On Mass Constraints Implied by the Relativistic Precession Model of Twinpeak Quasiperiodic Oscillations in Circinus X1
Abstract
Boutloukos et al. discovered twinpeak quasiperiodic oscillations (QPOs) in 11 observations of the peculiar Zsource Circinus X1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M _{0} = 2.2 ± 0.3 M _{sun}. We present a more detailed analysis of the estimate which involves the framedragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j = cJ/GM ^{2}. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M ~ M _{0}[1 + 0.55(j + j ^{2})]. It is therefore impossible to estimate the mass without independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M _{sun}. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.
 Publication:

The Astrophysical Journal
 Pub Date:
 May 2010
 DOI:
 10.1088/0004637X/714/1/748
 arXiv:
 arXiv:1008.0088
 Bibcode:
 2010ApJ...714..748T
 Keywords:

 stars: neutron;
 Xrays: binaries;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 10 pages, 9 figures (in colour)