A Caltech Library Service

Broadband Spectrum of the X-ray Binary M33 X-6 from NuSTAR and Swift-XRT Data: An Extragalactic Z-Source?

Nikolaeva, S. M. and Krivonos, R. A. and Sazonov, S. Yu. (2018) Broadband Spectrum of the X-ray Binary M33 X-6 from NuSTAR and Swift-XRT Data: An Extragalactic Z-Source? Astronomy Letters, 44 (10). pp. 593-602. ISSN 1063-7737. doi:10.1134/S1063773718100055.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


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 of M33 X-6 measured for the first time in the wide energy range 0.3–20 keV is ~2 × 10^(38) 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ReadCube access
Krivonos, R. A.0000-0003-2737-5673
Additional Information:© 2018 Pleiades Publishing, Inc. Original Russian Text © S.M. Nikolaeva, R.A. Krivonos, S.Yu. Sazonov, 2018, published in Pis’ma v Astronomicheskii Zhurnal, 2018, Vol. 44, No. 10, pp. 648–658. First Online: 18 October 2018. The results presented in this paper were obtained with the Neil Gehrels (Swift) and NuSTAR orbital observatories. This work was supported by the Russian Science Foundation (project no. 14-12-01315).
Funding AgencyGrant Number
Russian Science Foundation14-12-01315
Subject Keywords:mass accretion, X-ray binaries, nearby galaxies, galaxy M33
Issue or Number:10
Record Number:CaltechAUTHORS:20180912-093210194
Persistent URL:
Official Citation:Nikolaeva, S.M., Krivonos, R.A. & Sazonov, S.Y. Astron. Lett. (2018) 44: 593.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89560
Deposited By: Joy Painter
Deposited On:12 Sep 2018 19:06
Last Modified:16 Nov 2021 00:36

Repository Staff Only: item control page