Search results for "LSA"
showing 10 items of 832 documents
Dark, Cold, and Noisy: Constraining Secluded Hidden Sectors with Gravitational Waves
2018
We explore gravitational wave signals arising from first-order phase transitions occurring in a secluded hidden sector, allowing for the possibility that the hidden sector may have a different temperature than the Standard Model sector. We present the sensitivity to such scenarios for both current and future gravitational wave detectors in a model-independent fashion. Since secluded hidden sectors are of particular interest for dark matter models at the MeV scale or below, we pay special attention to the reach of pulsar timing arrays. Cosmological constraints on light degrees of freedom restrict the number of sub-MeV particles in a hidden sector, as well as the hidden sector temperature. Ne…
Highly Magnetized Accreting Pulsars: Are There Accreting Magnetars?
2014
2S 0114+650, GX 301-2, IGR J16358-4726, X Per, 4U 2206+54, SXP 1062, and 3A 1954+319 are thought to possess high magnetic elds. They have recently been named accreting magnetars, or highly magnetized accreting pulsars. In this work their properties are reviewed. Within the context of their observational properties (mainly from INTEGRAL data), and the recent models of accretion onto highly magnetized neutron stars, their similarities and dierences are analyzed. The aim is to find a common framework to understand the evolution (in terms of past and present history) of these sources, and to establish the basis of a possible new kind of accreting sources. Two of these sources, namely X Per and …
The BeppoSAX 0.1-100 keV Spectrum of the X-Ray Pulsar 4U 1538-52
2001
We report the results of temporal and spectral analysis performed on the X-ray pulsar 4U 1538-52 observed by BeppoSAX. We obtained a new estimate of the spin period of the neutron star P=528.24 \pm 0.01 s (corrected for the orbital motion of the X-ray source): the source is still in the spin-up state, as since 1988. The pulse profile is double peaked, although significant variations of the relative intensity of the peaks with energy are present. The broad band (0.12-100 keV) out-of-eclipse spectrum is well described by an absorbed power law modified by a high energy cutoff at \sim 16 keV (e-folding energy \sim 10 keV) plus an iron emission line at \sim 6.4 keV. A cyclotron line at \sim 21 k…
XMM-Newton observations of the supernova remnant IC 443: II. evidence of stellar ejecta in the inner regions
2008
We investigate the spatial distribution of the physical and chemical properties of the hot X-ray emitting plasma of the supernova remnant IC 443, in order to get important constraints on its ionization stage, on the progenitor supernova explosion, on the age of the remnant, and its physical association with a close pulsar wind nebula. The hard X-ray thermal emission (1.4-5.0 keV) of IC 443 displays a centrally-peaked morphology, its brightness peaks being associated with hot (kT>1 keV) X-ray emitting plasma. A ring-shaped structure, characterized by high values of equivalent widths and median photon energy, encloses the PWN. Its hard X-ray emission is spectrally characterized by a collis…
Kicked neutron stars and microlensing
1996
Due to the large kick velocities with which neutron stars are born in supernovae explosions, their spatial distribution is more extended than that of their progenitor stars. The large scale height of the neutron stars above the disk plane makes them potential candidates for microlensing of stars in the Large Magellanic Cloud. Adopting for the distribution of kicks the measured velocities of young pulsars, we obtain a microlensing optical depth of $\tau \sim 2 N_{10} \times 10^{-8}$ (where $N_{10}$ is the total number of neutron stars born in the disk in units of $10^{10}$). The event duration distribution has the interesting property of being peaked at $T \sim 60$--80 d, but for the rates t…
Coupling Between Periodic and Aperiodic Variability in SAX J1808.4-3658
2003
We detect a significant broadening in the wings of the 401 Hz peak in the power spectrum of the accreting millisecond binary pulsar SAX J1808.4-3658. This feature is consistent with the convolution of the red noise present in the power spectrum with the harmonic line. We conclude that the flux modulated by the spin period shows aperiodic variability similar to the red noise in the overall flux, suggesting such variability also originates at the magnetic caps close to the neutron star surface. This is analogous to the results found in some longer period, higher magnetic field pulsators in high mass X-ray binaries.
Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658
2006
We present a timing analysis of the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. A study of the phase delays of the entire pulse profile shows a behavior that is surprising and difficult to interpret: superposed to a general trend, a big jump by about 0.2 in phase is visible, starting at day 14 after the beginning of the outburst. An analysis of the pulse profile indicates the presence of a significant first harmonic. Studying the fundamental and the first harmonic separately, we find that the phase delays of the first harmonic are more regular, with no sign of the jump observed in the fundamental. The fitting of the phase delays of the first harmonic with a model whi…
Order in the chaos? The strange case of accreting millisecond pulsars
2007
We review recent results from the X-ray timing of accreting millisecond pulsars in Low Mass X-ray Binaries. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, we derive information on the mass accretion rate and magnetic field of the neutron star in these systems. We also find that the phase delays behavior as a function of time in these sources is sometimes quite complex and difficult to interpret, since phase shifts, most probably …
XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
2008
We report on a 63-ks long XMM-Newton observation of the accreting millisecond pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on September 21st 2008. The pn spectrum shows a highly significant emission line in the energy band where the iron K-alpha line is expected, and which we identify as emission from neutral (or mildly ionized) iron. The line profile appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most probable explanation for this profile is Doppler and relativistic broadening from the inner accretion disc. From a fit with a diskline profile we find an inner radius of the disc of 8.7^(+3.7)_(-2.7) R_g, corresponding to 18.0^(+7.6)_(-5.6) km f…
Optical counterpart of the XTE J0929-314 in quiescence: constraints on the magnetic field
2005
We present VLT observations of the optical counterpart of th X-ray millisecond pulsar XTE J0929-314 in quiescence. We detected a very faint candidate in agreement with the position given by radio and X observation. From the observed optical flux we inferred un upper limit to the magnetic field of the system. © 2005 American Institute of Physics.