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Kovalev Y.Y.,Max Planck Institute for Radio Astronomy | Kovalev Y.Y.,RAS Lebedev Physical Institute | Petrov L.,Astrogeo Center | Plavin A.V.,Moscow Institute of Physics and Technology
Astronomy and Astrophysics | Year: 2017

Context. The data release 1 (DR1) of milliarcsecond-scale accurate optical positions of stars and galaxies was recently published by the space mission Gaia. Aims. We study the offsets of highly accurate absolute radio (very long baseline interferometry, VLBI) and optical positions of active galactic nuclei (AGN) to see whether or not a signature of wavelength-dependent parsec-scale structure can be seen. Methods. We analyzed VLBI and Gaia positions and determined the direction of jets in 2957 AGNs from their VLBI images. Results. We find that there is a statistically significant excess of sources with VLBI-to-Gaia position offset in directions along and opposite to the jet. Offsets along the jet vary from 0 to tens of mas. Offsets in the opposite direction do not exceed 3 mas. Conclusions. The presense of strong, extended parsec-scale optical jet structures in many AGNs is required to explain all observed VLBI-Gaia offsets along the jet direction. The offsets in the opposite direction shorter than 1 mas can be explained either by a non-point-like VLBI jet structure or a "core-shift" effect due to synchrotron opacity. © 2017 ESO.


News Article | November 2, 2016
Site: phys.org

The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across. The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centers of galaxies. Supermassive black holes reside at the centers of most galaxies. Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging. "We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said James Condon, of the National Radio Astronomy Observatory. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it," he added. "We've not seen anything like this before," Condon said. The astronomers began their quest by using the VLBA to make very high resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies. However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionized gas behind it. The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter—a "nearly naked" supermassive black hole. The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars. "In a billion years or so, it probably will be invisible," Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can't detect. The scientists will keep looking, however. They're observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use "filler time" when the telescope is not in use for other observations. "The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison," Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images. They hope that this will allow them to discover more objects like B3 1714+425. "And also maybe some of the binary supermassive black holes we originally sought," he said. Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. The scientists are reporting their findings in the Astrophysical Journal. The VLBA, dedicated in 1993, now is part of the Long Baseline Observatory. It uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology.


News Article | November 2, 2016
Site: www.eurekalert.org

Astronomers using the super-sharp radio vision of the National Science Foundation's Very Long Baseline Array (VLBA) have found the shredded remains of a galaxy that passed through a larger galaxy, leaving only the smaller galaxy's nearly-naked supermassive black hole to emerge and speed away at more than 2,000 miles per second. The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across. The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centers of galaxies. Supermassive black holes reside at the centers of most galaxies. Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging. "We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said James Condon, of the National Radio Astronomy Observatory. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it," he added. "We've not seen anything like this before," Condon said. The astronomers began their quest by using the VLBA to make very high resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies. However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionized gas behind it. The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter -- a "nearly naked" supermassive black hole. The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars. "In a billion years or so, it probably will be invisible," Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can't detect. The scientists will keep looking, however. They're observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use "filler time" when the telescope is not in use for other observations. "The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison," Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images. They hope that this will allow them to discover more objects like B3 1714+425. "And also maybe some of the binary supermassive black holes we originally sought," he said. Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. The scientists are reporting their findings in the Astrophysical Journal. The VLBA, dedicated in 1993, now is part of the Long Baseline Observatory. It uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology. The Long Baseline Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


News Article | November 3, 2016
Site: spaceref.com

Astronomers using the super-sharp radio vision of the Very Long Baseline Array (VLBA) have found the shredded remains of a galaxy that passed through a larger galaxy. This left only the smaller galaxy's nearly-naked supermassive black hole to emerge and speed away at more than 2,000 miles per second. The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across. The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centers of galaxies. Supermassive black holes reside at the centers of most galaxies. Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging. "We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said James Condon, of the National Radio Astronomy Observatory. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it," he added. "We've not seen anything like this before," Condon said. The astronomers began their quest by using the VLBA to make very high resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies. However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionized gas behind it. The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter -- a "nearly naked" supermassive black hole. The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars. "In a billion years or so, it probably will be invisible," Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can't detect. The scientists will keep looking, however. They're observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use "filler time" when the telescope is not in use for other observations. "The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison," Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images. They hope that this will allow them to discover more objects like B3 1714+425. "And also maybe some of the binary supermassive black holes we originally sought," he said. Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. The scientists are reporting their findings in the Astrophysical Journal. The VLBA, dedicated in 1993, now is part of the Long Baseline Observatory. It uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology. Please follow SpaceRef on Twitter and Like us on Facebook.


Lehtinen K.,Finnish Geospatial Research Institute FGI | Bach U.,Max Planck Institute for Radio Astronomy | Muinonen K.,Finnish Geospatial Research Institute FGI | Muinonen K.,University of Helsinki | And 2 more authors.
Astrophysical Journal Letters | Year: 2016

Stellar occultations by asteroids observed at visual wavelengths have been an important tool for studying the size and shape of asteroids and for revising the orbital parameters of asteroids. At radio frequencies, a shadow of an asteroid on the Earth is dominated by diffraction effects. Here, we show, for the first time, that a single observation of an occultation of a compact radio source at a frequency of 5 GHz can be used to derive the effective size of the occulting object and to derive the distance between the observer and the center of the occultation path on the Earth. The derived diameter of the occulting object, asteroid (115) Thyra, is 75 ± 6 km. The observed occultation profile shows features that cannot be explained by diffraction of a single asteroid. © 2016. The American Astronomical Society. All rights reserved.


Bartel N.,York University | Bietenholz M.F.,York University | Bietenholz M.F.,Hartebeesthoek Radio Astronomy Observatory | Lebach D.E.,Harvard - Smithsonian Center for Astrophysics | And 7 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

We made very long baseline interferometry observations at 8.4GHz between 1997 and 2005 to estimate the coordinates of the "core" component of the superluminal quasar, 3C454.3, the ultimate reference point in the distant universe for the NASA/Stanford Gyroscope Relativity Mission, Gravity Probe B (GP-B). These coordinates are determined relative to those of the brightness peaks of two other compact extragalactic sources, B2250+194 and B2252+172, nearby on the sky, and within a celestial reference frame (CRF), defined by a large suite of compact extragalactic radio sources, and nearly identical to the International Celestial Reference Frame 2 (ICRF2). We find that B2250+194 and B2252+172 are stationary relative to each other, and also in the CRF, to within 1σ upper limits of 15 and 30 μasyr -1 in α and δ, respectively. The core of 3C454.3 appears to jitter in its position along the jet direction over 0.2mas, likely due to activity close to the putative supermassive black hole nearby, but on average is stationary in the CRF within 1σ upper limits on its proper motion of 39 μasyr -1 (1.0c) and 30 μasyr -1 (0.8c) in α and δ, respectively, for the period 2002-2005. Our corresponding limit over the longer interval, 1998-2005, of more importance to GP-B, is 46 and 56 μasyr -1 in α and δ, respectively. Some of 3C454.3's jet components show significantly superluminal motion with speeds of up to 200 μasyr -1 or 5c in the CRF. The core of 3C454.3 thus provides for GP-B a sufficiently stable reference in the distant universe. © 2012. The American Astronomical Society. All rights reserved..


Petrov L.,Astrogeo Center | Honma M.,Japan National Astronomical Observatory | Shibata S.M.,Japan National Astronomical Observatory
Astronomical Journal | Year: 2012

We observed a sample of 1536 sources with correlated flux densities brighter than 200mJy at 8GHz with the very long baseline interferometry (VLBI) array VLBI Exploration of Radio Astrometry at 22GHz. One half of the target sources has been detected. The detection limit was around 200mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22GHz brighter than a given correlated flux density level is two times less than that at 8GHz. © 2012. The American Astronomical Society. All rights reserved.


Petrov L.,Astrogeo Center | Mahony E.K.,Netherlands Institute for Radio Astronomy | Edwards P.G.,CSIRO | Sadler E.M.,University of Sydney | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We report results of the first phase of observations with the Australia Telescope Compact Array (ATCA) at 5 and 9 GHz of the fields around 411 γ -ray sources with declinations < +10 ° detected by Fermi but marked as unassociated in the Fermi Large Area Telescope 2-Year Source Catalog (2FGL). We have detected 424 sources with flux densities in the range 2-6 Jy that lie within the 99 per cent localization uncertainty of 283 γ -ray sources. Of these, 146 objects were detected in both 5- and 9-GHz bands. We found 84 sources in our sample with a spectral index flatter than -0.5. The majority of detected sources are weaker than 100 mJy and for this reason were not found in previous surveys. Approximately one third of our sample, 128 objects, have a probability of being associated more than 10 times greater than the probability of being a background source found in the vicinity of a γ -ray object by chance.We present the catalogue of positions of these sources, estimates of their flux densities and spectral indices where available. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Schinzel F.K.,University of New Mexico | Petrov L.,Astrogeo Center | Taylor G.B.,University of New Mexico | Taylor G.B.,U.S. National Radio Astronomy Observatory | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2015

We present the results of an all-sky radio survey between 5 and 9 GHz of sky areas surrounding all unassociated γ-ray objects listed in the Fermi Large Area Telescope Second Source Catalog (2FGL). The goal of these observations is to find all new γ-ray active galactic nucleus (AGN) associations with radio sources >10 mJy at 8 GHz. We observed with the Very Large Array and the Australia Telescope Compact Array the areas around unassociated sources, providing localizations of weak radio point sources found in 2FGL fields at arcmin scales. Then we followed-up a subset of those with the Very Long Baseline and the Long Baseline Arrays to confirm detections of radio emission on parsec-scales. We quantified association probabilities based on known statistics of source counts and assuming a uniform distribution of background sources. In total we found 865 radio sources at arcsec scales as candidates for association and detected 95 of 170 selected for follow-up observations at milliarcsecond resolution. Based on this we obtained firm associations for 76 previously unknown γ-ray AGNs. Comparison of these new AGN associations with the predictions from using the Wide-field Infrared Survey Explorer color-color diagram shows that half of the associations are missed. We found that 129 out of 588 observed γ-ray sources at arcmin scales not a single radio continuum source was detected above our sensitivity limit within the γ-ray localization. These «empty» fields were found to be particularly concentrated at low Galactic latitudes. The nature of these Galactic γ-ray emitters is not yet determined. © 2015. The American Astronomical Society. All rights reserved.


Petrov L.,Astrogeo Center
Astronomical Journal | Year: 2013

Future space-borne astrometry missions, such as Gaia, will be able to determine the optical positions of hundreds of quasars with submilliarcsecond accuracies comparable to those achieved in radio by very long baseline interferometry (VLBI). Comparisons of coordinate systems from space-borne missions and VLBI will be very important, first for investigations of possible systematic errors and second for investigations of possible shifts between centroids of radio and optical emissions in active galactic nuclei. In order to make such a comparison more robust, a program for densification of the grid of radio sources detectable with both VLBI and Gaia was launched in 2006. Program sources are 398 quasars with declinations >-10° that are brighter than 18 mag at the V band. The first two observing campaigns were run in 2007-2008. In the third campaign, a set of 291 objects from that list was observed with the VLBA+EVN in 2010-2011 with the primary goal of producing their images with milliarcsecond resolution. In this paper, following the method of absolute astrometry, coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these observations. The catalog of positions of 295 target sources, estimates of their correlated flux densities at 2.2 and 8.4 GHz, and their images are presented. The accuracies of source coordinates are in a range of 2-200 mas, with a median of 3.2 mas. © 2013. The American Astronomical Society. All rights reserved.

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