Subjects: Astronomy >> Astrophysics submitted time 2024-01-22
Abstract： Deconvolution of radio astronomy images is a key data processing technique. Its main goal is to remove the effects introduced by the instrument from the observed sky images to recover the original sky images.However, radio interferometer arrays employ sparse interferometric arrays, whose imaging principles differfrom those of optical telescopes. If the sampling points in the UV space are not sufficiently dense, this will lead to insufficient high-resolution information during image reconstruction. Traditional radio astronomy image reconstruction algorithms fail to fundamentally solve the problem of UV space undersampling. This paper adopts the compressed sensing theoretical framework, combines prior knowledge of the sparsity of radio astronomy images, and studies a new radio astronomy image deconvolution algorithm, namely the IUWT-CS-based radio interferometric image reconstruction algorithm. This algorithm transforms the dirty image deconvolution process into a convex optimization problem to find the global minimum. To evaluate the reconstruction performance of this algorithm, we used the OSKAR radio astronomy simulation software package to simulate low SKA1 observations and performed deconvolution processing on the extended radio sources obtained. Experimental results show that, compared with the HOGBOM-CLEAN, MS-CLEAN,and IUWT-FISTA methods, the IUWT-CS method significantly improves the reconstruction quality of radio images and achieves finer denoising and restoration effects.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2024-01-16
Abstract：
The pulsar radio emission mechanism remains an enigma over half a century.
A successful radiation process requires not only to explain the coherency, but also
microstructures, characteristic frequency of emission, and the “death line" problem, etc.
These challenge both the long standing gap models and recent models of magnetic reconnection
with emission based on open field lines.
This article points out that each intermittent plasma ejection from Y-point,
the boundary of closed zone intersecting the equatorial plane,
near the light cylinder of pulsar magnetosphere can
stretch a bundle of closed field lines significantly. Corresponding magnetic pressure imposed on the trapped plasma provides ideal site of
magnetic reconnection and hence generating pairs and Alfven wave near light cylinder.
The resultant marginal stable instability is expected for coherent curvature emission. This not only interprets above problems in a simple and unified way, but also offers hints to the behavior of Rotating Radio Transients (RRATs) and Fast Radio Bursts (FRBs).
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-12-29
Zhiyuan Ren
Xi Chen
Tie Liu
Emma Mannfors
Leonardo Bronfman
Fengwei Xu
Siyi Feng
Hongli Liu
Fanyi Meng
Amelia M. Stutz,
Shanghuo Li
Chang Won Lee,
Ke Wang
Jianwen Zhou
Di Li
Chen Wang
Chakali Eswaraiah
Anandmayee Tej
Long-Fei Chen
Hui Shi
Abstract： We studied the unique kinematic properties in massive filament G352.63-1.07 at 1000-AU spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We find the central massive core M1 (12 Msun) being separated from the surrounding filament with a velocity difference of v-v_sys=-2 km/s and a transverse separation within 3 arcsec. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament towards its both ends. M1 thus represents a very beginning state for a massive young star-forming core escaping from the parental filament, within a time scale of ~4000 years. Based on its kinetic energy (3.5x10^44 erg), the core escape is unlikely solely due to the original filament motion or magnetic field, but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again.
Subjects: Physics >> Nuclear Physics Subjects: Astronomy >> Astrophysics submitted time 2023-12-28
Abstract：相对论 Brueckner-Hartree-Fock (RBHF) 理论是相对论框架下重要的第一性原理方法，仅包含两体力即可以满意描述核物质的饱和性质。在完备的 Dirac 空间中自洽求解核物质 RBHF 方程，唯一确定了单粒子势的标量和矢量分量，避免了已有工作中由于忽略负能态所导致的不确定性，解决了 40 多年来 RBHF 计算中不能唯一确定单粒子势的问题。文章简要回顾 RBHF 理论的发展历史，阐述包含负能态做 RBHF 计算的必要性，介绍利用完备 Dirac 空间的 RBHF 理论，研究核物质性质和中子星物质性质的最新进展，包括有效质量、纯中子物质的每核子结合能、对称和纯中子物质的压强、中子星物质的粒子分数和状态方程、中子星的质量半径关系和潮汐形变等。文章还展望了完备 Dirac 空间的RBHF 理论在确定密度泛函理论参数、描述核子原子核弹性散射和研究中子星内部强子夸克相变等方面的可能应用。
Subjects: Astronomy >> Astrophysics submitted time 2023-12-17
Yuxiao Wu
Zhichen Pan
Lei Qian
Scott Ransom
BoJun Wang
Zhen Yan
Jintao Luo
Liyun Zhang
Minghui Li
Dejiang Yin
Baoda Li
Yifeng Li
Yinfeng Dai
Yaowei Li
Xinnan Zhang
Tong Liu
Yu Pan
Abstract： We present the discovery of three pulsars in Globular Cluster M15 (NGC 7078) by the Five-hundred-meter Aperture Spherical radio Telescope (FAST).
In the three pulsars, PSR~J2129+1210J (M15J) is a millisecond pulsar with a spinning period of 11.84 ms and a dispersion measure of 66.68 pc cm$^{-3}$.
Both PSR~J2129+1210K and L (M15K and L) are long period pulsars with spinning periods of 1928 ms and 3961 ms, respectively,
while M15L is the GC pulsar with the longest spinning period till now.
The discoveries of M15K and L support the theory that core-collapsed Globular Clusters may contain partially recycled long period pulsars citep{verbunt-2014-slowpulsar}.
With the same dataset, the timing solutions of M15A to H were updated,
and the timing parameter P1 of M15F is different from the previous results, which is approximately 0.027$ times 10^{-18} ss^{-1}$ from our work and $0.032 times 10^{-18} ss^{-1}$ from Anderson's citep{anderson-1993}.
As predicted by Rodolfi et al. citep{ridolfi-2017},
the luminosity of M15C kept decreasing and the latest detection in our dataset is on December 20$^{ rm th}$, 2022.
We also detected M15I for one more time.
The different barycentric spin periods indicate that this pulsar should locate in a binary system,
manifesting itself as the exceptional one in such a core-collapsing GC.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-12-04
Abstract： The pulsar radio emission mechanism remains an enigma over half a century.
A successful radiation process requires not only to explain the coherency and high degree of polarization of the emission, but also
microstructures, characteristic frequency of emission, and the “death line" problem, etc. These issues challenge both the long standing cap models and recent models of magnetic reconnection assuming stationary magnetosphere of a pulsar.
This article proposes a radio emission through global-local interaction of pulsar magnetosphere. The centrifugal force at the light cylinder leads to the concentration of both field lines and plasma in an equatorial layer much less than that of a pulsar magnetosphere.
The resultant magnetic reconnection with chain of plasmoids interprets not only the above problems in a simple and unified way, but also Rotating Radio Transients (RRATs) and Fast Radio Bursts (FRBs).
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-09-15
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Subjects: Astronomy >> Astrophysics Subjects: Astronomy >> Astrophysical processes submitted time 2023-08-31
Abstract： The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.
Subjects: Astronomy >> Astrophysics submitted time 2023-07-29
Abstract： The pulsar radio emission mechanism remains an enigma since its discovery in 1967. The critical issue of origin of coherent emission is usually investigated separately from the micro-structure of individual pulses and characteristic emission frequency of pulsars... In this letter, these issues are interpreted in an unified scenario. The pulsar spin piles up magnetic field at the apex of last closed field line triggering magnetic reconnection. The resultant Alfven wave interacts with open field lines giving rise to coherent maser curvature and cyclotron emission. Such a scenario of coherent emission not only imposes new limit to emission site, nanoburst, and characteristic frequency, but also affects polarization and pair production required in maintaining a marginal stable circuit in radio emission of pulsars.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-07-23
Abstract： The distance $D$ to an exoplanet system with imaging and spectral measurement can be obtained by using the orbit as a ruler. The measurement of the Distance to a typical exoplanet system with imaging
and spectral measurement can be accurate to $\delta D/D\sim 0.2$, if the orbital velocity of the planet can be accurate to $\sim 3 {\ \rm km/s}$.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-07-11
Abstract： We propose to use the rotation period to constrain the average density of an object with gravitationally confined surface. The average density is inverse proportional to the square of the rotation period, while independent of the size of the object. The lower limit of the average density can be written as $\rho_0=10.9 {\ \rm g\ cm^{-3}}\left(\frac{{\ \rm hours}}{P}\right)^2$. An asteroid with rotating period shorter than 0.7 h should consist of some unknown matter, or it is a whole rock or a bulk of ice with no rubble piles on the surface.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-05-16
Abstract： The corona is a key region of solar atmospheric activity,and the source of solar-terrestrial space weather.Limited by observation,research on the plasma structure and magnetic field state of the lower coronal atmosphere is still very lacking, and there are few international studies on the brightness stratification of the lower coronal atmosphere in the visible light band.In this paper,the coronal green line (FeXIV 5303 Å)
observation data of Lijiang coronagraph YOGIS is used to analyze the bright structure and mid-coronal loops in the inner coronal region (1.03R⊙-1.25R⊙) effectively.By fitting the exponential decay of the intensity of the bright structures at the radial height of the sun,comparing these fitting results,it is found that the decay index of the static inner coronal loops obtained is around a fixed value.Then,the more obvious coronal loops are extracted,and by performing the same exponential fitting on the intensities of different heights,the obtained decay index is also relatively similar to that of the bright structure,which provides a reference for further study of the evolution of physical parameters in the corona.
Subjects: Astronomy >> Astrophysics submitted time 2023-02-21
Chaojun Wang
B. Luo
W. N. Brandt
D. M. Alexander
F. E. Bauer
S. C. Gallagher
Jian Huang
Hezhen Liu
D. Stern
Abstract： We utilize recent NuSTAR observations (co-added depth ≈55-120 ks) of PG 1001+054, PG 1254+047, and PHL 1811 to constrain their hard X-ray (≳5 keV) weakness and spectral shapes, and thus to investigate the nature of their extreme X-ray weakness. These quasars showed very weak soft X-ray emission, and they were proposed to be intrinsically X-ray weak, with the X-ray coronae producing weak continuum emission relative to their optical/UV emission. However, the new observations suggest an alternative explanation. The NuSTAR 3-24 keV spectral shapes for PG 1001+054 and PHL 1811 are likely flat (effective power-law photon indices \Gamma_{\rm eff}=1.0^{+0.5}_{-0.6} and \Gamma_{\rm eff}=1.4^{+0.8}_{-0.7}, respectively), while the shape is nominal for PG 1254+047 (\Gamma_{\rm eff}=1.8\pm0.3). PG 1001+054 and PHL 1811 are significantly weak at hard X-ray energies (by factors of ≈26-74 at rest-frame 8 keV) compared to the expectations from their optical/UV emission, while PG 1254+047 is only hard X-ray weak by a factor of ≈3. We suggest that X-ray obscuration is present in all three quasars. We propose that, as an alternative to the intrinsic X-ray weakness + X-ray obscuration scenario, the soft and hard X-ray weakness of these quasars can be uniformly explained under an obscuration-only scenario. This model provides adequate descriptions of the multi-epoch soft and hard X-ray data of these quasars, with variable column density and leaked fraction of the partial-covering absorber. We suggest that the absorber is the clumpy dust-free wind launched from the accretion disk. These quasars probably have super-Eddington accretion rates that drive powerful and high-density winds.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-02-21
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
Abstract： We present the analysis of seven microlensing planetary events with planet/host mass ratios q < 10^{-4}: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016--2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with q < 10^{-4} from 2016--2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals (A≳65), and a follow-up project for KMTNet high-magnification events could detect at least two more q < 10^{-4} planets per year and form an independent statistical sample.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-02-21
H. Hu
M. Kramer
D. J. Champion
N. Wex
A. Parthasarathy
T. T. Pennucci
N. K. Porayko
W. van Straten
V. Venkatraman Krishnan
M. Burgay
P. C. C. Freire
R. N. Manchester
A. Possenti
I. H. Stairs
M. Bailes
S. Buchner
A. D. Cameron
F. Camilo
M. Serylak
Abstract： The Double Pulsar, PSR J0737-3039A/B, has offered a wealth of gravitational experiments in the strong-field regime, all of which GR has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the Double Pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in future, the SKA can greatly improve the accuracy of current tests and facilitate tests of NLO contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737-3039A, made using the MeerKAT telescope over the last 3 years. The increased timing precision offered by MeerKAT yields a 2 times better measurement of Shapiro delay parameter s and improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16-yr data by a factor of 1.65. These effects include the retardation effect due to the movement of B and the deflection of the signal by the gravitational field of B. We also investigate novel effects which are expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line-of-sight due to latitudinal signal deflection and find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the Double Pulsar system that meets the timing precision expected from future instruments such as the full SKA.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2023-01-06
Abstract：
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Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2020-03-09
Abstract： We present spectroscopy of stars in the immediate vicinity of the dwarf nova (DN) KZ Gem to confirm its identification, which had been ambiguous in the literature. Analysis of 73 radial velocities spanning from 2014 to 2019 provides a high-precision orbital period of 0.2224628(2) d (~5.34 hr) and shows KZ Gem to be a double-lined DN. Time series photometry taken from 2016 to 2018 shows a variable double-hump modulation with a full amplitude of ~0.3 mag, along with five Gaussian-like transient events lasting ~30 min or more. Using the light curve code XRBinary and nonlinear fitting code NMfit, we obtain an optimized binary model of the dwarf nova (DN) KZ Gem, from time series photometry, consisting of a Roche-lobe-filling K type dwarf with a mass transfer rate of 2.7 - 7.9 x 10^{-10} solar mass per yr to a large, cool and thick disk surrounding a white dwarf, in an orbit with an inclination of 51.6(+/-1.4) degree. Two hotspots on the disk are demonstrated to cause the observed variations in the ellipsoidal modulations from the secondary star. This physical model is compatible with the Gaia distance of KZ Gem.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2018-09-16
Abstract： This paper introduces the inverse dissipation potential into the Newtonian Dynamic equation and studies the motion equations of the objects in the isolated gravitational system. It is found that at large scales it can derive the dynamical equation of cosmic expansion similar to the ΛCDM model and yield the flat rotation curves for spiral galaxy. Different from the usual dark matter models, the derived flat rotation curves are the result of time accumulation rather than the direct action of mechanics. And the Tully-Fisher relationship is also discussed, it is found that the basic constant a0 in the MOND model and the form of the function μ have a clear corresponding physical significance in the model of this paper.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics Subjects: Astronomy >> Star and Galactic System submitted time 2018-09-12
Dai, zhibin
Szkody, Paula
Kennedy, Mark
Su Jie
Medagangoda, N. Indika
Robinson, Edward L.
Garnavich, Peter M.
De Silva, L. Malith M.
Abstract： We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS\,J0632+2536 (J0632+2536), RZ\,Leo, TW\,Vir and the pre-CV WD\,1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ\,Leo and TW\,Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD\,1144+011 can explain its single-hump modulation and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of $\sim0.11$. The disk model of RZ\,Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ\,Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW\,Vir and WD\,1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semi-empirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy."
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysics submitted time 2018-02-07
Abstract： In the present letter, with the help of a semi-analytical code we show how taking into account baryonic physics in the #3;CDM model can solve the discrepancy between the numerical predictions of dark matter haloes in the #3;CDM framework and observations from dwarf galaxy scale to clusters of galaxies without the need of different forms of dark matter as recently advocated by [1]. Combining well established results, the paper shows, for the first time, how the flat profiles of galaxy clusters and correlations between several of their main properties, are naturally obtained when baryon physics is correctly taken into account; how the so called ”diversity problem” can be solved and how the challenging, extremely low rising rotation curve of IC2574 can very well be reproduced when baryon physics is taken into account. We therefore suggest that before introducing new exotic features in the standard cosmological model, albeit legitimate, baryonic physics should be treated properly to reach agreement with observations.
Peer Review Status:Awaiting Review
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