1,638 research outputs found
A ground-based measurement of the relativistic beaming effect in a detached double WD binary
We report on the first ground-based measurement of the relativistic beaming
effect (aka Doppler boosting). We observed the beaming effect in the detached,
non-interacting eclipsing double white dwarf (WD) binary NLTT 11748. Our
observations were motivated by the system's high mass ratio and low luminosity
ratio, leading to a large beaming-induced variability amplitude at the orbital
period of 5.6 hr. We observed the system during 3 nights at the 2.0m Faulkes
Telescope North with the SDSS-g' filter, and fitted the data simultaneously for
the beaming, ellipsoidal and reflection effects. Our fitted relative beaming
amplitude is (3.0 +/- 0.4) x 10^(-3), consistent with the expected amplitude
from a blackbody spectrum given the photometric primary radial velocity
amplitude and effective temperature. This result is a first step in testing the
relation between the photometric beaming amplitude and the spectroscopic radial
velocity amplitude in NLTT 11748 and similar systems. We did not identify any
variability due to the ellipsoidal or reflection effects, consistent with their
expected undetectable amplitude for this system. Low-mass, helium-core WDs are
expected to reside in binary systems where in some of those systems the binary
companion is a faint C/O WD and the two stars are detached and non-interacting,
as in the case of NLTT 11748. The beaming effect can be used to search for the
faint binary companion in those systems using wide-band photometry.Comment: Submitted to ApJL on September 18, 2010. Comments are welcome. v2:
replaced with accepted version, minor correction
Discovery of GeV gamma-ray emission from PSR B1259-63/LS 2883
The binary system PSR B1259-63/LS 2883 consists of a 47.8 ms radio pulsar
that orbits the companion Be star with a period of 3.4 years in a highly
eccentric orbit. The system is well sampled in radio, X-rays, and TeV
gamma-rays, and shows orbital-phase-dependent variability in all observed
frequencies. Here we report on the discovery of >100 MeV gamma-rays from PSR
B1259-63/LS 2883 through the 2010 pariastron passage. Using data collected with
the Large Area Telescope aboard Fermi from 33 days before pariastron to 75 days
after pariastron, PSR B1259-63/LS 2883 is detected at a significance of 13.6
standard deviations. The gamma-ray light curve is highly variable over the
above period, with changing photon index that correlates with gamma-ray flux.
In particular, two major flares that occur after the pariastron passage were
observed. The onset of gamma-ray emission occurs close to, but not at the same
orbital phases as, the two disk passages that occur ~1 month before and ~1
month after the pariastron passage. The fact that the GeV orbital light curve
is different from that of the X-ray and TeV light curves strongly suggests that
GeV gamma-ray emission originates from a different component. We speculate that
the observed GeV flares may be resulting from Doppler boosting effects.Comment: ApJ Letters, in press 7 pages, 4 figures (Fig. 4 added), 1 tabl
Seeing relativity -- I. Ray tracing in a Schwarzschild metric to explore the maximal analytic extension of the metric and making a proper rendering of the stars
We present an implementation of a ray tracing code in the Schwarzschild
metric. We aim at building a numerical code with a correct implementation of
both special (aberration, amplification, Doppler) and general (deflection of
light, lensing, gravitational redshift) relativistic effects so as to simulate
what an observer with arbitrary velocity would see near, or possibly within,
the black hole. We also pay some specific attention to perform a satisfactory
rendering of stars. Using this code, we then show several unexplored features
of the maximal analytical extension of the metric. In particular, we study the
aspect of the second asymptotic region of the metric as seen by an observer
crossing the horizon. We also address several aspects related to the white hole
region (i.e., past singularity) seen both from outside the black hole, inside
the future horizon and inside the past horizon, which gives rise to the most
counter-intuitive effects
Relativistic Effects for Time-Resolved Light Transport
We present a real-time framework which allows interactive visualization of relativistic effects for time-resolved light transport. We leverage data from two different sources: real-world data acquired with an effective exposure time of less than 2 picoseconds, using an ultra-fast imaging technique termed femto-photography, and a transient renderer based on ray-tracing. We explore the effects of time dilation, light aberration, frequency shift and radiance accumulation by modifying existing models of these relativistic effects to take into account the time-resolved nature of light propagation. Unlike previous works, we do not impose limiting constraints in the visualization, allowing the virtual camera to explore freely a reconstructed 3D scene depicting dynamic illumination. Moreover, we consider not only linear motion, but also acceleration and rotation of the camera. We further introduce, for the first time, a pinhole camera model into our relativistic rendering framework, and account for subsequent changes in focal length and field of view as the camera moves through the scene
Opacity, variability and kinematics of AGN jets
Synchrotron self-absorption in active galactic nuclei (AGN) jets manifests
itself as a time delay between flares observed at high and low radio
frequencies. It is also responsible for the observing frequency dependent
change in size and position of the apparent base of the jet, aka the core shift
effect, detected with very long baseline interferometry (VLBI). We measure the
time delays and the core shifts in 11 radio-loud AGN to estimate the speed of
their jets without relying on multi-epoch VLBI kinematics analysis. The 158
GHz total flux density time lags are obtained using Gaussian process
regression, the core shift values are measured using VLBI observations and
adopted from the literature. A strong correlation is found between the apparent
core shift and the observed time delay. Our estimate of the jet speed is higher
than the apparent speed of the fastest VLBI components by the median
coefficient of 1.4. The coefficient ranges for individual sources from 0.5 to
20. We derive Doppler factors, Lorentz factors and viewing angles of the jets,
as well as the corresponding de-projected distance from the jet base to the
core. The results support evidence for acceleration of the jets with bulk
motion Lorentz factor on de-projected scales
of 0.5500 parsecs.Comment: Accepted by MNRAS; 11 pages, 11 figures, 3 table
- …