102 research outputs found
Magnetar-like activity from the central compact object in the SNR RCW103
The 6.67 hr periodicity and the variable X-ray flux of the central compact
object (CCO) at the center of the SNR RCW 103, named 1E 161348-5055, have been
always difficult to interpret within the standard scenarios of an isolated
neutron star or a binary system. On 2016 June 22, the Burst Alert Telescope
(BAT) onboard Swift detected a magnetar-like short X-ray burst from the
direction of 1E 161348-5055, also coincident with a large long-term X-ray
outburst. Here we report on Chandra, NuSTAR, and Swift (BAT and XRT)
observations of this peculiar source during its 2016 outburst peak. In
particular, we study the properties of this magnetar-like burst, we discover a
hard X-ray tail in the CCO spectrum during outburst, and we study its long-term
outburst history (from 1999 to July 2016). We find the emission properties of
1E 161348-5055 consistent with it being a magnetar. However in this scenario,
the 6.67 hr periodicity can only be interpreted as the rotation period of this
strongly magnetized neutron star, which therefore represents the slowest pulsar
ever detected, by orders of magnitude. We briefly discuss the viable slow-down
scenarios, favoring a picture involving a period of fall-back accretion after
the supernova explosion, similarly to what is invoked (although in a different
regime) to explain the "anti-magnetar" scenario for other CCOs.Comment: 6 pages, 3 figures. To be published in the Astrophysical Journal
Letters; replaced to match the version accepted for publication on 2016
August 1
First evidence of a cyclotron feature in an anomalous X-ray pulsar
We report on the results of the longest uninterrupted observation of the
Anomalous X-ray Pulsar 1RXS J1708-4009 obtained with the BeppoSAX satellite in
August 2001. In the phase-resolved spectrum, corresponding to the rising part
of the pulse, we found an absorption-like feature at 8.1 keV (significance
level of 4 sigma), most likely due to cyclotron resonant scattering. The
centroid energy converts to a magnetic field of 9x10^{11} G and 1.6x10^{15} G
in the case of electrons and protons, respectively. If confirmed, this would be
the first detection of a cyclotron feature in the spectrum of an anomalous
X-ray pulsar. We discuss here the results also in ligh of recent theoretical
models for these class of sources.Comment: talk at the Restless High Energy Universe in Amsterdam; to be
published in Elsevier in Nucl. Physics B. Suppl. Se
Discovery of spin-up in the X-ray pulsar companion of the hot subdwarf HD 49798
The hot subdwarf HD 49798 has an X-ray emitting compact companion with a
spin-period of 13.2 s and a dynamically measured mass of 1.28+/-0.05 M_sun,
consistent with either a neutron star or a white dwarf. Using all the available
XMM-Newton and Swift observations of this source, we could perform a
phase-connected timing analysis extending back to the ROSAT data obtained in
1992. We found that the pulsar is spinning up at a rate of
(2.15+/-0.05)x10^{-15} s/s. This result is best interpreted in terms of a
neutron star accreting from the wind of its subdwarf companion, although the
remarkably steady period derivative over more than 20 years is unusual in
wind-accreting neutron stars. The possibility that the compact object is a
massive white dwarf accreting through a disk cannot be excluded, but it
requires a larger distance and/or properties of the stellar wind of HD 49798
different from those derived from the modelling of its optical/UV spectra.Comment: Accepted for publication in MNRA
Broad Band X-ray Spectra of M31 Sources with BeppoSAX
We present the first spectral study of the X-ray emitting stellar sources in
M31 in the energy band from 0.1 to 10 keV. We find that the globular cluster
sources have spectral characteristics consistent with those of the Milky Way
object, namely that the spectrum can be described by a thermal model with 6-20
keV from 2 to 10 keV. Evidence of high absorption in some of these sources is
most likely an indication that they lie in or behind the HI ring in the disk of
the galaxy.
We also find one peculiar globular cluster source, with spectral
characteristics more typically associated with either High Mass X-ray Binaries
or black hole candidates. We therefore suggest that either the source has been
wrongly identified with a globular cluster or that the system contains a Black
Hole. We confirm earlier report that the spectrum of the bulge of M31 is
consistent with the superposition of many LMXB spectra. It is likely that a
large fraction of the 15-30 keV detection obtained from the PDS instrument is
associated with the bulge, thus extending the spectral data for this complex of
sources up to 30 keV. The high energy part of the spectrum can be parameterized
with typical LMXB spectra, while at low energies an additional component is
required.Comment: Accepted for publication in A&A, main journa
Polarization shaping for control of nonlinear propagation
We study the nonlinear optical propagation of two different classes of
space-varying polarized light beams -- radially symmetric vector beams and
Poincar\'e beams with lemon and star topologies -- in a rubidium vapour cell.
Unlike Laguerre-Gauss and other types of beams that experience modulational
instabilities, we observe that their propagation is not marked by beam breakup
while still exhibiting traits such as nonlinear confinement and self-focusing.
Our results suggest that by tailoring the spatial structure of the
polarization, the effects of nonlinear propagation can be effectively
controlled. These findings provide a novel approach to transport high-power
light beams in nonlinear media with controllable distortions to their spatial
structure and polarization properties.Comment: 5 pages, and 4 figure
Evidence of a cyclotron feature in the spectrum of the anomalous X-ray pulsar 1RXS J170849-400910
We report the results of a long observation of the anomalous X-ray pulsar
1RXS J170849-400910 obtained with the BeppoSAX satellite in August 2001. The
best-fit phase-averaged spectrum was an absorbed power law plus blackbody
model, with photon index Gamma~2.4 and a blackbody temperature of kT_bb~0.4
keV. We confirm the presence of significant spectral variations with the
rotational phase of the pulsar. In the spectrum corresponding to the rising
part of the pulse we found an absorption-like feature at ~8.1 keV (a
significance of 4 sigma), most likely due to cyclotron resonant scattering. The
centroid energy converts to a magnetic field of 9x10^11 G and 1.6x10^15 G in
the case of electrons and protons, respectively. If confirmed, this would be
the first detection of a cyclotron feature in the spectrum of an anomalous
X-ray pulsar.Comment: 5 pages, 5 figures. Accepted for publication on ApJ Letter
Discovery of 3 s pulsations from the Brightest Hard X-ray Source in M31
We report the discovery with XMM-Newton of 3-s X-ray pulsations from 3XMM
J004232.1+411314, a dipping source that dominates the hard X-ray emission of
M31. This finding unambiguously assesses the neutron star (NS) nature of the
compact object. We also measured an orbital modulation of 4.15 h and a
projected semi-axis at lt-s, which implies a
low-mass companion of about 0.20.3 assuming a NS of 1.5
and an orbital inclination . The
barycentric orbit-corrected pulse period decreased by 28 ms in about 16
yr, corresponding to an average spin-up rate of s s ; pulse period variations, probably caused to by X-ray
luminosity changes, were observed on shorter time scales. We identify two
possible scenarios for the source: a mildly magnetic NS with
few G if the pulsar is far from its
equilibrium period , and a relatively young highly magnetic NS
with G if spinning close to .Comment: 5 pages, 3 figures, 2 tables, Submitted to the Astrophysical Journal
Letter
The Chandra ACIS Timing Survey Project: glimpsing a sample of faint X-ray pulsators
We report on the discovery of 41 new pulsating sources in the data of the Chandra Advanced CCD Imaging Spectrometer, which is sensitive to X-ray photons in the 0.3-10 keV band. The archival data of the first 15 yr of Chandra observations were retrieved and analysed by means of fast Fourier transforms, employing a peak-detection algorithm able to screen candidate signals in an automatic fashion. We carried out the search for new X-ray pulsators in light curves with more than 50 photons, for a total of about 190 000 light curves out of about 430 000 extracted. With these numbers, the ChAndra Timing Survey at Brera And Roma astronomical observatories (CATS @ BAR) - as we called the project - represents the largest ever systematic search for coherent signals in the classic X-ray band. More than 50 per cent of the signals were confirmed by further Chandra (for those sources with two or more pointings), XMM-Newton or ROSAT data. The period distribution of the new X-ray pulsators above ∼2000 s resembles that of cataclysmic variables, while there is a paucity of sources with shorter period and low fluxes. Since there is not an obvious bias against these detections, a possible interpretation is in terms of a magnetic gating mechanism in accreting neutron stars. Finally, we note that CATS @ BAR is a living project and the detection algorithm will continue to be routinely applied to the new Chandra data as they become public. Based on the results obtained so far, we expect to discover about three new pulsators every year
Pulsator-like Spectra from Ultraluminous X-Ray Sources and the Search for More Ultraluminous Pulsars
Ultraluminous X-ray sources (ULXs) are a population of extragalactic objects whose luminosity exceeds the Eddington limit for a 10 M ☉ black hole (BH). Their properties have been widely interpreted in terms of accreting stellar-mass or intermediate-mass BHs. However at least three neutron stars (NSs) have been recently identified in ULXs through the discovery of periodic pulsations. Motivated by these findings we studied the spectral properties of a sample of bright ULXs using a simple continuum model which was extensively used to fit the X-ray spectra of accreting magnetic NSs in the Galaxy. We found that such a model, consisting of a power-law with a high-energy exponential cut-off, fits most of the ULX spectra analyzed here very well, at a level comparable to that of models involving an accreting BH. On these grounds alone we suggest that other non-pulsating ULXs may host NSs. We also found that above 2 keV the spectrum of known pulsating ULXs is harder than that of the majority of the other ULXs of the sample, with only IC 342 X-1 and Ho IX X-1 displaying spectra of comparable hardness. We thus suggest that these two ULXs may host an accreting NS and encourage searches for periodic pulsations in the flux
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