Open AccessComptonization and QPO origins in accreting neutron star systems
Author(s) -
Lee Hyong C.,
Miller Guy S.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01842.x
Subject(s) - physics , astrophysics , neutron star , accretion (finance) , corona (planetary geology) , photon , oscillation (cell signaling) , soft photon , astronomy , electron , nuclear physics , optics , bremsstrahlung , astrobiology , biology , venus , genetics
We develop a simple, time‐dependent Comptonization model to probe the origins of spectral variability in accreting neutron star systems. In the model, soft ‘seed photons’ are injected into a corona of hot electrons, where they are Compton upscattered before escaping as hard X‐rays. The model describes how the hard X‐ray spectrum varies when the properties of either the soft photon source or the Comptonizing medium undergo small oscillations. Observations of the resulting spectral modulations can determine whether the variability is due to (i) oscillations in the injection of seed photons, (ii) oscillations in the coronal electron density, or (iii) oscillations in the coronal energy dissipation rate. Identifying the origin of spectral variability should help clarify how the corona operates and its relation to the accretion disc. It will also help in finding the mechanisms underlying the various quasi‐periodic oscillations (QPOs) observed in the X‐ray outputs of many accreting neutron star and black hole systems. As a sample application of our model, we analyse a kilohertz QPO observed in the atoll source 4U 1608–52. We find that the QPO is driven predominantly by an oscillation in the electron density of the Comptonizing gas.