35,964 research outputs found
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 NuSTAR View of a QPO Evolution of GRS 1915+105
We report a timing analysis of the black hole binary GRS 1915+105 with the
NuSTAR observatory. A strong type-C QPO below 2 Hz appears in the power density
spectrum during the whole observation, whose frequency is correlated with the
3-25 keV count rate. The QPO shows a sudden increase in frequency along with an
increase in flux and a softening of the spectrum. We discuss the possible
origin of the QPO and the reasons that lead to the QPO frequency variation. It
is suggested that the reflection component has little influence on QPO
frequency and the increase in QPO frequency could be associated with the inward
motion of the outer part of the disk.Comment: 21 pages, 8 figures, published in A
PM2.5-Related Health Economic Benefits Evaluation Based on Air Improvement Action Plan in Wuhan City, Middle China
On the basis of PM2.5 data of the national air quality monitoring sites, local population data, and baseline all-cause mortality rate, PM2.5-related health economic benefits of the Air Improvement Action Plan implemented in Wuhan in 2013–2017 were investigated using health-impact and valuation functions. Annual avoided premature deaths driven by the average concentration of PM2.5 decrease were evaluated, and the economic benefits were computed by using the value of statistical life (VSL) method. Results showed that the number of avoided premature deaths in Wuhan are 21,384 (95% confidence interval (CI): 15,004 to 27,255) during 2013–2017, due to the implementation of the Air Improvement Action Plan. According to the VSL method, the obtained economic benefits of Huangpi, Wuchang, Hongshan, Xinzhou, Jiang’an, Hanyang, Jiangxia, Qiaokou, Jianghan, Qingshan, Caidian, Dongxihu, and Hannan District were 8.55, 8.19, 8.04, 7.39, 5.78, 4.84, 4.37, 4.04, 3.90, 3.30, 2.87, 2.42, and 0.66 billion RMB (1 RMB = 0.1417 USD On 14 October 2019), respectively. These economic benefits added up to 64.35 billion RMB (95% CI: 45.15 to 82.02 billion RMB), accounting for 4.80% (95% CI: 3.37% to 6.12%) of the total GDP of Wuhan in 2017. Therefore, in the process of formulating a regional air quality improvement scheme, apart from establishing hierarchical emission-reduction standards and policies, policy makers should give integrated consideration to the relationship between regional economic development, environmental protection and residents’ health benefits. Furthermore, for improving air quality, air quality compensation mechanisms can be established on the basis of the status quo and trends of air quality, population distribution, and economic development factors
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