Kavli Affiliate: Tadayuki Takahashi
| First 5 Authors: Aya Bamba, Kazumi Kashiyama, Shota Kisaka, Yukikatsu Terada, Tadayuki Takahashi
| Summary:
Strongly magnetized, rapidly rotating massive white dwarfs (WDs) emerge as
potential outcomes of double degenerate mergers. These WDs can act as sources
of non-thermal emission and cosmic rays, gethering attention as WD pulsars. In
this context, we studied the X-ray emissions from ZTF J190132.9+145808.7
(hereafter ZTF J1901+14), a notable massive isolated WD in the Galaxy, using
the Chandra X-ray observatory. Our results showed 3.5sigma level evidence of
X-ray signals, although it is marginal. Under the assumption of a photon index
of 2, we derived its intrinsic flux to be 2.3 (0.9–4.7) $times
10^{-15}$~erg~cm$^{-2}$s$^{-1}$ and luminosity 4.6 (2.0–9.5) $times
10^{26}$~erg~s$^{-1}$ for a 0.5–7 keV band in the 90% confidence range, given
its distance of 41 pc. We derived an X-ray efficiency (eta) concerning the
spin-down luminosity to be 0.012 (0.0022–0.074), a value comparable to that of
ordnary neutron star pulsars. The inferred X-ray luminosity may be compatible
with curvature radiation from sub-TeV electrons accelerated within open
magnetic fields in the magnetosphere of ZTF J1901+14. Conducting more extensive
X-ray observations is crucial to confirm whether ZTF J1901+14-like isolated WDs
are also significant sources of X-rays and sub-TeV electron cosmic rays,
similar to other WD pulsars in accreting systems.
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