Nonthermal emission model of isolated X-ray pulsar RX J0420.0-5022

In this paper, an alternative theoretical interpretation to the generally assumed thermal emission models of the observed X-ray spectrum of isolated pulsar RX J0420.0-5022 is presented. It is well-known that at a pulsar surface, the distribution function of relativistic particles is one-dimensional. However, cyclotron instability causes an appearance of transverse momenta of relativistic electrons, which as a result start to radiate in the synchrotron regime. On the basis of the Vlasov kinetic equation we study the process of quasi-linear difusion (QLD) developed by means of the cyclotron instability. This mechanism enables the generation optical and X-ray emissions on the light cylinder lengthscales. An analysis of the three archival XMM-Newton observations of RX J0420.0-5022, is performed. Considering a different approach to synchrotron emission theory, a spectral energy distribution was obtained, which was in a good agreement with the observational data. A fit to the X-ray spectrum was conducted using both the present synchrotron emission model spectrum absorbed by cold interstellar matter, as well as the generally assumed black-body absorption model

Chandra observations of ten galaxy clusters

In the present study the X-ray properties of 10 galaxy clusters (CL0024+17, RXJ1347.5+1145, A223, A521, A611, A697, A907, A1204, A1413 and A2744) are analysed using the archival X-ray data of the Chandra observatory. The average temperature of each cluster is estimated to be ∼ 4 − 10 keV, and the radial temperature profiles are reconstructed. Using the Navarro-Frenk-White (NFW) density pro le of the dark matter the density and mass profiles for the dark matter and the hot diffuse gas, and also the total mass profiles are derived. The typical size of galaxy clusters and the density of the dark matter halo are estimated to be ∼ 0.1−2 Mpc and ∼ 10⁻²²−10⁻²⁴ kg/m³, respectively. The fraction of each component in the total cluster mass for the whole sample is found to be ∼ 80-90% for dark matter and ∼ 10 − 20% for intracluster gas, respectively

The distribution of dark matter and intracluster gas in galaxy clusters

We present the temperature radial profiles of intracluster gas, and the radial profiles of density and mass for dark matter and intracluster gas for five galaxy clusters: Abell 1413, Abell 1204, Abell 2744, Abell 223 and CL 0024+17 observed by Chandra X-ray Observatory. These profiles were obtained based on the well-established fact, that the X-ray observed surface brightness of clusters are described well with the Navarro-Frenk-White density profile of the underlying dark matter distribution. We have found that density and mass profiles for all considered clusters have the same shape. Temperatures, masses and densities of these clusters lie within the ranges 5−10 keV, ∼ 10¹⁴ − 10¹⁵ Mꙩ and ∼ 10⁻²³ − 10⁻²⁵ kg/m3 respectively. We also determined the values of R₂₀₀ and M₂₀₀ for the clusters and estimated the fraction of gas and dark matter in total mass of each cluster to be ∼ 10 − 20% and ∼ 80 − 90% respectively

Multi-wavelength observations of the binary system PSR B1259-63/LS 2883 around the 2010-2011 periastron passage

We report on broad multi-wavelength observations of the 2010-2011 periastron passage of the gamma-ray loud binary system PSR B1259-63. High resolution interferometric radio observations establish extended radio emission trailing the position of the pulsar. Observations with the Fermi Gamma-ray Space Telescope reveal GeV gamma-ray flaring activity of the system, reaching the spin-down luminosity of the pulsar, around 30 days after periastron. There are no clear signatures of variability at radio, X-ray and TeV energies at the time of the GeV flare. Variability around periastron in the H$\alpha$ emission line, can be interpreted as the gravitational interaction between the pulsar and the circumstellar disk. The equivalent width of the H$\alpha$ grows from a few days before periastron until a few days later, and decreases again between 18 and 46 days after periastron. In near infrared we observe the similar decrease of the equivalent width of Br$\gamma$ line between the 40th and 117th day after the periastron. For the idealized disk, the variability of the H$\alpha$ line represents the variability of the mass and size of the disk. We discuss possible physical relations between the state of the disk and GeV emission under assumption that GeV flare is directly related to the decrease of the disk size.Comment: accepted to MNRA

Circumgalactic Gas and the Precipitation Limit

During the last decade, numerous and varied observations, along with increasingly sophisticated numerical simulations, have awakened astronomers to the central role the circumgalactic medium (CGM) plays in regulating galaxy evolution. It contains the majority of the baryonic matter associated with a galaxy, along with most of the metals, and must continually replenish the star forming gas in galaxies that continue to sustain star formation. And while the CGM is complex, containing gas ranging over orders of magnitude in temperature and density, a simple emergent property may be governing its structure and role. Observations increasingly suggest that the ambient CGM pressure cannot exceed the limit at which cold clouds start to condense out and precipitate toward the center of the potential well. If feedback fueled by those clouds then heats the CGM and causes it to expand, the pressure will drop and the "rain" will diminish. Such a feedback loop tends to suspend the CGM at the threshold pressure for precipitation. The coming decade will offer many opportunities to test this potentially fundamental principle of galaxy evolution.Comment: Astro2020 White Paper, 8 pages, 2 figures (differences from Astro2020 version: some typos fixed, some references added

A Distant Chandra Galaxy Cluster CL J1415.1+3612: Constraint on Evidence of the Cool-Core Phenomenon

Deep Chandra observations of the distant cluster of galaxies, CLJ1415.1+3612, are analyzed in order to determine the main physical characteristics of the intracluster medium. We also investigate some properties of a cool-core phenomenon at ~ 10 kpc. Combining all Chandra observations, we derive the average temperature (kT = 6.77±0.54 keV) and the metal abundance (Z = 0.84±0.16 Z⊙) of the cluster. Assuming hydrostatic equilibrium and spherical symmetry, and using deprojected temperature and surface profiles, we estimate the value of total mass of the cluster within R2500, R500 and R200 and find the fraction of gas for these radii. The gas mass fraction of CL J1415.1+3612 at R500 is typical for X-ray clusters, (2.2±0.5)·1014M⊙. The total mass is equal to 3.8±0.4·1014M⊙ at R200 and the corresponding gas fraction is f = 0.21±0.06. In addition, we measured the cooling time of the central region (~10 kpc) as tcool = 0.163±0.021 Gyr. The value of entropy in the same region is Kc = 12.1±2.6 keV cm2. We also checked the redshift value of the cluster using the iron line Kα in the X-ray spectra of CLJ1415.1+3612. Our analysis makes this galaxy cluster to be one of the best investigated distant massive clusters in the X-ray range