18221217
A REFINED EPHEMERIS AND PHASE-RESOLVED X-RAY SPECTROSCOPY OF THE GEMINGA PULSAR
We present a refined, phase-connected, postglitch ephemeris for the Geminga pulsar that is a good fit to all the postglitch data from EGRET, ASCA, and XMM-Newton. We also present the results of phase-resolved spectroscopy of two XMM-Newton X-ray observations of the Geminga pulsar obtained in 2002 and 2004. An investigation is made into a previously claimed existence of a small hot spot on the neutron star surface. We conclude that that interpretation was more likely an artifact of an overly restrictive assumption used to fit the phase-resolved spectra: namely, that the spectral index of the nonthermal component is constant. When we allow the spectral index to vary as a function of rotation phase, we find systematic variations in spectral index, and such fits do not require an additional hot blackbody component.
16544780
XMM-Newton, Chandra, and CGPS observations of the Supernova Remnants G85.4+0.7 and G85.9–0.6
We present an XMM-Newton detection of two low radio surface brightness supernova remnants (SNRs), G85.4+0.7 and G85.9–0.6, discovered with the Canadian Galactic Plane Survey (CGPS). High-resolution XMM-Newton images revealing the morphology of the diffuse emission, as well as discrete point sources, are presented and correlated with radio and Chandra images. The new data also permit a spectroscopic analysis of the diffuse emission regions, and a spectroscopic and timing analysis of the point sources. Distances have been determined from H I and CO data to be 3.5 ± 1.0 kpc for SNR G85.4+0.7 and 4.8 ± 1.6 kpc for SNR G85.9–0.6. The SNR G85.4+0.7 is found to have a temperature of ~12-13 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1033D23.5 erg s−1 (where D3.5 is the distance in units of 3.5 kpc), with an electron density ne of ~(0.07–0.16) (fD3.5)−1/2 cm−3 (where f is the volume filling factor) and a shock age of ~(9–49) (fD3.5)1/2 kyr. The SNR G85.9–0.6 is found to have a temperature of ~15-19 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1034D24.8 erg s−1 (where D4.8 is the distance in units of 4.8 kpc), with an electron density ne of ~(0.04–0.10) (fD4.8)−1/2 cm−3 and a shock age of ~(12–42) (fD4.8)1/2 kyr. Based on the data presented here, none of the point sources appears to be the neutron star associated with either SNR.
119245531
Observational evidence of dissipative photospheres in gamma-ray bursts
The emission from a gamma-ray burst (GRB) photosphere can give rise to a variety of spectral shapes. The spectrum can retain the shape of a Planck function or it can be broadened and have the shape ...
14372942
A NEW SPIN ON QUANTUM GRAVITY
We suggest that the (small but nonvanishing) cosmological constant, and the holographic properties of gravitational entropy, may both reflect unconventional quantum spin statistics at a fundamental level. This conjecture is motivated by the nonlocality of quantum gravity and the fact that spin is an inherent property of space–time. As an illustration we consider the "quon" model, which interpolates between Fermi and Bose statistics, and show that this can naturally lead to an arbitrarily small cosmological constant. In addition to laboratory tests, we briefly discuss the possible observable imprint on cosmological fluctuations from inflation.
13946666
A Quantum Mechanical Model of Spherical Supermembranes
We present a quantum mechanical model of spherical supermembranes. Using superfields to represent the cartesian coordinates of the membrane, we are able to exactly determine its supersymmetric vacua. We find there are two classical vacua, one corresponding to an extended membrane and one corresponding to a point-like membrane. For the = 2 case, instanton effects then lift these vacua to massive states. For the = 4 case, there is no instanton tunneling, and the vacua remain massless. Similarities to spherical supermembranes as giant gravitons and in Matrix theory on pp-waves is discussed.
6930144
GRAVITY FROM A MODIFIED COMMUTATOR
We show that a suitably chosen position-momentum commutator can elegantly describe many features of gravity, including the IR/UV correspondence and dimensional reduction ("holography"). Using the most simplistic example based on dimensional analysis of black holes, we construct a commutator which qualitatively exhibits these novel properties of gravity. Dimensional reduction occurs because the quanta size grow quickly with momenta, and thus cannot be "packed together" as densely as naively expected. We conjecture that a more precise form of this commutator should be able to quantitatively reproduce all of these features.
276424
Gravitational Wave Bursts from Cosmic Superstring Reconnections
We compute the gravitational waveform produced by cosmic superstring reconnections. This is done by first constructing the superstring reconnection trajectory, which closely resembles that of classical, instantaneous reconnection but with the singularities smoothed out due to the string path integral. We then evaluate the graviton vertex operator in this background to obtain the burst amplitude. The result is compared to the detection threshold for current and future gravitational wave detectors, finding that neither bursts nor the stochastic background would be detectable by Advanced LIGO. This disappointing but anticipated conclusion holds even for the most optimistic values of the reconnection probability and loop sizes.