arXiv subjects

John Baker

Publications and source records attributed to John Baker.

29 records · Page 2Linked to original sources

arXiv2013

X-ray Transients in the Advanced LIGO/Virgo Horizon

Advanced LIGO and Advanced Virgo will be all-sky monitors for merging compact objects within a few hundred Mpc. Finding the electromagnetic counterparts to these events will require an understanding of the transient sky at low red-shift (z<0.1). We performed a systematic search for extragalactic, low red-shift, transient events in the XMM-Newton Slew Survey. In a flux limited sample, we found that highly-variable objects comprised 10% of the sample, and that of these, 10% were spatially coincident with cataloged optical galaxies. This led to 4x10^-4 transients per square degree above a flux threshold of 3x10^-12 erg cm-2 s-1 [0.2-2 keV] which might be confused with LIGO/Virgo counterparts. This represents the first extragalactic measurement of the soft X-ray transient rate within the Advanced LIGO/Virgo horizon. Our search revealed six objects that were spatially coincident with previously cataloged galaxies, lacked evidence for optical AGNs, displayed high luminosities around 10^43 erg s-1, and varied in flux by more than a factor of ten when compared with the ROSAT All-Sky Survey. At least four of these displayed properties consistent with previously observed tidal disruption events.

astro-ph.HE↗

arXiv2013

The Transient Gravitational-Wave Sky

Interferometric detectors will very soon give us an unprecedented view of the gravitational-wave sky, and in particular of the explosive and transient Universe. Now is the time to challenge our theoretical understanding of short-duration gravitational-wave signatures from cataclysmic events, their connection to more traditional electromagnetic and particle astrophysics, and the data analysis techniques that will make the observations a reality. This paper summarizes the state of the art, future science opportunities, and current challenges in understanding gravitational-wave transients.

gr-qc↗

arXiv2006

Evolving a puncture black hole with fixed mesh refinement

We present an algorithm for treating mesh refinement interfaces in numerical relativity. We detail the behavior of the solution near such interfaces located in the strong field regions of dynamical black hole spacetimes, with particular attention to the convergence properties of the simulations. In our applications of this technique to the evolution of puncture initial data with vanishing shift, we demonstrate that it is possible to simultaneously maintain second order convergence near the puncture and extend the outer boundary beyond 100M, thereby approaching the asymptotically flat region in which boundary condition problems are less difficult and wave extraction is meaningful.

gr-qc↗

arXiv2001

Coulomb Drag between One-Dimensional Wigner Crystal Rings

We consider the Coulomb drag between two metal rings in which the long range Coulomb interaction leads to the formation of a Wigner crystal. The first ring is threaded by an Ahranov Bohm flux creating a persistent current J_0. The second ring is brought in close proximity to the second and due to the Coulomb interaction between the two rings a drag current J_D is produced in the second. We investigate this system at zero temperature for perfect rings as well as the effects of impurities. We show that the Wigner crystal state can in principle lead to a higher ratio of drag current to drive current J_D/J_0 than in weakly interacting electron systems.

cond-mat.str-el↗

arXiv1999

Inspiralling black holes: the close limit

Using several approximations, we calculate an estimate of the gravitational radiation emitted when two equal mass black holes coalesce at the end of their binary inspiral. We find that about 1% of the mass energy of the pair will emerge as gravitational waves during the final ringdown and a negligible fraction of the angular momentum will be radiated.

gr-qc↗

arXiv1999

Effect of disorder on the non-dissipative drag

In this paper we consider the effect of disorder on the non-dissipative Coulomb drag between two mesoscopic metal rings at zero temperature. Ring 1 has an Aharonov-Bohm flux present which creates a persistent current J_0. Ring 2 interacts with ring 1 via the Coulomb potential and a drag current, J_d is produced. We show that this drag current persists with finite disorder in each ring, and that for small disorder, J_d decreases with the square of the disorder amplitude.

cond-mat.mes-hall↗

arXiv1998

The imposition of Cauchy data to the Teukolsky equation III: The rotating case

We solve the problem of expressing the Weyl scalars $ψ$ that describe gravitational perturbations of a Kerr black hole in terms of Cauchy data. To do so we use geometrical identities (like the Gauss-Codazzi relations) as well as Einstein equations. We are able to explicitly express $ψ$ and $\partial _tψ$ as functions only of the extrinsic curvature and the three-metric (and geometrical objects built out of it) of a generic spacelike slice of the spacetime. These results provide the link between initial data and $ψ$ to be evolved by the Teukolsky equation, and can be used to compute the gravitational radiation generated by two orbiting black holes in the close limit approximation. They can also be used to extract waveforms from spacetimes completely generated by numerical methods.

gr-qc↗

arXiv1998

A New Method for Solving the Initial Value Problem with Application to Multiple Black Holes

This work consists of two distinct parts. In the first part we present a new method for solving the initial value problem of general relativity. Given any spatial metric with a surface orthogonal Killing field and two freely specified components of the extrinsic curvature we solve for extrinsic curvature's remaining components. For the second part, after noting that initial data for the Kerr spacetime can be derived within our formalism we construct data for axisymmetric configurations of spinning black holes. Though our method is limited to axisymmetry, it offers an advantage over the Bowen-York proceedure that our data approach those for Kerr holes in the limit of large separations and in the close limit.

gr-qc↗

arXiv1997

A slightly less grand challenge: Colliding Black Holes using perturbation techniques

Perturbation techniques can be used as an alternative to supercomputer calculations in calculating gravitational radiation emitted by colliding black holes, provided the process starts with the black holes close to each other. We give a summary of the method and of the results obtained for various initial configurations, both axisymmetric and without symmetry: Initially static, boosted towards each other, counter-rotating, or boosted at an angle (pseudo-inspiral). Where applicable, we compare the perturbation results with supercomputer calculations.

gr-qc↗

arXiv1997

The two-phase approximation for black hole collisions: Is it robust?

Recently Abrahams and Cook devised a method of estimating the total radiated energy resulting from collisions of distant black holes by applying Newtonian evolution to the holes up to the point where a common apparent horizon forms around the two black holes and subsequently applying Schwarzschild perturbation techniques . Despite the crudeness of their method, their results for the case of head-on collisions were surprisingly accurate. Here we take advantage of the simple radiated energy formula devised in the close-slow approximation for black hole collisions to test how strongly the Abrahams-Cook result depends on the choice of moment when the method of evolution switches over from Newtonian to general relativistic evolution. We find that their result is robust, not depending strongly on this choice.

gr-qc↗

arXiv1996

The collision of boosted black holes

We study the radiation from a collision of black holes with equal and opposite linear momenta. Results are presented from a full numerical relativity treatment and are compared with the results from a ``close-slow'' approximation. The agreement is remarkable, and suggests several insights about the generation of gravitational radiation in black hole collisions.

gr-qc↗