scholarly journals Quasar Astrophysics with the Space Interferometry Mission

2002 ◽  
Vol 19 (1) ◽  
pp. 5-9 ◽  
Author(s):  
S. C. Unwin ◽  
A. E. Wehrle ◽  
D. L. Jones ◽  
D. L. Meier ◽  
B. G. Piner
Keyword(s):  
Accretion Disk ◽  
Optical Emission ◽  
Galaxy Mergers ◽  
Proper Motions ◽  
Optical Interferometer ◽  
Photometric Variability ◽  
Relativistic Jet ◽  
Precision Astrometry ◽  
Insight Into ◽  
Space Interferometry

AbstractPrecision optical astrometry of quasars and active galaxies can provide important insight into the spatial distribution and variability of emission in compact nuclei. SIM — the Space Interferometry Mission — will be the first optical interferometer capable of precision astrometry on quasars. Although it is not expected to resolve the emission, it will be very sensitive to astrometric shifts, for objects as faint as R magnitude 20. In its wide-angle mode, SIM will yield 4 microarcsecond absolute positions, and proper motions to about 2 microarcsecond/yr. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. SIM should be able to answer the following questions. Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? Do the relative positions of the radio core and optical photocentre of quasars used for the reference frame tie change on the timescales of their photometric variability? Do the cores of galaxies harbour binary supermassive black holes remaining from galaxy mergers? In this paper we briefly describe the operation of SIM and the quasar measurements it will make. We estimate the size of the astrometric signatures which may be expected, and we discuss prospects for using astrometry as a fundamental tool for understanding quasar nuclei.

scholarly journals Quasar astrophysics with the Space Interferometry Mission

2007 ◽  
Vol 3 (S248) ◽  
pp. 288-289
Author(s):  
S. C. Unwin ◽  
A. E. Wehrle ◽  
D. L. Meier ◽  
D. L. Jones ◽  
B. G. Piner
Keyword(s):  
Spatial Distribution ◽  
Accretion Disk ◽  
Spectral Dependence ◽  
Active Galaxies ◽  
Time Dependent ◽  
Emission Mechanism ◽  
Unique Data ◽  
Science Question ◽  
Insight Into ◽  
Space Interferometry

AbstractOptical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V=19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.

scholarly journals The Effect of Companions on the SIM Reference Frame

2000 ◽  
Vol 180 ◽  
pp. 386-391
Author(s):  
Christopher S. Jacobs ◽  
Slava G. Turyshev
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Field Of View ◽  
Optical Interferometer ◽  
Galactic Astronomy ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
Precision Astrometry ◽  
Accuracy And Stability ◽  
Space Interferometry

AbstractThe Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4μas, 3μas/yr) with better accuracy hoped for over a narrow field of view. It is intended to search for planets and investigate a number of problems in Galactic and extra-galactic astronomy.The accuracy and stability of SIM’s celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. We present the results of simulations which show the sensitivity of reference frame accuracy to companions as a function of mass and period. We assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity > 10 m/s. We further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion.

scholarly journals Maser, infrared and optical emission for late-type stars in the Galactic plane

2017 ◽  
Vol 13 (S336) ◽  
pp. 184-186
Author(s):  
L. H. Quiroga-Nuñez ◽  
H. J. van Langevelde ◽  
L. O. Sjouwerman ◽  
Y. M. Pihlström ◽  
M. J. Reid ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Population Distribution ◽  
Massive Stars ◽  
Optical Emission ◽  
Proper Motions ◽  
Late Type ◽  
Intrinsic Properties ◽  
Radio Observations ◽  
Evolved Stars

AbstractRadio astrometric campaigns using VLBI have provided distances and proper motions for masers associated with young massive stars (BeSSeL survey). The ongoing BAaDE project plans to obtain astrometric information of SiO maser stars located in the inner Galaxy. These stars are associated with evolved, mass-losing stars. By overlapping optical (Gaia), infrared (2MASS, MSX and WISE) and radio (BAaDE) sources, we expect to obtain important clues on the intrinsic properties and population distribution of late-type stars. Moreover, a comparison of the Galactic parameters obtained with Gaia and VLBI can be done using radio observations on different targets: young massive stars (BeSSeL) and evolved stars (BAaDE).

scholarly journals Astrometric and Photometric Variability in Quasars

2009 ◽  
Vol 5 (S267) ◽  
pp. 103-103
Author(s):  
A. H. Andrei ◽  
S. Bouquillon ◽  
J. L. Penna ◽  
F. Taris ◽  
S. Anton ◽  
...  
Keyword(s):  
Strong Support ◽  
Optical Emission ◽  
Optical Observations ◽  
Massive Black Hole ◽  
Full Account ◽  
Photometric Variability ◽  
Central Engine ◽  
Relationship Of ◽  
The Relationship

Quasars are the choicest objects to define a quasi-inertial reference frame. At the same time, they are active galactic nuclei powered by a massive black hole. As the astrometric precision of ground-based optical observations approaches the limit set by the forthcoming GAIA mission, astrometric stability can be investigated. Though the optical emission from the core region usually exceeds the other components by a factor of a hundred, the variability of those components must surely imply some measure of variability of the astrometric baricenter. Whether this is confirmed or not, it puts important constraints on the relationship of the quasar's central engine to the surrounding distribution of matter. To investigate the correlation between long-term optical variability and what is dubbed as the “random walk” of the astrometric center, a program is being pursued at the WFI/ESO 2.2m. The sample was selected from quasars known to undergo large-amplitude and long-term optical variations (Smith et al. 1993; Teerikorpi 2000). The observations are typically made every two months. The treatment is differential, comparing the quasar position and brightness against a sample of selected stars for which the average relative distances and magnitudes remain constant. The provisional results for four objects bring strong support to the hypothesis of a relationship between astrometric and photometric variability. A full account is provided by Andrei et al. (2009).

scholarly journals Astrometric and Astrophysical Insights into the Hipparcos Data Quality

1995 ◽  
Vol 166 ◽  
pp. 83-86 ◽  
Author(s):  
M.A.C. Perryman
Keyword(s):  
Data Quality ◽  
Error Estimates ◽  
Photographic Plate ◽  
Meridian Circle ◽  
Proper Motions ◽  
Photometric Variability ◽  
Multiple Stars ◽  
Hipparcos Catalogue ◽  
Double And Multiple Stars ◽  
Internal Error

Internal error estimates and external verifications indicate that median errors for the 120000 stars in the Hipparcos Catalogue, for each of the five astrometric parameters, will be in the range 1–1.5 mas. This paper illustrates some of the statistical investigations that have been conducted so far, including comparisons with catalogues of ground-based positions and proper motions, the structure of the Hertzsprung-Russell diagram, results of the reanalysis of meridian circle and photographic plate data using the positions determined from the satellite, and expected results on double and multiple stars and photometric variability.

scholarly journals Gamma-ray-emitting narrow-line Seyfert 1 galaxies: the Swift view

2020 ◽  
Vol 496 (2) ◽  
pp. 2213-2229 ◽  
Author(s):  
F D’Ammando
Keyword(s):  
Gamma Ray ◽  
Thermal Emission ◽  
Optical Emission ◽  
X Rays ◽  
Narrow Line ◽  
X Ray ◽  
Relativistic Jet ◽  
Photon Index ◽  
Γ Ray ◽  
Lower Variability

ABSTRACT We report the analysis of all Swift observations available up to 2019 April of γ-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). The distribution of X-ray luminosities (and fluxes) indicates that the jet radiation significantly contributes to their X-ray emission, with Doppler boosting making values higher than other radio-loud NLSy1. The 0.3–10 keV photon indices are on average harder with respect to radio-quiet and radio-loud NLSy1, confirming a dominant jet contribution in X-rays. However, the lower variability amplitude with respect to blazars and the softening of the spectrum in some periods suggests that also the corona radiation contributes to the X-ray emission. In optical and ultraviolet (UV) significant flux changes have been observed on daily, weekly, and monthly time-scale, providing a clear indication of the significant contribution of the jet radiation in this part of spectrum. A strong correlation between X-ray, UV, and optical emission and simultaneous flux variations have been observed in 1H 0323+342, SBS 0846+513, PMN J0948+0022 as expected in case the jet radiation is the dominant mechanism. Correlated multiband variability favours the jet-dominated scenario also in FBQS J1644+2619 and PKS 2004−447. The summed X-ray Telescope spectra of 1H 0323+342, SBS 0846+513, PMN J0948+0022, and FBQS J1644+2619 are well fitted by a broken power law with a break around 2 keV. The spectrum above 2 keV is dominated by the non-thermal emission from a beamed relativistic jet, as suggested by the hard photon index. A Seyfert-like feature like the soft X-ray excess has been observed below 2 keV, making these γ-ray-emitting NLSy1 different from typical blazars.

scholarly journals Accuracy Assessment of Hipparcos Optical and VLA Radio Positions of Stars

1993 ◽  
Vol 156 ◽  
pp. 377-380
Author(s):  
H. G. Walter ◽  
R. Hering ◽  
H. Lenhardt ◽  
Chr. deVegt ◽  
D.R. Florkowski ◽  
...  
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Accuracy Assessment ◽  
Optical Emission ◽  
Relative Orientation ◽  
Large Array ◽  
Proper Motions ◽  
Data Noise ◽  
Very Large Array ◽  
Radio Stars

Optical positions of some 30 radio stars derived from 12 months of HIPPARCOS measurements are compared with their radio positions obtained with the Very Large Array (VLA). — Once the lengths of arcs between optical and radio positions of pairs of stars are calculated the differences of the arcs are formed. They provide an estimate of the coincidence of the optical and radio emission centres. — From the comparison of optical and radio positions infinitesimal rotation angles of the HIPPARCOS frame with respect to the VLA extragalactic reference frame are determined by rigid rotations. After taking account of the relative orientation of the frames the standard deviations of the remaining residuals are approximately of the order of the VLA observation errors, thus demonstrating the reliability of the HIPPARCOS results. However, they also indicate some data noise very likely caused by the low accuracy of optical proper motions used to bridge the HIPPARCOS-radio epoch differences up to 9 years, and possible discrepancies of radio-optical emission centres of some stars.

scholarly journals General Relativistic Simulation of Jet Formation from Magnetized Accretion Disk

1997 ◽  
Vol 163 ◽  
pp. 667-671
Author(s):  
Shinji Koide ◽  
Kazunari Shibata ◽  
Takahiro Kudoh
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Numerical Code ◽  
Jet Formation ◽  
Relativistic Jet ◽  
Relativistic Regime ◽  
General Relativistic

AbstractRecently, superluminal motions are observed not only from active galactic nuclei but also in our Galaxy. These phenomena are explained as relativistic jets propagating almost toward us with Lorentz factor more than 2. For the formation of such a relativistic jet, magnetically driven mechanism around a black hole is most promising. We have extended the 2.5D Newtonian MHD jet model (Shibata & Uchida 1986) to general relativistic regime. For this purpose, we have developed a general relativistic magnetohydrodynamic (GRMHD) numerical code and applied it to the simulation of the magnetized accretion disk around a black hole. We have found the formation of magnetically driven jets with 86 percent of light velocity (i.e. Lorentz factor ~ 2.0).

scholarly journals Time lags between starburst and AGN activity in galaxy mergers

2013 ◽  
Vol 9 (S303) ◽  
pp. 379-381
Author(s):  
M. Blank ◽  
W. J. Duschl
Keyword(s):  
Black Hole ◽  
Accretion Disk ◽  
Velocity Dispersion ◽  
Time Lag ◽  
Time Lags ◽  
Galaxy Mergers ◽  
Black Hole Mass ◽  
Central Black Hole ◽  
Stellar Velocity ◽  
Flow Through

AbstractWe show that the observed time lag between starburst and AGN activity can be explained by a viscous time lag the gas needs to flow through the AGN's accretion disk before reaching the central black hole. Our calculations reproduce the observed time lag and are in agreement with the observed correlation between black hole mass and stellar velocity dispersion.

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