A Peculiar Cyclotron Line near 16 keV Detected in the 2015 Outburst of 4U 0115+63?
Abstract
In 2015 October, the Be/X-ray binary 4U 0115+63 underwent a type II outburst, reaching an X-ray luminosity of ∼1038 erg s-1. During the outburst, Nuclear Spectroscopic Telescope Array (NuSTAR) performed two Target of Opportunity observations. Using the broadband spectra from NuSTAR (3-79 keV), we have detected multiple cyclotron lines of the source, i.e., ∼12, 16, 22, and 33/35 keV. Obviously, the 16 keV line is not a harmonic component of the 12 keV line. As described by the phase-dependent equivalent widths of these cyclotron lines, the 16 keV and 12 keV lines are two different fundamental lines. In our work, we apply the two-poles cyclotron line model to the observation, i.e., the two line sets are formed at the same altitude (∼0.2 km over the NS surface) of different magnetic poles, with ∼1.1 × 1012 and 1.4 × 1012 G in two poles, respectively.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2020
- DOI:
- 10.3847/1538-4357/aba4a5
- arXiv:
- arXiv:1911.12025
- Bibcode:
- 2020ApJ...900...41L
- Keywords:
-
- Accretion;
- Neutron stars;
- High mass x-ray binary stars;
- Binary pulsars;
- 14;
- 1108;
- 733;
- 153;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 22 pages, 7 figures, in a newest revised version, accepted by ApJ