arXiv subjects

Rashid A. Sunyaev

Publications and source records attributed to Rashid A. Sunyaev.

At least 19 recordsLinked to original sources

arXiv2025

XRISM observations of solar flare X-ray emission reflected in the Earth's atmosphere

The X-ray Imaging and Spectroscopy Mission (XRISM), launched into low-Earth orbit in 2023, observes the reflection of solar flare X-rays in the Earth's atmosphere as a by-product of celestial observations. Using a $\sim$one-year data set covering from October 2023 to November 2024, we report on our first results of the measurement of the metal abundance pattern and high-resolution Fe-K spectroscopy. The abundances of Mg, Si, S, Ar, Ca, and Fe measured with the CCD detector Xtend during M- and X-class flares show the inverse-first-ionization-potential (inverse-FIP) effect, which is consistent with the results of Katsuda et al., ApJ, 2020 using the Suzaku satellite. The abundances of Si, S, and Ar are found to decrease with increasing flare magnitude, which is consistent with the theoretical model by Laming (Laming, ApJ, 2021), whereas Ca exhibits an opposite trend. The large effective area and field of view of Xtend allow us to trace the evolution of the abundances in several X-class flare loops on a timescale of a few 100 s, finding an enrichment of low-FIP elements before flare peaks. The high-resolution Fe-K spectrum obtained with the microcalorimeter Resolve successfully separates the Rayleigh- and Compton-scattered Fe XXIV/XXV lines and neutral or low-ionized Fe-K$α$ lines. The neutral/low-ionized Fe-K$α$ equivalent width shows an anti-correlation with hard X-ray flux with the best-fit power-law slope of $-0.14 \pm 0.09$, suggesting that hard X-rays from flare loops are stimulating the Fe K$α$ fluorescence. This work demonstrates that XRISM can be a powerful tool in the field of solar physics, offering valuable high-statistic CCD data and high-resolution microcalorimeter spectra in the energy range extending to the Fe-K band.

astro-ph.SR↗

arXiv2024

Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE

The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds the critical value, known as the Eddington limit. Discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity significantly exceeds this limit. High apparent luminosity might be produced thanks to geometric beaming of the radiation by an outflow. The outflow half-opening angle, which determines the amplification due to beaming, has never been robustly constrained. Using the Imaging X-ray Polarimetry Explorer, we made the measurement of X-ray polarization in the Galactic X-ray binary Cyg X-3. We find high, over 20%, nearly energy-independent linear polarization, orthogonal to the direction of the radio ejections. These properties unambiguously indicate the presence of a collimating outflow in the X-ray binary Cyg~X-3 and constrain its half-opening angle, <15 degrees. Thus, the source can be used as a laboratory for studying the super-critical accretion regime. This finding underscores the importance of X-ray polarimetry in advancing our understanding of accreting sources.

astro-ph.HE↗

arXiv2024

Study of X-ray emission from the S147 nebula by SRG/eROSITA: supernova-in-the-cavity scenario

The Simeis~147 nebula (S147), particularly well known for a spectacular net of ${\rm H}_α$-emitting filaments, is often considered one of the largest and oldest known supernova remnants in the Milky Way. Here, and in a companion paper, we present studies of X-ray emission from the S147 nebula using the data of SRG/eROSITA All-Sky Survey observations. In this paper, we argue that many inferred properties of the X-ray emitting gas are broadly consistent with a scenario of the supernova explosion in a low-density cavity, e.g. a wind-blown-bubble. This scenario assumes that a $\sim 20\,{\rm M_\odot}$ progenitor star has had small velocity with respect to the ambient ISM, so it stayed close to the center of a dense shell created during its Main Sequence evolution till the moment of the core-collapse explosion. The ejecta first propagate through the low-density cavity until they collide with the dense shell, and only then the reverse shock goes deeper into the ejecta and powers the observed X-ray emission of the nebula. The part of the remnant inside the dense shell remains non-radiative till now and, plausibly, in a state with $T_e<T_i$ and Non-Equilibrium Ionization (NEI). On the contrary, the forward shock becomes radiative immediately after entering the dense shell, and, being subject to instabilities, creates a characteristic "foamy" appearance of the nebula in ${\rm H}_α$ and radio emission.

astro-ph.HE↗

arXiv2023

IXPE observations of the quintessential wind-accreting X-ray pulsar Vela X-1

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer (IXPE). Vela X-1 is considered to be the archetypal example of a wind-accreting high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectro-polarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3$\pm$0.4% at the polarization angle (PA) of -47.3$\pm$5.4 deg. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6-10%, and a 90 deg difference in the PA compared to the data in the 2-3 keV range. The phase-resolved spectro-polarimetric analysis finds a PD in the range 0-9% with the PA varying between -80 and 40 deg.

astro-ph.HE↗

arXiv2023

Determination of X-ray pulsar geometry with IXPE polarimetry

Using observations of X-ray pulsar Her X-1 by the Imaging X-ray Polarimetry Explorer, we report on a highly significant ($>17σ$) detection of the polarization signal from an accreting neutron star. The observed degree of the linear polarization of $\sim$10\% is found to be far below theoretical expectations for this object, and stays low throughout the spin cycle of the pulsar. Both the polarization degree and the angle exhibit variability with pulse phase, which allowed us to measure the pulsar spin position angle 57(2) deg and the magnetic obliquity 12(4) deg, which is an essential step towards detailed modelling of the intrinsic emission of X-ray pulsars. Combining our results with the optical polarimetric data, we find that the spin axis of the neutron star and the angular momentum of the binary orbit are misaligned by at least $\sim$20 deg, which is a strong argument in support of the models explaining stability of the observed super-orbital variability with the precession of the neutron star.

astro-ph.HE↗

arXiv2022

The X-ray polarimetry view of the accreting pulsar Cen X-3

Cen X-3 is the first X-ray pulsar discovered 50 years ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ~20 in flux. In the low-luminosity state no significant polarization was found either in pulse phase-averaged (with the 3$σ$ upper limit of 12%) or phase-resolved data (the 3$σ$ upper limits are 20-30%). In the bright state the polarization degree of 5.8$\pm$0.3% and polarization angle of $49.6°\pm1.5°$ with significance of about 20$σ$ was measured from the spectro-polarimetric analysis of the phase-averaged data. The phase-resolved analysis showed a significant anti-correlation between the flux and the polarization degree as well as strong variations of the polarization angle. The fit with the rotating vector model indicates a position angle of the pulsar spin axis of about 49$°$ and a magnetic obliquity of 17$°$. The detected relatively low polarization can be explained if the upper layers of the neutron star surface are overheated by the accreted matter and the conversion of the polarization modes occurs within the transition region between the upper hot layer and a cooler underlying atmosphere. A fraction of polarization signal can also be produced by reflection of radiation from the neutron star surface and the accretion curtain.

astro-ph.HE↗

arXiv2021

INTEGRAL reloaded: spacecraft, instruments and ground system

ESA's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was launched on 17 Oct 2002 at 06:41 CEST. Since then, it has been providing long, uninterrupted observations (up to about 47 hr, or 170 ksec, per satellite orbit of 2.7 days) with a large field-of-view (fully coded: 100 deg^2), msec time resolution, keV energy resolution, polarization measurements, as well as additional coverage in the optical. This is realized by two main instruments in the 15 keV to 10 MeV range, the spectrometer SPI (spectral resolution 3 keV at 1.8 MeV) and the imager IBIS (angular resolution 12 arcmin FWHM), complemented by X-ray (JEM-X; 3-35 keV) and optical (OMC; Johnson V-band) monitors. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments are also efficient all-sky gamma-ray detectors, which provide omni-directional monitoring above ~75 keV. INTEGRAL can also rapidly (within a couple of hours) re-point and conduct Target of Opportunity observations. INTEGRAL has build an impressive legacy: e.g. discovery of >600 new high-energy sources; first-ever direct detection of 56Ni and 56Co radio-active decay lines from a Type Ia supernova; new insights on positron annihilation in the Galactic bulge and disk; pioneering gamma-ray polarization studies. INTEGRAL is also a successful in multi-messenger astronomy: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. More than 1750 papers based on INTEGRAL data have been published in refereed journals. Here we give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment.

astro-ph.IM↗

arXiv2017

Distortions of the Cosmic Microwave Background through cooling lines during the epoch of Reionization

By using N-body hydrodynamical cosmological simulations in which the chemistry of major metals and molecules is consistently solved for, we study the interaction of metallic fine-structure lines with the CMB. Our analysis shows that the collisional induced emissions in the OI 145 $μ$m and CII 158 $μ$m lines during reionization introduce a distortion of the CMB spectrum at low frequencies ($ν< 300$ GHz) with amplitudes up to $ΔI_ν/B_ν(T_{\rm CMB})\sim 10^{-8}$-$10^{-7}$, i.e., at the $\sim 0.1$ percent level of FIRAS upper limits. Shorter wavelength fine-structure transitions (OI 63 $μ$m, FeII 26 $μ$m, and SiII 35 $μ$m) typically sample the reionization epoch at higher observing frequencies ($ν> 400$ GHz). This corresponds to the Wien tail of the CMB spectrum and the distortion level induced by those lines may be as high as $ΔI_ν/B_ν(T_{\rm CMB})\sim 10^{-4}$. The angular anisotropy produced by these lines should be more relevant at higher frequencies: while practically negligible at $ν=145 $GHz, signatures from CII 158 $μ$m and OI 145 $μ$m should amount to 1%-5% of the anisotropy power measured at $l \sim 5000$ and $ν=220 $GHz by the ACT and SPT collaborations (after assuming $Δν_{\rm obs}/ν_{\rm obs}\simeq 0.005$ for the line observations). Our simulations show that anisotropy maps from different lines (e.g., OI 145 $μ$m and CII 158 $μ$m) at the same redshift show a very high degree ($>0.8$) of spatial correlation, allowing for the use of observations at different frequencies to unveil the same snapshot of the reionization epoch. Finally, our simulations demonstrate that line-emission anisotropies extracted in narrow frequency/redshift shells are practically uncorrelated in frequency space, thus enabling standard methods for removal of foregrounds that vary smoothly in frequency, just as in HI 21 cm studies.

astro-ph.CO↗

arXiv2016

Galactic survey of 44Ti sources with the IBIS telescope onboard INTEGRAL

We report the results of the deepest Galactic Plane (|b| < 17.5 deg) survey in the 67.9 and 78.4 keV nuclear de-excitation lines of titanium-44 (44Ti) performed using the data acquired with the IBIS/ISGRI instrument onboard the INTEGRAL satellite during 12 years of operation. The peak sensitivity of our survey reached an unprecedented level of $4.8\times10^{-6}$ erg s$^{-1}$ cm$^{-2}$ (3 sigma) that improves the sensitivity of the survey done by CGRO/COMPTEL by a factor of ~5. As a result, constraining upper limits for all sources from the catalog of Galactic supernova remnants (SNRs; Green 2014) are derived. These upper limits can be used to estimate the exposure needed to detect 44Ti emission from any known SNR using existing and prospective X- and gamma-ray telescopes. Among the youngest Galactic SNRs, only Cas A shows significant 44Ti emission flux in good agreement with the NuSTAR measurements. We did not detect any other sources of titanium emission in the Galactic Plane at significance level higher than 5 sigma confirming previous claims of the rarity of such 44Ti-producing SNRs.

astro-ph.HE↗

arXiv2016

INTEGRAL/IBIS deep extragalactic survey: M81, LMC and 3C 273/Coma fields

We present results of deep surveys of three extragalactic fields, M81 (exposure of 9.7 Ms), LMC (6.8 Ms) and 3C 273/Coma (9.3 Ms), in the hard X-ray (17-60 keV) energy band with the IBIS telescope onboard the INTEGRAL observatory, based on 12 years of observations (2003-2015). The combined survey reaches a $4σ$ peak sensitivity of 0.18 mCrab (2.6$\times$10$^{-12}$ erg s$^{-1}$ cm$^{-2}$) and sensitivity better than 0.25 and 0.87 mCrab over 10% and 90% of its full area of 4900 deg$^{2}$, respectively. We have detected in total 147 sources at $S/N>4σ$, including 37 sources observed in hard X-rays for the first time. The survey is dominated by extragalactic sources, mostly by active galactic nuclei (AGN). The sample of identified sources contains 98 AGN (including 64 Seyfert galaxies, 7 LINERs, 3 XBONGs, 16 blazars and 8 AGN of unclear optical class), two galaxy clusters (Coma and Abell 3266), 17 objects located in the Large and Small Magellanic Clouds (13 high- and 2 low-mass X-ray binaries and 2 X-ray pulsars), three Galactic cataclysmic variables, one ultraluminous X-ray source (ULX, M82 X-1) and one blended source (SWIFT J1105.7+5854). The nature of 25 sources remains unknown, so that the surveys identification is currently complete at 83%. We have constructed AGN number-flux relations ($\log{N}$-$\log{S}$) and calculated AGN number densities in the local Universe for the entire survey and for each of the three extragalactic fields.

astro-ph.HE↗

arXiv2014

INTEGRAL 11-year hard X-ray survey above 100 keV

We present results of all sky survey, performed with data acquired by the IBIS telescope onboard the INTEGRAL observatory over eleven years of operation, at energies above 100 keV. A catalogue of detected sources includes 132 objects. The statistical sample detected on the time-averaged 100-150 keV map at a significance above 5 sigma contains 88 sources: 28 AGNs, 38 LMXBs, 10 HMXBs and 12 rotation-powered young X-ray pulsars. The catalogue includes also 15 persistent sources, which were registered with the significance 4 sigma < S/N < 5 in hard X-rays, but at the same time were firmly detected (>12 sigma) in the 17-60 keV energy band. All sources from these two groups are known X-ray emitters, that means that the catalogue has 100% purity in respect to them. Additionally, 29 sources were found in different time intervals. In the context of the survey we present a hardness ratio of galactic and extragalactic sources, a LMXBs longitudinal asymmetry and a number-flux relation for non-blazar AGNs. At higher energies, in the 150-300 keV energy band, 25 sources have been detected with a signal-to-noise ratio S/N > 5 sigma, including 7 AGNs, 13 LMXBs, 3 HMXBs, and 2 rotation-powered pulsars. Among LMXBs and HMXBs we identified 12 black hole candidates (BHC) and 4 neutron star (NS) binaries.

astro-ph.IM↗

arXiv2013

XIPE: the X-ray Imaging Polarimetry Explorer

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).

astro-ph.HE↗

arXiv2013

Forecasts for CMB μ- and i-type spectral distortion constraints on the primordial power spectrum on scales 8 < k < 10^4 Mpc^-1 with the future Pixie-like experiments

Silk damping at redshifts 1.5 x 10^4 < z < 2 x 10^6 erases CMB anisotropies on scales corresponding to the comoving wavenumbers 8 < k < 10^4 Mpc^-1 (10^5 < \ell < 10^8). This dissipated energy is gained by the CMB monopole, creating distortions from a blackbody in the CMB spectrum of the μ-type and the i-type. We study, using Fisher matrices, the constraints we can get from measurements of these spectral distortions on the primordial power spectrum from future experiments such as Pixie, and how these constraints change as we change the frequency resolution and the sensitivity of the experiment. We show that the additional information in the shape of the $i$-type distortions, in combination with the μ-type distortions, allows us to break the degeneracy between the amplitude and the spectral index of the power spectrum on these scales and leads to much tighter constraints. We quantify the information contained in both the μ-type distortions and the i-type distortions taking into account the partial degeneracy with the y-type distortions and the temperature of the blackbody part of the CMB. We also calculate the constraints possible on the primordial power spectrum when the spectral distortion information is combined with the CMB anisotropies measured by the WMAP, SPT, ACT and Planck experiments.

astro-ph.CO↗

arXiv2013

Unavoidable CMB spectral features and blackbody photosphere of our Universe

Spectral features in the CMB energy spectrum contain a wealth of information about the physical processes in the early Universe, z < 2 x 10^6. The CMB spectral distortions are complementary to all other probes of cosmology. In fact, most of the information contained in the CMB spectrum is inaccessible by any other means. This review outlines the main physics behind the spectral features in the CMB throughout the history of the Universe, concentrating on the distortions which are inevitable and must be present at a level observable by the next generation of proposed CMB experiments. The spectral distortions considered here include spectral features from cosmological recombination, resonant scattering of CMB by metals during reionization which allows us to measure their abundances, y-type distortions during and after reionization and μ-type and i-type (intermediate between μand y) distortions created at redshifts z > 1.5 x 10^4.

astro-ph.CO↗

arXiv2013

Motion induced second order temperature and y-type anisotropies after the subtraction of linear dipole in the CMB maps

y-type spectral distortions of the cosmic microwave background allow us to detect clusters and groups of galaxies, filaments of hot gas and the non-uniformities in the warm hot intergalactic medium. Several CMB experiments (on small areas of sky) and theoretical groups (for full sky) have recently published y-type distortion maps. We propose to search for two artificial hot spots in such y-type maps resulting from the incomplete subtraction of the effect of the motion induced dipole on the cosmic microwave background sky. This dipole introduces, at second order, additional temperature and y-distortion anisotropy on the sky of amplitude few μK which could potentially be measured by Planck HFI and Pixie experiments and can be used as a source of cross channel calibration by CMB experiments. This y-type distortion is present in every pixel and is not the result of averaging the whole sky. This distortion, calculated exactly from the known linear dipole, can be subtracted from the final y-type maps, if desired.

astro-ph.CO↗

arXiv2012

Beyond y and μ: the shape of the CMB spectral distortions in the intermediate epoch, 1.5x10^4 < z < 2x10^5

We calculate numerical solutions and analytic approximations for the intermediate-type spectral distortions. Detection of a μ-type distortion (saturated comptonization) in the CMB will constrain the time of energy injection to be at a redshift 2x10^6> z > 2x10^5, while a detection of a y-type distortion (minimal comptonization) will mean that there was heating of CMB at redshift z< 1.5x10^4. We point out that the partially comptonized spectral distortions, generated in the redshift range 1.5x10^4 < z x 2x10^5, are much richer in information than the pure y and μ-type distortions. The spectrum created during this period is intermediate between y and μ-type distortions and depends sensitively on the redshift of energy injection. These intermediate-type distortions cannot be mimicked by a mixture of y and μ-type distortions at all frequencies and vice versa. The measurement of these intermediate-type CMB spectral distortions has the possibility to constrain precisely not only the amount of energy release in the early Universe but also the mechanism, for example, particle annihilation and Silk damping can be distinguished from particle decay. The intermediate-type distortion templates and software code using these templates to calculate the CMB spectral distortions for user-defined energy injection rate are made publicly available.

astro-ph.CO↗

arXiv2012

Mixing of blackbodies: entropy production and dissipation of sound waves in the early Universe

Mixing of blackbodies with different temperatures creates a spectral distortion which, at lowest order, is a y-type distortion, indistinguishable from the thermal y-type distortion produced by the scattering of CMB photons by hot electrons residing in clusters of galaxies. This process occurs in the radiation-pressure dominated early Universe, when the primordial perturbations excite standing sound waves on entering the sound horizon. Photons from different phases of the sound waves, having different temperatures, diffuse through the electron-baryon plasma and mix together. This diffusion, with the length defined by Thomson scattering, dissipates sound waves and creates spectral distortions in the CMB. Of the total dissipated energy, 2/3 raises the average temperature of the blackbody part of spectrum, while 1/3 creates a distortion of y-type. It is well known that at redshifts 10^5< z< 2x10^6, comptonization rapidly transforms y-distortions into a Bose-Einstein spectrum. The chemical potential of the Bose-Einstein spectrum is again 1/3 the value we would get if all the dissipated energy was injected into a blackbody spectrum but no extra photons were added. We study the mixing of blackbody spectra, emphasizing the thermodynamic point of view, and identifying spectral distortions with entropy creation. This allows us to obtain the main results connected with the dissipation of sound waves in the early Universe in a very simple way. We also show that mixing of blackbodies in general, and dissipation of sound waves in particular, leads to creation of entropy.

astro-ph.CO↗

arXiv2012

CMB at 2x2 order: the dissipation of primordial acoustic waves and the observable part of the associated energy release

Silk damping of primordial small-scale perturbations in the photon-baryon fluid due to diffusion of photons inevitably creates spectral distortions in the CMB. With the proposed CMB experiment PIXIE it might become possible to measure these distortions and thereby constrain the primordial power spectrum at comoving wavenumbers 50 Mpc^{-1} < k < 10^4 Mpc^{-1}. Since primordial fluctuations in the CMB on these scales are completely erased by Silk damping, these distortions may provide the only way to shed light on otherwise unobservable aspects of inflationary physics. A consistent treatment of the primordial dissipation problem requires going to second order in perturbation theory, while thermalization of these distortions necessitates consideration of second order in Compton scattering energy transfer. Here we give a full 2x2 treatment for the creation and evolution of spectral distortions due to the acoustic dissipation process, consistently including the effect of polarization and photon mixing in the free streaming regime. We show that 1/3 of the total energy (9/4 larger than previous estimates) stored in small-scale temperature perturbations imprints observable spectral distortions, while the remaining 2/3 only raises the average CMB temperature, an effect that is unobservable. At high redshift dissipation is mainly mediated through the quadrupole anisotropies, while after recombination peculiar motions are most important. During recombination the damping of the higher multipoles is also significant. We compute the average distortion for several examples using CosmoTherm, analyzing their dependence on parameters of the primordial power spectrum. For one of the best fit WMAP7 cosmologies, with n_S=1.027 and n_run=-0.034, the cooling of baryonic matter practically compensates the heating from acoustic dissipation in the mu-era. (abridged)

astro-ph.CO↗