X-ray afterglow light curves : toward standard candle ?

We investigate the clustering of afterglow light curves observed at X-ray and optical wavelengths. We have constructed a sample of 61 bursts with known dis tance and X-ray afterglow. This sample includes bursts observed by BeppoSAX, XMM-Newton, Chandra, and SWIFT. We correct the light curves for cosmological ef fects and compare the observed X-ray fluxes one day after the burst. We check for correlations between the observed flux and the burst spectral and temporal properties. We confirm the previous result of Boer and Gendre (2000) that X-ray afterglow light curves cluster in luminosity, even when we consider the l ast SWIFT data. We observe this clustering only for the afterglow light curves; the inclusion of prompt-related data broaden the distribution. A similar clu stering is observed for the optical light curves; GRB sources can be divided in three classes, namely optical and X-ray bright afterglows, optical and X-ray dim ones, and optically bright -X-ray dim ones. We argue that this clustering is related to the fireball total energy, the external medium density, the fraction of fireball energy going in relativistic electrons and magnetic fields. These parameters can be either fixed to a standard va lue, or correlated. We finally propose a method for the estimation of the GRB source redshift based on the observed X-ray flux one day after the burst and optical properties. Using this method, we compute a redshift of 1.4 +/- 0.2 for GRB 980519 and of 1.9 \+/- 0.3 for GRB 040827. We tested this method on three recently detected SWIFT GRBs with known redshift, and found it in good agreement with the reported distance from optical spectroscopy .Comment: 17 pages, 10 color figures, 1 b&w figure. Accepted for publication by Ap

Constraining the rate of GRB visible afterglows with the CFHTLS Very Wide Survey

We analyze images of the CFHTLS Very Wide Survey to search for visible orphan afterglows from gamma-ray bursts (GRBs). We have searched 490 square degrees down to magnitude r'=22.5 for visible transients similar to GRB afterglows. We translate our observations into constraints on the number of GRB visible afterglows in the sky, by measuring the detection efficiency of our search with a simulation reproducing the characteristics of our observational strategy and the properties of on-axis GRB afterglows. We have found only three potential candidates, of which two are most probably variable stars, and one presents similarities to an orphan afterglow. We constrain the number of visible afterglows to be less than 220 down to r'=22.5 in the whole sky at any time. Our observations are marginally consistent with the most optimistic model, which predicts orphan afterglows to be about 10 times more frequent than GRBs. This search has led to the detection of one possible GRB afterglow, and provides the strongest constraints on the rate of GRB visible afterglows as well as an estimation of the observing time required to detect a significant number of GRB afterglows.Comment: 4 pages, 3 figures, 2 tables. Accepted by A&A Lette

Search for subsolar-mass black hole binaries in the second part of Advanced LIGO’s and Advanced Virgo’s third observing run

We describe a search for gravitational waves from compact binaries with at least one component with mass 0.2–1.0 M and mass ratio q ≥ 0.1 in Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo data collected between 2019 November 1, 15:00 UTC and 2020 March 27, 17:00 UTC. No signals were detected. The most significant candidate has a false alarm rate of 0.2 yr−1. We estimate the sensitivity of our search over the entirety of Advanced LIGO’s and Advanced Virgo’s third observing run, and present the most stringent limits to date on the merger rate of binary black holes with at least one subsolar-mass component. We use the upper limits to constrain two fiducial scenarios that could produce subsolar-mass black holes: primordial black holes (PBH) and a model of dissipative dark matter. The PBH model uses recent prescriptions for the merger rate of PBH binaries that include a rate suppression factor to effectively account for PBH early binary disruptions. If the PBHs are monochromatically distributed, we can exclude a dark matter fraction in PBHs fPBH 0.6 (at 90 per cent confidence) in the probed subsolar-mass range. However, if we allow for broad PBH mass distributions, we are unable to rule out fPBH = 1. For the dissipative model, where the dark matter has chemistry that allows a small fraction to cool and collapse into black holes, we find an upper bound fDBH < 10−5 on the fraction of atomic dark matter collapsed into black holes

Search for Eccentric Black Hole Coalescences during the Third Observing Run of LIGO and Virgo

Despite the growing number of binary black hole coalescences confidently observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include the effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that have already been identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total source-frame mass M > 70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz emitted gravitational-wave frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place a conservative upper limit for the merger rate density of high-mass binaries with eccentricities 0 < e ≤ 0.3 at 16.9 Gpc−3 yr−1 at the 90% confidence level

All-sky search for gravitational wave emission from scalar boson clouds around spinning black holes in LIGO O3 data

This paper describes the first all-sky search for long-duration, quasimonochromatic gravitational-wave signals emitted by ultralight scalar boson clouds around spinning black holes using data from the third observing run of Advanced LIGO. We analyze the frequency range from 20 to 610 Hz, over a small frequency derivative range around zero, and use multiple frequency resolutions to be robust towards possible signal frequency wanderings. Outliers from this search are followed up using two different methods, one more suitable for nearly monochromatic signals, and the other more robust towards frequency fluctuations. We do not find any evidence for such signals and set upper limits on the signal strain amplitude, the most stringent being ≈10−25 at around 130 Hz. We interpret these upper limits as both an “exclusion region” in the boson mass/black hole mass plane and the maximum detectable distance for a given boson mass, based on an assumption of the age of the black hole/boson cloud system

All-sky search for gravitational wave emission from scalar boson clouds around spinning black holes in LIGO O3 data

This paper describes the first all-sky search for long-duration, quasimonochromatic gravitational-wave signals emitted by ultralight scalar boson clouds around spinning black holes using data from the third observing run of Advanced LIGO. We analyze the frequency range from 20 to 610 Hz, over a small frequency derivative range around zero, and use multiple frequency resolutions to be robust towards possible signal frequency wanderings. Outliers from this search are followed up using two different methods, one more suitable for nearly monochromatic signals, and the other more robust towards frequency fluctuations. We do not find any evidence for such signals and set upper limits on the signal strain amplitude, the most stringent being ≈10^−25 at around 130 Hz. We interpret these upper limits as both an “exclusion region” in the boson mass/black hole mass plane and the maximum detectable distance for a given boson mass, based on an assumption of the age of the black hole/boson cloud system

Search for continuous gravitational wave emission from the Milky Way center in O3 LIGO-Virgo data

We present a directed search for continuous gravitational wave (CW) signals emitted by spinning neutron stars located in the inner parsecs of the Galactic Center (GC). Compelling evidence for the presence of a numerous population of neutron stars has been reported in the literature, turning this region into a very interesting place to look for CWs. In this search, data from the full O3 LIGO-Virgo run in the detector frequency band [10,2000] Hz have been used. No significant detection was found and 95% confidence level upper limits on the signal strain amplitude were computed, over the full search band, with the deepest limit of about 7.6×10−26 at ≃ 142 Hz. These results are significantly more constraining than those reported in previous searches. We use these limits to put constraints on the fiducial neutron star ellipticity and r-mode amplitude. These limits can be also translated into constraints in the black hole mass–boson mass plane for a hypothetical population of boson clouds around spinning black holes located in the GC

Search for Gravitational-lensing Signatures in the Full Third Observing Run of the LIGO–Virgo Network

Gravitational lensing by massive objects along the line of sight to the source causes distortions to gravitational wave (GW) signals; such distortions may reveal information about fundamental physics, cosmology, and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO-Virgo network. We search for repeated signals from strong lensing by (1) performing targeted searches for subthreshold signals, (2) calculating the degree of overlap among the intrinsic parameters and sky location of pairs of signals, (3) comparing the similarities of the spectrograms among pairs of signals, and (4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by (1) frequency-independent phase shifts in strongly lensed images, and (2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the nondetection of GW lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects