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Yurii Pidopryhora

Publications and source records attributed to Yurii Pidopryhora.

5 recordsLinked to original sources
arXiv2021

An 86-GHz search for Pulsars in the Galactic Center with the Atacama Large Millimeter/submillimeter Array

We report on the first pulsar and transient survey of the Galactic Center (GC) with the Atacama Large Millimeter/submillimeter Array (ALMA). The observations were conducted during the Global Millimeter VLBI Array campaign in 2017 and 2018. We carry out searches using timeseries of both total intensity and other polarization components in the form of Stokes parameters. We incorporate acceleration and its derivative in the pulsar search, and also search in segments of the entire observation to compensate for potential orbital motion of the pulsar. While no new pulsar is found, our observations yield the polarization profile of the GC magnetar PSR J1745-2900 at mm-wavelength for the first time, which turns out to be nearly 100 % linearly polarized. Additionally, we estimate the survey sensitivity placed by both system and red noise, and evaluate its capability of finding pulsars in orbital motion with either Sgr A* or a binary companion. We show that the survey is sensitive to only the most luminous pulsars in the known population, and future observations with ALMA in Band-1 will deliver significantly deeper survey sensitivity on the GC pulsar population.

astro-ph.HE↗
arXiv2015

High-Resolution Images of Diffuse Neutral Clouds in the Milky Way. I. Observations, Imaging, and Basic Cloud Properties

A set of diffuse interstellar clouds in the inner Galaxy within a few hundred pc of the Galactic plane has been observed at an angular resolution of ~1 arcmin combining data from the NRAO Green Bank Telescope and the Very Large Array. At the distance of the clouds the linear resolution ranges from ~1.9 pc to ~2.8 pc. These clouds have been selected to be somewhat out of the Galactic plane and are thus not confused with unrelated emission, but in other respects they are a Galactic population. They are located near the tangent points in the inner Galaxy, and thus at a quantifiable distance: $2.3 \leq R \leq 6.0$ kpc from the Galactic Center, and $-1000 \leq z \leq +610$ pc from the Galactic plane. These are the first images of the diffuse neutral HI clouds that may constitute a considerable fraction of the ISM. Peak HI column densities range from $N_{HI} = 0.8-2.9 \times 10^{20}$ cm$^{-2}$. Cloud diameters vary between about 10 and 100 pc, and their HI mass spans the range from less than a hundred to a few thousands Msun. The clouds show no morphological consistency of any kind except that their shapes are highly irregular. One cloud may lie within the hot wind from the nucleus of the Galaxy, and some clouds show evidence of two distinct thermal phases as would be expected from equilibrium models of the interstellar medium.

astro-ph.GA↗
arXiv2006

The Ophiuchus Superbubble: A Gigantic Eruption from the Inner Disk of the Milky Way

While studying extraplanar neutral hydrogen in the disk-halo transition of the inner Galaxy we have discovered what appears to be a huge superbubble centered around l ~ 30 deg, whose top extends to latitudes > 25 deg at a distance of about 7 kpc. It is detected in both HI and Halpha. Using the Green Bank Telescope of the NRAO, we have measured more than 220,000 HI spectra at 9' angular resolution in and around this structure. The total HI mass in the system is ~ 10^6 Msol and it has an equal mass in H+. The Plume of HI capping its top is 1.2 x 0.6 kpc in l and b and contains 3 x 10^4 Msol of HI. Despite its location, (the main section is 3.4 kpc above the Galactic plane) the kinematics of the Plume appears to be dominated by Galactic rotation, but with a lag of 27 km/s from corotation. At the base of this structure there are ``whiskers'' of HI several hundreds of pc wide, reaching more than 1 kpc into the halo; they have a vertical density structure suggesting that they are the bubble walls and have been created by sideways rather than upwards motion. They resemble the vertical dust lanes seen in NGC891. From a Kompaneets model of an expanding bubble, we estimate that the age of this system is ~ 30 Myr and its total energy content ~ 10^53 ergs. It may just now be at the stage where its expansion has ceased and the shell is beginning to undergo significant instabilities. This system offers an unprecedented opportunity to study a number of important phenomena at close range, including superbubble evolution, turbulence in an HI shell, and the magnitude of the ionizing flux above the Galactic disk.

astro-ph↗
arXiv2004

Extra-planar H I in the Inner Milky Way

The extra-planar H I in the inner parts of the Milky Way has been discovered to contain numerous cloud-like structures when observed in the 21cm line with the Green Bank Telescope (GBT). These halo clouds have motions consistent with Galactic rotation and do not seem to be related to the classic high-velocity clouds. They are found to distances >1 kpc from the plane and can contain hundreds of solar masses of H I. Spectra of many of the halo clouds show evidence of coexisting cool and warm H I phases. A preliminary high-resolution study of one of the clouds suggests that it consists of a diffuse envelope and a few dense cores, with a peak H I column density reaching 4 x 10^20 cm^-2. The clouds are often organized into larger structures, one example of which was discovered near 35 degrees Galactic longitude rising higher than 2 kpc above the Galactic plane. New observations should answer some fundamental questions about the nature of these clouds.

astro-ph↗