 are ∼4 × 10 −25 near 170 Hz. For a circularly polarized source (most favorable orientation), the smallest upper limits obtained are ∼1.5 × 10 −25 . These upper limits refer to all sky locations and the entire range of frequency derivative values. For a population-averaged ensemble of sky locations and stellar orientations, the lowest upper limits obtained for the strain amplitude are ∼2.5 × 10 −25 .

We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. Three different semicoherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from −1 × 10 −8 to 2 × 10 −9 Hz=s. None of these searches has found clear evidence for a CW signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved.

This paper presents the gravitational-wave measurement of the Hubble constant H 0 using the detections from the first and second observing runs of the Advanced LIGO and Virgo detector network. The presence of the transient electromagnetic counterpart of the binary neutron star GW170817 led to the first standard-siren measurement of H 0. Here we additionally use binary black hole detections in conjunction with galaxy catalogs and report a joint measurement. Our updated measurement is H 0 = 68 +14 −7 km s −1 Mpc −1 (68.3% highest density posterior interval with a flat-in-log prior) which is a 7% improvement over the GW170817-only value of 68 +18 −8 km s −1 Mpc −1. A significant additional contribution currently comes from GW170814, a loud and well-localized detection from a part of the sky thoroughly covered by the Dark Energy Survey. Inclusion of contributions from all binary black hole detections entails a thorough marginalization over unknown population parameters. With numerous detections anticipated over the upcoming years, an exhaustive understanding of other systematic effects are also going to become increasingly important. These results establish the path to cosmology using gravitational-wave observations with and without transient electromagnetic counterparts.

We employ gravitational-wave radiometry to map the gravitational waves stochastic background expected from a variety of contributing mechanisms and test the assumption of isotropy using data from Advanced LIGO's first observing run. We also search for persistent gravitational waves from point sources with only minimal assumptions over the 20 -1726 Hz frequency band. Finding no evidence of gravitational waves from either point sources or a stochastic background, we set limits at 90% confidence. For broadband point sources, we report upper limits on the gravitational wave energy flux per unit frequency in the range Fα,Θ(f ) < (0.1 − 56) × 10 −8 erg cm −2 s −1 Hz −1 (f /25 Hz) α−1 depending on the sky location Θ and the spectral power index α. For extended sources, we report upper limits on the fractional gravitational wave energy density required to close the Universe of Ω(f, Θ) < (0.39−7.6)×10−8 sr −1 (f /25 Hz) α depending on Θ and 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 on strain amplitude of h0 < (6.7, 5.5, and 7.0) × 10 −25 respectively, at the most sensitive detector frequencies between 130 -175 Hz. This represents a mean improvement of a factor of 2 across the band compared to previous searches of this kind for these sky locations, considering the different quantities of strain constrained in each case.Introduction.-A stochastic gravitational-wave background (SGWB) is expected from a variety of mechanisms [1][2][3][4][5]. Given the recent observations of binary black hole mergers GW150914 and GW151226 [6,7], we expect the SGWB to be nearly isotropic [8] and dominated [9] by compact binary coalescences [10][11][12]. The LIGO and Virgo Collaborations have pursued the search for an isotropic stochastic background from LIGO's first observational run [13]. Here, we adopt an eyes-wide-open philosophy and relax the assumption of isotropy in order to allow for the greater range of possible signals. We search for an anisotropic background, which could indicate a richer, more interesting cosmology than current models. We present the results of a generalized search for a stochastic signal with an arbitrary angular distribution mapped over all directions in the sky.Our search has three components. First, we utilize a broadband radiometer analysis [14,15], optimized for detecting a small number of resolvable point sources. This method is not applicable to extended sources. Second, we employ a spherical harmonic decomposition [16,17], which can be employed for point sources but is better suited to extended sources. Last, we carry out a narrowband radiometer search directed at the sky position of three astrophysically interesting objects: Scorpius X-1 (Sco X-1) [18,19], Supernova 1987 [20,21], and the Galactic Center (GC) [22].These three search methods are capable of detecting a wide range of possible signals with only minimal assumptions about the signal morphology. ...