The LIGO Scientific and Virgo Collaborations have announced the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated ...from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star background will add to the background from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude \(\Omega_{\rm GW} (f=25 \text{Hz}) = 1.8_{-1.3}^{+2.7} \times 10^{-9}\) with \(90\%\) confidence, compared with \(\Omega_{\rm GW} (f=25 \text{Hz}) = 1.1_{-0.7}^{+1.2} \times 10^{-9}\) from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40 months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. ...This source, for the first time, permits tests of strong-field dynamics of compact binaries in presence of matter. In this paper, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. Finally, the polarization content of the gravitational wave signal is studied. The results of all tests performed here show good agreement with GR.
We present the results of the one year long observational campaign of the type II-plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the Whirlpool Galaxy). This extensive dataset ...makes SN 2005cs the best observed low-luminosity, 56Ni-poor type II-plateau event so far and one of the best core-collapse supernovae ever. The optical and near-infrared spectra show narrow P-Cygni lines characteristic of this SN family, which are indicative of a very low expansion velocity (about 1000 km/s) of the ejected material. The optical light curves cover both the plateau phase and the late-time radioactive tail, until about 380 days after core-collapse. Numerous unfiltered observations obtained by amateur astronomers give us the rare opportunity to monitor the fast rise to maximum light, lasting about 2 days. In addition to optical observations, we also present near-infrared light curves that (together with already published UV observations) allow us to construct for the first time a reliable bolometric light curve for an object of this class. Finally, comparing the observed data with those derived from a semi-analytic model, we infer for SN 2005cs a 56Ni mass of about 0.003 solar masses, a total ejected mass of 8-13 solar masses and an explosion energy of about 3 x 10^50 erg.
The primary cause of treatment failures in acute myeloid leukemia (AML) is the emergence of both resistant disease and early relapse. Among the most frequent agents of these phenomena are defects in ...the mitochondrial-mediated apoptotic pathway. This pathway is regulated by bcl-2 family of anti-apoptotic (bcl-2, bcl-xl, mcl-1) and pro-apoptotic proteins (bax, bad, bak). In particular, bcl-2 dimerizes with several members of bcl-2 family of proteins, altering the threshold of cell death. The flow cytometric quantitative measurement of bcl-2 and bax expression for the determination of bax/bcl-2 ratio provided crucial clinical information in AML: in our hands, lower bax/bcl-2 ratio conferred a very poor prognosis with decreased rates of complete remission (CR) and overall survival (OS). Moreover, striking correlations were found between lower bax/bcl-2 ratio and higher progenitor marker expression, such as CD34, CD117 and CD133 antigens, confirming the link between this apoptotic index and the maturation pathways. However, the capacity of bax/bcl-2 ratio to clearly identify patients with different prognosis with regard to CR and OS within the CD34+, CD117+ and CD133+ subgroups implies that other mechanisms, such as proliferation and/or cell cycle dysregulation may be involved to explain its clinical significance. Finally, small molecules that target both the receptor- and mitochondrial-mediated pathway of apoptosis are providing encouraging results in patients with relapsed and/or refractory disease (i.e. CDDOMe, bcl-2 antisense oligonucleotides, CEP-701, etc), confirming the key role of apoptotic mechanisms on the outcome of AML patients.
We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10:11:58.6 UTC by ...the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70,000 years. The inferred component black hole masses are \(31.2^{+8.4}_{-6.0}\,M_\odot\) and \(19.4^{+5.3}_{-5.9}\,M_\odot\) (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, \(\chi_\mathrm{eff} = -0.12^{+0.21}_{-0.30}.\) This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is \(880^{+450}_{-390}~\mathrm{Mpc}\) corresponding to a redshift of \(z = 0.18^{+0.08}_{-0.07}\). We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to \(m_g \le 7.7 \times 10^{-23}~\mathrm{eV}/c^2\). In all cases, we find that GW170104 is consistent with general relativity.
The LIGO detection of GW150914 provides an unprecedented opportunity to study the two-body motion of a compact-object binary in the large velocity, highly nonlinear regime, and to witness the final ...merger of the binary and the excitation of uniquely relativistic modes of the gravitational field. We carry out several investigations to determine whether GW150914 is consistent with a binary black-hole merger in general relativity. We find that the final remnant's mass and spin, as determined from the low-frequency (inspiral) and high-frequency (post-inspiral) phases of the signal, are mutually consistent with the binary black-hole solution in general relativity. Furthermore, the data following the peak of GW150914 are consistent with the least-damped quasi-normal mode inferred from the mass and spin of the remnant black hole. By using waveform models that allow for parameterized general-relativity violations during the inspiral and merger phases, we perform quantitative tests on the gravitational-wave phase in the dynamical regime and we determine the first empirical bounds on several high-order post-Newtonian coefficients. We constrain the graviton Compton wavelength, assuming that gravitons are dispersed in vacuum in the same way as particles with mass, obtaining a \(90\%\)-confidence lower bound of \(10^{13}\) km. In conclusion, within our statistical uncertainties, we find no evidence for violations of general relativity in the genuinely strong-field regime of gravity.
The first observational run of the Advanced LIGO detectors, from September 12, 2015 to January 19, 2016, saw the first detections of gravitational waves from binary black hole mergers. In this paper ...we present full results from a search for binary black hole merger signals with total masses up to \(100 M_\odot\) and detailed implications from our observations of these systems. Our search, based on general-relativistic models of gravitational wave signals from binary black hole systems, unambiguously identified two signals, GW150914 and GW151226, with a significance of greater than \(5\sigma\) over the observing period. It also identified a third possible signal, LVT151012, with substantially lower significance, and with an 87% probability of being of astrophysical origin. We provide detailed estimates of the parameters of the observed systems. Both GW150914 and GW151226 provide an unprecedented opportunity to study the two-body motion of a compact-object binary in the large velocity, highly nonlinear regime. We do not observe any deviations from general relativity, and place improved empirical bounds on several high-order post-Newtonian coefficients. From our observations we infer stellar-mass binary black hole merger rates lying in the range \(9-240 \mathrm{Gpc}^{-3} \mathrm{yr}^{-1}\). These observations are beginning to inform astrophysical predictions of binary black hole formation rates, and indicate that future observing runs of the Advanced detector network will yield many more gravitational wave detections.
We analyze the impact of a proposed tidal instability coupling \(p\)-modes and \(g\)-modes within neutron stars on GW170817. This non-resonant instability transfers energy from the orbit of the ...binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: an overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes Factor (\(\ln B^{pg}_{!pg}\)) comparing our \(p\)-\(g\) model to a standard one. We find that the observed signal is consistent with waveform models that neglect \(p\)-\(g\) effects, with \(\ln B^{pg}_{!pg} = 0.03^{+0.70}_{-0.58}\) (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include \(p\)-\(g\) effects and recovering them with the \(p\)-\(g\) model, we show that there is a \(\simeq 50\%\) probability of obtaining similar \(\ln B^{pg}_{!pg}\) even when \(p\)-\(g\) effects are absent. We find that the \(p\)-\(g\) amplitude for 1.4 \(M_\odot\) neutron stars is constrained to \(\lesssim \text{few}\times10^{-7}\), with maxima a posteriori near \(\sim 10^{-7}\) and \(p\)-\(g\) saturation frequency \(\sim 70\, \mathrm{Hz}\). This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest a \(p\)-\(g\) amplitude \(\lesssim 10^{-6}\) and \(\lesssim 10^{3}\) modes saturating by wave breaking. Thus, the measured constraints only rule out extreme values of the \(p\)-\(g\) parameters. They also imply that the instability dissipates \(\lesssim 10^{51}\, \mathrm{ergs}\) over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves.
