QPO emission from moving hot spots on the surface of neutron stars: a model

Tiziana Di Salvo, Luciano Burderi, Marina M. Romanova, Akshay Kulkarni, Matteo Bachetti

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

We present recent results of 3D magnetohydrodynamic simulations of neutron stars with small misalignment angles, as regards the features in light curves produced by regular movements of the hot spots during accretion on to the star. In particular, we show that the variation of position of the hot spot created by the infalling matter, as observed in 3D simulations, can produce high-frequency quasi-periodic oscillations (QPOs) with frequencies associated with the inner zone of the disc. Previously reported simulations show that the usual assumption of a fixed hot spot near the polar region is valid only for misalignment angles Θ relatively large. Otherwise, two phenomena challenge the assumption: one is the presence of Rayleigh-Taylor instabilities at the disc-magnetospheric boundary, which produce tongues of accreting matter that can reach the star almost anywhere between the equator and the polar region; the other one is the motion of the hot spot around the magnetic pole during stable accretion. In this paper, we start by showing that both phenomena are capable of producing short-term oscillations in the light curves. We then use Monte Carlo techniques to produce model light curves based on the features of the movements observed, and we show that the main features of kHz QPOs can be reproduced. Finally, we show the behaviour of the frequencies of the moving spots as the mass accretion rate changes, and propose a mechanism for the production of double QPO peaks.
Original languageEnglish
Pages (from-to)1193-1205
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume430
Publication statusPublished - 2010

Fingerprint

neutron stars
hot spot
oscillation
light curve
oscillations
accretion
polar region
misalignment
polar regions
simulation
stars
magnetic poles
magnetohydrodynamic simulation
tongue
Taylor instability
equators
magnetohydrodynamics

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

QPO emission from moving hot spots on the surface of neutron stars: a model. / Di Salvo, Tiziana; Burderi, Luciano; Romanova, Marina M.; Kulkarni, Akshay; Bachetti, Matteo.

In: Monthly Notices of the Royal Astronomical Society, Vol. 430, 2010, p. 1193-1205.

Research output: Contribution to journalArticle

Di Salvo, T, Burderi, L, Romanova, MM, Kulkarni, A & Bachetti, M 2010, 'QPO emission from moving hot spots on the surface of neutron stars: a model', Monthly Notices of the Royal Astronomical Society, vol. 430, pp. 1193-1205.
Di Salvo, Tiziana ; Burderi, Luciano ; Romanova, Marina M. ; Kulkarni, Akshay ; Bachetti, Matteo. / QPO emission from moving hot spots on the surface of neutron stars: a model. In: Monthly Notices of the Royal Astronomical Society. 2010 ; Vol. 430. pp. 1193-1205.
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T1 - QPO emission from moving hot spots on the surface of neutron stars: a model

AU - Di Salvo, Tiziana

AU - Burderi, Luciano

AU - Romanova, Marina M.

AU - Kulkarni, Akshay

AU - Bachetti, Matteo

PY - 2010

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N2 - We present recent results of 3D magnetohydrodynamic simulations of neutron stars with small misalignment angles, as regards the features in light curves produced by regular movements of the hot spots during accretion on to the star. In particular, we show that the variation of position of the hot spot created by the infalling matter, as observed in 3D simulations, can produce high-frequency quasi-periodic oscillations (QPOs) with frequencies associated with the inner zone of the disc. Previously reported simulations show that the usual assumption of a fixed hot spot near the polar region is valid only for misalignment angles Θ relatively large. Otherwise, two phenomena challenge the assumption: one is the presence of Rayleigh-Taylor instabilities at the disc-magnetospheric boundary, which produce tongues of accreting matter that can reach the star almost anywhere between the equator and the polar region; the other one is the motion of the hot spot around the magnetic pole during stable accretion. In this paper, we start by showing that both phenomena are capable of producing short-term oscillations in the light curves. We then use Monte Carlo techniques to produce model light curves based on the features of the movements observed, and we show that the main features of kHz QPOs can be reproduced. Finally, we show the behaviour of the frequencies of the moving spots as the mass accretion rate changes, and propose a mechanism for the production of double QPO peaks.

AB - We present recent results of 3D magnetohydrodynamic simulations of neutron stars with small misalignment angles, as regards the features in light curves produced by regular movements of the hot spots during accretion on to the star. In particular, we show that the variation of position of the hot spot created by the infalling matter, as observed in 3D simulations, can produce high-frequency quasi-periodic oscillations (QPOs) with frequencies associated with the inner zone of the disc. Previously reported simulations show that the usual assumption of a fixed hot spot near the polar region is valid only for misalignment angles Θ relatively large. Otherwise, two phenomena challenge the assumption: one is the presence of Rayleigh-Taylor instabilities at the disc-magnetospheric boundary, which produce tongues of accreting matter that can reach the star almost anywhere between the equator and the polar region; the other one is the motion of the hot spot around the magnetic pole during stable accretion. In this paper, we start by showing that both phenomena are capable of producing short-term oscillations in the light curves. We then use Monte Carlo techniques to produce model light curves based on the features of the movements observed, and we show that the main features of kHz QPOs can be reproduced. Finally, we show the behaviour of the frequencies of the moving spots as the mass accretion rate changes, and propose a mechanism for the production of double QPO peaks.

KW - accretion, accretion discs, instabilities, MHD, stars: magnetic fields, stars: neutron, stars: oscillations

UR - http://hdl.handle.net/10447/50588

UR - http://adsabs.harvard.edu/doi/10.1111/j.1365-2966.2010.16203.x

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