26 research outputs found
Microlensing in phase space II: Correlations analysis
Applications of the phase space approach to the calculation of the
microlensing autocorrelation function are presented. The continuous propagation
equation for a random star field with a Gaussian velocity distribution is
solved in the leading non-trivial approximation using the perturbation
technique. It is shown that microlensing modulations can be important in the
interpretation of optical and shorter-wavelength light curves of pulsars, power
spectra of active galactic nuclei and coherence estimates for quasi-periodic
oscillations of dwarf novae and low-mass X-ray binaries. Extra scatter in the
brightness of type Ia supernovae due to gravitational microlensing is shown to
be of order up to 0.2 stellar magnitudes depending on the extent of the light
curves.Comment: Accepted for publication in MNRAS. 17 pages, 8 figures. The first
part of this little series is available at
http://www.arxiv.org/abs/astro-ph/0604302 . Replaced to add a link to the
first par
Microlensing in phase space I: Continuous propagation of variability moments
A method to calculate the statistical properties of microlensing light curves
is developed. The approach follows works by Deguchi & Watson, Seitz & Schneider
and Neindorf, attempting to clarify the ideas involved and techniques used in
the calculations. The method is then modified to include scattering by multiple
lensing planes along the line of sight and transition to a continuous limit of
this treatment for average quantities is performed leading to a Fokker-Planck
type equation. The equation is solved for a particular model of the random star
field and microlensing effect on the flux temporal variability is extracted.
Applications in astrophysically relevant situations are discussed.Comment: Accepted for publication in MNRAS. 15 pages, 4 figures. The second
part of this little series is available at
http://www.arxiv.org/abs/astro-ph/060419
Constraints on the massive graviton dark matter from pulsar timing and precision astrometry
The effect of a narrow-band isotropic stochastic GW background on pulsar
timing and astrometric measurements is studied. Such a background appears in
some theories of gravity. We show that the existing millisecond pulsar timing
accuracy () strongly constrains possible observational
consequences of theory of massive gravity with spontaneous Lorentz braking
\cite{dtt:2005}, essentially ruling out significant contribution of massive
gravitons to the local dark halo density. The present-day accuracy of
astrometrical measurements () sets less stringent
constraints on this theory.Comment: 4 pages, 1 figure; changes in content, references added, accepted for
publication in PR
Optical study of PKS B1322-110, the intra-hour variable radio source
Observations with the Australia Telescope Compact Array revealed intra-hour variations in the radio source PKS B1322-110 (Bignall et al. 2019). As part of an optical follow-up, we obtained Gemini Hα and Hα continuum (HαC) images of the PKS B1322-110 field. A robust 19 σ detection of PKS B1322- 110 in the Hα−HαC image prompted us to obtain the first optical spectrum of PKS B1322-110. With the Gemini spectrum we determine that PKS B1322-110 is a flat-spectrum radio quasar at a redshift of z = 3.007 ± 0.002. The apparent flux detected in the Hα filter is likely to originate from He ii emission redshifted precisely on the Galactic Hα narrow-band filter. We set upper limits on the emission measure of the Galactic plasma, for various possible cloud geometries
Measuring transverse velocities in gravitationally lensed extragalactic systems using an annual parallax effect
A parallax method to determine transverse velocity in a gravitationally
lensed system is described. Using the annual motion of the Earth around the Sun
allows us to probe the local structure of the magnification map that, under
certain assumptions, can be used to infer the effective transverse velocity.
The method is applied to OGLE data for QSO2237+0305 and the velocity value is
estimated to be about (15 +/- 10) km/s if attributed to the lensing galaxy or
about (420 +/- 300) km/s if attributed to the quasar. We find this estimate
unreasonably small and conclude that we have not measured a parallax effect. We
give a short list of properties that a system should possess to allow a
successful implementation of this method.Comment: v2: journal reference update
Optical study of PKS B1322-110, the intra-hour variable radio source
Observations with the Australia Telescope Compact Array revealed intra-hour
variations in the radio source PKS B1322-110 (Bignall et al. 2019). As part of
an optical follow-up, we obtained Gemini Halpha and Halpha continuum (HalphaC)
images of the PKS B1322-110 field. A robust 19-sigma detection of PKS B1322-110
in the Halpha-HalphaC image prompted us to obtain the first optical spectrum of
PKS B1322-110. With the Gemini spectrum we determine that PKS B1322-110 is a
flat-spectrum radio quasar at a redshift of z=3.007 +/- 0.002. The apparent
flux detected in the Halpha filter is likely to originate from HeII emission
redshifted precisely on the Galactic Halpha narrow-band filter. We set upper
limits on the emission measure of the Galactic plasma, for various possible
cloud geometries