610 research outputs found
Constraints on the collimated X-ray emission of SS 433 from the reflection on molecular clouds
We calculate X-ray signal that should arise due to reflection of the putative
collimated X-ray emission of the Galactic supercritical accretor SS 433 on
molecular clouds in its vicinity. The molecular gas distribution in the region
of interest has been constructed based on the data of the BU-FCRAO GRS in
CO emission line, while the collimated emission was
assumed to be aligned with the direction of the relativistic jets, which are
continuously launched by the system. We consider all the available
observations covering the regions possibly containing the reflection signal and
put constraints on the apparent face-on luminosity of SS 433 above 4 keV. No
signatures of the predicted signal have been found in the analysed regions down
to a 4-8 keV surface brightness level of erg/s/cm/deg.
This translates into the limit on the apparent face-on 2-10 keV luminosity of
SS 433 erg/s, provided that the considered
clouds do fall inside the illumination cone of the collimated emission. This,
however, might not be the case due to persisting uncertainty in the
line-of-sight distances to SS 433 (4.5-5.5 kpc) and to the
considered molecular clouds. For half-opening angle of the collimation cone
larger than or comparable to the amplitude of the jets' precession
(), the stringent upper limit quoted above is most relevant if
kpc, provided that the kinematic distances to the considered
molecular clouds are sufficiently accurate. Dropping the last assumption, a
more conservative constraint is erg/s for
kpc (and yet worse outside this range). We conclude that
SS 433 is not likely to belong to the brightest ultraluminous X-ray sources if
it could be observed face-on, unless its X-ray emission is highly collimated.
(Abridged)Comment: Astronomy Letters, in press; 16 pages, 8 figure
Polarization and long-term variability of Sgr A* X-ray echo
We use a model of the molecular gas distribution within ~100 pc from the
center of the Milky Way (Kruijssen, Dale & Longmore) to simulate time evolution
and polarization properties of the reflected X-ray emission, associated with
the past outbursts from Sgr A*. While this model is too simple to describe the
complexity of the true gas distribution, it illustrates the importance and
power of long-term observations of the reflected emission. We show that the
variable part of X-ray emission observed by Chandra and XMM from prominent
molecular clouds is well described by a pure reflection model, providing strong
support of the reflection scenario. While the identification of Sgr A* as a
primary source for this reflected emission is already a very appealing
hypothesis, a decisive test of this model can be provided by future X-ray
polarimetric observations, that will allow placing constraints on the location
of the primary source. In addition, X-ray polarimeters (like, e.g., XIPE) have
sufficient sensitivity to constrain the line-of-sight positions of molecular
complexes, removing major uncertainty in the model.Comment: 17 pages, 10 figures, accepted for publication in MNRA
Polarization of Sunyaev-Zeldovich signal due to electron pressure anisotropy in galaxy clusters
We describe polarization of the Sunyaev-Zel'dovich (SZ) effect associated
with electron pressure anisotropy likely present in the intracluster medium
(ICM). The ICM is an astrophysical example of a weakly collisional plasma where
the Larmor frequencies of charged particles greatly exceed their collision
frequencies. This permits formation of pressure anisotropies, driven by
evolving magnetic fields via adiabatic invariance, or by heat fluxes. SZ
polarization arises in the process of Compton scattering of the cosmic
microwave background (CMB) photons off the thermal ICM electrons due to the
difference in the characteristic thermal velocities of the electrons along two
mutually orthogonal directions in the sky plane. The signal scales linearly
with the optical depth of the region containing large-scale correlated
anisotropy, and with the degree of anisotropy itself. It has the same spectral
dependence as the polarization induced by cluster motion with respect to the
CMB frame (kinematic SZ effect polarization), but can be distinguished by its
spatial pattern. { For the illustrative case of a galaxy cluster with a cold
front, where electron transport is mediated by Coulomb collisions, we estimate
the CMB polarization degree at the level of 10 ( nK). An
increase of the effective electron collisionality due to plasma instabilities
will reduce the effect. Such polarization, therefore, may be an independent
probe of the electron collisionality in the ICM, which is one of the key
properties of a high- weakly collisional plasma from the point of view
of both astrophysics and plasma theory.Comment: 13 pages, 5 figures, accepted for publication in MNRA
Can Sgr A* flares reveal the molecular gas density PDF?
Illumination of dense gas in the Central Molecular Zone (CMZ) by powerful
X-ray flares from Sgr A* leads to prominent structures in the reflected
emission that can be observed long after the end of the flare. By studying this
emission we learn about past activity of the supermassive black hole in our
Galactic Center and, at the same time, we obtain unique information on the
structure of molecular clouds that is essentially impossible to get by other
means. Here we discuss how X-ray data can improve our knowledge of both sides
of the problem. Existing data already provide: i) an estimate of the flare age,
ii) a model-independent lower limit on the luminosity of Sgr A* during the
flare and iii) an estimate of the total emitted energy during Sgr A* flare. On
the molecular clouds side, the data clearly show a voids-and-walls structure of
the clouds and can provide an almost unbiased probe of the mass/density
distribution of the molecular gas with the hydrogen column densities lower than
few . For instance, the probability distribution
function of the gas density can be measured this way. Future high
energy resolution X-ray missions will provide the information on the gas
velocities, allowing, for example a reconstruction of the velocity field
structure functions and cross-matching the X-ray and molecular data based on
positions and velocities.Comment: 13 pages, 7 figures; Accepted for publication in MNRA
Not that long time ago in the nearest galaxy: 3D slice of molecular gas revealed by a 110 years old flare of Sgr A*
A powerful outburst of X-ray radiation from the supermassive black hole Sgr
A* at the center of the Milky Way is believed to be responsible for the
illumination of molecular clouds in the central ~100 pc of the Galaxy (Sunyaev
et al., 1993, Koyama et al., 1996). The reflected/reprocessed radiation comes
to us with a delay corresponding to the light propagation time that depends on
the 3D position of molecular clouds with respect to Sgr A*. We suggest a novel
way of determining the age of the outburst and positions of the clouds by
studying characteristic imprints left by the outburst in the spatial and time
variations of the reflected emission. We estimated the age of the outburst that
illuminates the Sgr A molecular complex to be ~110 yr. This estimate implies
that we see the gas located ~10 pc further away from us than Sgr A*. If the Sgr
B2 complex is also illuminated by the same outburst, then it is located ~130 pc
closer than our Galactic Center. The outburst was short (less than a few years)
and the total amount of emitted energy in X-rays is erg, where is the mean hydrogen density of the
cloud complex in units of . Energetically, such fluence can
be provided by a partial tidal disruption event or even by a capture of a
planet. Further progress in more accurate positioning and timing of the
outburst should be possible with future X-ray polarimetric observations and
long-term systematic observations with Chandra and XMM-Newton. A few
hundred-years long X-ray observations would provide a detailed 3D map of the
gas density distribution in the central pc region.Comment: 10 pages, 7 figures, accepted for publication in MNRA
An upper limit on nickel overabundance in the supercritical accretion disk wind of SS 433 from X-ray spectroscopy
We take advantage of a long (with a total exposure time of 120 ks) X-ray
observation of the unique Galactic microquasar SS 433, carried out with the
XMM-Newton space observatory, to search for a fluorescent line of neutral (or
weakly ionized) nickel at the energy 7.5 keV. We consider two models of the
formation of fluorescent lines in the spectrum of SS 433: 1) due to reflection
of hard X-ray radiation from a putative central source on the optically thick
walls of the accretion disk "funnel"; and 2) due to scattering of the radiation
coming from the hottest parts of the jets in the optically thin wind of the
system. It is shown, that for these cases, the photon flux of Ni I K
fluorescent line is expected to be 0.45 of the flux of Fe I K
fluorescent line at 6.4 keV, for the relative nickel overabundance , as observed in the jets of SS 433. For the continuum model without the
absorption edge of neutral iron, we set a 90 per cent upper limit on the flux
of the narrow Ni I K line at the level of ph
s cm. For the continuum model with the absorption edge, the
corresponding upper limit is ph s cm. At the
same time, for the Fe I K line, we measure the flux of
ph s cm. Taken at the face
value, the results imply that the relative overabundance of nickel in the wind
of the accretion disc should be at least 1.5 times less than the corresponding
excess of nickel observed in the jets of SS 433.Comment: 17 pages, 12 figures, 4 tables, Astronomy Letters, in press, 2018,
Volume 44, Issue
Probing 3D Density and Velocity Fields of ISM in Centers of Galaxies with Future X-Ray Observations
Observations of bright and variable "reflected" X-ray emission from molecular
clouds located within inner hundred parsec of our Galaxy have demonstrated that
the central supermassive black hole, Sgr A*, experienced short and powerful
flares in the past few hundred years. These flares offer a truly unique
opportunity to determine 3D location of the illuminated clouds (with ~10 pc
accuracy) and to reveal their internal structure (down to 0.1 pc scales). Short
duration of the flare(s), combined with X-rays high penetration power and
insensitivity of the reflection signal to thermo- and chemo-dynamical state of
the gas, ensures that the provided diagnostics of the density and velocity
fields is unbiased and almost free of the projection and opacity effects. Sharp
and sensitive snapshots of molecular gas accessible with aid of future X-ray
observatories featuring large collecting area and high angular (arcsec-level)
and spectral (eV-level) resolution cryogenic bolometers will present invaluable
information on properties of the supersonic turbulence inside the illuminated
clouds, map their shear velocity field and allow cross-matching between X-ray
data and velocity-resolved emission of various molecular species provided by
ALMA and other ground-based facilities. This will highlight large and
small-scale dynamics of the dense gas and help uncovering specifics of the ISM
lifecycle and high-mass star formation under very extreme conditions of
galactic centers. While the former is of particular importance for the SMBH
feeding and triggering AGN feedback, the latter might be an excellent test case
for star formation taking place in high-redshift galaxies.Comment: White paper submitted to the Astro2020 Decadal Surve
Prospects of detecting soft X-ray emission from typical WHIM filaments around massive clusters and the Coma cluster soft excess
While hot ICM in galaxy clusters makes these objects powerful X-ray sources,
the cluster's outskirts and overdense gaseous filaments might give rise to much
fainter sub-keV emission. Cosmological simulations show a prominent "focusing"
effect of rich clusters on the space density of the Warm-Hot Intergalactic
Medium (WHIM) filaments up to a distance of (
turnaround radius, ) and beyond. Here, we use Magneticum simulations to
characterize their properties in terms of integrated emission measure for a
given temperature and overdensity cut and the level of contamination by the
more dense gas. We suggest that the annuli around
massive clusters might be the most promising sites for the search of the gas
with overdensity . We model spectral signatures of the WHIM in the
X-ray band and identify two distinct regimes for the gas at temperatures below
and above . Using this model, we estimate the sensitivity
of X-ray telescopes to the WHIM spectral signatures. We found that the WHIM
structures are within reach of future high spectral resolution missions,
provided that the low-density gas is not extremely metal-poor. We then consider
the Coma cluster observed by SRG/eROSITA during the CalPV phase as an example
of a nearby massive object. We found that beyond the central () circle, where calibration uncertainties preclude clean
separation of the extremely bright cluster emission from a possible softer
component, the conservative upper limits are about an order of magnitude larger
than the levels expected from simulations.Comment: Submitted to MNRA
Integrable boundary conditions for classical sine-Gordon theory
The possible boundary conditions consistent with the integrability of the
classical sine-Gordon equation are studied. A boundary value problem on the
half-line with local boundary condition at the origin is considered.
The most general form of this boundary condition is found such that the problem
be integrable. For the resulting system an infinite number of involutive
integrals of motion exist. These integrals are calculated and one is identified
as the Hamiltonian. The results found agree with some recent work of Ghoshal
and Zamolodchikov.Comment: 10 pages, DTP/94-3
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