Denys Malyshev

Constraints on 3.55 keV line emission from stacked observations of dwarf spheroidal galaxies

Several recent works have reported the detection of an unidentified x-ray line at 3.55 keV, which could possibly be attributed to the decay of dark matter (DM) particles in the halos of galaxy clusters and in the M31 galaxy. We analyze all publicly available XMM-Newton satellite data of dwarf spheroidal galaxies to test the possible DM origin of the line. Dwarf spheroidal galaxies have high mass-to-light ratios, and their interstellar medium is not a source of diffuse x-ray emission; thus, they are expected to provide the cleanest DM decay line signal. Our analysis shows no evidence for the presence of the line in the stacked spectra of the dwarf galaxies. It excludes the sterile neutrino DM decay origin of the 3.5 keV line reported by Bulbul et al. (2014) at the level of

THE HIGH-ENERGY, ARCMINUTE-SCALE GALACTIC CENTER GAMMA-RAY SOURCE

4.1ensuremath{sigma}

High-energy gamma-ray emission from Cyg X-1 measured by Fermi and its theoretical implications

under standard assumptions about the Galactic DM column density in the direction of selected dwarf galaxies and at the level of

Constraining extended gamma-ray emission from galaxy clusters

3.2ensuremath{sigma}

Searching for decaying dark matter in deep XMM–Newton observation of the Draco dwarf spheroidal

assuming minimal Galactic DM column density. Our analysis is still consistent with the estimate of sterile neutrino DM parameters by Boyarsky et al. (2014) because of its larger uncertainty. However, the central value of their estimate of the mixing angle is inconsistent with our dwarf spheroidals data at the

Decaying dark matter search with NuSTAR deep sky observations

3.4ensuremath{sigma}

Variability of the GeV sky

(

High energy emission from the center of our Galaxy

2.5ensuremath{sigma}

Spectral and spatial variations of the diffuse γ-ray background in the vicinity of the Galactic plane and possible nature of the feature at 130 GeV

) level assuming the mean (minimal) Galactic DM column density. As a byproduct of our analysis, we provide updated upper limits to the mixing angle of sterile neutrino DM in the mass range between 2 and 20 keV.

Central engine of a gamma-ray blazar resolved through the magnifying glass of gravitational microlensing

Employing data collected during the first 25 months of observations by the Fermi-LAT, we describe and subsequently seek to model the very high energy (>300 MeV) emission from the central few parsecs of our Galaxy. We analyze the morphological, spectral, and temporal characteristics of the central source, 1FGL J1745.6-2900. The data show a clear, statistically significant signal at energies above 10 GeV, where the Fermi-LAT has angular resolution comparable to that of HESS at TeV energies. This makes a meaningful joint analysis of the data possible. Our analysis of the Fermi data (alone) does not uncover any statistically significant variability of 1FGL J1745.6-2900 at GeV energies on the month timescale. Using the combination of Fermi data on 1FGL J1745.6-2900 and HESS data on the coincident, TeV source HESS J1745-290, we show that the spectrum of the central gamma-ray source is inflected with a relatively steep spectral region matching between the flatter spectrum found at both low and high energies. We model the gamma-ray production in the inner 10 pc of the Galaxy and examine cosmic ray (CR) proton propagation scenarios that reproduce the observed spectrum of the central source. We show that a model that instantiates a transition from diffusivemorexa0» propagation of the CR protons at low energy to almost rectilinear propagation at high energies can explain well the spectral phenomenology. We find considerable degeneracy between different parameter choices which will only be broken with the addition of morphological information that gamma-ray telescopes cannot deliver given current angular resolution limits. We argue that a future analysis performed in combination with higher-resolution radio continuum data holds out the promise of breaking this degeneracy.«xa0lessEmploying data collected during the first 25 months’ observa tions by the Fermi -LAT, we describe and subsequently seek to model the very high energy ( > 300 MeV) emission from the central few parsecs of our Galaxy. We analyse, in particular, the morphological, spec tral and temporal characteristics of the central source, 1FGL J1745.6-2900. Remarkably, the data show a clear, stati stic lly significant signal at energies above 10 GeV, where the Fermi -LAT has an excellent angular resolutio n comparable to the angular resolution of HESS at TeV energies. This not only reduces dramatically the cont amination both from the diffuse background and the nearby gamma-ray sources, but also makes meaningful the joint analysis of the Fermi and HESS data. Our analysis does not show statistically significant variab ility of 1FGL J1745.6-2900. Using the combination of Fermi data on 1FGL J1745.6-2900 and HESS data on the coinci de t, TeV source HESS J1745-290, we show that the spectrum of the central γ-ray source is inflected with a relatively steep spectral reg ion matching between the flatter spectrum found at both low and high energi es. We seek to model the gamma-ray production in the inner 10 pc of the Galaxy and examine, in particular, co smic ray (CR) proton propagation scenarios that reproduce the observed spectrum of the central source. We show that a model that instantiates a transition from diffusive propagation of the CR protons at low energy to almost rectilinear propagation at high energies (given a reasonable energy-dependence of the assumed diffu sion coefficient) can well explain the spectral phenomenology. In general, however, we find considerable de g neracy between different parameter choices which will only be broken with the addition of morphological information thatγ-ray telescopes cannot deliver given current angular resolution limits. We argue that a fut ure analysis done in combination with higherresolution radio continuum data holds out the promise of bre aking this degeneracy. Subject headings: Galaxy: center — synchrotron radiation: cosmic rays — molec ular clouds: general