40 research outputs found
The formation of the double neutron star pulsar J0737--3039
We find that the orbital period (2.4 hours), eccentricity (0.09), dipole
magnetic field strength (6.9 x 10^9 Gauss) and spin period (22 ms) of the new
highly relativistic double neutron star system PSR J0737-3039 can all be
consistently explained if this system originated from a close helium star plus
neutron star binary (HeS-NS) in which at the onset of the evolution the helium
star had a mass in the range 4.0 to 6.5 M_sun and an orbital period in the
range 0.1 to 0.2 days. Such systems are the post-Common-Envelope remnants of
wide Be/X-ray binaries (orbital period ~ 100 to 1000 days) which consist of a
normal hydrogen-rich star with a mass in the range 10 - 20 M_sun and a neutron
star. The close HeS-NS progenitor system went through a phase of mass transfer
by Roche-lobe overflow at a high rate lasting a few times 10^4 years; assuming
Eddington-limited disk accretion onto the neutron star this star was spun up to
its present rapid spin rate. At the moment of the second supernova explosion
the He star had a mass in the range 2.3 to 3.3 M_sun and in order to obtain the
present orbital parameters of PSR J0737-3039 a kick velocity in the range 70 -
230 km/s must have been imparted to the second neutron star at its birth.Comment: accepted by MNRA
Thin Disk Models of Anomalous X-ray Pulsars
We discuss the options of the fall-back disk model of Anomalous X-Ray Pulsars
(AXPs). We argue that the power-law index of the mass inflow rate during the
propeller stage can be lower than those employed in earlier models. We take
into account the effect of the super-critical mass inflow at the earliest
stages on the inner radius of the disk and argue that the system starts as a
propeller. Our results show that, assuming a fraction of the mass inflow is
accreted onto the neutron star, the fall-back disk scenario can produce AXPs
for acceptable parameters.Comment: 6 pages, 2 figures, Proc. of the II BeppoSAX Meeting: "The Restless
High-Energy Universe" (Amsterdam, May 5-8, 2003), E.P.J. van den Heuvel,
J.J.M. in 't Zand, and R.A.M.J. Wijers Ed
The Evolution of Relativistic Binary Progenitor Systems
Relativistic binary pulsars, such as B1534+12 and B1913+16 are characterized
by having close orbits with a binary separation of ~ 3 R_\sun. The progenitor
of such a system is a neutron star, helium star binary. The helium star, with a
strong stellar wind, is able to spin up its compact companion via accretion.
The neutron star's magnetic field is then lowered to observed values of about
10^{10} Gauss. As the pulsar lifetime is inversely proportional to its magnetic
field, the possibility of observing such a system is, thus, enhanced by this
type of evolution. We will show that a nascent (Crab-like) pulsar in such a
system can, through accretion-braking torques (i.e. the "propeller effect") and
wind-induced spin-up rates, reach equilibrium periods that are close to
observed values. Such processes occur within the relatively short helium star
lifetimes. Additionally, we find that the final outcome of such evolutionary
scenarios depends strongly on initial parameters, particularly the initial
binary separation and helium star mass. It is, indeed, determined that the
majority of such systems end up in the pulsar "graveyard", and only a small
fraction are strongly recycled. This fact might help to reconcile theoretically
expected birth rates with limited observations of relativistic binary pulsars.Comment: 24 pages, 10 Postscript figures, Submitted to The Astrophysical
Journa
Progenitor neutron stars of the lightest and heaviest millisecond pulsars
The recent mass measurements of two binary millisecond pulsars, PSR
J1614-2230 and PSR J0751+1807 with a mass M=1.97+/-0.04 Msun and M= 1.26 +/-
0.14 Msun, respectively, indicate a wide range of masses for such objects and
possibly also a broad spectrum of masses of neutron stars born in core-collapse
supernovae.
Starting from the zero-age main sequence binary stage, we aim at inferring
the birth masses of PSR J1614-2230 and PSR J0751+1807 by taking the differences
in the evolutionary stages preceding their formation into account.
Using simulations for the evolution of binary stars, we reconstruct the
evolutionary tracks leading to the formation of PSR J1614-2230 and PSR
J0751+1807. We analyze in detail the spin evolution due to the accretion of
matter from a disk in the intermediate-mass/low-mass X-ray binary. We consider
two equations of state of dense matter, one for purely nucleonic matter and the
other one including a high-density softening due to the appearance of hyperons.
Stationary and axisymmetric stellar configurations in general relativity are
used, together with a recent magnetic torque model and
observationally-motivated laws for the decay of magnetic field.
The estimated birth mass of the neutron stars PSR J0751+1807 and PSR
J1614-2230 could be as low as 1.0 Msun and as high as 1.9 Msun, respectively.
These values depend weakly on the equation of state and the assumed model for
the magnetic field and its accretion-induced decay.
The masses of progenitor neutron stars of recycled pulsars span a broad
interval from 1.0 Msun to 1.9 Msun. Including the effect of a slow Roche-lobe
detachment phase, which could be relevant for PSR J0751+1807, would make the
lower mass limit even lower. A realistic theory for core-collapse supernovae
should account for this wide range of mass.Comment: 13 pages, 10 figures, accepted in A&
Possible changes of state and relevant timescales for a neutron star in LS I +61{\deg}303
The properties of the short, energetic bursts recently observed from the
gamma-ray binary LS I +61{\deg}303, are typical of those showed by high
magnetic field neutron stars, and thus provide a strong indication in favor of
a neutron star being the compact object in the system. Here, we discuss the
transitions among the states accessible to a neutron star in a system like LS I
+61{\deg}303, such as the ejector, propeller and accretor phases, depending on
the NS spin period, magnetic field and rate of mass captured. We show how the
observed bolometric luminosity (>= few x 1E35 erg/s), and its broad-band
spectral distribution, indicate that the compact object is most probably close
to the transition between working as an ejector all along its orbit, and being
powered by the propeller effect when it is close to the orbit periastron, in a
so-called flip-flop state. By assessing the torques acting onto the compact
object in the various states, we follow the spin evolution of the system,
evaluating the time spent by the system in each of them. Even taking into
account the constraint set by the observed gamma-ray luminosity, we found that
the total age of the system is compatible with being ~5-10 kyr, comparable to
the typical spin-down ages of high-field neutron stars. The results obtained
are discussed in the context of the various evolutionary stages expected for a
neutron star with a high mass companion.Comment: 12 pages, 6 figures. Accepted for publication in Ap
On the progenitors of millisecond pulsars by the recycling evolutionary channel
The recycling model suggested that low-mass X-ray binaries (LMXBs) could
evolve into binary millisecond pulsars (BMSPs). In this work, we attempt to
investigate the progenitor properties of BMSPs formed by the recycling
evolutionary channel, and if sub-millisecond pulsars can be produced by this
channel. Using Eggleton's stellar evolution code, considering that the dead
pulsars can be spun up to a short spin period by the accreting material and
angular momentum from the donor star, we have calculated the evolution of close
binaries consisting of a neutron star and a low-mass main-sequence donor star,
and the spin evolution of NSs. In calculation, some physical process such as
the thermal and viscous instability of a accretion disk, propeller effect, and
magnetic braking are included. Our calculated results indicate that, all LMXBs
with a low-mass donor star of 1.0 - 2.0 and a short orbital period
(\la 3-4 \rm d) can form millisecond pulsars with a spin period less than 10
ms. However, it is difficult to produce sub-millisecond pulsars by this
evolutionary channel. In addition, our evolutionary scenario cannot account for
the existence of BMSPs with a long orbital period (P_{\rm orb}\ga 70-80\rm
d).Comment: 7 pages,5 figures, MNRAS in pres
Spectral properties of anomalous X-ray pulsars
In this paper, the spectra of the persistent emission from anomalous X-ray
pulsars (AXPs) and their variation with spin-down rate is
considered. Firstly, based on an accretion-powered model, the influences of
both magnetic field and mass accretion rate on the spectra properties of AXPs
are addressed. Subsequently, the relation between the spectral property of AXPs
and mass accretion rate is investigated. The result shows that there
exists a linear correlation between the photon index and mass accretion rate,
and the spectral hardness increases with increasing . A possible
emission mechanism for the explanation of spectral properties of AXPs is also
discussed.Comment: 11pages, 3 figures, Chin. J. Astron. Astrophys. in pres
Treatment of periorbital syringomas: review of scientific literature in the last 5 years
Introduction: Syringomas are benign adnexal tumors with histopathological characteristics arising from the eccrine ducts, in yellowish or skin-colored papules, 1-3 mm, commonly in the lower periorbital region, which can cause important cosmetic problems. The goal of treatment is to improve appearance by destroying the tumor using minimally invasive methods and including surgery. There are multiple treatment options in the literature with varying degrees of success, but little is known about their effectiveness. Complete removal is unsuccessful, and side effects have been described, recurrence being the most frequent.Methods: This is a narrative review of the literature of scientific publications in the period 2014-2019.Results: After reviewing 45 articles and identifying those published in the last five years that had a record of the number of patients, treatment description, scales of evaluation of results and follow-up, six articles were selected. Of the total number of six articles, we found: a systematic review and five retrospective studies, one being a comparative one. A number was assigned to each article analyzed, and the number of patients included, treatment performed, assessment scales and results, complications and conclusions were collected.
Conclusions: Periorbital syringomas are still a therapeutic challenge, and so far, no treatment is consistently effective. The CO2 laser remains the first choice of treatment when used fractionally, and intralesional electrocoagulation represents a second alternative with moderate results and a lower risk of complications. New treatments such as Laser Erbium Yttrium Aluminum Garnet, Neodymium-Doped Yttrium Aluminum Garnet and botulinum toxin A monotherapy could be good alternatives. Comparative prospective studies are needed
A Fallback Disk Accretion-Involved Formation Channel to PSR J1903+0327
The discovery of the eccentric binary and millisecond pulsar PSR J1903+03273
has raised interesting questions about the formation mechanisms of this
peculiar system. Here we present a born-fast scenario for PSR J1903+03273. We
assume that during the supernova (SN) explosion that produced the pulsar, a
fallback disk was formed around and accreted onto the newborn neutron star.
Mass accretion could accelerate the neutron star's spin to milliseconds, and
decrease its magnetic field to G, provided that there was
sufficient mass (\sim 0.1 M_{\sun}) in the fallback disk. The neutron star
became a millisecond pulsar after mass accretion terminated. In the meanwhile
the binary orbit has kept to be eccentric (due to the SN explosion) for yr. We have performed population synthesis calculations of the
evolutions of neutron stars with a fallback disk, and found that there might be
tens to hundreds of PSR J1903+03273-like systems in the Galaxy. This scenario
also suggests that some fraction of isolated millisecond pulsars in the
Galactic disk could be formed through the same channel.Comment: 17 pages, 2 figures, accepted to Ap