Context. As the importance of Gravitational Wave (GW) Astrophysics increases rapidly, astronomers in different fields and with different backgrounds can have the need to get a quick idea of which GW source populations can be detected by which detecto
rs and with what measurement uncertainties. Aims. The GW-Toolbox is an easy-to-use, flexible tool to simulate observations on the GW universe with different detectors, including ground-based interferometers (advanced LIGO, advanced VIRGO, KAGRA, Einstein Telescope, and also customised designs), space-borne interferometers (LISA and a customised design), pulsar timing arrays mimicking the current working ones (EPTA, PPTA, NANOGrav, IPTA) and future ones. We include a broad range of sources such as mergers of stellar mass compact objects, namely black holes, neutron stars and black hole-neutron stars; and supermassive black hole binaries mergers and inspirals, Galactic double white dwarfs in ultra-compact orbit, extreme mass ratio inspirals and Stochastic GW backgrounds. Methods. We collect methods to simulate source populations and determine their detectability with the various detectors. The paper aims at giving a comprehensive description on the algorithm and functionality of the GW-Toolbox. Results. The GW-Toolbox produces results that are consistent with more detailed calculations of the different source classes and can be accessed with a website interface (gw-universe.org) or as a python package (https://bitbucket.org/radboudradiolab/gwtoolbox). In the future, it will be upgraded with more functionality.
Multi-messenger astronomy combining Gravitational Wave (GW) and Electromagnetic Wave (EM) observation brings huge impact on physics, astrophysics and cosmology. However, the majority of sources to be detected with currently running ground-based GW ob
servatories are binary black hole (BBH) mergers, which are expected disappointedly to have no EM counterparts. In this letter, we propose that if the BBH merger happens in a gaseous disk around a supermassive black hole, the merger can be accompanied by a transient radio flare alike a fast radio burst (FRB). We argue that the total mass and the effective spin derived from GW detection can be used to distinguish such a source from other channels of BBH mergers. If the prediction is confirmed with future observation, multi-messenger astronomy can be brought to a distance which is one order of magnitude farther than present. The mystery of the origin of FRBs can also be revealed partially.
Among the four black hole binary merger events detected by LIGO, six progenitor black holes have masses greater than 20,$M_odot$. The existence of such massive BHs calls for extreme metal-poor stars as the progenitors. An alternative possibility that
a pair of stellar mass black holes each with mass $sim7,M_odot$ increases to $>20,M_odot$ via accretion from a disk surrounding a super massive black hole in an active galactic nucleus is considered. The growth of mass of the binary and the transfer of orbital angular momentum to the disk accelerates the merger. Based on the recent numerical work of Tang et al. (2017), it is found that, in the disk of a low mass AGN with mass $sim10^6,M_odot$ and Eddington ratio $>0.01$, the mass of an individual BH in the binary can grow to $>20,M_odot$ before coalescence provided that accretion takes place at a rate more than 10 times the Eddington value. The mechanism predicts a new class of gravitational wave sources involving the merger of two extreme Kerr black holes associated with active galactic nuclei and a possible electromagnetic wave counterpart.
PSR B1259-63/LS2883 is a binary system composed of a pulsar and a Be star. The Be star has an equatorial circumstellar disk (CD). The {it Fermi} satellite discovered unexpected gamma-ray flares around 30 days after the last two periastron passages. T
he origin of the flares remain puzzling. In this work, we explore the possibility that, the GeV flares are consequences of inverse Compton-scattering of soft photons by the pulsar wind. The soft photons are from an accretion disk around the pulsar, which is composed by the matter from CD captured by the pulsars gravity at disk-crossing before the periastron. At the other disk-crossing after the periastron, the density of the CD is not high enough so that accretion is prevented by the pulsar wind shock. This model can reproduce the observed SEDs and light curves satisfactorily.
We study the possibility that the long term red timing-noise in pulsars originates from the evolution of the magnetic inclination angle $chi$. The braking torque under consideration is a combination of the dipole radiation and the current loss. We fi
nd that the evolution of $chi$ can give rise to extra cubic and fourth-order polynomial terms in the timing residuals. These two terms are determined by the efficiency of the dipole radiation, the relative electric-current density in the pulsar tube and $chi$. The following observation facts can be explained with this model: a) young pulsars have positive $ddot{ u}$; b) old pulsars can have both positive and negative $ddot{ u}$; c) the absolute values of $ddot{ u}$ are proportional to $-dot{ u}$; d) the absolute values of the braking indices are proportional to the characteristic ages of pulsars. If the evolution of $chi$ is purely due to rotation kinematics, then it can not explain the pulsars with braking index less than 3, and thus the intrinsic change of the magnetic field is needed in this case. Comparing the model with observations, we conclude that the drift direction of $chi$ might oscillate many times during the lifetime of a pulsar. The evolution of $chi$ is not sufficient to explain the rotation behavior of the Crab pulsar, because the observed $chi$ and $dot{chi}$ are inconsistent with the values indicated from the timing residuals using this model.
