23 research outputs found
Uniting the Quiescent Emission and Burst Spectra of Magnetar Candidates
Spectral studies of quiescent emission and bursts of magnetar candidates
using XMM-Newton, Chandra and Swift data are presented. Spectra of both the
quiescent emission and the bursts for most magnetar candidates are reproduced
by a photoelectrically absorbed two blackbody function (2BB). There is a strong
correlation between lower and higher temperatures of 2BB (kT_LT and kT_HT) for
the magnetar candidates of which the spectra are well reproduced by 2BB. In
addition, a square of radius for kT_T (R_LT^2) is well correlated with a square
of radius for kT_HT (R_HT^2). A ratio kT_LT/kT_HT ~ 0.4 is nearly constant
irrespective of objects and/or emission types (i.e., the quiescent emission and
the bursts). This would imply a common emission mechanism among the magnetar
candidates. The relation between the quiescent emission and the bursts might be
analogous to a relation between microflares and solar flares of the sun. Three
AXPs (4U 0142+614, 1RXS J170849.0-400910 and 1E 2259+586) seem to have an
excess above ~7 keV which well agrees with a non-thermal hard component
discovered by INTEGRAL.Comment: 17 pages, 5 figures, 12 tables, Accepted for publication in PAS
Pulse Profile Change Possibly Associated with a Glitch in an Anomalous X-Ray Pulsar 4U 0142+61
We report a glitch-like pulse frequency deviation from the simple spin-down
law in an anomalous X-ray pulsar (AXP) 4U 0142+61 detected by ASCA
observations. We also found a significant pulse profile change after the
putative glitch. The glitch parameters resemble those found in another AXP 1RXS
J170849.0400910, in the Vela pulsar, and in other radio pulsars. This
suggests that the radio pulsars and AXPs have the same internal structure and
glitch mechanism. It must be noted, however, that the pulse frequency anomaly
can also be explained by a gradual change of the spin-down rate ()
without invoking a glitch.Comment: 14 pages, 4 figures, accepted by Ap
Giant flare of SGR 1806-20 from a relativistic jet
Japanese magnetospheric explorer GEOTAIL recorded a detailed light curve
during the initial 600 msec of a giant flare from SGR 1806-20 on December 27,
2004. We show that the observed light curve is well explained by an emission
from relativistically expanding fireballs, like those of gamma-ray bursts
(GRBs). Especially, the observed rapid fading after 500msec suggests that
ejecta is collimated in a jet. We derive an upper limit on the jet opening
half-angle of 0.2 radian that is as narrow as those of GRBs.Comment: 4 pages, 2 figures, accepted by Publications of the Astronomical
Society of Japan (PASJ
Soft and Hard X-Ray Emissions from the Anomalous X-ray Pulsar 4U 0142+61 Observed with Suzaku
The anomalous X-ray pulsar 4U 0142+61 was observed with Suzaku on 2007 August
15 for a net exposure of -100 ks, and was detected in a 0.4 to ~70 keV energy
band. The intrinsic pulse period was determined as 8.68878 \pm 0.00005 s, in
agreement with an extrapolation from previous measurements. The broadband
Suzaku spectra enabled a first simultaneous and accurate measurement of the
soft and hard components of this object by a single satellite. The former can
be reproduced by two blackbodies, or slightly better by a resonant cyclotron
scattering model. The hard component can be approximated by a power-law of
photon index \Gamma h ~0.9 when the soft component is represented by the
resonant cyclotron scattering model, and its high-energy cutoff is constrained
as >180 keV. Assuming an isotropic emission at a distance of 3.6 kpc, the
unabsorbed 1-10 keV and 10-70 keV luminosities of the soft and hard components
are calculated as 2.8e+35 erg s^{-1} and 6.8e+34 erg s^{-1}, respectively.
Their sum becomes ~10^3 times as large as the estimated spin-down luminosity.
On a time scale of 30 ks, the hard component exhibited evidence of variations
either in its normalization or pulse shape.Comment: 24 pages, 8 figures, accepted for publication in Publications of the
Astronomical Society of Japa
Search for Near-Infrared Pulsation of the Anomalous X-ray Pulsar 4U 0142+61
We have searched for pulsation of the anomalous X-ray pulsar (AXP) 4U 0142+61
in the K' band ( m) using the fast-readout mode
of IRCS at the Subaru 8.2-m telescope. We found no significant signal at the
pulse frequency expected by the precise ephemeris obtained by the X-ray
monitoring observation with RXTE. Nonetheless, we obtained a best upper limit
of 17% (90% C.L.) for the root-mean-square pulse fraction in the K' band.
Combined with i' band pulsation (Dhillon et al. 2005), the slope of the pulsed
component () was constrained to (90%
C.L.) for an interstellar extinction of .Comment: 11 pages, 3 figures, Accepted for publication in PAS
Suzaku Observation of the Anomalous X-ray Pulsar 1E 1841-045
We report the results of a Suzaku observation of the anomalous X-ray pulsar
(AXP) 1E 1841-045 at a center of the supernova remnant Kes 73. We confirmed
that the energy-dependent spectral models obtained by the previous separate
observations were also satisfied over a wide energy range from 0.4 to ~70 keV,
simultaneously. Here, the models below ~10 keV were a combination of blackbody
(BB) and power-law (PL) functions or of two BBs wit h different temperatures at
0.6 - 7.0 keV (Morii et al. 2003), and that above ~20 keV was a PL function
(Kuiper Hermsen Mendez 2004). The combination BB + PL + PL was found to best
represent the phase-averaged spectrum. Phase-resolved spectroscopy indicated
the existence of two emission regions, one with a thermal and the other with a
non-thermal nature. The combination BB + BB + PL was also found to represent
the phase-averaged spectrum well. However, we found that this model is
physically unacceptable due to an excessively large area of the emission region
of the blackbody. Nonetheless, we found that the temperatures and radii of the
two blackbody components showed moderate correlations in the phase-resolved
spectra. The fact that the same correlations have been observed between the
phase-averaged spectra of various magnetars (Nakagawa et al. 2009) suggests
that a self-similar function can approximate the intrinsic energy spectra of
magnetars below ~10 keV.Comment: Accepted for publication in the PAS