ترغب بنشر مسار تعليمي؟ اضغط هنا

Parsec-scale jet properties of the gamma-ray quasar 3C 286

123   0   0.0 ( 0 )
 نشر من قبل Tao An
 تاريخ النشر 2016
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

The quasar 3C~286 is one of two compact steep spectrum sources detected by the {it Fermi}/LAT. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the $gamma$-ray emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core--jet structure extending to the southwest at a projected distance of $sim$1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of $2.8times 10^{9}$~K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of $-135^circ$ to $-115^circ$. Based on the available VLBI data, we inferred the proper motion speed of the inner jet as $0.013 pm 0.011$ mas yr$^{-1}$ ($beta_{rm app} = 0.6 pm 0.5$), corresponding to a jet speed of about $0.5,c$ at an inclination angle of $48^circ$ between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of $gamma$-ray-emitting blazars, implying that the pc-scale jet in 3C~286 is mildly relativistic. Unlike blazars in which $gamma$-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of $gamma$-ray emission in 3C~286 may be different as indicated by the current radio data. Multi-band spectrum fitting may offer a complementary diagnostic clue of the $gamma$-ray production mechanism in this source.



قيم البحث

اقرأ أيضاً

207 - Mikhail Lisakov 2017
We present a comprehensive 5-43 GHz VLBA study of the blazar 3C 273 initiated after an onset of a strong $gamma$-ray flare in this source. We have analyzed the kinematics of new-born components, light curves, and position of the apparent core to pinp oint the location of the $gamma$-ray emission. Estimated location of the $gamma$-ray emission zone is close to the jet apex, 2 pc to 7 pc upstream from the observed 7 mm core. This is supported by ejection of a new component. The apparent core position was found to be inversely proportional to frequency. The brightness temperature in the 7 mm core reached values up to at least $10^{13}$ K during the flare. This supports the dominance of particle energy density over that of magnetic field in the 7 mm core. Particle density increased during the radio flare at the apparent jet base, affecting synchrotron opacity. This manifested itself as an apparent core shuttle along the jet during the 7 mm flare. It is also shown that a region where optical depth decreases from $tausim1$ to $tau<<1$ spans over several parsecs along the jet. The jet bulk flow speed estimated at the level of 12c on the basis of time lags between 7 mm light curves of stationary jet features is 1.5 times higher than that derived from VLBI apparent kinematics analysis.
We analyze the multifrequency behavior of the quasar 3C 454.3 during three prominent gamma-ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each ga mma-ray outburst, which implies similar mechanism(s) and location for all three events. The multi-frequency behavior indicates that the lower frequency events are co-spatial with the gamma-ray outbursts, although the gamma-ray emission varies on the shortest timescales. We determine that the variability from UV to IR wavelengths during an outburst results from a single synchrotron component whose properties do not change significantly over the different outbursts. Despite a general increase in the degree of optical linear polarization during an outburst, the polarization drops significantly at the peak of the gamma-ray event, which suggests that both shocks and turbulent processes are involved. We detect two disturbances (knots) with superluminal apparent speeds in the parsec-scale jet associated with the outbursts in 2009 Autumn and 2010 Autumn. The kinematic properties of the knots can explain the difference in amplitudes of the gamma-ray events, while their millimeter-wave polarization is related to the optical polarization during the outbursts. We interpret the multi-frequency behavior within models involving either a system of standing conical shocks or magnetic reconnection events located in the parsec-scale millimeter-wave core of the jet. We argue that gamma-ray outbursts with variability timescales as short as ~ 3 hr can occur on parsec scales if flares take place in localized regions such as turbulent cells.
We analyze total and polarized intensity images of the quasar 3C 454.3 obtained monthly with the VLBA at 43 GHz within the ongoing Boston U. monitoring program of gamma-ray blazars started in June 2007. The data are supplemented by VLBA observations performed during intense campaigns of 2 week duration when the quasar was observed 3 times per campaign. We find a strong increase of activity in the parsec-scale jet of the quasar during high gamma-ray states in December 2009, April 2010, and November 2010. We detect new superluminal knots, K09 and K10, associated with the autumn 2009 and 2010 outbursts, respectively, and compare their kinematic parameters. We analyze optical polarimetric behavior along with polarization parameters of the parsec-scale jet and outline similarities and differences in polarization properties across wavelengths. The results of the analysis support the conclusions that the optical polarized emission is produced in a region located in the vicinity of the mm-wave core of the jet of the quasar, and that the gamma-ray outbursts occur when a superluminal disturbance passes through the core.
155 - M. L. Lister , M. Aller , H. Aller 2011
We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the brightest 173 AGNs in these bands above declination -30 deg. during this period, and thus probes the full range of gamma-ray loudness (gamma-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least four orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the gamma-ray emission in these BL Lacs over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED peak - gamma-ray loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQ) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lacs have generally lower Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our sample.
We performed multi-frequency studies on the gigahertz-peaked spectrum high-redshift quasar 0858-279. Initially, the source presented itself at early VLBI images as a very peculiar resolved blob. We observed the quasar with the VLBA at 1.4-24 GHz in d ual-polarization mode. The high spatial resolution and spectral index maps enabled us to resolve the core-jet structure and locate a weak and compact core by its inverted spectrum. The dominant jet component 20 parsecs away from the core was found to be optically thin above 10 GHz and opaque below it. We also estimated an uncommonly strong magnetic field in the bright jet feature which turned out to be around 3 G. Faraday rotation measure maps revealed high RM values over 6000 rad/m^2. Additionally, these maps allowed us to follow the magnetic field direction in the bright jet feature being perpendicular to the propagation direction of the jet. All the results strongly indicated the formation of a shock wave in the dominant component arising from an interaction with the surrounding matter. Using the proposed hypothesis as well as the core shift approach, we discovered that the magnetic field in the core region is of the order of 0.1 G.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا