Kavli Affiliate: Tadayuki Takahashi
| First 5 Authors: Kazuo Makishima, Nagomi Uchida, Hiroki Yoneda, Teruaki Enoto, Tadayuki Takahashi
| Summary:
The present study aims to reinforce the evidence for the ~9 s pulsation in
the gamma-ray binary LS 5039, derived with a Suzaku observation in 2007 and
that with NuSTAR in 2016 (Yoneda et al 2000). Through a reanalysis of the
NuSTAR data incorporating the orbital Doppler correction, the 9.0538 s
pulsation was confirmed successfully even in the 3–10 keV range, where it was
undetectable previously. This was attained by perceiving an energy-dependent
drift in the pulse phase below 10 keV, and correcting the pulse timing of
individual photons for that effect. Similarly, an archival 0.7–12 keV data set
of LS 5039, taken with the ASCA GIS in 1999 October, was analyzed. The data
showed possible periodicity at about 8.882 s, but again the energy-dependent
phase drift was noticed below 10 keV. By correcting for this effect, and for
the orbital Doppler delays in the LS 5039 system, the 2.8–12 keV periodicity
became statistically significant at 8.891+- 0.001 s. The periods measured with
ASCA, Suzaku, and NuSTAR approximately follow an average period derivative of
dP/dt = 3.0 e-10 s/s. These results provide further evidence for the pulsation
in this object, and strengthen the scenario by (Yoneda et al 2000), that the
compact object in LS 5039 is a strongly magnetized neutron star.
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