81 research outputs found
Detecting massive gravitons using pulsar timing arrays
At the limit of weak static fields, general relativity becomes Newtonian gravity with a potential field that falls off as inverse distance rather than a theory of Yukawa-type fields with a finite range. General relativity also predicts that the speed of disturbances of its waves is c, the vacuum light speed, and is non-dispersive. For these reasons, the graviton, the boson for general relativity, can be considered to be massless. Massive gravitons, however, are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero-mass graviton of general relativity, but further tests will be valuable. A basis for new tests may be the high sensitivity gravitational wave (GW) experiments that are now being performed and the higher sensitivity experiments that are being planned. In these experiments, it should be feasible to detect low levels of dispersion due to non-zero graviton mass. One of the most promising techniques for such a detection may be the pulsar timing program that is sensitive to nano-Hertz GWs. Here, we present some details of such a detection scheme. The pulsar timing response to a GW background with the massive graviton is calculated, and the algorithm to detect the massive graviton is presented. We conclude that, with 90% probability, massless gravitons can be distinguished from gravitons heavier than 3 × 10-22 eV (Compton wavelength λg = 4.1 × 1012 km), if bi-weekly observation of 60 pulsars is performed for 5 years with a pulsar rms timing accuracy of 100 ns. If 60 pulsars are observed for 10 years with the same accuracy, the detectible graviton mass is reduced to 5 × 10-23 eV (λg = 2.5 × 1013 km); for 5 year observations of 100 or 300 pulsars, the sensitivity is respectively 2.5 × 10-22 (λg = 5.0 × 1012 km) and 10-22 eV (λg = 1.2 × 1013 km). Finally, a 10 year observation of 300 pulsars with 100 ns timing accuracy would probe graviton masses down to 3 × 10-23 eV (λ g = 4.1 × 1013 km). © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A
No bursts detected from FRB121102 in two 5-hour observing campaigns with the Robert C. Byrd Green Bank Telescope
Here, we report non-detection of radio bursts from Fast Radio Burst FRB
121102 during two 5-hour observation sessions on the Robert C. Byrd 100-m Green
Bank Telescope in West Virginia, USA, on December 11, 2017, and January 12,
2018. In addition, we report non-detection during an abutting 10-hour
observation with the Kunming 40-m telescope in China, which commenced UTC 10:00
January 12, 2018. These are among the longest published contiguous observations
of FRB 121102, and support the notion that FRB 121102 bursts are episodic.
These observations were part of a simultaneous optical and radio monitoring
campaign with the the Caltech HIgh- speed Multi-color CamERA (CHIMERA)
instrument on the Hale 5.1-m telescope.Comment: 1 table, Submitted to RN of AA
Radio pulsar B095008: Radiation in Magnetosphere and Sparks above Surface
The nearby radio pulsar B095008 with full duty cycle is targeted by the
Five-hundred-meter Aperture Spherical radio Telescope (FAST, 110 minutes
allocated), via adopting polarization calibration on two ways of baseline
determination, in order to understand its magnetospheric radiation geometry as
well as the polar cap sparking. % The radiation of the main pulse could not be
informative of magnetic field line planes due to its low linear polarization
() and the position angle jumps, and the polarization position angle in
the pulse longitudes whose linear fractions are larger than is
thus fitted in the classical rotating vector model (RVM). % The best RVM fit
indicates that the inclination angle, , and the impact angle, ,
of this pulsar are and , respectively,
suggesting that the radio emission comes from two poles. % Polar cap sparking
in the vacuum gap model, either the annular gap or the core gap, is therefore
investigated in this RVM geometry, resulting in a high-altitude magnetospheric
emission at heights from to , with
the light cylinder radius. % It is evident that both sparking
points of the main and inter pulses are located mainly away from the magnetic
pole, that is meaningful in the physics of pulsar surface and is even relevant
to pulsar's inner structure.Comment: 13 pages, 9 figures, submitte
Detecting massive gravitons using pulsar timing arrays
Massive gravitons are features of some alternatives to general relativity.
This has motivated experiments and observations that, so far, have been
consistent with the zero mass graviton of general relativity, but further tests
will be valuable. A basis for new tests may be the high sensitivity
gravitational wave experiments that are now being performed, and the higher
sensitivity experiments that are being planned. In these experiments it should
be feasible to detect low levels of dispersion due to nonzero graviton mass.
One of the most promising techniques for such a detection may be the pulsar
timing program that is sensitive to nano-Hertz gravitational waves.
Here we present some details of such a detection scheme. The pulsar timing
response to a gravitational wave background with the massive graviton is
calculated, and the algorithm to detect the massive graviton is presented. We
conclude that, with 90% probability, massles gravitons can be distinguished
from gravitons heavier than eV (Compton wave length
km), if biweekly observation of 60 pulsars
are performed for 5 years with pulsar RMS timing accuracy of 100 ns. If 60
pulsars are observed for 10 years with the same accuracy, the detectable
graviton mass is reduced to eV ( km); for 5-year observations of 100 or 300 pulsars, the sensitivity is
respectively ( km) and
eV ( km). Finally, a 10-year
observation of 300 pulsars with 100 ns timing accuracy would probe graviton
masses down to eV ( km).Comment: 13 pages, 5 figures, Accepted by Ap
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