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Register a new userParsec-scale Structure and Kinematics of Faint TeV HBLs
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We present new multi-epoch Very Long Baseline Array (VLBA) observations of a set of TeV blazars drawn from our VLBA program to monitor all TeV-detected high-frequency peaked BL Lac objects (HBLs) at parsec scales. Most of these sources are faint in the radio, so they have not been well observed with VLBI by other surveys. Our previous measurements of apparent jet speeds in TeV HBLs showed apparent jet speeds that were subluminal or barely superluminal, suggesting jets with velocity structures at the parsec-scale. Here we present apparent jet speed measurements for eight new TeV HBLs, which for the first time show a superluminal tail to the apparent speed distribution for the TeV HBLs.
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Several narrow-line Seyfert 1 galaxies (NLS1s) have now been detected in gamma rays, providing firm evidence that at least some of this class of active galactic nuclei (AGN) produce relativistic jets. The presence of jets in NLS1s is surprising, as these sources are typified by comparatively small black hole masses and near- or super-Eddington accretion rates. This challenges the current understanding of the conditions necessary for jet production. Comparing the properties of the jets in NLS1s with those in more familiar jetted systems is thus essential to improve jet production models. We present early results from our campaign to monitor the kinematics and polarization of the parsec-scale jets in a sample of 15 NLS1s through multifrequency observations with the Very Long Baseline Array. These observations are complemented by fast-cadence 15 GHz monitoring with the Owens Valley Radio Observatory 40m telescope and optical spectroscopic monitoring with with the 2m class telescope at the Guillermo Haro Astrophysics Observatory in Cananea, Mexico.
We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of $gamma$-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43~GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BL~Lacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02$c$ to 78$c$; 21% of the knots are quasi-stationary. Approximately 1/3 of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5~pc (projected) of the core, and knots in the BLLacs tending to decelerate near the core. Using apparent speeds of components and timescales of variability from their light curves, we derive physical parameters of 120 superluminal knots, including variability Doppler factors, Lorentz factors, and viewing angles. We estimate the half-opening angle of each jet based on the projected opening angle and scatter of intrinsic viewing angles of knots. We determine characteristic values of physical parameters for each jet and AGN class based on the range of values obtained for individual features. We calculate intrinsic brightness temperatures of the cores, $T_{rm b,int}^{rm core}$, at all epochs, finding that the radio galaxies usually maintain equipartition conditions in the cores, while $sim$30% of $T_{rm b,int}^{rm core}$ measurements in the quasars and BLLacs deviate from equipartition values by a factor $>$10. This probably occurs during transient events connected with active states. In the Appendix we briefly describe the behavior of each blazar during the period analyzed.
We report new results from a sub-parsec scale study of the inner jet in M87 performed at 15 GHz with the Very Long Baseline Array. We have detected a limb brightened structure of the jet along with a faint 3 mas long counter-feature which we also find to be limb brightened. Typical speeds of separate jet features are measured to be less than 0.05 speed of light, despite the highly asymmetric jet structure and the implications of the canonical relativistic beaming scenario. The observed intrinsic jet structure can be described in terms of a two stream spine-sheath velocity gradient across the jet according to theoretical predications based on the recently discovered strong and variable TeV emission from M87. The jet to counter-jet flux density ratio is measured to be greater than 200. The observed intrinsic jet structure is broadly consistent with theoretical predictions of a spine-sheath velocity gradient suggested by recently discovered TeV emission from M87.
We made simultaneous single-dish and very long baseline interferometer (VLBI) observations of a narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342, showing gamma-ray activity revealed by Fermi/LAT observations. We found significant variation of the total flux density at 8 GHz on the time scale of one month by the single-dish monitoring. The total flux density varied by 5.5% in 32 days, which is comparable to the gamma-ray variability time scale, corresponding to the variability brightness temperature of $7.0 times 10^{11}$ K. The source consists of central and southeastern components on the parsec (pc) scale. The flux of only the central component decreased in the same way as the total flux density, indicating that the short-term radio variability, and probably the gamma-ray emitting region, is associated with this component. From the VLBI observations we obtained the brightness temperatures of greater than $(5.2 pm 0.3) times 10^{10}$ K, and derived the equipartition Doppler factor of greater than 1.7, the variability Doppler factor of 2.2, and the 8 GHz radio power of $10^{24.6}$ W Hz$^{-1}$. Combining them we conclude that acceleration of radio jets and creation of high-energy particles are ongoing in the central engine, and that the apparent very radio-loud feature of the source is due to the Doppler-boosting effect, resulting in the intrinsic radio loudness to be an order of magnitude smaller than the observed values. We also conclude that the pc-scale jet represents recurrent activity from the the spectral fitting and the estimated kinematic age of pc- and kpc-scale extended components with different position angle.
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