Broadband Spectrum of the X-ray Binary M33 X-6 from NuSTAR and Swift-XRT Data: An Extragalactic Z-Source?
Abstract
We present the results of our study of the X-ray spectrum for the source X-6 in the nearby galaxy M33 obtained for the first time at energies above 10 keV from the data of the NuSTAR orbital telescope. The archival Swift-XRT data for energy coverage below 3 keV have been used, which has allowed the spectrum of M33 X-6 to be constructed in the wide energy range 0.3-20 keV. The spectrum of the source is well described by the model of an optically and geometrically thick accretion disk with a maximum temperature of 2 keV and an inner radius of 5 cos-1/2 θ km (where > θ is the unknown disk inclination angle with respect to the observer). There is also evidence for the presence of an additional hard component in the spectrum. The X-ray luminosity ofM33 X-6 measured for the first time in the wide energy range 0.3-20 keV is 2 × 1038 erg s-1, with the luminosity in the hard 10-20 keV X-ray band being 10% of the source's total luminosity. The results obtained suggest that X-6 may be a Z-source, i.e., an X-ray binary with subcritical accretion onto a weakly magnetized neutron star.
- Publication:
-
Astronomy Letters
- Pub Date:
- October 2018
- DOI:
- 10.1134/S1063773718100055
- arXiv:
- arXiv:1809.02871
- Bibcode:
- 2018AstL...44..593N
- Keywords:
-
- mass accretion;
- X-ray binaries;
- nearby galaxies;
- galaxy M33;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 15 pages, 7 figures, 7 tables, accepted in Astronomy Letters