398 research outputs found
Radio-quiet X-ray pulsars in Supernova Remnants and the ``Missing'' Pulsar Problem
The paradigm that young neutron stars (NSs) evolve as rapidly rotating
Crab-like pulsars requires re-examination. Evidence is accumulating that, in
fact, many young NS are slowly rotating (P ~ 10-s) X-ray pulsars, lacking in
detectable radio emission. We present new results on three radio-quiet NS
candidates associated with supernova remnants, which suggests that alternative
evolutionary-paths exist for young pulsars. These include the 12-s pulsator in
Kes 73, the 7-s pulsar near Kes 75, and the enigmatic X-ray source in RCW 103.
We postulate that such objects account for the apparent paucity of radio
pulsars in supernova remnants.Comment: 6 pages, 3 eps figures, LaTex (memsait, epsf). To appear in a special
issue of Memorie della Societa' Astronomica Italiana (Proceedings
X-Ray Emission from the Radio Pulsar PSR J1105-6107
We have detected significant X-ray emission from the direction of the young
radio pulsar PSR J1105-6107 using the ASCA Observatory. The 11 sigma detection
includes 460 background-subtracted source counts derived using data from all
four ASCA detectors. The emission shows no evidence of pulsations; the pulsed
fraction is less than 31%, at the 90% confidence level. The X-ray emission can
be characterized by a power-law spectrum with photon index alpha = 1.8 +/- 0.4,
for a neutral hydrogen column density Nh = 7 X 10E21 cm^-2. The unabsorbed 2 -
10 keV flux assuming the power-law model is (6.4 +/- 0.8) X 10E-13 ergs cm^-2
s^-1. The implied efficiency for conversion of spin-down luminosity to
ASCA-band emission is (1.6 +/- 0.2) X 10E-3, assuming a distance of 7 kpc to
the source. Within the limited statistics, the source is consistent with being
unresolved. We argue that the X-rays are best explained as originating from a
pulsar-powered synchrotron nebula.Comment: 9 pages with 1 eps figure, LaTex (aas2pp2, psfig). To appear in the
Astrophysical Journal Letter
NuSTAR Hard X-ray Observations of the Energetic Millisecond Pulsars PSR B1821-24, PSR B1937+21, and PSR J0218+4232
We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray timing
and spectroscopy of the three exceptionally energetic rotation-powered
millisecond pulsars PSRs B1821-24, B1937+21, and J0218+4232. By correcting the
NuSTAR onboard clock for phase and frequency drifts between observation
intervals, we are able to recover the intrinsic hard X-ray pulse profiles of
all three pulsars with a resolution down to < 15 microsec. The substantial
reduction of background emission relative to previous broadband X-ray
observations allows us to detect for the first time pulsed emission up to ~50
keV, ~20 keV, and ~25 keV, for the three pulsars, respectively. We conduct
phase-resolved spectroscopy in the 0.5-79 keV range for all three objects,
obtaining the best measurements yet of the broad-band spectral shape and
high-energy pulsed emission to date. We find extensions of the same power-law
continua seen at lower energies, with no evidence for a spectral turnover or
break. Extrapolation of the X-ray power-law spectrum to higher energies reveals
that a turnover in the 100 keV to 100 MeV range is required to accommodate the
high-energy gamma-ray emission observed with Fermi-LAT, similar to the spectral
energy distribution observed for the Crab pulsar.Comment: 12 pages, 10 figures, 2 tables; Latex, emulateapj style. To appear in
the Astrophysical Journa
A New View on Young Pulsars in Supernova Remnants: Slow, Radio-quiet, & X-ray Bright
We propose a simple explanation for the apparent dearth of radio pulsars
associated with young supernova remnants (SNRs). Recent X-ray observations of
young remnants have revealed slowly rotating (P ~ 10-s) central pulsars with
pulsed emission above 2 keV, lacking in detectable radio emission. Some of
these objects apparently have enormous magnetic fields, evolving in a manner
distinct from the Crab pulsar. We argue that these X-ray pulsars can account
for a substantial fraction of the long sought after neutron stars in SNRs and
that Crab-like pulsars are perhaps the rarer, but more highly visible example
of these stellar embers. Magnetic field decay likely accounts for their high
X-ray luminosity, which cannot be explained as rotational energy loss, as for
the Crab-like pulsars. We suggest that the natal magnetic field strength of
these objects control their subsequent evolution. There are currently almost a
dozen slow X-ray pulsars associated with young SNRs. Remarkably, these objects,
taken together, represent at least half of the confirmed pulsars in supernova
remnants. This being the case, these pulsars must be the progenitors of a vast
population of previously unrecognized neutron stars.Comment: 4 pages, latex, one figure, to appear in "IAU Colloquium 177: 2000
and Beyond", ASP Conf. Serie
Kes 73: A Young Supernova Remnant with an X-ray Bright, Radio-quiet Central Source
We clarify the nature of the small-diameter supernova remnant (SNR) Kes 73
and its central compact source, 1E 1841-045, using X-ray data acquired with the
ASCA Observatory. We introduce a spatio-spectral decomposition technique
necessary to disentangle the ASCA spectrum of the compact source from the
barely resolved shell-type remnant. The source spectrum (1 - 8 keV) is
characterized by an absorbed power-law with a photon index ~ 3.4 and N_H ~
3.0E22 cm^-2, possibly non-thermal in nature. This bright X-ray source is
likely a slowly spinning pulsar, whose detection is reported in our companion
paper (Vasisht & Gotthelf 1997). The SNR spectrum is characteristic of a
thermal plasma, with kT ~ 0.7 keV, and emission lines typical of a young
remnants. The element Mg and possibly O and Ne are found to be over-abundant,
qualitatively suggesting an origin from a massive progenitor. We find that Kes
73 is a young (~ 2000 yr) type II/Ib SNR containing a neutron star pulsar
spinning anomalously slow for its age. Kes 73 is yet another member of a
growing class of SNRs containing radio-quiet compact sources with a hard
spectral signature.Comment: 14 pages with 9 eps figures, LATEX, aastex, psfig. To appear in the
Astrophysical Journal Letter
Two Magnetar Candidates in HESS Supernova Remnants
We identify two candidate magnetars in archival X-ray observations of HESS
detected shell-type SNRs. X-ray point sources in CTB 37B coincident with HESS
J1713-381 and in G353.6-0.7 coincident with HESS J1731-347 both have AXP-like
spectra, much softer than those of ordinary, rotation powered pulsars, and no
optical/IR counterparts. The spectrum of CXOU J171405.7-381031 in CTB 37B has a
hard excess above 6 keV, which may be similar to such components seen in some
AXPs. A new Chandra observation of this object reveals a highly significant
pulsed signal at P = 3.82 s with pulsed fraction f_p = 0.31. Analysis of an
XMM-Newton observation of the second candidate, XMMU J173203.3-344518 in
G353.6-0.7, yields only marginal evidence for a 1 s period. If it is not a
magnetar, then it could be a weakly magnetized central compact object (CCO).
Considering that these HESS sources previously attributed to the SNR shells are
possibly centrally peaked, we hypothesize that their pulsars may contribute to
diffuse TeV emission. These identifications potentially double the number of
magnetar/SNR associations in the Galaxy, and can be used to investigate the
energetics and asymmetries of the supernovae that give rise to magnetars.Comment: 7 pages, 5 figures, accepted by The Astrophysical Journa
Proper Motion and Timing of Two Unusual Pulsars: Calvera and 1E 1207.4-5209
Using pairs of images from the Chandra High-Resolution Camera we examine the
proper motion of the central compact object (CCO) 1E 1207.4-5209 in the
supernova remnant (SNR) PKS 1209-51/52, and the unusual pulsar Calvera that is
possibly a CCO descendant. For 1E 1207.4-5209, an insignificant proper motion
of 15+/-7 mas/yr is measured, corresponding to a corrected tangential velocity
of <180 km/s at the distance of 2 kpc. This proves that the previously noted
large offset of the pulsar from the apparent geometric center of the SNR is not
due to high proper motion; evidently the symmetry of the remnant does not
indicate its center of expansion. Calvera has a marginally significant proper
motion of 69+/-26 mas/yr, corresponding to 86+/-33 km/s for a hypothetical
distance of 0.3 kpc. Notably, its vector is away from the Galactic plane,
although its high Galactic latitude of b = +37 deg may be more a consequence of
its proximity than its velocity. We also provide updated timing solutions for
each pulsar. Spanning 14.5 yr, the ephemeris of 1E 1207.4-5209 has a small and
steady frequency derivative that, because of the negligible proper motion,
requires no kinematic correction. The derived surface dipole magnetic field
strength of 1E 1207.4-5209 thus remains B_s = 9.8e10 G. Calvera has B_s =
4.4e11 G, intermediate between those of ordinary young pulsars and CCOs,
suggesting that it may be on a trajectory of field growth that could account
for the absence of descendants in the neighborhood of CCOs in the P-Pdot
diagram.Comment: 7 pages, 2 figures, accepted for publication in Ap
The First Glitch in a Central Compact Object Pulsar: 1E 1207.4-5209
Since its discovery as a pulsar in 2000, the central compact object (CCO) 1E
1207.4-5209 in the supernova remnant PKS 1209-51/52 had been a stable 0.424 s
rotator with an extremely small spin-down rate and weak (Bs ~ 9E10 G) surface
dipole magnetic field. In 2016 we observed a glitch from 1E 1207.4-5209 of at
least Delta f/f = (2.8+/-0.4)E-9, which is typical in size for the general
pulsar population. However, glitch activity is closely correlated with
spin-down rate fdot, and pulsars with fdot as small as that of 1E 1207.4-5209
are never seen to glitch. Unlike in glitches of ordinary pulsars, there may
have been a large increase in fdot as well. The thermal X-ray spectrum of 1E
1207.4-5209, with its unique cyclotron absorption lines that measure the
surface magnetic field strength, did not show any measurable change after the
glitch, which rules out a major disruption in the dipole field as a cause or
result of the glitch. A leading theory of the origin and evolution of CCOs,
involving prompt burial of the magnetic field by fall-back of supernova ejecta,
might hold the explanation for the glitch.Comment: 6 pages, 2 figures, 3 tables; Latex, emulateapj style; accepted for
publication in Ap
Chandra Spectroscopy of Pulsars and their Wind Nebulae
We present preliminary results from a systematic spectral study of pulsars
and their wind nebulae using the Chandra X-Ray Observatory. The superb spatial
resolution of Chandra allows us to differentiate the compact object's spectrum
from that of its surrounding nebulae. Specifically, for six Crab-like pulsars,
we compare spectral fits of the averaged pulsar wind nebulae (PWN) emission to
that of the central core using an absorbed power-law model. These results
suggest an empirical relationship between the bulk averaged photon indicies
(Gamma) for the PWNe and the pulsar cores; Gamma_PWN = 0.8 X Gamma_core + 0.8.
The photon indices of PWNe are found to fall in the range of 1.3 < Gamma_PWN <
2.3. We propose that the morphological and spectral characteristics of the
pulsars observed herein seem to indicate consistent emission mechanisms common
to all young pulsars. We point out that the previous spectral results obtained
for most X-ray pulsars are likely contaminated by PWN emission.Comment: 4 pages, 2 figures, latex, newpasp style file. To appear in "Neutron
Stars in Supernova Remnants" (ASP Conference Proceedings), eds P. O. Slane
and B. M. Gaensle
Discovery of a Highly Energetic X-ray Pulsar Powering HESS J1813-178 in the Young Supernova Remnant G12.82-0.02
We report the discovery of 44.7 ms pulsations from the X-ray source CXOU
J181335.1-174957 using data obtained with the XMM-Newton Observatory. PSR
J1813-1749 lies near the center of the young radio supernova remnant
G12.82-0.02, which overlaps the compact TeV source HESS J1813-178. This
rotation-powered pulsar is the second most energetic in the Galaxy, with a
spin-down luminosity of Edot = (6.8 +/- 2.7)E37 erg/s. In the rotating dipole
model, the surface dipole magnetic field strength is B_s = (2.7 +/- 0.6)E12 G
and the spin-down age of 3.3-7.5 kyr, consistent with the location in the
small, shell-type radio remnant. At an assumed distance of 4.7 kpc by
association with an adjacent young stellar cluster, the efficiency of PSR
J1813-1749 in converting spin-down luminosity to radiation is approx. 0.03% for
its 2-10 keV flux, approx. 0.1% for its 20-100 keV INTEGRAL flux, and approx.
0.07% for the >200 GeV emission of HESS J1813-178, making it a likely power
source for the latter. The nearby young stellar cluster is possibly the
birthplace of the pulsar progenitor, as well as an additional source of seed
photons for inverse Compton scattering to TeV energies.Comment: 5 pages, 3 figure, Latex, emulateapj style. To appear in the
Astrophysical Journal Letter
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