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The Milky Way galaxy is surrounded by a circumgalactic medium (CGM) that may play a key role in galaxy evolution as the source of gas for star formation and a repository of metals and energy produced by star formation and nuclear activity. The CGM may also be a repository for baryons seen in the early universe, but undetected locally. The CGM has an ionized component at temperatures near 2 x 10^6 K studied primarily in the soft X-ray band. Here we report a survey of the southern Galactic sky with a soft X-ray spectrometer optimized to study diffuse soft X-ray emission. The X-ray emission is best fit with a disc-like model based on the radial profile of the surface density of molecular hydrogen, a tracer of star formation, suggesting that the X-ray emission is predominantly from hot plasma produced via stellar feedback. Strong variations in the X-ray emission on angular scales of ~10 degrees indicate that the CGM is clumpy. Addition of an extended, and possibly massive, halo component is needed to match the halo density inferred from other observations.

We report multicolour photometric observations of the 2003 eclipse of the long-period (5.6 yr) eclipsing binary EE Cep. Measurements were obtained with ten telescopes at eight observatories in four countries. In most cases, UBV(RI) sub(C) broad band filters have been used. The light curve shape shows that the obscuring body is an almost dark disk around a low-luminosity central object. However, variations of the colour indices during the eclipse indicate that the obscuring body emits a considerable amount of radiation in the near infrared.

High-resolution spectroscopy during the eclipse of EE Cep was obtained and presented for the first time. The star's spectroscopic behaviour can be roughly interpreted as a partial eclipse of the high luminosity Be primary and its emitting gaseous ring by the semi-transparent gaseous envelope around an invisible, opaque secondary, most probably a dark disk.

The Vela and Puppis A supernova remnants (SNRs) comprise a large emission region of \\(\\sim 8^{\\circ}\\) diameter in the soft X-ray sky. The HaloSat CubeSat mission provides the first soft X-ray (\\(0.4-7\\) keV) observation of the entire Vela SNR and Puppis A SNR region with a single pointing and moderate spectral resolution. HaloSat observations of the Vela SNR are best fit with a two-temperature thermal plasma model consisting of a cooler component with \\(kT_{1} = 0.19^{+0.01}_{-0.01}\\) keV in collisional ionization equilibrium and a hotter component with \\(kT_{2} = 1.06^{+0.45}_{-0.27}\\) keV in non-equilibrium ionization. Observations of the Puppis A SNR are best fit with a single-component plane-parallel shocked plasma model with \\(kT = 0.86^{+0.06}_{-0.05}\\) keV in non-equilibrium ionization. For the first time, we find the total X-ray luminosities of both components of the Vela SNR spectrum in the \\(0.5-7\\) keV energy band to be \\(L_X = 4.4^{+1.4}_{-1.4} \\times 10^{34}\\) erg s\\(^{-1}\\) for the cooler component and \\(L_X = 4.1^{+1.8}_{-1.5} \\times 10^{34}\\) erg s\\(^{-1}\\) for the hotter component. We find the total X-ray luminosities of the Vela and Puppis A SNRs to be \\(L_{\\text{X}} = 8.4 \\times 10^{34}\\) erg s\\(^{-1}\\) and \\(L_X = 6.7^{+1.1}_{-0.9} \\times 10^{36}\\) erg s\\(^{-1}\\).

The Milky Way galaxy is surrounded by a circumgalactic medium (CGM) that may play a key role in galaxy evolution as the source of gas for star formation and a repository of metals and energy produced by star formation and nuclear activity. The CGM may also be a repository for baryons seen in the early universe, but undetected locally. The CGM has an ionized component at temperatures near \\(2 10^6\\)~K studied primarily in the soft X-ray band. Here we report a survey of the southern Galactic sky with a soft X-ray spectrometer optimized to study diffuse soft X-ray emission. The X-ray emission is best fit with a disc-like model based on the radial profile of the surface density of molecular hydrogen, a tracer of star formation, suggesting that the X-ray emission is predominantly from hot plasma produced via stellar feedback. Strong variations in the X-ray emission on angular scales of \\(10^\\) indicate that the CGM is clumpy. Addition of an extended, and possibly massive, halo component is needed to match the halo density inferred from other observations.

Globular clusters are source of gamma-ray radiation. At GeV energies, their emission is attributed to magnetospheric activity of millisecond pulsars residing in the clusters. Inverse Compton scattering of ambient photon fields on relativistic particles diffusing through cluster environment is thought to be the source of GeV-TeV emission of globular clusters. Using pair starved polar cap model gamma-ray emission from synthetic millisecond pulsar was modelled. In addition to pulsar emission characteristics, the synthetic pulsar model yielded spectra of electrons escaping pulsar magnetosphere. To simulate gamma-ray emission of globular cluster, both products of synthetic millisecond pulsar modelling were used. Gamma-ray spectra of synthetic millisecond pulsars residing in the cluster were summed to produce the magnetospheric component of cluster emission. Electrons ejected by these pulsars were injected into synthetic globular cluster environment. Their diffusion and interaction, both, with cluster magnetic field and ambient photon fields, were performed with Bednarek & Sitarek (2007) model yielding ICS component of cluster emission. The sum of the magnetospheric and ICS components gives the synthetic gamma-ray spectrum of globular cluster. The synthetic cluster spectrum stretches from GeV to TeV energies. Detailed modelling was preformed for two globular clusters: Ter 5 and 47 Tuc. Simulations are able to reproduce (within errors) the shape and the flux level of the GeV part of the spectrum observed for both clusters with the Fermi/LAT instrument. The synthetic flux level obtained in the TeV part of the clusters' spectrum is in agreement with a H.E.S.S. upper limit determined for 47 Tuc, and with emission level recently detected for Ter 5 with H.E.S.S. telescope. The synthetic globular cluster model, however, is not able to reproduce the exact shape of the TeV spectrum observed for Ter 5.

Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way's galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report non-detections of a \\(\\sim\\)3.5 keV emission line in four HaloSat observations near the Galactic Center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux and 7.1 keV sterile neutrino mixing angle: \\(F \\leq 0.077\\) ph cm\\(^{-2}\\) s\\(^{-1}\\) sr\\(^{-1}\\) and \\(\\sin^2(2\\theta) \\leq 4.25 \\times 10^{-11}\\). The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way's dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way's dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature.

We constrain the LMC’s global parameters by modeling the first soft X-ray (0.4–6.8 keV) observations of the entire Large Magellanic Cloud (LMC) produced in a single pointing with moderate spectral resolution by the HaloSat CubeSat. These data are best fit with the sum of two thermal plasma components in collisional ionization equilibrium and a power-law. We find cool (0.210±0.014keV) and hot (0.89±0.14keV) components. The LMC’s total X-ray luminosity is(1.08±0.14)×1039erg s−1.X-ray binaries make up a large fraction of the emission with a luminosity of(6.0±0.8)×1038ergs−1, followed by cool gas from superbubbles, supernovae, and diffuse emission with a luminosity of(3.0±0.3)×1038erg s−1. The hot gas from star formation contributes the smallest fraction, with a luminosity of(1.9±0.5)×1038erg s−1. We estimate the total volume of the cool gas to be between(0.2–1.2)×1010pc3and the hot gas to be between(1.0–5)×107pc3for filling factors off= 1and0.2. These volumes result in a total thermal energy for the cool gas between (1.4–3)×1054ergs for electron densities of 0.017–0.04 cm−3, and a thermal energy for the hot gas between (1.7–4)×1053ergs for electron densities of 0.12–0.3 cm−3. This yields cooling timescales for the cool and hot gas of(1.5–3)×108years and(1.8–6)×107years, respectively

HaloSat is a small satellite (CubeSat) designed to map soft X-ray oxygen line emission across the sky in order to constrain the mass and spatial distribution of hot gas in the Milky Way. The goal of HaloSat is to help determine if hot gas gravitationally bound to individual galaxies makes a significant contribution to the cosmological baryon budget. HaloSat was deployed from the International Space Station in July 2018 and began routine science operations in October 2018. We describe the goals and design of the mission, the on-orbit performance of the science instrument, and initial observations.

Relative and absolute emission line shifts have been previously found for symbiotic binaries, but their cause was not clear. This work aims to better understand the emission line shifts. Positions of strong emission lines were measured on archival UV spectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and relative shifts between the lines of different ions compared. Profiles of lines of RW Hya and Z And were also examined. The reality of the relative shift between resonance and intercombination lines of several times ionised atoms was clearly shown except for AG Dra. This redshift shows a well defined variation with orbital phase for Z And and RW Hya. In addition the intercombination lines from more ionised atoms and especially OIV are redshifted with respect to those from less ionised atoms. Other effects are seen in the profiles. The resonance-intercombination line shift variation can be explained in quiescence by P Cygni shorter wavelength component absorption, due to the wind of the cool component, which is specially strong in inferior conjunction of this cool giant. The velocity stratification permits absorption of line emission. The relative intercombination line shifts may be connected with varying occultation of line emission near an accretion disk, which is optically thick in the continuum.