arXiv subjects

Dipanjan Mukherjee

Publications and source records attributed to Dipanjan Mukherjee.

58 records · Page 4Linked to original sources

arXiv2013

MHD instabilities in accretion mounds - II. 3D simulations

We investigate the onset of pressure driven toroidal mode instabilities in accretion mounds on neutron stars by 3D MHD simulations using the PLUTO MHD code. Our results confirm that for mounds beyond a threshold mass, instabilities form finger like channels at the periphery, resulting in mass loss from the magnetically confined mound. Ring like mounds with hollow interior show the instabilities at the inner edge as well. We perform the simulations for mounds of different sizes to investigate the effect of the mound mass on the growth rate of the instabilities. We also investigate the effect of such instabilities on observables such as cyclotron resonant scattering features and timing properties of such systems.

astro-ph.HE↗

arXiv2013

MHD instabilities in accretion mounds on neutron star binaries

We have numerically solved the Grad-Shafranov equation for axisymmetric static MHD equilibria of matter confined at the polar cap of neutron stars. From the equilibrium solutions we explore the stability of the accretion mounds using the PLUTO MHD code. We find that pressure driven modes disrupt the equilibria beyond a threshold mound mass, forming dynamic structures, as matter spreads over the neutron star surface. Our results show that local variation of magnetic field will significantly affect the shape and nature of the cyclotron features observed in the spectra of High Mass X-ray Binaries.

astro-ph.HE↗

arXiv2013

MHD instabilities in accretion mounds - 1: 2D axisymmetric simulations

We have performed stability analysis of axisymmetric accretion mounds on neutron stars in High Mass X-ray Binaries (HMXB) by 2-D MHD simulations with the PLUTO MHD code. We find that the mounds are stable with respect to interchange instabilities, but addition of excess mass destabilizes the equilibria. Our simulations confirm that accretion mounds are unstable with respect to MHD instabilities beyond a threshold mass. We investigate both filled and hollow mounds and the for the latter also compute the expected profile of cyclotron resonance scattering features (CRSF). In comparison to CRSF from filled mounds reported in our earlier work, hollow mounds display wider and more complex line profiles.

astro-ph.HE↗

arXiv2012

Phase dependent view of Cyclotron lines from model accretion mounds on Neutron Stars

In this paper we make a phase dependent study of the effect of the distortion of local magnetic field due to confinement of accreted matter in X-ray pulsars on the cyclotron spectra emitted from the hotspot . We have numerically solved the Grad-Shafranov equation for axisymmetric static MHD equilibria of matter confined at the polar cap of neutron stars. From our solution we model the cyclotron spectra that will be emitted from the region, using a simple prescription and integrating over the entire mound. Radiative transfer through the accretion column overlying the mound may significantly modify the spectra in comparison to those presented here. However we ignore this in the present paper in order to expose the effects directly attributable to the mound itself. We perform a spin phase dependent analysis of the spectra to study the effect of the viewing geometry.

astro-ph.HE↗