arXiv subjects

E. Mikhailov

Publications and source records attributed to E. Mikhailov.

3 recordsLinked to original sources

arXiv2021

The SRG X-ray orbital observatory, its telescopes and first scientific results

The orbital observatory Spectrum-Roentgen-Gamma (SRG), equipped with the grazing-incidence X-ray telescopes Mikhail Pavlinsky ART-XC and eROSITA, was launched by Roscosmos to the Lagrange L2 point of the Sun-Earth system on July 13, 2019. The launch was carried out from the Baikonur Cosmodrome by a Proton-M rocket with a DM-03 upper stage. The German telescope eROSITA was installed on SRG under an agreement between Roskosmos and the DLR, the German Aerospace Agency. In December 2019, SRG started to perform its main scientific task: scanning the celestial sphere to obtain X-ray maps of the entire sky in several energy ranges (from 0.2 to 8 keV with eROSITA, and from 4 to 30 keV with ART-XC). By mid-June 2021, the third six-month all-sky survey had been completed. Over a period of four years, it is planned to obtain eight independent maps of the entire sky in each of the energy ranges. The sum of these maps will provide high sensitivity and reveal more than three million quasars and over one hundred thousand massive galaxy clusters and galaxy groups. The availability of eight sky maps will enable monitoring of long-term variability (every six months) of a huge number of extragalactic and Galactic X-ray sources, including hundreds of thousands of stars with hot coronae. The rotation of the satellite around the axis directed toward the Sun with a period of four hours enables tracking the faster variability of bright X-ray sources during one day every half year. The chosen strategy of scanning the sky leads to the formation of deep survey zones near both ecliptic poles. The paper presents sky maps obtained by the telescopes on board SRG during the first survey of the entire sky and a number of results of deep observations performed during the flight to the L2 point in the frame of the performance verification program.(Abriged)

astro-ph.HE↗

arXiv2016

Magnetic fields in ring galaxies

Many galaxies contain magnetic fields supported by galactic dynamo action. However, nothing definitive is known about magnetic fields in ring galaxies. Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. We use tested methods for modelling $α-Ω$ galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513 where the ring counter-rotates with respect to the disc. Strong shear in the region between the disc and the ring is associated with unusually strong dynamo drivers for the counter-rotators. The effect of the strong drivers is found to be unexpectedly moderate. With counter-rotation in the disc, a generic model shows that a steady mixed parity magnetic configuration, unknown for classical spiral galaxies, may be excited, although we do not specifically model NGC 4513. We deduce that ring galaxies constitute a morphological class of galaxies in which identification of large-scale magnetic fields from observations of polarized radio emission, as well as dynamo modelling, may be possible. Such studies have the potential to throw additional light on the physical nature of rings, their lifetimes and evolution.

astro-ph.GA↗

arXiv2014

Magnetic fields near the peripheries of galactic discs

Magnetic fields are observed beyond the peripheries of optically detected galactic discs, while numerical models of their origin and the typical magnitudes are still absent. Previously, studies of galactic dynamo have avoided considering the peripheries of galactic discs because of the very limited (though gradually growing) knowledge about the local properties of the interstellar medium. Here we investigate the possibility that magnetic fields can be generated in the outskirts of discs, taking the Milky Way as an example. We consider a simple evolving galactic dynamo model in the "no-z" formulation, applicable to peripheral regions of galaxies, for various assumptions about the radial and vertical profiles of the ionized gas disc. The magnetic field may grow as galaxies evolve, even in the more remote parts of the galactic disc, out to radii of 15 to 30 kpc, becoming substantial after times of about 10 Gyr. This result depends weakly on the adopted distributions of the half thickness and surface density of the ionized gas component. The model is robust to changes in the amplitude of the initial field and the position of its maximum strength. The magnetic field in the remote parts of the galactic disc could be generated in situ from a seed field by local dynamo action. Another possibility is field production in the central regions of a galaxy, followed by transport to the disc's periphery by the joint action of the dynamo and turbulent diffusivity. Our results demonstrate the possibilities for the appearance and strengthening of magnetic fields at the peripheries of disc galaxies and emphasize the need for observational tests with new and anticipated radio telescopes (LOFAR, MWA, and SKA).

astro-ph.GA↗