Gravitational Waves from Accreting Neutron Stars
Contact V.Re
As members of the LIGO scientific collaboration (LSC), we are engaged in the search for continuous gravitational waves from resolved sources. The main target of our search in this field is Scorpius-X1, a Neutron star in binary system, accreting matter from its low mass red Giant companion. There are at present two theories explaining the origins of gravitational wave emission for these systems:
-Gravitational waves are generated after the breaking of symmetry driven by the accretion of matter on the neutron star leading to structural assymetries in the neutron star crust (the formation of "mountains" on the surface). A quadrupole mass moment is generated and gravitational waves are emmitted.
-The other possible scenario for the emission of gravitational waves is the presence of r-modes (Rossby waves) in the inner fluid core of the Neutron Star. R-modes are driven by the Coriolis force and are excited by the emission of their own gravitational waves, through a mechanism regulated by the Chandrasekhar-Friedmann-Schutz instability.
The main physical procedure used in the analysis of gravitational waves from sources in binary systems, is the demodulation of the Doppler modulated signal recieved at the gravitational wave detectors on earth. Effects due to the motion of the detector, in its epicyclic motion within the solar system, and the orbital motion of the source within its binary system need to be removed. Moreover, as the source is accreting matter from its companion, it is intrinsically non-monochromatic: in fact, the accretion can spin the Neutron Star up and down over time.
The plan for the immediate future is to extend our search to other Low Mass X-Ray Binaries (LMXB) and in particular to some interesting millisecond Pulsars , like Sax-J 1808. Even though these sources are fainter than Sco-X1, many of them present the advantage of having well known ephemerides. This gives us the chance to reduce considerably the parameter space for the search and to increase the integration time.
Selected Publications
Sanjeev V. Dhurander, Alberto Vecchio, Searching for continuous gravitational waves sources from binary systems, PRD 63, 122001
Piotr Jaranowski, Andrzej Krolak, Bernard F. Schutz, Data analysis of gravitational-wave signals from spinning neutron stars: The signal and its detection, PRD 58, 063001
Patrick R Brady, Teviet Creighton, Curt Cutler, Bernard F. Schutz, Searching for periodic sources with ligo, PRD 57, 1998
D. Steeghs, J. Cesares, The mass donor of Scorpius X-1 revealed, ApJ 568:273-278, 2002
Greg Ushomirsky, Curt Cutler, Lars Bildsten, Deformations of accreting neutron star crusts and gravitational wave emmision, Mon. Not. R. Astron. Soc, 319, 902-932, 2002
External Links
LIGO scientific collaboration
LAL software archive
LIGO pulsar upperlimit working group
Official LSC publications
