A deep XMM-Newton look on the thermally emitting isolated neutron star RX J1605.3+3249. (arXiv:1901.08533v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pires_A/0/1/0/all/0/1">Adriana M. Pires</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schwope_A/0/1/0/all/0/1">Axel D. Schwope</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haberl_F/0/1/0/all/0/1">Frank Haberl</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zavlin_V/0/1/0/all/0/1">Vyacheslav E. Zavlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Motch_C/0/1/0/all/0/1">Christian Motch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zane_S/0/1/0/all/0/1">Silvia Zane</a>
Previous XMM-Newton observations of the thermally emitting isolated neutron
star RX J1605.3+3249 provided a candidate for a shallow periodic signal and
evidence of a fast spin down, which suggested a high dipolar magnetic field and
an evolution from a magnetar. We obtained a large programme with XMM-Newton to
confirm its candidate timing solution, understand the energy-dependent
amplitude of the modulation, and investigate the spectral features of the
source. We performed extensive high-resolution and broadband periodicity
searches in the new observations, using the combined photons of the three EPIC
cameras and allowing for moderate changes of pulsed fraction and the optimal
energy range for detection. A deep $4sigma$ upper limit of $1.33(6)%$ for
modulations in the relevant frequency range conservatively rules out the
candidate period previously reported. Blind searches revealed no other periodic
signal above the $1.5%$ level $(3sigma$) in any of the four new observations.
While theoretical models fall short at physically describing the complex energy
distribution of the source, best-fit X-ray spectral parameters are obtained for
a fully or partially ionized neutron star hydrogen atmosphere model with
$B=10^{13}$ G, modified by a broad Gaussian absorption line at $385pm10$ eV.
The deep limits from the timing analysis disfavour equally well-fit double
temperature blackbody models where both the star surface and small hotspots
contribute to the X-ray flux of the source. We identified a low significance
($1sigma$) temporal trend on the parameters of the source in the analysis of
RGS data dating back to 2002, which may be explained by unaccounted calibration
issues and spectral model uncertainties. The new dataset also shows no evidence
of the previously reported narrow absorption feature at $sim570$ eV, whose
possible transient nature disfavours an atmospheric origin.
Previous XMM-Newton observations of the thermally emitting isolated neutron
star RX J1605.3+3249 provided a candidate for a shallow periodic signal and
evidence of a fast spin down, which suggested a high dipolar magnetic field and
an evolution from a magnetar. We obtained a large programme with XMM-Newton to
confirm its candidate timing solution, understand the energy-dependent
amplitude of the modulation, and investigate the spectral features of the
source. We performed extensive high-resolution and broadband periodicity
searches in the new observations, using the combined photons of the three EPIC
cameras and allowing for moderate changes of pulsed fraction and the optimal
energy range for detection. A deep $4sigma$ upper limit of $1.33(6)%$ for
modulations in the relevant frequency range conservatively rules out the
candidate period previously reported. Blind searches revealed no other periodic
signal above the $1.5%$ level $(3sigma$) in any of the four new observations.
While theoretical models fall short at physically describing the complex energy
distribution of the source, best-fit X-ray spectral parameters are obtained for
a fully or partially ionized neutron star hydrogen atmosphere model with
$B=10^{13}$ G, modified by a broad Gaussian absorption line at $385pm10$ eV.
The deep limits from the timing analysis disfavour equally well-fit double
temperature blackbody models where both the star surface and small hotspots
contribute to the X-ray flux of the source. We identified a low significance
($1sigma$) temporal trend on the parameters of the source in the analysis of
RGS data dating back to 2002, which may be explained by unaccounted calibration
issues and spectral model uncertainties. The new dataset also shows no evidence
of the previously reported narrow absorption feature at $sim570$ eV, whose
possible transient nature disfavours an atmospheric origin.
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