Search results for "quasar"
showing 10 items of 133 documents
PROBING THE DARK MATTER RADIAL PROFILE IN LENS GALAXIES AND THE SIZE OF X-RAY EMITTING REGION IN QUASARS WITH MICROLENSING
2015
We use X-ray and optical microlensing measurements to study the shape of the dark matter density profile in the lens galaxies and the size of the (soft) X-ray emission region. We show that single epoch X-ray microlensing is sensitive to the source size. Our results, in good agreement with previous estimates, show that the size of the X-ray emission region scales roughly linearly with the black hole mass, with a half-light radius of where . This corresponds to a size of or ?1 lt-day for a black hole mass of . We simultaneously estimated the fraction of the local surface mass density in stars, finding that the stellar mass fraction is ? = 0.20 ? 0.05 at an average radius of , where Re is the …
SHARDS: A global view of the star formation activity at z~0.84 and z~1.23
2015
et al.
VLBI imaging of the gravitational lens MGJ0414+0534
2000
6 pages, 3 figures, accepted for publication in Astronomy & Astrophysics.-- Final full-text version of the paper available at: http://aa.springer.de/papers/0362003/2300845.pdf
OBSERVATIONS OF THE LENSED QUASAR Q2237+0305 WITH CANARICAM AT GTC
2016
We present new mid-IR observations of the quadruply lensed quasar Q2237+0305 taken with CanariCam on the Gran Telescopio Canarias. Mid-IR emission by hot dust, unlike the optical and near-IR emission from the accretion disk, is unaffected by the interstellar medium (extinction/scattering) or stellar microlensing. We compare these "true" ratios to the (stellar) microlensed flux ratios observed in the optical/near-IR to constrain the structure of the quasar accretion disk. We find a half-light radius of $R_{1/2}=3.4_{-2.1}^{+5.3}\sqrt{\langle M \rangle/0.3\,\rm{M_{\odot}}}$ light-days at $\lambda_{rest}=1736$ {\AA}, and an exponent for the temperature profile $R \propto \lambda^{p}$ of $p=0.7…
A Connection Between Apparent VLBA Jet Speeds and Initial Active Galactic Nucleus Detections Made by the Fermi Gamma-ray Observatory
2009
In its first three months of operations, the Fermi Gamma-Ray Observatory has detected approximately one quarter of the radio-flux-limited MOJAVE sample of bright flat-spectrum active galactic nuclei (AGNs) at energies above 100 MeV. We have investigated the apparent parsec-scale jet speeds of 26 MOJAVE AGNs measured by the Very Long Baseline Array (VLBA) that are in the LAT bright AGN sample (LBAS). We find that the gamma-ray bright quasars have faster jets on average than the non-LBAS quasars, with a median of 15 c, and values ranging up to 34 c. The LBAS AGNs in which the LAT has detected significant gamma-ray flux variability generally have faster jets than the nonvariable ones. These fi…
A possible jet precession in the periodic quasar B0605-085
2010
The quasar B0605-085 (OH 010) shows a hint for probable periodical variability in the radio total flux-density light curves. We study the possible periodicity of B0605-085 in the total flux-density, spectra and opacity changes in order to compare it with jet kinematics on parsec scales. We have analyzed archival total flux-density variability at ten frequencies (408 MHz, 4.8 GHz, 6.7 GHz, 8 GHz, 10.7 GHz, 14.5 GHz, 22 GHz, 37 GHz, 90 GHz, and 230 GHz) together with the archival high-resolution very long baseline interferometry data at 15 GHz from the MOJAVE monitoring campaign. Using the Fourier transform and discrete autocorrelation methods we have searched for periods in the total flux-de…
TANAMI: tracking active galactic nuclei with austral milliarcsecond interferometry
2010
We introduce the TANAMI program (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) which is monitoring an initial sample of 43 extragalactic jets located south of -30 degrees declination at 8.4 GHz and 22 GHz since 2007. All aspects of the program are discussed. First epoch results at 8.4 GHz are presented along with physical parameters derived therefrom. We present first epoch images for 43 sources, some observed for the first time at milliarcsecond resolution. Parameters of these images as well as physical parameters derived from them are also presented and discussed. These and subsequent images from the TANAMI survey are available at http://pulsar.sternwarte.uni…
First hints of pressure waves in a helical extragalactic jet: S5~0836+710
2014
One of the open questions in extragalactic jet Astrophysics is related to the nature of the observed radio jet, namely whether it traces a pattern or the flow structure itself. In this paper I summarize the evidence collected for the presence of waves in extragalactic jets. The evidence points towards the peak of emission in helical jets corresponding to pressure-maxima of a wave that is generated within the core region and propagates downstream. Making use of a number of very long baseline interferometry (VLBI) observations of the radio jet in the quasar S5~0836+710 at different frequencies and epochs, Perucho et al. (2012) were able to observe wave-like behavior within the observed radio-…
Kinetic power of quasars and statistical excess of MOJAVE superluminal motions
2012
The MOJAVE survey contains 101 quasars with a total of 354 observed radio components that are different from the radio cores, among which 95% move with apparent projected superluminal velocities with respect to the core, and 45% have projected velocities larger than 10c (with a maximum velocity 60c). Doppler boosting effects are analyzed to determine the statistics of the superluminal motions. We integrate over all possible values of the Lorentz factor the values of the kinetic energy corresponding to each component. The calculation of the mass in the ejection is carried out by assuming the minimum energy state. This kinetic energy is multiplied by the frequency at which the portions of the…
Highlights from the ARGO-YBJ Experiment
2012
""The ARGO-YBJ experiment at YangBaJing in Tibet (4300m a.s.l.) has been taking data with its full layout since October 2007. Here we present a few significant results obtained in gamma-ray astronomy and cosmic-ray physics. Emphasis is placed on the analysis of gamma-ray emission from point-like sources (Crab Nebula, MRK 421), on the preliminary limit on the antiproton\\\/proton flux ratio, on the large-scale cosmic-ray anisotropy and on the proton-air cross-section. The performance of the detector is also discussed, and the perspectives of the experiment are outlined.""