Astronomische Nachrichten最新文献

We evaluate the feasibility of Bose–Einstein condensate stars (BECS) as models for the interior of neutron stars (NSs). BECS are compact objects composed of bosons, formed through the spin-parallel pairing of neutrons. Here, we utilize the astronomical data from GW170817, XMMU J173203.3-344518 (the lightest NS known), and a novel lower limit on NS core heat capacity to scrutinize the compatibility of BECS with these recent observations of NSs. Our specific focus is to constrain the values of the scattering length $��a�$, parameter determining the strength of particle interactions in the model. Our analysis suggests that if the stars involved in GW170817 were BECSs, the scattering length of their constituent bosons should fall within the $��4�$ to $��10�$ fm range. Additionally, at a scattering length of $��a�\sim �3.1�-�4�$ fm, stars with mass and radius characteristics akin to XMMU J173203.3-344518 are identified. Moreover, we find that the heat capacity depends on the mass and temperature of BECS, and surpasses the established lower bound for NS cores when $��a�>�2�-�5�$ fm. In summary, our results endorse BECS models with $��a�\sim �4�$ fm, providing NS observables in agreement with diverse observations and contributing to the understanding of NS interiors.

Achieving a comprehensive understanding of the star and planet formation process is one of the fundamental tasks of astrophysics, requiring detailed knowledge of the physical conditions during the different phases of this process. During the earliest stages, that is, concerning physical processes in molecular clouds and filaments, the column density N(H₂), dust temperature $��T�$ and dust emissivity index $��\beta �$ of these objects can be derived by adopting a modified blackbody fit of the far-infrared (FIR) to (sub-)millimeter spectral energy distributions (SEDs). However, this often applied method is based on various assumptions. In addition, the observational basis and required, but only assumed cloud properties, such as a limited wavelength-coverage of the SED and dust properties, respectively, may differ between different studies. We review the basic limitations of this method and evaluate their impact on the derived physical properties of the objects of interest, that is, molecular clouds and filaments. We find that the highest uncertainty when applying this method is introduced by the often poorly constrained dust properties. Therefore, we propose to first derive the optical depth and subsequently the column density with the help of a suitable dust model as the optical depth can be obtained with high accuracy, especially at longer wavelengths. The method provides reliable results up to the high densities and corresponding optical depths observed in molecular clouds. Considering typically used observational data, that is, measurements obtained with FIR instruments like Herschel/PACS, JCMT/SCUBA-2 and SOFIA/HAWC+, data at four wavelengths are sufficient to obtain accurate results. Furthermore, we find that the dust emissivity index $��\beta �$ derived from this method is not suitable as an indicator of dust grain size.

One normal outburst and three mini-outbursts have been detected by Rossi X-ray Timing Explorer (RXTE) satellite after 2000 in the well-known black hole X-ray binary XTE J1550-564. In our work, we explored the energy spectral properties of the four outbursts and the three mini-outbursts retained in the Low/Hard state. The results show that the X-ray spectra of the three mini-outbursts are harder than that of normal outburst and have no disk component. In the correlation analysis, the $��\Gamma �-�L_X�/�L_{\mathrm{Edd}}�$ anti-relationship of the three mini-outbursts suggested that it may be a result of the incomplete evolutionary success of Shakura-Sunyaev disk. The whole X-ray spectral correlation evolution shows well the state transition from the Shakura-Sunyaev disk to the advection-dominated accretion flow. We think that the three mini-outbursts may originated from a small discrete accretion event.

A lobster eye (LE) is a wide-field type of X-ray optics, which provides a large field of view at the expense of angular resolution. The optics presented in this paper are the LE optics in Schmidt arrangement made from glass sheets with golden reflective coatings. It was used as a scientific payload on the WRXR rocket experiment. Before the mission itself, the optics was tested on ground to obtain more information about its behavior. Part of these tests were several nights of observation at the Ondrejov observatory. We used the optics in combination with a CMOS camera to acquire images in visible light of various bright sources in the sky. In order to enable long-time exposures, the robotic mount of the BART telescope was used. The goal of this experiment was to confirm the focal length of the optics using a source at infinity, and to show how the optics, designed for X-ray observations, performs in visible light. This brief article describes the methods used for evaluation and presents and discusses the results obtained within the night observation experiment.

In this work, we study how to improve well-known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of $��120�$ clusters, with masses greater than $��{10}^{13.25}�M_{\odot }�$, selected from the IllustrisTNG simulations (namely, the TNG100 runs). In $��99�\%�$ of the cases (i.e., $��119�$ systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is $��28�\%�$ in the identification of descendants for this sample of cluster galaxies.

A study of double-charmed meson production in high-energy proton–proton collisions at the Large Hadron Collider is presented. Considering the color dipole formalism developed in the transverse momentum representation along with the double parton scattering mechanism, predictions are made for the transverse momentum differential cross section for different pairs of $��D�$-mesons. The theoretical results cover the center-of-mass energy and forward rapidities available by the LHCb experiment. The proton–proton results considering different unintegrated gluon distributions are compared to the respective data collected at the LHC.

We study the energy distribution of hard gluons traversing a dense quark-gluon plasma by comparing various transverse momentum broadening rates $��\hat{q}��\left(�t�\right)��$, using a probabilistic perturbative approach. These results were applied to address the thermalization problem in heavy ion collisions. Within the weak coupling model, thermalization follows a “bottom-up” process: early-formed high-energy partons emit low-energy gluons, leading to their equilibrium formation, creating a thermal bath that facilitates equilibrium in the high-energy sector. Under this scenario, we model the time dependencies of $��\hat{q}��\left(�t�\right)��$ as a power-law $��\hat{q}��\left(�t�\right)��\sim �t^n�$, and assess the impact of $��n�$ on the distribution of hard gluons passing through the medium.

We fitted 75 pulses from 44 gamma-ray burst (GRB) prompt emission lightcurves, including four short ones and 40 long ones. Each pulse is fitted by a fast-rising exponential-decay (FRED) model. The statistical properties of these pulses are analyzed and compared with previous works. We found that the FRED model is almost suitable to describe all the pulses. We reconfirmed that there is a linear correlation between the full width at half maximum $��\text{FWHM}�$ and the pulse rising time $��T_{\text{rise}}�$, which supports the idea that the individual pulse is emitted at once within one explosion. Moreover, we found that several pulses do not obey the $��\text{FWHM}�-�T_{\text{rise}}�$ correlation, this implies that the radiation process of the prompt emission especially in the multi-pulse GRBs might involve more than one type and even possibly change with time. The innovation of this work lies in examining the statistical characteristics of lightcurves of both long and short-duration GRBs and re-evaluating the applicability of empirical relationships discovered by predecessors to both types of GRBs while paying special attention to the existence of outlier pulses. This work has positive implications for further exploring the diversity of GRB prompt radiation mechanisms.

In this work, we study the photoproduction of $��\rho �$ mesons considering the proton and the nucleus as the target. Utilizing the dipole picture and the wave functions obtained via AdS/QCD, we were able to describe the HERA $���\gamma �p��$ data and extend the formalism to the nuclear case considering the Glauber–Gribov model. The preliminary results obtained in the nuclear regime are compared to the recent LHC $��\text{PbPb}�\to �\text{ρPbPb}�$ data and suggest the presence of a nuclear effect called shadowing.