Title:X-Ray Views of Galactic Accreting Pulsars in High-Mass X-Ray Binaries

Abstract:Accreting X-ray pulsars, located in X-ray binaries, are neutron stars with magnetic fields as strong as $B\sim10^{12\text{--}13}$ G. This review offers a concise overview of the accretion and radiation processes of X-ray pulsars and summarizes their rich observational features, particularly focusing on complex and variable temporal phenomena, spectral properties, and evolution, the new window for X-ray polarimetry and multi-wavelength advances. We also briefly discuss other related systems, i.e., gamma-ray binaries and pulsating ultraluminous X-ray sources.

Comments:

Universe 2024, 10(12), 453

Abstract: 2412.17649
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Title:Neutrinos as background and signal in Migdal search

Authors:Tarak Nath Maity

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Abstract:Ionization or excitation resulting from the delayed response of the electron cloud to nuclear recoil is known as the Migdal effect. Dark matter searches utilizing this process set the most stringent bounds on the spin-independent dark matter-nucleon scattering cross section over a large region of the sub-GeV dark matter parameter space, underscoring its significance in dark matter detection. In this paper, we quantify the regions of dark matter parameter space that are challenging to probe via the Migdal effect due to the presence of dominant solar neutrino backgrounds for both liquid noble and semiconductor targets. Our findings reveal that there is no hard floor in the dark matter parameter space. Instead, we map the so called neutrino fog. In mapping the neutrino fog, we identify the importance of incorporating the Migdal effect induced by neutrinos, as well as neutrino-electron scattering and dominant coherent neutrino-nucleus scattering, particularly for semiconductor targets. Furthermore, we demonstrate that a large portion of the relic density allowed parameter space lies within the neutrino fog. Finally, we estimate the exposure required to detect neutrino induced Migdal events in direct detection experiments.

Comments:

21 pages, 6 figures. Comments are welcome

Abstract: 2412.17447
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Title:A Search for Radio Millisecond Pulsar Companions around Extremely Low-mass White Dwarfs with Ellipsoidal Variability

Authors:W. J. Huang, Pak-Hin Thomas Tam, L. L. Ren, J. M. Lin

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Abstract:Extremely low-mass white dwarfs (ELM WDs) are helium-core white dwarfs with masses less than 0.3 $M_{\odot}$. Short-period ELM WD binaries that exhibit ellipsoidal variations may harbor heavier companions, either massive white dwarfs or millisecond pulsars (MSPs). In this study, we selected $\sim$ 12,000 ELM WDs or their candidates, and searched for ellipsoidal-like lightcurves with orbital periods shorter than one day, by using the public data from Zwicky Transient Facility. Finally 23 such systems were found, with 17 being newly discovered. We selected nine high-priority targets likely to evolve from the Roche-lobe overflow channel and estimated their companion masses from the extracted ellipsoidal variation amplitude. Among them, the four targets have companion masses exceeding 1 $M_{\odot}$. We performed a search for radio pulsations from six of these targets by using Five-hundred-meter Aperture Spherical radio Telescope. However, no convincing radio pulsed signals were found, resulting in upper limits for the radio flux at around 8 $\mu$Jy. Given the non-detection of radio pulsations from a total of 11 similar systems, the fraction of ellipsoidal ELM WDs around MSPs is estimated to be below 15$^{+6}_{-3}$%. We anticipate that multi-wavelength studies of more ellipsoidal-like ELM WDs will further constrain the fraction.

Comments:

14 pages, 7 figures, accepted in ApJ

Abstract: 2412.17446
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Title:Prediction of Star Formation Rates Using an Artificial Neural Network

Authors:Ashraf Ayubinia, Jong-hak Woo, Fatemeh Hafezianzadeh, Taehwan Kim, Changseok Kim

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Abstract:In this study, we develop an artificial neural network to estimate the infrared (IR) luminosity and star formation rates (SFR) of galaxies. Our network is trained using 'true' IR luminosity values derived from modeling the IR spectral energy distributions (SEDs) of FIR-detected galaxies. We explore five different sets of input features, each incorporating optical, mid-infrared (MIR), near-infrared (NIR), ultraviolet (UV), and emission line data, along with spectroscopic redshifts and uncertainties. All feature sets yield similar IR luminosity predictions, but including all photometric data leads to slightly improved performance. This suggests that comprehensive photometric information enhances the accuracy of our predictions. Our network is applied to a sample of SDSS galaxies defined as unseen data, and the results are compared with three published catalogs of SFRs. Overall, our network demonstrates excellent performance for star-forming galaxies while we observe discrepancies in composite and AGN samples. These inconsistencies may stem from uncertainties inherent in the compared catalogs or potential limitations in the performance of our network.

Comments:

13 pages, 7 figures, and 2 tables. Accepted for publication in ApJ

Abstract: 2412.18152
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Title:Extremely luminous optical afterglow of a distant and energetic gamma-ray burst GRB 230204B

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Abstract:Robotic telescope networks play an important role in capturing early and bright optical afterglows, providing critical insights into the energetics and emission mechanisms of GRBs. In this study, we analyze GRB 230204B, an exceptionally energetic and multi-pulsed long GRB, detected by the Fermi GBM and MAXI detectors, with an isotropic equivalent gamma-ray energy exceeding 10$^{54}$ erg. Time-resolved spectral analysis reveals a transition in the prompt emission from hard (sub-photospheric dominated) spectra during early pulses to softer (synchrotron radiation dominated) spectra in later pulses, indicative of a hybrid jet composition. We report the discovery and characterization of the optical afterglow using the MASTER and BOOTES robotic telescope networks, alongside long-term radio observations extending to 335 days post-burst with the ATCA. At ~1.3 ks post-burst, the optical luminosity was exceptionally high, surpassing even other bright GRBs, such as GRB 221009A (the ``BOAT"). Multi-wavelength modeling, incorporating data from MASTER, BOOTES, DOT, Swift/XRT, and radio observations, was conducted using an external ISM forward-shock top-hat jet model with afterglowpy. The results reveal a narrow and highly collimated jet with a circumburst density of n$_{0}$ ~ 28.12 cm$^{-3}$, kinetic energy E$_{K}$ ~ 4.18 x 10$^{55}$ erg, and a relatively low value of $\epsilon_{B}$ = 2.14 x 10$^{-6}$, indicating shock-compression of the magnetic field in the surrounding interstellar medium. We constrained a low radiative efficiency of ~ 4.3 %. This study highlights the indispensable contribution of robotic networks to early afterglow observations and advances our understanding of GRB 230204B unique characteristics and underlying jet physics.

Comments:

27 pages, 12 figures, 8 tables, submitted

Abstract: 2412.18767
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Title:Identifying New $γ$-Ray Sources in All-Sky Surveys Based on Fermipy's Advanced Algorithm

Authors:Y.C.Xiang, P.Feng, X.F.Lan

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Abstract:We employ an efficient method for identifying gamma-ray sources across the entire sky, leveraging advanced algorithms from Fermi p y, and cleverly utilizing the Galactic diffuse background emission model to partition the entire sky into 72 regions,thereby greatly enhancing the efficiency of discovering new sources throughout the sky through multi-threaded parallel computing. After confirming the reliability of the new method, we applied it for the first time to analyze data from the Fermi Large Area Telescope encompassing approximately 15.41yr of all sky surveys.
Through this analysis, we successfully identified 1379 new sources with levels exceeding 4sigma, of which 497 sources exhibited higher significance levels exceeding 5sigma. Subsequently, we performed a systematic analysis of the spatial extension, spectra, and light variation characteristics of these newly identified sources. We identified 21 extended sources and 23 sources exhibiting spectral curvature above 10GeV. Additionally, we identified 44 variable sources above 1GeV.

Abstract: 2412.12577
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Title:The stochastic MHD equations driven by pure jump noise in $L^p$ spaces

Authors:Kaicheng Ni, Heling Su, Jiahui Zhu

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Abstract:We consider the stochastic incompressible magnetohydrodynamic equations driven by additive jump noises on either the whole space $\mathbb{R}^d$, $d=2,3$ or a smooth bounded domain $D$ in $\mathbb{R}^d$. We establish the local existence and uniqueness of a mild solution in the space $L^q(0,T;\mathbb{L}^{p\otimes}_{\sigma}(D))$ allowing for initial data with less regularity, including the marginal case $u_0\in \mathbb{L}^{d\otimes}_{\sigma}(D)$. In the two-dimensional case, we also prove the global existence of mild solutions.

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