MAXI J0556-332: An unique laboratory for testing formation/evolution of X-ray binaries and GR in the strong-field limit
Abstract
I will discuss recent multi-wavelength observations of the newly discovered X-ray binary system MAXI J0556-332. The source offers a rare opportunity to study its soft-X-ray spectrum in detail, thanks to the extremely low extinction in the direction of the source. High-resolution X-ray gratings spectra obtained with XMM-Newton have revealed a strong, narrow emission line at 0.5 keV (24.8 angstrom) in this source. The measured line center is consistent with the Ly-α transition of N VII in the rest frame. However the XMM spectra do not show any other prominent narrow line, making the identification of the 0.5 keV line difficult. If the line is due to N VII, this would require a very unusual donor star with an extremely high N/O abundance (>57) relative to solar, and would thus constrain binary formation/evolution models. Another intriguing, albeit less-likely possibility, assuming solar-abundance plasma, is that the observed emission line is a gravitationally redshifted O VIII Ly-α line originating from the neutron star's surface. I will also discuss results obtained from ground-based optical spectroscopy, and summarize the recent progress in understanding this unique source.
- Publication:
-
39th COSPAR Scientific Assembly
- Pub Date:
- July 2012
- Bibcode:
- 2012cosp...39.1149M