Equivalent width, shape and proper motion of the iron fluorescent line emission from the molecular clouds as an indicator of the illuminating source X-ray flux history

Observations of the diffuse emission in the 8--22 keV energy range, elongated parallel to the Galactic plane (Sunyaev et al. 1993) and detection of the strong 6.4 keV fluorescent line with $\sim$ 1 keV equivalent width from some giant molecular clouds (e.g. Sgr B2) in the Galactic Centre region (Koyama 1994) suggest that the neutral matter of these clouds is (or was) illuminated by powerful X-ray radiation, which gave rise to the reprocessed radiation. The source of this radiation remains unknown. Transient source close to the Sgr B2 cloud or short outburst of the X-ray emission from supermassive black hole at the Galactic Centre are the two prime candidates under consideration. We argue that new generation of X-ray telescopes combining very high sensitivity and excellent energy and angular resolutions would be able to discriminate between these two possibilities studying time dependent changes of the morphology of the surface brightness distribution, the equivalent width and the shape of the fluorescent line in the Sgr B2 and other molecular clouds in the region. We note also that detection of broad and complex structures near the 6.4 keV line in the spectra of distant AGNs, which are X-ray weak now, may prove the presence of violent activity of the central engines of these objects in the past. Accurate measurements of the line shape may provide an information on the time elapsed since the outburst. Proper motion (super or subluminal) of the fluorescent radiation wave front can give additional information on the location of the source. Observations of the described effects can provide unique information on the matter distribution inside Sgr B2 and other giant molecular clouds.Comment: 14 pages, 10 figures, accepted for publication in MNRA

Polarization of MeV gamma-rays and 511 keV line shape as probes of SNIa asymmetry and magnetic field

We discuss gamma-ray signatures associated with an asymmetric explosion and transport of positrons in SN Ia ejecta. In particular, Compton scattering of gamma-ray line photons can induce polarization in the continuum, which would be a direct probe of the asymmetries in the distribution of radioactive isotopes and/or of the scattering medium. Even more interesting would be a comparison of the shapes of $\gamma$-ray lines and that of the electron-positron annihilation line at 511 keV. The shapes of $\gamma$-ray lines associated with the decay of Co56 (e.g., lines at 847 and 1238 keV) directly reflect the velocity distribution of Co56. On the other hand, the 511 keV line arises from the annihilation of positions, which are also produced by the Co56 decay but can propagate through the ejecta before they slow down and annihilate. Therefore, the shape of the annihilation line might differ from other gamma-ray lines, providing constraints on the efficiency of positrons propagation through the ejecta and, as consequence, on the topology of magnetic fields in the ejecta and on the fraction of positrons that escape to the interstellar medium. We illustrate the above effects with two models aimed at capturing the main predicted signatures.Comment: 10 pages, 10 figures; replaced with accepted version (MNRAS

Sound wave generation by a spherically symmetric outburst and AGN Feedback in Galaxy Clusters

We consider the evolution of an outburst in a uniform medium under spherical symmetry, having in mind AGN feedback in the intra cluster medium (ICM). For a given density and pressure of the medium, the spatial structure and energy partition at a given time $t_{age}$ (since the onset of the outburst) are fully determined by the total injected energy $E_{inj}$ and the duration $t_b$ of the outburst. We are particularly interested in the late phase evolution when the strong shock transforms into a sound wave. We studied the energy partition during such transition with different combinations of $E_{inj}$ and $t_b$. For an instantaneous outburst with $t_b\rightarrow 0$, which corresponds to the extension of classic Sedov-Taylor solution with counter-pressure, the fraction of energy that can be carried away by sound waves is $\lesssim$12% of $E_{inj}$. As $t_b$ increases, the solution approaches the "slow piston" limit, with the fraction of energy in sound waves approaching zero. We then repeat the simulations using radial density and temperature profiles measured in Perseus and M87/Virgo clusters. We find that the results with a uniform medium broadly reproduce an outburst in more realistic conditions once proper scaling is applied. We also develop techniques to map intrinsic properties of an outburst $(E_{inj}, t_b$ and $t_{age})$ to the observables like the Mach number of the shock and radii of the shock and ejecta. For the Perseus cluster and M87, the estimated $(E_{inj}, t_b$ and $t_{age})$ agree with numerical simulations tailored for these objects with $20-30\%$ accuracy.Comment: Accepted by MNRAS, add one figure in appendix and minor changes in text based on referee's commen

(No) dimming of X-ray clusters beyond z~1 at fixed mass: crude redhshifts and masses from raw X-ray and SZ data

Scaling relations in the LCDM Cosmology predict that for a given mass the clusters formed at larger redshift are hotter, denser and therefore more luminous in X-rays than their local z~0 counterparts. This effect overturns the decrease in the observable X-ray flux so that it does not decrease at z > 1, similar to the SZ signal. Provided that scaling relations remain valid at larger redshifts, X-ray surveys will not miss massive clusters at any redshift, no matter how far they are. At the same time, the difference in scaling with mass and distance of the observable SZ and X-ray signals from galaxy clusters at redshifts $z\lesssim 2$ offers a possibility to crudely estimate the redshift and the mass of a cluster. This might be especially useful for preselection of massive high-redshift clusters and planning of optical follow-up for overlapping surveys in X-ray (e.g., by SRG/eRosita) and SZ (e.g. Planck, SPT and ACT).Comment: 7 pages, 5 figures, MNRAS accepte

Frequency resolved spectroscopy of Cyg X-1: fast variability of the reflected emission in the soft state

Using the RXTE/PCA data we study the fast variability of the reflected emission in the soft spectral state of Cyg X-1 by means of Fourier frequency resolved spectroscopy. We find that the rms amplitude of variations of the reflected emission has the same frequency dependence as the primary radiation down to time scales of <30-50 msec. This might indicate that the reflected flux reproduces, with nearly flat response, variations of the primary emission. Such behavior differs notably from the hard spectral state, in which variations of the reflected flux are significantly suppressed in comparison with the primary emission, on time scales shorter than ~0.5-1 sec. If related to the finite light crossing time of the reflector, these results suggest that the characteristic size of the reflector -- presumably an optically thick accretion disk, in the hard spectral state is larger by a factor of >5-10 than in the soft spectral state. Modeling the transfer function of the disk, we estimate the inner radius of the accretion disk R_in~100R_g in the hard and R_in<10R_g in the soft state for a 10M_sun black hole.Comment: submitted to MNRA