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

Abstract

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. ...

Searching for primordial black holes with stochastic gravitational-wave background in the space-based detector frequency band

“…Therefore the comparison only serves as an order of magnitude estimation due to the lack of sensitivity curve for a directional source. The search for persistent GW signals from point-like sources has been performed by Advanced [47,48] and Initial LIGO and Virgo [49]. Especially, using the data from the first and second observational runs of Advanced LIGO and Virgo, the upper limits for GW strain amplitude have been given for three sources with targeting directions: Scorpius X-1, Supernova 1987 A and the Galactic Center, respectively.…”

Estimating the angular power spectrum of the gravitational-wave background in the presence of shot noise

“…The first line is true by definition, while the second states that each SHC in each time interval has equal shot noise (22). The dark blue line is the chosen "true" spectrum to be estimated, which is here taken as scale-invariant for simplicity, ( + 1)C ≈ constant.…”

“…Since the components of CBCs are the results of stellar evolution, they should reside in galaxies, 1 and the AGWB should trace the distribution of galaxies throughout the local Universe. There has therefore been significant recent interest in AGWB anisotropies [15][16][17][18][19][20][21] and associated observational searches [22][23][24] and data-analysis methods [25][26][27][28][29][30][31], as these might provide an entirely new probe of galaxy clustering and large-scale structure (LSS).…”

Identification and mitigation of narrow spectral artifacts that degrade searches for persistent gravitational waves in the first two observing runs of Advanced LIGO

“…In directed, narrow-band searches [29] we do not search for GWs at frequencies of known instrumental lines. For both CW and SGWB searches, lists of known instrumental artifacts are created following the end of an observing run (further details are provided in Sec.…”