scholarly journals The next generation space VLBI project, VSOP-2

2007 ◽  
Vol 3 (S242) ◽  
pp. 517-521 ◽  
Author(s):  
Yasuhiro Murata ◽  
Nanako Mochizuki ◽  
Hirofumi Saito ◽  
Hisashi Hirabayashi ◽  
Makoto Inoue ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Space Observatory ◽  
Space Agency ◽  
Maser Line ◽  
Successful Launch ◽  
Astronomical Satellite

AbstractThe first dedicated space-VLBI project, the VLBI Space Observatory Programme (VSOP), commenced with the successful launch of radio-astronomical satellite HALCA in 1997. Plans for a second generation space-VLBI project have been made by a working group over a number of years. This project, VSOP-2, has now been approved by Japan's space agency, JAXA, as the ASTRO-G project. It is planned for the spacecraft to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, which include important maser lines. It will have a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. Although the VSOP project mainly observed continuum emission from active galactic nuclei (AGN), VSOP-2/ASTRO-G is expected to enable a variety of high angular resolution maser line observations.

scholarly journals NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?

2020 ◽  
Vol 497 (1) ◽  
pp. 229-245 ◽  
Author(s):  
A Annuar ◽  
D M Alexander ◽  
P Gandhi ◽  
G B Lansbury ◽  
D Asmus ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Broad Band ◽  
Galactic Nuclei ◽  
Current Data ◽  
High Angular Resolution ◽  
X Ray ◽  
Ir Imaging ◽  
Nuclear Dust

ABSTRACT We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L2–10 keV,obs ≲ 1039 erg s−1, classifying them as low-luminosity AGN (LLAGN). We perform broad-band X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM–Newton observations to directly measure their column densities (NH) and infer their intrinsic power. We complement our X-ray data with archival and new high-angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (NH > 1023 cm−2; L2–10 keV,int ∼ 1041 erg s−1), and NGC 660 may be Compton thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L2–10 keV,int < 1039 erg s−1, i.e. genuine LLAGN. Both of the heavily obscured AGNs have Lbol > 1041 erg s−1 and λEdd ≳ 10−3, and are detected in high-angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486, however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.

JET CONFINEMENT BY NONLINEAR MAGNETO-TORSIONAL OSCILLATIONS

2008 ◽  
Vol 17 (10) ◽  
pp. 1695-1706
Author(s):  
G. S. BISNOVATYI-KOGAN
Keyword(s):  
Magnetic Field ◽  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Simplified Model ◽  
High Angular Resolution ◽  
Cylinder Axis ◽  
Azimuthal Magnetic Field ◽  
Torsional Oscillations ◽  
Oscillations Of A Cylinder

Many quasars and active galactic nuclei are connected with long, thin jets. When observed with high angular resolution, these jets show a structure with bright knots separated by relatively dark regions. We consider magnetic collimation, connected with torsional oscillations of a cylinder with elongated magnetic field, and periodically distributed initial rotation around the cylinder axis. The stabilizing azimuthal magnetic field is created here by torsional oscillations. An approximate, simplified model is developed. The parameters for which jets may be stabilized by torsional oscillations are estimated quantitatively.

scholarly journals The sharpest view of the local AGN population at mid-infrared wavelengths

2013 ◽  
Vol 9 (S304) ◽  
pp. 225-226
Author(s):  
Daniel Asmus ◽  
Sebastian F. Hönig ◽  
Poshak Gandhi ◽  
Alain Smette ◽  
Wolfgang J. Duschl
Keyword(s):  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Spatial Scales ◽  
Galactic Nuclei ◽  
High Angular Resolution ◽  
Mid Infrared ◽  
X Ray ◽  
Infrared Wavelengths ◽  
Photometric Measurements

AbstractWe present the largest mid-infrared (MIR) atlas of active galactic nuclei at sub-arcsec spatial scales containing 253 objects with a median redshift of 0.016. It comprises all available ground-based high-angular resolution MIR observations performed to date with 8-meter class telescopes and includes 895 photometric measurements. All types of AGN are present in the atlas, which also includes 80 per cent of the 9-month BAT AGN sample. Therefore, this atlas and its subsamples are very well-suited for AGN unification studies. A first application of the atlas is the extension of the MIR–X-ray luminosity correlation for AGN.

scholarly journals Radio spectral properties of cores and extended regions in blazars in the MHz regime

2019 ◽  
Vol 490 (4) ◽  
pp. 5798-5806 ◽  
Author(s):  
D d’Antonio ◽  
M Giroletti ◽  
G Giovannini ◽  
A Maini
Keyword(s):  
Radio Frequency ◽  
Active Galactic Nuclei ◽  
High Frequency ◽  
Spectral Properties ◽  
Gamma Ray ◽  
Angular Resolution ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
High Angular Resolution ◽  
Murchison Widefield Array

ABSTRACT Low-frequency radio surveys allow in-depth studies and new analyses of classes of sources that were previously known and characterized only in other bands. In recent years, low radio frequency observations of blazars have become available as a result of new surveys, such as the GaLactic and Extragalactic All-sky Murchison Widefield Array (MWA) survey (GLEAM). We search for gamma-ray blazars in a low-frequency (ν < 240 MHz) survey, to characterize the spectral properties of the spatial components. We cross-correlate GLEAM with the fourth catalogue of active galactic nuclei (4LAC) detected by the Fermi satellite. This improves on previous works by using a low-frequency catalogue that is wider and deeper, with a better spectral coverage and the latest and most sensitive gamma-ray source list. Compared with a previous study based on the commissioning survey, the detection rate increased from 35 to 70 per cent. We include data from the Australia Telescope 20-GHz (AT20G) survey in order to extract high-frequency high-angular resolution information about the radio cores of blazars. We find low radio frequency counterparts for 1274 out of 1827 blazars in the range of 72–231 MHz. Blazars have flat spectra at the ∼100-MHz regime, with a mean spectral index α = −0.44 ± 0.01 (assuming Sν ∝ να). Low synchrotron peaked objects have a flatter spectrum than high synchrotron peaked objects. Low frequency radio and gamma-ray emissions show a significant but scattered correlation. The ratio between lobe and core radio emission in gamma-ray blazars is smaller than previously estimated.

Extragalactic class I methanol maser: A new probe for starbursts and feedback of galaxies

2017 ◽  
Vol 13 (S336) ◽  
pp. 99-104
Author(s):  
Xi Chen ◽  
Simon P. Ellingsen
Keyword(s):  
Active Galactic Nuclei ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Active Galaxies ◽  
Class I ◽  
High Angular Resolution ◽  
Methanol Maser ◽  
Methanol Masers

AbstractWe report progress on research relating to 36.2 GHz extragalactic class I methanol masers, including a review of published work and new observations at high angular resolution. These observations reveal that extragalactic class I masers are excited in shocked gas and maybe associated with starbursts, galactic-scale outflows from active galactic nuclei (AGNs) feedback, or the inner-end region of the galactic bar. The current observational results suggests that extragalactic class I methanol masers provide a new probe for starbursts and feedback in active galaxies.

scholarly journals High gas-to-dust size ratio indicating efficient radial drift in the mm-faint CX Tauri disk

2019 ◽  
Vol 626 ◽  
pp. L2 ◽  
Author(s):  
S. Facchini ◽  
E. F. van Dishoeck ◽  
C. F. Manara ◽  
M. Tazzari ◽  
L. Maud ◽  
...  
Keyword(s):  
Near Infrared ◽  
Angular Resolution ◽  
Spectral Energy Distribution ◽  
Theoretical Models ◽  
Intensity Profile ◽  
Continuum Emission ◽  
Spectral Energy ◽  
High Angular Resolution ◽  
Sharp Drop ◽  
Large Program

The large majority of protoplanetary disks have very compact continuum emission (≲15 AU) at millimeter wavelengths. However, high angular resolution observations that resolve these small disks are still lacking, due to their intrinsically fainter emission compared with large bright disks. In this Letter we present 1.3 mm ALMA data of the faint disk (∼10 mJy) orbiting the TTauri star CX Tau at a resolution of ∼40 mas, ∼5 AU in diameter. The millimeter dust disk is compact, with a 68% enclosing flux radius of 14 AU, and the intensity profile exhibits a sharp drop between 10 and 20 AU, and a shallow tail between 20 and 40 AU. No clear signatures of substructure in the dust continuum are observed, down to the same sensitivity level of the DSHARP large program. However, the angular resolution does not allow us to detect substructures on the scale of the disk aspect ratio in the inner regions. The radial intensity profile closely resembles the inner regions of more extended disks imaged at the same resolution in DSHARP, but with no rings present in the outer disk. No inner cavity is detected, even though the disk has been classified as a transition disk from the spectral energy distribution in the near-infrared. The emission of 12CO is much more extended, with a 68% enclosing flux radius of 75 AU. The large difference of the millimeter dust and gas extents (> 5) strongly points to radial drift, and closely matches the predictions of theoretical models.

scholarly journals The Infrared Space Observatory

1990 ◽  
Vol 123 ◽  
pp. 205-214 ◽  
Author(s):  
C.J. Cesarsky ◽  
M.F. Kessler
Keyword(s):  
Optical Sensors ◽  
European Space Agency ◽  
Space Observatory ◽  
Infrared Space Observatory ◽  
Long Wavelength ◽  
Space Agency ◽  
Pointing Accuracy ◽  
Funded Project ◽  
Astronomical Satellite ◽  
The Universe

AbstractThe Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), is an astronomical satellite, which will operate at wavelengths from 3–200 μm. ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to distant extragalactic sources. The satellite essentially consists of a large cryostat containing at launch about 2300 litres of superfluid helium to maintain the Ritchey-Chrétien telescope, the scientific instruments and the optical baffles at temperatures between 2K and 8K. The telescope has a 60-cm diameter primary mirror and is diffraction-limited at a wavelength of 5μm. A pointing accuracy of a few arc seconds is provided by a three-axis-stabilisation system consisting of reaction wheels, gyros and optical sensors. ISO’s instrument complement consists of four instruments, namely: a photo-polarimeter (3–200μm), a camera (3–17μm), a short wavelength spectrometer (3–45μm) and a long wavelength spectrometer (45–180μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. ISO will be launched in 1993 by an Ariane 4 into an elliptical orbit (apogee 70000km and perigee 1000km) and will be operational for at least 18 months. In keeping with ISO’s role as an observatory, two-thirds of its observing time will be made available to the european and american astronomical community.

scholarly journals VSOP, A Space VLBI Programme

1990 ◽  
Vol 123 ◽  
pp. 263-269
Author(s):  
H. Hirabayashi
Keyword(s):  
Active Galactic Nuclei ◽  
Phase Transfer ◽  
Galactic Nuclei ◽  
Satellite Orbit ◽  
Radio Sources ◽  
Space Observatory ◽  
Stellar Objects ◽  
Radio Observatory ◽  
Star Forming ◽  
Star Forming Regions

AbstractVSOP, VLBI Space Observatory Programme, is an approved space VLBI programme of ISAS for the study of very compact radio sources with the synthesized aperture of 30,000 km diameter, by connecting an orbiting radio observatory with ground radiotelescopes. The VSOP satellite carrying 10 m antenna with 1.6, 5, and 22 GHz band receivers will be launched in early 1995 by M-V rocket of ISAS into an eccentric orbit with 20,000 km in apogee height. The tracking network will be formed for the satellite orbit determination, phase transfer and IF down-link. VSOP aims imaging capability with best resolution of 0.0001 arc second in 22 GHz band. Imaging of active galactic nuclei, star forming regions and stellar objects, and radioastrometry are main scientific targets.

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