233 research outputs found
Simultaneous constraints on the mass and radius of Aql X-1 from quiescence and X-ray burst observations
The measurement of neutron star mass and radius is one of the most direct way
to distinguish between various dense matter equations of state. The mass and
radius of accreting neutron stars hosted in low mass X-ray binaries can be
constrained by several methods, including photospheric radius expansion from
type-I X-ray bursts and from quiescent spectra. In this paper, we apply for the
first time these two methods simultaneously to constrain the mass and radius of
Aql X-1, as a reliable distance estimation, high signal-to-noise ratio
quiescent spectra from Chandra and XMM-Newton, and photospheric radius
expansion bursts from RXTE are available. This is also used to verify the
consistency between the two methods, and to narrow down the uncertainties of
the neutron star mass and radius. It is found that the distance to Aql X-1
should be in the range of kpc, based on the overlapping confidence
regions between photospheric radius expansion burst and quiescent spectra
methods. In addition, we show that the mass and radius determined for the
compact star in Aql X-1 are compatible with strange star equations of state and
conventional neutron star models.Comment: 16 pages, 9 figures, accepted by Ap
An Ultra Low Mass and Small Radius Compact Object in 4U 1746-37?
Photospheric radius expansion (PRE) bursts have already been used to
constrain the masses and radii of neutron stars. RXTE observed three PRE bursts
in 4U 1746-37, all with low touchdown fluxes. We discuss here the possibility
of low mass neutron star in 4U 1746-37 because the Eddington luminosity depends
on stellar mass. With typical values of hydrogen mass fraction and color
correction factor, a Monte-Carlo simulation was applied to constrain the mass
and radius of neutron star in 4U 1746-37. 4U 1746-37 has a high inclination
angle. Two geometric effects, the reflection of the far side accretion disc and
the obscuration of the near side accretion disc have also been included in the
mass and radius constraints of 4U 1746-37. If the reflection of the far side
accretion disc is accounted, a low mass compact object (mass of
and radius of at 68% confidence)
exists in 4U 1746-37. If another effect operated, 4U 1746-37 may contain an
ultra low mass and small radius object
( at 68% confidence). Combined
all possibilities, the mass of 4U 1746-37 is at
99.7% confidence. For such low mass NS, it could be reproduced by a self-bound
compact star, i.e., quark star or quark-cluster star.Comment: accepted by Ap
The accretion rate independence of horizontal branch oscillation in XTE J1701-462
We study the temporal and energy spectral properties of the unique neutron
star low-mass X-ray binary XTE J1701-462. After assuming the HB/NB vertex as a
reference position of accretion rate, the horizontal branch oscillation (HBO)
of the HB/NB vertex is roughly 50 Hz. It indicates that the HBO is independent
with the accretion rate or the source intensity. The spectral analysis shows
in the HB/NB vertex and
in the NB/FB vertex, which
implies that different accretion rate may be produced in the HB/NB vertex and
the NB/FB vertex. The Comptonization component could be fitted by constrained
broken power law (CBPL) or nthComp. Different with GX 17+2, the frequencies of
HBO positively correlate with the inner disk radius, which contradict with the
prediction of Lense-Thirring precession model. XTE J1701-462, both in the
Cyg-like phase and in the Sco-like phase, follows a positive correlation
between the break frequency of broad band noise and the characteristic
frequency of HBO, which is called the W-K relation. An anticorrelation between
the frequency of HBO and photon energy is observed. Moreover, the rms of HBO
increases with photon energy till ~10 keV. We discuss the possible origin of
HBO from corona in XTE J1701-462.Comment: 45 pages, 18 figures, accepted by Ap
Normalized solutions for Sobolev critical Schr\"odinger-Bopp-Podolsky systems
We study the Sobolev critical Schr\"odinger-Bopp-Podolsky system
\begin{gather*}
-\Delta u+\phi u=\lambda u+\mu|u|^{p-2}u+|u|^4u\quad \text{in }\mathbb{R}^3,
-\Delta\phi+\Delta^2\phi=4\pi u^2\quad \text{in } \mathbb{R}^3, \end{gather*}
under the mass constraint for some prescribed , where ,
is a parameter, and is a Lagrange multiplier. By
developing a constraint minimizing approach, we show that the above system
admits a local minimizer. Furthermore, we establish the existence of normalized
ground state solutions.Comment: 19 page
Traveling wave phenomena in a nonlocal dispersal predator-prey system with the Beddington-DeAngelis functional response and harvesting
This paper is devoted to studying the existence and nonexistence of traveling wave solution for a nonlocal dispersal delayed predator-prey system with the Beddington-DeAngelis functional response and harvesting. By constructing the suitable upper-lower solutions and applying Schauder\u27s fixed point theorem, we show that there exists a positive constant c∗ such that the system possesses a traveling wave solution for any given c\u3ec∗. Moreover, the asymptotic behavior of traveling wave solution at infinity is obtained by the contracting rectangles method. The existence of traveling wave solution for c=c∗ is established by means of Corduneanu\u27s theorem. The nonexistence of traveling wave solution in the case of
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