Astrophysics and Space Science最新文献

The initiation of the Coronal Mass Ejection (CME) on 30 December 2004 at 10:57 UT, with an initial speed of 1250 km/s, has been studied using multiwavelength data. EUV and radio H-alpha images play a significant role in identifying multiple reconnections. The reconnection occurring in the northern and southern parts of Active Region (AR10715) led to C1.3 and M2.2 flares. The southern arcade system expands and reconnects with the overlying field lines, resulting in a fast, wide CME. Hence, our multiwavelength analysis provides evidence that internal reconnection, followed by external reconnection, causes large-scale eruption at 10:50 UT. Radio signatures also support this scenario.

Gamma-ray bursts, or GRBs, are the most energetic phenomena in the universe that may occur as a result of mergers between compact objects and supernova explosions. While many GRBs are characterized by having a single emission peak, a few have been found to occur with multiple peaks having potential emission gaps dubbed “quiescent episodes.” While the occurrence of such intervals remains in debate, the spectral study of these GRBs can provide an insight about the evolution of parameters within different peaks of the same GRB. We have performed the time-resolved analysis of a sample of four GRBs having emission in both the GBM and LAT range. These GRBs were selected based on a particular criteria. We have also studied the evolution of spectral parameters and tested each interval for the Amati Correlation through the E_iso and E_i,peak relations. We have found the individual peaks to fit with simple models. The low-energy index was typically found to evolve with a hard-to-soft spectrum. The flux indicates a decay in time, while peak energy evolution may reveal different trends. One of the GRBs in our sample with a potential precursor emission seems to evolve differently than the rest of the GRBs in the sample.

We present an approach that can be utilized in order to account for the covariate shift between two datasets of the same observable with different distributions. This helps improve the generalizability of a neural network model trained on in-distribution samples (IDs) when inferring cosmology at the field level on out-of-distribution samples (OODs) of unknown labels. We make use of HI maps from the two simulation suites in CAMELS, IllustrisTNG and SIMBA. We consider two different techniques, namely adversarial approach and optimal transport, to adapt a target network whose initial weights are those of a source network pre-trained on a labeled dataset. Results show that after adaptation, salient features that are extracted by source and target encoders are well aligned in the embedding space. This indicates that the target encoder has learned the representations of the target domain via the adversarial training and optimal transport. Furthermore, in all scenarios considered in our analyses, the target encoder, which does not have access to any labels ((Omega _{mathrm{m}})) during adaptation phase, is able to retrieve the underlying (Omega _{mathrm{m}}) from out-of-distribution maps to a great accuracy of (R^{2}) score ≥ 0.9, comparable to the performance of the source encoder trained in a supervised learning setup. We further test the viability of the techniques when only a few out-of-distribution instances are available for training and find that the target encoder still reasonably recovers the matter density. Our approach is critical in extracting information from upcoming large scale surveys.

The flare ribbon and an associated filament eruption are diagnosed using O iv 1401.16 Å, Si iv 1402.77 Å, and Mg ii k 2796.35 Å spectral lines provided by Interface Region Imaging Spectrograph (IRIS). The flare ribbons have downflow (redshifts) in all these lines, and this redshift decreases from the transition region to the chromosphere. While the overlapping region (flare-ribbon+filament rise/eruption) is dominated by upflows (blueshifts) in all three spectral lines. We found an extremely blueshifted Si iv profile (i.e., blueshift around −180 km/s) in the overlapping region. The mean non-thermal velocity (v_nt) in the flare ribbons is higher in O iv than Si iv. While, in the overlapping region, O iv have lower v_nt than Si iv. Note that very high v_nt around 80 km/s (in Si iv) exists in this weak B-class flare. The Mg ii k line widths are almost the same in the flare ribbon and overlapping region but, they are extremely broad than previously reported. We found double peak profiles of Si iv and O iv in the overlapping region. Most probably, one peak is due to downflow (flare ribbon) and another due to upflow (filament rise/eruption). We report a high redshift of more than 150 km/s in the weak B-class flare. In some cases, both peaks show upflows which might be the result of the superposition of two different sources, i.e., overlapping of two different velocity distributions in the line of sight.

On 9 February 2020 at 11:03 pm EST, an Atlas V 411 rocket launched the ESA/ NASA Solar Orbiter mission. This mission was the culmination of decades of work across many countries to achieve the goal of getting close to the Sun and measuring how the Sun creates and maintains the heliosphere. The mission’s goal is to understand how the inner heliosphere works and how solar activity impacts it. The spacecraft achieves this with a specially designed highly elliptical orbit that gets close to the Sun twice a year. It reaches as close as 0.28 au requiring a novel heat shield to protect the instruments from the intense heat (the front side of the heat shield reaches around 500 ^∘C at this location). There are ten scientific instruments onboard: Six remote-sensing instruments observe solar activity across the electromagnetic spectrum on small and large scales, including imaging the source regions of the solar wind. They are accompanied by four in-situ instruments to probe the properties of the solar wind as it flows past the spacecraft. This review paper describes a selection of results from Solar Orbiter during its cruise phase and the beginning of its nominal scientific operations phase, and looks towards the next phases of the mission, when the spacecraft leaves the ecliptic plane to observe the solar poles for the first time.

The study of massive binary systems has steadily progressed over the past decades, with increasing focus on their evolution, interactions and mergers, driven by improvements in computational modelling and observational techniques. In particular, when a binary system involves a massive giant and a neutron star (NS) or a black hole (BH) that go through common envelope evolution (CEE), it might result in the merger of the compact object with the core of its giant companion, giving rise to various high energy astrophysical phenomena. We review the different evolutionary channels that lead to compact object-core mergers, key physical processes with emphasis on the role of accretion physics, feasibility of r-process nucleosynthesis, expected observable electromagnetic, neutrino and gravitational-wave (GW) signatures, as well as potential correlation with detected core collapse supernovae (CCSNe), luminous fast blue optical transients (LFBOTs) and low luminosity long gamma-ray bursts (LGRBs). After presenting our current understanding of these mergers, we conclude discussing prospects for future advancements.

In this paper, we calibrate the luminosity relation of gamma-ray bursts (GRBs) with the machine learning (ML) algorithms from the Pantheon+ sample of type Ia supernovae in a cosmology-independent way. By using K-Nearest Neighbors (KNN) and Random Forest (RF) selected with the best performance in the ML algorithms, we calibrate the Amati relation ((E_{mathrm{p}})-(E_{mathrm{iso}})) relation with the A219 sample to construct the Hubble diagram of GRBs. Via the Markov Chain Monte Carlo numerical method with GRBs at high redshift and latest observational Hubble data, we find the results of constraints on cosmological models by using KNN and RF algorithms are consistent with those obtained from GRBs calibrated by using the Gaussian Process.

In this paper, an efficient wavelet-based algorithm is introduced to investigate the approximate solutions for a few nonlinear singular initial value problems arising in astrophysics. Ultraspherical wavelet method (USWM) is utilized for solving the Lane-Emden type equations. The proposed method is utilized to convert the given nonlinear singular value differential equations into a system of algebraic equations using operational matrices of derivatives. Convergence analysis of the method is discussed. The obtained solutions are compared with LWM, CWM and exact solutions. A few numerical experiments are given to demonstrate the accuracy and efficiency of the proposed method. Satisfactory agreement with exact and other numerical solutions is observed. The efficiency of the proposed method is confirmed by means of computational CPU runtime. Moreover, the use of USWM is investigated to be simple, accurate and less computational cost.

We studied the dependence of selected structural and kinematic properties of early-type galaxies (ETGs) on their environments. The selected sample, extracted from the SDSS-DR17 MaNGA survey, consists of 946 ETGs in clusters (cETGs) and 288 isolated ETGs (iETGs) within a spectroscopic redshift (zleq 0.15). We investigated the distribution of these galaxies in the Fundamental Plane (FP), Kormendy Relation (KR), Faber-Jackson Relation (FJR) and the Mass-Size Relation (MSR). We found that massive galaxies, whose stellar masses (M_{*}> 10^{11}M_{odot }), are predominantly elliptical ((>65%)). The analysis of the four scaling relations showed that the effect of the host environment is negligible for massive ((M_{*}>10^{11.5}M_{odot })) ETGs, most likely because of their passive evolution through dry mergers and/or stellar aging. On the other hand, low-mass ETGs are influenced by their environment, where iETGs with (M_{*}<10^{10}M_{odot }) and velocity dispersion (sigma _{0}leq 100) km/sec are (25%) more luminous and (11.5%) larger than cETGs. Low-mass cETGs may have suffered processes that removed their gas content and hence quenched star formation while low-mass iETGs may have experienced a recent wet merger that triggered star formation and led to their, currently, observed low mass-to-light ratio. However, further spectral analysis is needed to confirm these findings.

On 28 January 2018, the High Energy Stereoscopic System (H.E.S.S.) reported a significant very-high-energy (VHE) gamma-ray activity, occurring nearly 11 days after the high-energy (HE) gamma-ray flare observed by Fermi-LAT from the blazar 3C 279. It has long been considered a candidate site for accelerating particles to ultra-high energies (UHE) and producing subsequent secondaries. Such an event can be crucial to explore the different phenomena of secondary production from the UHEs and viable to understand the energetics of the sources. Our study finds that the multi-wavelength flare, spanning UV, optical, X-rays, and HE gamma rays, originates from leptonic emissions, whereas the delayed VHE activity by proton synchrotron emission within the source, results from the extended duration of particle acceleration. To explain the prolonged electromagnetic emission, our model requires a magnetic field luminosity ((L^{prime }_{B})) (6.9 times 10^{43}) erg/sec, a proton luminosity ((L^{prime }_{p})) (1.2 times 10^{46}) erg/sec in the jet frame.