arXiv subjects

D. Malyshev

Publications and source records attributed to D. Malyshev.

At least 73 records · Page 4Linked to original sources

arXiv2019

Overview of non-transient gamma-ray binaries and prospects for the Cherenkov Telescope Array

We simulate the spectral behaviour of the non-transient gamma-ray binaries using archival observations as a reference. With this we test the CTA capability to measure the sources' spectral parameters and detect variability on various time scales. We review the known properties of gamma-ray binaries and the theoretical models that have been used to describe their spectral and timing characteristics. We show that CTA is capable of studying these sources on time scales comparable to their characteristic variability time scales. For most of the binaries, the unprecedented sensitivity of CTA will allow the spectral evolution to be studied on a time scale as short as 30 min. This will enable a direct comparison of the TeV and lower energy (radio to GeV) properties of these sources from simultaneous observations. We also review the source-specific questions that can be addressed with such high-accuracy CTA measurements.

astro-ph.HE↗

arXiv2019

Multi-wavelength observation of MAXI J1820+070 with MAGIC, VERITAS and H.E.S.S

MAXI J1820+070 is a new low-mass microquasar hosting a black hole recently discovered in X-rays by the MAXI instrument. It is the counterpart of ASASSN-18ey, discovered in optical a few days before by ASAS-SN. This source underwent a major outburst in 2018, during which it completed the typical "q-shaped" path in the hardness-intensity diagram. MAGIC, VERITAS and H.E.S.S. gamma-ray telescopes observed the sky position of MAXI J1820+070 for a total of more than 90 hours in 2018. In addition, some observations were carried out using MAGIC Central Pixel - a dedicated central pixel capable of detecting fast optical signals (10 kHz sampling rate, peak sensitivity in the U-band). This contribution presents the methods used to search for transient optical and very high energy gamma-ray emission from MAXI J1820+070, as well as the latest results in these energy ranges.

astro-ph.HE↗

arXiv2019

Long-term gamma-ray observations of the binary HESS J0632+057 with H.E.S.S., MAGIC and VERITAS

The gamma-ray binary HESS J0632+057 has been observed at very-high energies (E $>$ 100 GeV) for more than ten years by the major systems of imaging atmospheric Cherenkov telescopes. We present a summary of results obtained with the H.E.S.S., MAGIC, and VERITAS experiments based on roughly 440 h of observations in total. This includes a discussion of an unusually bright TeV outburst of HESS J0632+057 in January 2018. The updated gamma-ray light curve now covers all phases of the orbital period with significant detections in almost all orbital phases. Results are discussed in context with simultaneous observations with the X-ray Telescope onboard the Neil Gehrels Swift Observatory.

astro-ph.HE↗

arXiv2019

Decade-long X-ray observations of HESS J0632+057

We present results of a decade of X-ray observations of the gamma-ray loud binary HESS J0632+057, and interpret the available broadband data in view of the system geometry and emission mechanisms. We have performed an analysis of all X-ray data available to date from Swift, XMM-Newton, Chandra, NuSTAR and Suzaku. We refine the orbital period of the system to be $316.8^{+2.6}_{-1.4}$~d (95% c.l.), consistent with previous studies but measured with significantly better accuracy. We report on a hydrogen column density and spectral slope variation along the orbit. We argue that the observed variability can be explained within an "inclined disk" model in which the orbit of the compact object is inclined to the disk of the Be star. We show that the observed X-ray to TeV emission can originate from a broken cut-off power-law population of electrons and describe a way in which future X-ray/TeV observations can distinguish between the proposed model and the alternative flip-flop emission scenario of this system.

astro-ph.HE↗

arXiv2019

Unresolved Gamma-Ray Sky through its Angular Power Spectrum

The gamma-ray sky has been observed with unprecedented accuracy in the last decade by the Fermi large area telescope (LAT), allowing us to resolve and understand the high-energy Universe. The nature of the remaining unresolved emission (unresolved gamma-ray background, UGRB) below the LAT source detection threshold can be uncovered by characterizing the amplitude and angular scale of the UGRB fluctuation field. This work presents a measurement of the UGRB autocorrelation angular power spectrum based on eight years of Fermi LAT Pass 8 data products. The analysis is designed to be robust against contamination from resolved sources and noise systematics. The sensitivity to subthreshold sources is greatly enhanced with respect to previous measurements. We find evidence (with $\sim$3.7$σ$ significance) that the scenario in which two classes of sources contribute to the UGRB signal is favored over a single class. A double power law with exponential cutoff can explain the anisotropy energy spectrum well, with photon indices of the two populations being 2.55 $\pm$ 0.23 and 1.86 $\pm$ 0.15.

astro-ph.HE↗

arXiv2018

Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays

We analyze the processes governing cosmic-ray (CR) penetration into molecular clouds and the resulting generation of gamma-ray emission. The density of CRs inside a cloud is depleted at lower energies due to the self-excited MHD turbulence. The depletion depends on the effective gas column density ("size") of the cloud. We consider two different environments where the depletion effect is expected to be observed. For the Central Molecular Zone, the expected range of CR energy depletion is $E\lesssim 10$ GeV, leading to the depletion of gamma-ray flux below $E_γ\approx 2$ GeV. This effect can be important for the interpretation of the GeV gamma-ray excess in the Galactic Center, which has been revealed from the standard model of CR propagation (assuming the CR spectrum inside a cloud to be equal to the interstellar spectrum). Furthermore, recent observations of some local molecular clouds suggest the depletion of the gamma-ray emission, indicating possible self-modulation of the penetrating low-energy CRs.

astro-ph.HE↗

arXiv2018

Improved limit on axion-like particles from gamma-ray data on Perseus cluster

Coupling of axion-like particles (ALPs) to photons in the presence of background magnetic field affects propagation of gamma-rays through magnetized environments. This results in modification in the gamma-ray spectra of sources in or behind galaxy clusters. We search for the ALP induced effects in the Fermi/LAT and MAGIC telescope spectra of the radio galaxy NGC 1275 embedded in Perseus galaxy cluster. We report an order-of-magnitude improved upper limit on the ALP-photon coupling constant in the 0.1-10 neV mass range from non-detection of the ALP imprints on the gamma-ray spectra. The improved upper limit extends into the coupling range in which the ALP particles could form the dark matter. We estimate the sensitivity improvements for the ALP search achievable with extension of the measurements to lower and higher energies with e-ASTROGAM and CTA and show that the gamma-ray probe of ALPs with masses in $10^{-11}-10^{-7}$ eV range will be have order-of-magnitude better sensitivity compared to ground-based experiment IAXO.

astro-ph.HE↗

arXiv2018

Search for extended sources in the Galactic Plane using 6 years of Fermi-Large Area Telescope Pass 8 data above 10 GeV

The spatial extension of a gamma-ray source is an essential ingredient to determine its spectral properties as well as its potential multi-wavelength counterpart. The capability to spatially resolve gamma-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis which provides a greater acceptance and an improved point spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7 degrees from the Galactic plane, using 6 years of LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectral characteristics. This constitutes the first catalog of hard LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.

astro-ph.HE↗

arXiv2017

Study of orbital and superorbital variability of LSI +61 303 with X-ray data

LSI +61 303 is one of the few X-ray binaries with a Be star companion from which radio, X-rays and high-energy gamma-ray (GeV and TeV) emission have been observed. The nature of the high energy activity of the system is not yet fully understood, but it is widely believed that it is generated due to the interaction of the relativistic electrons leaving the compact object with the photons and non-relativistic wind of the Be star. The superorbital variability of the system has been observed in the radio, optical and X-ray domains and could be due to the cyclic change of the Be star disk size. In this paper we systematically review all publicly available data from Suzaku, XMM-Newton, Chandra and Swift observatories in order to measure the absorption profile of the circumstellar Be disk as a function of orbital and superorbital phases. We also discuss short-term variability of the system, found during the analysis and its implications for the understanding of the physical processes in this system.

astro-ph.HE↗

arXiv2017

Cosmic-ray electron+positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope

We present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of $3.07 \pm 0.02 \; (\text{stat+syst}) \pm 0.04 \; (\text{energy measurement})$. An exponential cutoff lower than 1.8 TeV is excluded at 95\% CL.

astro-ph.HE↗

arXiv2016

Searching the Gamma-ray Sky for Counterparts to Gravitational Wave Sources: Fermi GBM and LAT Observations of LVT151012 and GW151226

We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candi- date LVT151012. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for char- acterizing the upper limits across a large area of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, dif- ferences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914.

astro-ph.HE↗

arXiv2016

Toward the full test of the nuMSM sterile neutrino dark matter model with Athena

We discuss the potential of Athena X-ray telescope, in particular of its X-ray Integral Field Unit (X-IFU), for detection of the signal from the light-weight decaying dark matter with mass in the keV range. We show that high energy resolution and large collection area of X-IFU will provide an improvement of sensitivity which will be sufficient for the full test of the neutrino Minimal extension of the Standard Model (nuMSM). Search for the narrow spectral line produced by the decay of the dark matter sterile neutrino in the spectra of dwarf spheroidal galaxies with X-IFU will explore the whole allowed range masses and mixing angles of the nuMSM lightest sterile neutrino and in this way either to find the dark matter signal or rule out the nuMSM model.

astro-ph.HE↗

arXiv2016

Hard X-ray view of microlensing events in RX J1131-1231

RX J1131-1231 is a gravitationally lensed system which includes four images of a quasar lensed by an elliptical galaxy. The flux in the individual images is known to be affected by microlensing effect in the visible and X-ray bands. We study the multi-wavelength properties of RX J1131-1231 over a broad energy range, from optical to hard X-ray, during the periods of the microlensing caustic crossings. We aim to constrain the spatial extent of the X-ray emission region at different energies. We combine the data of the source monitoring in the visible band with the X-ray data of the Burst Alert Telescope (BAT) on board of SWIFT satellite and Chandra X-ray observatory. Inspecting the broad band spectrum and lightcurves of the source we identify several microlensing caustic crossing events, and study the details of variability of the source during these events. The caustic crossings of image A on MJD 55150 and 55500 produce strong variations of the overall X-ray flux from the source. In the soft X-ray band, the caustic crossing events are characterised by the exponential growth / decay of the flux ratio between the source images with the exponentiating time scale T_d~60 d, which corresponds to the caustic transit time of the source of the size ~10^{14} cm. Variability induced by the microlensing dominates the overall variability of the sum of the fluxes of four images of the source which should also be detectable in the hard X-ray lightcurve, if the hard X-ray source is comparably compact. Non-detection of the caustic crossing events in the SWIFT/BAT lightcurve of the source indicates that geometry of the region of emission of X-rays with energies above 15 keV is different from that of the lower energy X-rays, with the hard X-ray emission an order of magnitude larger in size.

astro-ph.HE↗

arXiv2016

Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

Most of the celestial gamma rays detected by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point and extended source studies rely on the modeling of this diffuse emission for accurate characterization. We describe here the development of the Galactic Interstellar Emission Model (GIEM) that is the standard adopted by the LAT Collaboration and is publicly available. The model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse Compton emission produced in the Galaxy. We also include in the GIEM large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20 degrees and we observe an enhanced emission toward their base extending in the North and South Galactic direction and located within 4 degrees of the Galactic Center.

astro-ph.HE↗

arXiv2016

Very high energy Fermi/LAT detection of HESS J0632+057

We report on the results of ~7 yrs of the very-high energy (10-600 GeV) observations of HESS J0632+057 with FERMI/LAT. In the highest energy band, 200-600 GeV, the source is clearly detected with the statistical significance >3.6sigma at orbital phases 0.2-0.4 and 0.6-0.8 at which HESS J0632+057 is known to demonstrate enhanced emission in TeV energy band. The analysis did not reveal the emission from HESS J0632+057 at lower energies and different orbital phases. Using the upper limits on source's flux we locate the break of the spectrum to >80 GeV and low-energy slope <2.0 (2sigma statistical significance).

astro-ph.HE↗

arXiv2015

Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT

Galaxy clusters are one of the prime sites to search for dark matter (DM) annihilation signals. Depending on the substructure of the DM halo of a galaxy cluster and the cross sections for DM annihilation channels, these signals might be detectable by the latest generation of $γ$-ray telescopes. Here we use three years of Fermi Large Area Telescope (LAT) data, which are the most suitable for searching for very extended emission in the vicinity of nearby Virgo galaxy cluster. Our analysis reveals statistically significant extended emission which can be well characterized by a uniformly emitting disk profile with a radius of 3°that moreover is offset from the cluster center. We demonstrate that the significance of this extended emission strongly depends on the adopted interstellar emission model (IEM) and is most likely an artifact of our incomplete description of the IEM in this region. We also search for and find new point source candidates in the region. We then derive conservative upper limits on the velocity-averaged DM pair annihilation cross section from Virgo. We take into account the potential $γ$-ray flux enhancement due to DM sub-halos and its complex morphology as a merging cluster. For DM annihilating into $b\overline{b}$, assuming a conservative sub-halo model setup, we find limits that are between 1 and 1.5 orders of magnitude above the expectation from the thermal cross section for $m_{\mathrm{DM}}\lesssim100\,\mathrm{GeV}$. In a more optimistic scenario, we exclude $\langle σv \rangle\sim3\times10^{-26}\,\mathrm{cm^{3}\,s^{-1}}$ for $m_{\mathrm{DM}}\lesssim40\,\mathrm{GeV}$ for the same channel. Finally, we derive upper limits on the $γ$-ray-flux produced by hadronic cosmic-ray interactions in the inter cluster medium. We find that the volume-averaged cosmic-ray-to-thermal pressure ratio is less than $\sim6\%$.

astro-ph.HE↗

arXiv2015

Limits on Dark Matter Annihilation Signals from the Fermi LAT 4-year Measurement of the Isotropic Gamma-Ray Background

We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologically-induced gamma-ray intensity to have an uncertainty of a factor ~20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former on the IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. We quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.

astro-ph.CO↗

arXiv2015

Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre

The Galactic centre is a bright gamma-ray source with the GeV-TeV band spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV energy ranges. The nature of these two components is not clearly understood. We investigate the gamma-ray properties of the Galactic centre to clarify the origin of the observed emission. We report imaging, spectral, and timing analysis of data from 74 months of observations of the Galactic centre by FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately ten years of INTEGRAL/PICsIT observations. We find that the Galactic centre is spatially consistent with the point source in the GeV band. The tightest 3 sigma upper limit on its radius is 0.13 degree in the 10-300 GeV energy band. The spectrum of the source in the 100 MeV energy range does not have a characteristic turnover that would point to the pion decay origin of the signal. Instead, the source spectrum is consistent with a model of inverse Compton scattering by high-energy electrons. In this a model, the GeV bump in the spectrum originates from an episode of injection of high-energy particles, which happened ~300 years ago. This injection episode coincides with the known activity episode of the Galactic centre region, previously identified using X-ray observations. The hadronic model of source activity could be still compatible with the data if bremsstrahlung emission from high-energy electrons was present in addition to pion decay emission.

astro-ph.HE↗