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15 pages, 3192 KiB

Open AccessArticle

Search for DA White Dwarf Binary Candidates from LAMOST DR7

by Hua-Hui Yan, Jing-Kun Zhao, Wei-Bin Shi, Jin-Cheng Guo, Liang Wang, Zhen-Xin Lei and Gang Zhao

Universe 2023, 9(4), 177; https://doi.org/10.3390/universe9040177 - 3 Apr 2023

Viewed by 1624

Abstract

We obtained spectroscopy data for 761 Degenerate A (DA)white dwarfs (WDs) with multiple LAMOST observations. The radial velocity (RV) of each spectrum was calculated using the cross-correlation function method (CCF), and 60 DA WD binary candidates were selected based on the variation of [...] Read more.

We obtained spectroscopy data for 761 Degenerate A (DA)white dwarfs (WDs) with multiple LAMOST observations. The radial velocity (RV) of each spectrum was calculated using the cross-correlation function method (CCF), and 60 DA WD binary candidates were selected based on the variation of the RV. Then, the atmosphere parameter

T_{e f f}

,

log g

, and the mass of these DA WDs were estimated by the Balmer line fitting method and interpolation in theoretical evolution tracks, respectively. Our parameters are consistent with those from SDSS and Gaia for the common stars. No evident difference in the mass distribution of binary candidates compared with total DA WDs was found. We surmise these DA WD binary candidates are mainly composed of two WDs. With the Zwicky Transient Facility (ZTF) data, we obtained the light curve periods of two targets with significant light curve periods in the DA WD binary candidates. For the spectra with anomalous CCF curves or with large errors in their RV calculations, we re-certified their spectral types by visual review. Based on their spectral features, we found 11 DA + M-type binaries and four cataclysmic variables (CVs). The light curve period of one CV was obtained with ZTF data. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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14 pages, 497 KiB

Open AccessArticle

Jet Cloud–Star Interaction as an Interpretation of Neutrino Outburst from the Blazar TXS 0506+056

by Kai Wang, Ruo-Yu Liu, Zhuo Li, Xiang-Yu Wang and Zi-Gao Dai

Universe 2023, 9(1), 1; https://doi.org/10.3390/universe9010001 - 20 Dec 2022

Cited by 26 | Viewed by 1572

Abstract

A neutrino outburst between September 2014 and March 2015 was discovered from the blazar TXS 0506+056 by an investigation of

9.5

years of IceCube data, while the blazar was in a quiescent state during the outburst with a gamma-ray flux of only about [...] Read more.

A neutrino outburst between September 2014 and March 2015 was discovered from the blazar TXS 0506+056 by an investigation of

9.5

years of IceCube data, while the blazar was in a quiescent state during the outburst with a gamma-ray flux of only about one-fifth of the neutrino flux. In this work, we give a possible interpretation of the abnormal feature by proposing that the neutrino outburst originated from the interaction between a relativistic jet and a dense gas cloud formed via the tidally disrupted envelope of a red giant being blown apart by the impact of the jet. Gamma-ray photons and electron/positron pairs produced through the hadronuclear interactions, correspondingly, will induce electromagnetic cascades and then make the cloud ionized and thermalized. The EM radiation from jet cloud–star interaction is mainly contributed by the relatively low-energy relativistic protons which propagate in the diffusion regime inside the cloud due to magnetic deflections, whereas the observed high-energy neutrinos (≳100 TeV) are produced by the relatively high-energy protons which can continue to beam owing to the weak magnetic deflections, inducing a much higher flux of neutrinos than electromagnetic radiation. The observed low-energy electromagnetic radiations during the neutrino outburst period are almost the same as that in the quiescent state of the source, so it may arise mainly as the same state as the generally quiescent. As a result, due to the intrusion of a dense cloud, the neutrino outburst can be expected, and, in the meantime, the accompanying electromagnetic radiations from hadronic processes will not cause any enhancement in the blazar’s electromagnetic flux. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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13 pages, 11424 KiB

Open AccessArticle

Magnetar Wind-Driven Shock Breakout Emission after Double Neutron Star Mergers: The Effect of the Anisotropy of the Merger Ejecta

by Guang-Lei Wu, Yun-Wei Yu and Shao-Ze Li

Universe 2022, 8(12), 633; https://doi.org/10.3390/universe8120633 - 29 Nov 2022

Cited by 3 | Viewed by 1331

Abstract

A rapidly rotating and highly magnetized remnant neutron star (NS; magnetar) could survive from a merger of double NSs and drive a powerful relativistic wind. The early interaction of this wind with the previous merger ejecta can lead to shock breakout (SBO) emission [...] Read more.

A rapidly rotating and highly magnetized remnant neutron star (NS; magnetar) could survive from a merger of double NSs and drive a powerful relativistic wind. The early interaction of this wind with the previous merger ejecta can lead to shock breakout (SBO) emission mainly in ultraviolet and soft X-ray bands, which provides an observational signature for the existence of the remnant magnetar. Here, we investigate the effect of an anisotropic structure of the merger ejecta on the SBO emission. It is found that the bolometric light curve of the SBO emission can be broadened, since the SBO can occur at different times for different directions. In more detail, the profile of the SBO light curve can be highly dependent on the ejecta structure and, thus, we can in principle use the SBO light curves to probe the structure of the merger ejecta in future. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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19 pages, 775 KiB

Open AccessArticle

Afterglow Light Curves from Off-Axis GRB Jets in Stratified Circumburst Medium

by Xiao-Hong Zhao and Kang-Fa Cheng

Universe 2022, 8(11), 588; https://doi.org/10.3390/universe8110588 - 7 Nov 2022

Cited by 1 | Viewed by 1599

Abstract

We study the gamma-ray burst (GRB) afterglow light curves produced by an off-axis jet in a stratified circumburst medium and summarize the temporal indices of the coasting phase, the deceleration phase, the Newtonian phase, and the deep Newtonian phase for various viewing angles [...] Read more.

We study the gamma-ray burst (GRB) afterglow light curves produced by an off-axis jet in a stratified circumburst medium and summarize the temporal indices of the coasting phase, the deceleration phase, the Newtonian phase, and the deep Newtonian phase for various viewing angles and power-law indices of medium density. Generally, the afterglow light curves of off-axis GRBs in the homogeneous interstellar medium have a steep rise arising due to jet deceleration. In the stratified medium, the flux rises is more shallow but peaks earlier for the same viewing angle due to faster deceleration of the jet running into the denser stratified medium, compared with the case of the interstellar medium (ISM). Observations of off-axis bursts will possibly increase over the coming years due to the arrival of the multi-messenger era and the forthcoming surveys in multiple bands. The temporal indices of off-axis afterglows derived in the paper will provide a reference for comparison with the observations and can diagnose the circumburst environment. The numerical code calculating the afterglow light curve also can be used to fit the multi-wavelength light curves. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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10 pages, 513 KiB

Open AccessArticle

An Unsupervised Machine Learning Method for Electron–Proton Discrimination of the DAMPE Experiment

by Zhihui Xu, Xiang Li, Mingyang Cui, Chuan Yue, Wei Jiang, Wenhao Li and Qiang Yuan

Universe 2022, 8(11), 570; https://doi.org/10.3390/universe8110570 - 30 Oct 2022

Cited by 1 | Viewed by 1351

Abstract

Galactic cosmic rays are mostly made up of energetic nuclei, with less than

1 %

of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we [...] Read more.

Galactic cosmic rays are mostly made up of energetic nuclei, with less than

1 %

of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we develop an unsupervised machine learning method to identify electrons and positrons from cosmic ray protons for the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the supervised learning method used in the DAMPE experiment, this unsupervised method relies solely on real data except for the background estimation process. As a result, it could effectively reduce the uncertainties from simulations. For three energy ranges of electrons and positrons, 80–128 GeV, 350–700 GeV, and 2–5 TeV, the residual background fractions in the electron sample are found to be about (0.45 ± 0.02)%, (0.52 ± 0.04)%, and (10.55 ± 1.80)%, and the background rejection power is about (6.21 ± 0.03) ×

10^{4}

, (9.03 ± 0.05) ×

10^{4}

, and (3.06 ± 0.32) ×

10^{4}

, respectively. This method gives a higher background rejection power in all energy ranges than the traditional morphological parameterization method and reaches comparable background rejection performance compared with supervised machine learning methods. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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8 pages, 604 KiB

Open AccessArticle

Observe Gamma-Rays and Neutrinos Associated with Ultra-High Energy Cosmic Rays

by Qinyuan Zhang, Xishui Tian and Zhuo Li

Universe 2022, 8(11), 560; https://doi.org/10.3390/universe8110560 - 27 Oct 2022

Viewed by 1314

Abstract

IceCube measures a diffuse neutrino flux comparable to the Waxman-Bahcall bound, which suggests the possibility that the ultra-high energy cosmic rays (UHECRs) have a common origin with diffuse high energy neutrinos. We propose high energy gamma-ray and/or neutrino observations toward the arrival directions [...] Read more.

IceCube measures a diffuse neutrino flux comparable to the Waxman-Bahcall bound, which suggests the possibility that the ultra-high energy cosmic rays (UHECRs) have a common origin with diffuse high energy neutrinos. We propose high energy gamma-ray and/or neutrino observations toward the arrival directions of UHECRs to search for the sources and test this possibility. We calculate the detection probability of gamma-ray/neutrino sources, and find that the average probability per UHECR of >10 EeV is ∼10% if the sensitivity of the gamma-ray or neutrino telescope is ∼10

^{- 12}

erg cm

^{- 2}

s

^{- 1}

and the source number density is ∼10

^{- 5}

Mpc

^{- 3}

. Future gamma-ray and neutrino observations toward UHECRs, e.g., by LHAASO-WCDA, CTA, IceCube/Gen2, are encouraged to constrain the density of UHECR sources or even identify the sources of UHECRs. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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15 pages, 528 KiB

Open AccessArticle

A PeVatron Candidate: Modeling the Boomerang Nebula in X-ray Band

by Xuan-Han Liang, Chao-Ming Li, Qi-Zuo Wu, Jia-Shu Pan and Ruo-Yu Liu

Universe 2022, 8(10), 547; https://doi.org/10.3390/universe8100547 - 21 Oct 2022

Cited by 9 | Viewed by 2087

Abstract

Pulsar wind nebula (PWN) Boomerang and the associated supernova remnant (SNR) G106.3+2.7 are among candidates for the ultra-high-energy (UHE) gamma-ray counterparts published by LHAASO. Although the centroid of the extended source, LHAASO J2226+6057, deviates from the pulsar’s position by about

{0.3}^{\circ}

, [...] Read more.

Pulsar wind nebula (PWN) Boomerang and the associated supernova remnant (SNR) G106.3+2.7 are among candidates for the ultra-high-energy (UHE) gamma-ray counterparts published by LHAASO. Although the centroid of the extended source, LHAASO J2226+6057, deviates from the pulsar’s position by about

{0.3}^{\circ}

, the source partially covers the PWN. Therefore, we cannot totally exclude the possibility that part of the UHE emission comes from the PWN. Previous studies mainly focus on whether the SNR is a PeVatron, while neglecting the energetic PWN. Here, we explore the possibility of the Boomerang Nebula being a PeVatron candidate by studying its X-ray radiation. By modeling the diffusion of relativistic electrons injected in the PWN, we fit the radial profiles of X-ray surface brightness and photon index. The solution with a magnetic field

B = 140 μ G

can well reproduce the observed profiles and implies a severe suppression of IC scattering of electrons. Hence, if future observations reveal part of the UHE emission originating from the PWN, we propose to introduce a proton component to account for the UHE emission in light of the recent LHAASO measurement on Crab Nebula. In this sense, Boomerang Nebula would be a hadronic PeVatron. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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12 pages, 3749 KiB

Open AccessArticle

Testing the Wave-Particle Duality of Gravitational Wave Using the Spin-Orbital-Hall Effect of Structured Light

by Qianfan Wu, Weishan Zhu and Longlong Feng

Universe 2022, 8(10), 535; https://doi.org/10.3390/universe8100535 - 16 Oct 2022

Cited by 5 | Viewed by 1795

Abstract

Probing the polarization of gravitational waves (GWs) would provide evidence of graviton, indicating the quantization of gravity. Motivated by the next generation of gravitational wave detectors, we make an attempt to study the possible helicity coupling of structured lights to GWs. With the [...] Read more.

Probing the polarization of gravitational waves (GWs) would provide evidence of graviton, indicating the quantization of gravity. Motivated by the next generation of gravitational wave detectors, we make an attempt to study the possible helicity coupling of structured lights to GWs. With the analog between gravitational fields and the generic electromagnetic media, we present a 4-vector optical Dirac equation based on the Maxwell theory under the paraxial approximation. It is found that twisted lights propagating in a gravitational field can be viewed as a non-Hermitian system with

PT

symmetry. We further demonstrate that the coupling effect between angular momentums of the GWs and twisted lights may make photons undergo both dipole and quadrupole transitions between different orbital-angular-momentum (OAM) eigenstates and lead to some measurable optical features, including the central intensity brightening and macroscopic rotation of the intensity pattern for twisted lights. The former is spin-independent, while the latter is a spin-dependent phenomenon, both of which can be viewed alternatively as the spin-orbital-Hall effect of structured lights in the GWs and can serve as an indicator of the particle nature of GWs. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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7 pages, 260 KiB

Open AccessArticle

The Possibility of Mirror Planet as Planet Nine in the Solar System

by Pei Wang, Yuchen Tang, Lei Zu, Yuanyuan Chen and Lei Feng

Universe 2022, 8(10), 523; https://doi.org/10.3390/universe8100523 - 8 Oct 2022

Cited by 1 | Viewed by 1384

Abstract

A series of dynamical anomalies in the orbits of distant trans-Neptunian objects points to a new celestial body (usually named Planet Nine) in the solar system. In this draft, we point out that a mirror planet captured from the outer solar system or [...] Read more.

A series of dynamical anomalies in the orbits of distant trans-Neptunian objects points to a new celestial body (usually named Planet Nine) in the solar system. In this draft, we point out that a mirror planet captured from the outer solar system or formed in the solar system is also a possible candidate. The introduction of the mirror matter model is due to an unbroken parity symmetry and is a potential explanation for dark matter. This mirror planet has null or fainter electromagnetic counterparts with a smaller optical radius and might be explored through gravitational effects. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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12 pages, 624 KiB

Open AccessArticle

Outliers in Spectral Time Lag-Selected Gamma Ray Bursts

by Fei-Fei Wang and Yuan-Chuan Zou

Universe 2022, 8(10), 521; https://doi.org/10.3390/universe8100521 - 8 Oct 2022

Viewed by 1420

Abstract

It is possible that astrophysical samples are polluted by some outliers, which might belong to a different sub-class. By removing the outliers, the underlying statistical features may be revealed. A more reliable correlation can be used as a standard candle relationship for cosmological [...] Read more.

It is possible that astrophysical samples are polluted by some outliers, which might belong to a different sub-class. By removing the outliers, the underlying statistical features may be revealed. A more reliable correlation can be used as a standard candle relationship for cosmological study. We present outlier searching for gamma ray bursts with the Partitioning Around Medoids (PAM) method. In this work, we choose three parameters from the sample, with all of them having rest-frame spectral time lag (

τ_{lag, i}

). In most cases, the outliers are GRBs 980425B and 030528A. Linear regression is carried out for the sample without the outliers. Some of them have passed hypothesis testing, while others have not. However, even for the passed sample, the correlation is not very significant. More parameter combinations should be considered in future work. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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13 pages, 1519 KiB

Open AccessEditor’s ChoiceArticle

Exploring Anisotropic Lorentz Invariance Violation from the Spectral-Lag Transitions of Gamma-Ray Bursts

by Jin-Nan Wei, Zi-Ke Liu, Jun-Jie Wei, Bin-Bin Zhang and Xue-Feng Wu

Universe 2022, 8(10), 519; https://doi.org/10.3390/universe8100519 - 6 Oct 2022

Cited by 1 | Viewed by 1674

Abstract

The observed spectral lags of gamma-ray bursts (GRBs) have been widely used to explore possible violations of Lorentz invariance. However, these studies were generally performed by concentrating on the rough time lag of a single highest-energy photon and ignoring the intrinsic time lag [...] Read more.

The observed spectral lags of gamma-ray bursts (GRBs) have been widely used to explore possible violations of Lorentz invariance. However, these studies were generally performed by concentrating on the rough time lag of a single highest-energy photon and ignoring the intrinsic time lag at the source. A new way to test nonbirefringent Lorentz-violating effects has been proposed by analyzing the multi-photon spectral-lag behavior of a GRB that displays a positive-to-negative transition. This method gives both a plausible description of the intrinsic energy-dependent time lag and comparatively robust constraints on Lorentz-violating effects. In this work, we conduct a systematic search for Lorentz-violating photon dispersion from the spectral-lag transition features of 32 GRBs. By fitting the spectral-lag data of these 32 GRBs, we place constraints on a variety of isotropic and anisotropic Lorentz-violating coefficients with mass dimension

d = 6

and 8. While our dispersion constraints are not competitive with existing bounds, they have the promise to complement the full coefficient space. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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10 pages, 372 KiB

Open AccessArticle

Searching for γ-ray Emission from Binary Black-Hole Mergers Detected in LIGO/Virgo O3 Run

by Chongyang Ren and Zhongxiang Wang

Universe 2022, 8(10), 517; https://doi.org/10.3390/universe8100517 - 3 Oct 2022

Cited by 1 | Viewed by 1556

Abstract

We conduct searches for γ-ray emission from the binary black-hole (BBH) mergers reported in the Gravitational-Wave Candidate Event Database (GraceDB). The γ-ray data are from the all-sky survey of the Large-Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi), [...] Read more.

We conduct searches for γ-ray emission from the binary black-hole (BBH) mergers reported in the Gravitational-Wave Candidate Event Database (GraceDB). The γ-ray data are from the all-sky survey of the Large-Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi), which allows searches for events of given time durations in large sky areas. The Two-Micron All-Sky Survey Photometric Redshift Catalog (2MPZ) is used for target selection, from which galaxy sources within the 90% credible areas and the distance ranges given by the gravitational-wave (GW) detections are determined. Excluding those BBH cases with large credible areas and/or dense fields (containing too many 2MPZ sources), searches for short transient events over the time duration of from −1 to 100 days of a trigger time for seven BBH mergers are conducted. We find two candidate short flaring events in the field of the GW event S200311bg and one in that of S190408an. However, the flaring events all have low significance (after considering the trial factor), and the third one appears off the position of the target galaxy. We discuss one of them from the first field that is detected in different short time-bin data and suggest that it is possibly a real flare arising from a radio galaxy. More such studies for the near-future GW detection run are planned, for which we will adjust our search strategy to be more effective and target flares of various time scales. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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14 pages, 9748 KiB

Open AccessArticle

X-ray Insight into High-Energy Processes in Extreme Galactic Nuclear Environment

by Q. Daniel Wang

Universe 2022, 8(10), 515; https://doi.org/10.3390/universe8100515 - 1 Oct 2022

Viewed by 2170

Abstract

Nuclear regions of galaxies apparently play a disproportionately large role in regulating their formation and evolution. How this regulation works, however, remains very uncertain. Here we review a few recent X-ray studies of our Galactic center and the inner bulge region of our [...] Read more.

Nuclear regions of galaxies apparently play a disproportionately large role in regulating their formation and evolution. How this regulation works, however, remains very uncertain. Here we review a few recent X-ray studies of our Galactic center and the inner bulge region of our major neighboring galaxy, M31, and focusing on addressing such questions as: Why are the majority of supermassive black holes (e.g., Sgr A*) so faint? What regulates the Galactic nuclear environment? Furthermore, what impact does a recent active galactic nucleus have on the ionization state of surrounding gas? These studies have provided new insight into how various relevant high-energy phenomena and processes interplay with extreme galactic nuclear environments and affect global galactic ecosystems. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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Graphical abstract

12 pages, 741 KiB

Open AccessArticle

A Comprehensive Study of Bright Fermi-GBM Short Gamma-Ray Bursts: II. Very Short Burst and Its Implications

by Ying-Yong Hu, Yao-Lin Huang, Jia-Wei Huang, Zan Zhu and Qing-Wen Tang

Universe 2022, 8(10), 512; https://doi.org/10.3390/universe8100512 - 1 Oct 2022

Viewed by 1392

Abstract

A thermal component is suggested to be the physical composition of the ejecta of several bright gamma-ray bursts (GRBs). Such a thermal component is discovered in the time-integrated spectra of several short GRBs as well as long GRBs. In this work, we present [...] Read more.

A thermal component is suggested to be the physical composition of the ejecta of several bright gamma-ray bursts (GRBs). Such a thermal component is discovered in the time-integrated spectra of several short GRBs as well as long GRBs. In this work, we present a comprehensive analysis of ten very short GRBs detected by Fermi Gamma-Ray Burst Monitor to search for the thermal component. We found that both the resultant low-energy spectral index and the peak energy in each GRB imply a common hard spectral feature, which is in favor of the main classification of the short/hard versus long/soft dichotomy in the GRB duration. We also found moderate evidence for the detection of thermal component in eight GRBs. Although such a thermal component contributes a small proportion of the global prompt gamma-ray emission, the modified thermal-radiation mechanism could enhance the proportion significantly, such as in subphotospheric dissipation. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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29 pages, 20193 KiB

Open AccessArticle

An Attempt to Construct an Activity Cycle Catalog with Kepler Long-Cadence Light Curves

by Yu-Fu Shen, Gang Zhao and Sarah A. Bird

Universe 2022, 8(9), 488; https://doi.org/10.3390/universe8090488 - 15 Sep 2022

Cited by 2 | Viewed by 1718

Abstract

Many stars show activity cycles like the Sun. Kepler has gathered ∼200,000 light curves. Most of the Kepler stars only have long-cadence light curves, which limits their applicable methods. Some metrics, for example

S_{p h}

, are effective for long-cadence light curves [...] Read more.

Many stars show activity cycles like the Sun. Kepler has gathered ∼200,000 light curves. Most of the Kepler stars only have long-cadence light curves, which limits their applicable methods. Some metrics, for example

S_{p h}

, are effective for long-cadence light curves but require rotation periods. In order to improve the utilization of Kepler light curves, we introduce and use the smoothness metric. The smoothness metric is able to analyze stars without a measured rotation period and is applicable for long-cadence light curves. We test and validate our metric, resulting in the detection of the 11 years solar cycle and a 457 days cycle for our prototype star KIC 9017220. We analyze 92,084 Kepler long-cadence light curves, and as our main results, we detect 4455 magnetic activity cycle candidates, but about 20 percent are false cycles and 50 percent are lower limits of the real cycles, and we analyze their causes in detail. As an investigation into the performance of our method, we simulate disturbance factors and prove that the p-value test is invalid under certain circumstances. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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8 pages, 755 KiB

Open AccessArticle

Gravitational Waves from Strange Star Core–Crust Oscillation

by Ze-Cheng Zou, Yong-Feng Huang and Xiao-Li Zhang

Universe 2022, 8(9), 442; https://doi.org/10.3390/universe8090442 - 25 Aug 2022

Cited by 2 | Viewed by 1755

Abstract

According to the strange quark matter hypothesis, pulsars may actually be strange stars composed of self-bound strange quark matter. The normal matter crust of a strange star, unlike that of a normal neutron star, is supported by a strong electric field. A gap [...] Read more.

According to the strange quark matter hypothesis, pulsars may actually be strange stars composed of self-bound strange quark matter. The normal matter crust of a strange star, unlike that of a normal neutron star, is supported by a strong electric field. A gap is then presented between the crust and the strange quark core. Therefore, peculiar core–crust oscillation may occur in a strange star, which can produce distinctive gravitational waves. In this paper, the waveforms of such gravitational waves are derived using a rigid model. We find that the gravitational waves are extremely weak and undetectable, even for the next-generation detectors. Therefore, the seismology of a strange star is not affected by the core–crust oscillation. Observers will have to search for other effects to diagnose the existence of the crust. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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9 pages, 348 KiB

Open AccessArticle

Search for Gamma-ray Emission from Accretion Flares of Tidal Disruption Events Possibly Associated with the IceCube Neutrinos

by Fang-Kun Peng, Ben-Yang Zhu, Lu-Ming Sun, Xin-Wen Shu and Xiang-Yu Wang

Universe 2022, 8(8), 433; https://doi.org/10.3390/universe8080433 - 21 Aug 2022

Viewed by 1767

Abstract

Outflows or disk-coronas generated in tidal disruption events (TDEs) of supermassive black holes have been suggested as possible sites of high-energy neutrinos. Three TDEs (AT2019dsg, AT2019fdr and AT2019aalc) have been claimed to be associated with high-energy astrophysical neutrinos in multi-messenger follow-ups. No GeV [...] Read more.

Outflows or disk-coronas generated in tidal disruption events (TDEs) of supermassive black holes have been suggested as possible sites of high-energy neutrinos. Three TDEs (AT2019dsg, AT2019fdr and AT2019aalc) have been claimed to be associated with high-energy astrophysical neutrinos in multi-messenger follow-ups. No GeV photons have been detected accompanying the neutrino for the three sources. In this work, we searched for the high-energy gamma-ray emission from a larger sample of TDE candidates observed by the Zwicky Transient Facility (ZTF). No significant GeV emission was observed, and the upper limits of the gamma-ray emission flux are reported. We then performed a stacking analysis for the sample sources and found that the collective gamma-ray emission of this class of sources was also not bright enough to be detected by the Fermi Large Area Telescope (Fermi-LAT). The nondetection of the high-energy gamma-ray emission from the sample TDEs could be due to the fact that the high-energy gamma rays are absorbed by soft photons in the source. Using a model-based hypothesis, the upper limit on the emission radius of the neutrino production is obtained for these TDEs:

R < 10^{16}

cm for typical TDE parameter values. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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13 pages, 603 KiB

Open AccessArticle

Explaining the ‘Outliers’ Track in Black Hole X-ray Binaries with a BZ-Jet and Inner-Disk Coupling

by Ning Chang, Xiang Liu, Fu-Guo Xie, Lang Cui and Hao Shan

Universe 2022, 8(6), 333; https://doi.org/10.3390/universe8060333 - 17 Jun 2022

Cited by 1 | Viewed by 1874

Abstract

In this paper, we investigate the black hole (BH) spin contribution to jet power, especially for the magnetic arrested disk (MAD), where only inner accretion disk luminosity is closely coupled with the spin-jet power, and try to explain the ‘outliers’ track of the [...] Read more.

In this paper, we investigate the black hole (BH) spin contribution to jet power, especially for the magnetic arrested disk (MAD), where only inner accretion disk luminosity is closely coupled with the spin-jet power, and try to explain the ‘outliers’ track of the radio

L_{R}

to X-ray luminosity

L_{X}

in two black hole X-ray binaries (BHXBs). Our results suggest that the BZ-jet and the inner-disk coupling could account for the ‘outliers’ track of the radio/X-ray correlation in two BHXBs, H1743-322 and MAXI J1348-630. Although the accretion disk of H1743-322 in the outburst could be in the MAD state, there is a lower probability that MAXI J1348-630 is in the MAD state due to its low jet production efficiency. The difference in the inner-disk bolometric luminosity ratio of the two sources implies that these two BHXBs are in different inner-disk accretion states. We further investigate the phase-changing regime of MAXI J1348-630 and find that there is a phase transition around

L_{X} / L_{Edd} \sim 10^{- 3}

. The assumption of sub-MAD is discussed as well. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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20 pages, 8772 KiB

Open AccessArticle

Antarctic Survey Telescope 3-3: Overview, System Performance and Preliminary Observations at Yaoan, Yunnan

by Tianrui Sun, Xiaoyan Li, Lei Hu, Kelai Meng, Zijian Han, Maokai Hu, Zhengyang Li, Haikun Wen, Fujia Du, Shihai Yang, Bozhong Gu, Xiangyan Yuan, Yun Li, Huihui Wang, Lei Liu, Zhenxi Zhu, Xuehai Huang, Chengming Lei, Lifan Wang and Xuefeng Wu

Universe 2022, 8(6), 303; https://doi.org/10.3390/universe8060303 - 26 May 2022

Cited by 2 | Viewed by 2547

Abstract

The third Antarctic Survey Telescope array instrument at Dome A in Antarctica, the AST3-3 telescope, has been in commissioning from March 2021. We deployed AST3-3 at the Yaoan astronomical station in Yunnan Province for an automatic time-domain survey and follow-up observations with an [...] Read more.

The third Antarctic Survey Telescope array instrument at Dome A in Antarctica, the AST3-3 telescope, has been in commissioning from March 2021. We deployed AST3-3 at the Yaoan astronomical station in Yunnan Province for an automatic time-domain survey and follow-up observations with an optimised observation and protection system. The telescope system of AST3-3 is similar to that of AST3-1 and AST3-2, except that it is equipped with a 14 K × 10 K QHY411 CMOS camera. AST3-3 has a field of view of

1 . 65^{\circ} \times 1 . 23^{\circ}

and is currently using the g band filter. During commissioning at Yaoan, AST3-3 aims to conduct an extragalactic transient survey, coupled with prompt follow-ups of opportunity targets. In this paper, we present the architecture of the AST3-3 automatic observation system. We demonstrate the data processing of observations by representatives SN 2022eyw and GRB 210420B. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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12 pages, 1307 KiB

Open AccessArticle

GRB 181110A: Constraining the Jet Structure, Circumburst Medium and the Initial Lorentz Factor

by Song Han, Xinyu Li, Luyao Jiang, Zhiping Jin, Haoning He, Yuanzhu Wang and Daming Wei

Universe 2022, 8(4), 248; https://doi.org/10.3390/universe8040248 - 18 Apr 2022

Cited by 3 | Viewed by 2191

Abstract

The afterglow data of gamma ray bursts (GRBs) can be used to constrain the physical properties of the fireball (e.g., the jet structure and opening angle) and the circumburst medium. With the peak time of the early afterglow light curve being taken as [...] Read more.

The afterglow data of gamma ray bursts (GRBs) can be used to constrain the physical properties of the fireball (e.g., the jet structure and opening angle) and the circumburst medium. With the peak time of the early afterglow light curve being taken as the deceleration time, one can estimate the initial Lorentz factor of the fireball. In this work, we perform a comprehensive analysis on the prompt emission and the afterglow data of GRB 181110A, where a clear peak is detected by Swift UVOT and XRT in optical to X-ray bands. Prompt emission spectral analysis shows that the spectrum of GRB 181110A is soft, and both hard-to-soft and intensity-tracking spectral evolution are found. By fitting the afterglow light curve and building spectral energy distribution, we find that the standard external forward shock model with a constant circumburst medium is favored, and the jet structure of GRB 181110A tends to be uniform rather than structured. With the peak time of early afterglow emission, we estimate the initial fireball Lorentz factor of GRB 181110A to be

Γ_{0} = 169_{- 40}^{+ 92}

. We also compare GRB 181110A with other typical long GRBs in a statistical context. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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Review

Jump to: Research

35 pages, 1365 KiB

Open AccessEditor’s ChoiceReview

Hubble Tension: The Evidence of New Physics

by Jian-Ping Hu and Fa-Yin Wang

Universe 2023, 9(2), 94; https://doi.org/10.3390/universe9020094 - 10 Feb 2023

Cited by 101 | Viewed by 5120

Abstract

The

Λ

CDM model provides a good fit to most astronomical observations but harbors large areas of phenomenology and ignorance. With the improvements in the precision and number of observations, discrepancies between key cosmological parameters of this model have emerged. Among them, the [...] Read more.

The

Λ

CDM model provides a good fit to most astronomical observations but harbors large areas of phenomenology and ignorance. With the improvements in the precision and number of observations, discrepancies between key cosmological parameters of this model have emerged. Among them, the most notable tension is the 4

σ

to 6

σ

deviation between the Hubble constant (

H_{0}

) estimations measured by the local distance ladder and the cosmic microwave background (CMB) measurement. In this review, we revisit the

H_{0}

tension based on the latest research and sort out evidence from solutions to this tension that might imply new physics beyond the

Λ

CDM model. The evidence leans more towards modifying the late-time universe. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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24 pages, 1493 KiB

Open AccessReview

Black Hole Hyperaccretion in Collapsars: A Review

by Yun-Feng Wei and Tong Liu

Universe 2022, 8(10), 529; https://doi.org/10.3390/universe8100529 - 12 Oct 2022

Cited by 3 | Viewed by 2373

Abstract

The collapsar model is widely accepted as one of the standard scenarios for gamma-ray bursts (GRBs). In the massive collapsar scenario, the core will collapse to a black hole (BH) surrounded by a temporary hyperaccretion disk with a very high accretion rate. The [...] Read more.

The collapsar model is widely accepted as one of the standard scenarios for gamma-ray bursts (GRBs). In the massive collapsar scenario, the core will collapse to a black hole (BH) surrounded by a temporary hyperaccretion disk with a very high accretion rate. The newborn BH hyperaccretion system would launch the relativistic jets via neutrino annihilation and Blandford-Znajek (BZ) mechanism. At the initial accretion stage, the accretion disk should be a neutrino-dominated accretion flow (NDAF). If the jets can break out from the envelope and circumstellar medium, then a GRB will be triggered. In this review, we summarize the theoretical progress on the multimessenger astronomy of the BH hyperaccretion in the center of collapsars. The main topics include: jet propagation in collapsar, MeV neutrinos from NDAFs and proto-neutron stars, gravitational waves from collapsars. Full article

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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