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Post Info TOPIC: LMC X-2


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Title: X-ray spectral evolution of the extragalactic Z-source, LMC X-2
Authors: V.K. Agrawal, R. Misra

We present the results obtained by a detailed study of the extragalactic Z source, LMC X-2, using broad band Suzaku data and a large (~750 ksec) data set obtained with the proportional counter array (PCA) onboard RXTE. The PCA data allows for studying the complete spectral evolution along the horizontal, normal and flaring branches of the Z-track. Comparison with previous study show that the details of spectral evolution (like variation of Comptonizing electron temperature), is similar to that of GX 17+2 but unlike that of Cyg X-2 and GX 349+2. This suggests that Z sources are heterogeneous group with perhaps LMC X-2 and GX 17+2 being member of a subclass. However non monotonic evolution of the Compton y-parameter seems to be generic to all sources. The broad band Suzaku data reveals that the additional soft component of the source modelled as a disk blackbody emission is strongly preferred over one where it is taken to be a blackbody spectrum. This component as well as the temperature of seed photons do not vary when source goes into a flaring mode and the entire variation can be ascribed to the Comptonizing cloud. The bolometric unabsorbed luminosity of the source is well constrained to be ~ 2.23 x 10^{38} ergs/sec which if the source is Eddington limited implies a neutron star mass of 1.6 solar masses. We discuss the implications of these results.

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