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SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 62, Issue 6: 069511(2019) https://doi.org/10.1007/s11433-018-9330-4

New clues to jet launching: The inner disks in radio loud quasars may be more stable

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  • ReceivedOct 19, 2018
  • AcceptedNov 20, 2018
  • PublishedDec 25, 2018
PACS numbers

Abstract

Jet launching in radio loud (RL) quasars is one of the fundamental problems in astrophysics.Exploring the differences in the inner accretion disk properties between RL and radio quiet (RQ) quasars might yield helpful clues to this puzzle.We previously discovered that the shorter term UV/optical variations of quasars are bluer than the longer term ones, i.e., the so-called timescale-dependent color variation. This is consistent with the scheme that the faster variations come from the inner and hotter disk regions, thus providing a useful tool to map the accretion disk which is otherwise unresolvable.In this work we compare the UV/optical variations of RL quasars in SDSS Stripe 82 to those of several RQ samples, including those matched in redshift-luminosity-black hole mass and/or color-magnitude.We find that while both RL and RQ populations appear bluer when they brighten, RL quasars potentially show a weaker/flatter dependence on timescale in their color variation.We further find that while both RL and RQ populations on average show similar variation amplitudes at long timescales, fast variations of RL sourcesappear weaker/smaller (at timescales of $\sim$25-300 d in the observer's frame),and the difference is more prominent in the $g$-band than in the $r$-band.Inhomogeneous disk simulations can qualitatively reproduce these observed differences if the inner accretion disk of RL quasars fluctuates less based on simple toy models. Though the implications are likely model dependent, the discovery points to an interesting diagram that magnetic fields in RL quasars may be prospectively stronger and play a key role in both jet launching and the stabilization of the inner accretion disk.


Acknowledgment

We thank Xinwu Cao for helpful discussion. This work was supported by the National Basic Research Program of China (Grant No. 2015CB857005), and the National Natural Science Foundation of China (Grant Nos. 11233002, 11421303, 11503024, and 11873045). JunXian Wang acknowledges support from Chinese Top-notch Young Talents Program, and Frontier Science Key Research Program, China Academy Sciences (Grant No. QYZDJ-SSW-SLH006). ZhenYi Cai acknowledges support from the Fundamental Research Funds for the Central Universities. Feng Yuan acknowledges the grant from the Ministry of Science and Technology of China (Grant No. 2016YFA0400704).


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  • Figure 1

    (Color online) An illustration of the $g$- (green) and $r$-band (red) light curves of RL (top) and RQ (bottom) quasars randomly selected from our final sample.

  • Figure 2

    (Color online) The histogram distributions of the observed $\Delta~C_{rg}$ for the real RL quasar sample (black solid line) and the simulated $\Delta~C_{rg}$ (blue dashed line; normalized at the peak of the solid histogram; see text for the detailed simulation in order to consider the effect of photometric uncertainty) in the timescale bin of 25-42.5 d. Note a few outliers with extreme values. The vertical black solid and blue dashed lines show the standard medians of the real and simulated distributions, respectively. The insert draws several “averages” and their uncertainties of the real $\Delta~C_{rg}$ derived through different approaches. From top to bottom, they are the geometric mean with $\sigma$/$\sqrt{N-1}$ uncertainty (grey open circle; but note this uncertainty is obviously underestimated), the geometric mean with bootstrap uncertainty (black filled circle), the standard median with bootstrap uncertainty (red cross), and the revised median with bootstrap uncertainty (blue open diamond; see sect. 2.2for details).

  • Figure 3

    (Color online) The histogram distribution of the number of $\Delta~C_{rg}$ contributed by each RL quasar in the timescale bin of 25-42.5 d. The vertical line plots the 80th percentile of source number, $N_{80%}$, to the right of which $\simeq~20%$ quasars contribute to $\simeq~54%$ of the total number of $\Delta~C_{rg}$.

  • Figure 4

    (Color online) The top panel shows the $r$- versus $g$-band color variations, $\langle~\Delta~C_{rg}\rangle$, for the whole RL (blue open circles) and RQ (red crosses) samples as a function of timescale, $\tau$, in the observer's frame. The color variation of RL quasars shows a weaker/flatter timescale dependency with a confidence level of $\simeq~99.2%~(\sim~2.6\sigma)$ estimated through bootstrapping. The total source number of each sample is nominated within the corresponding bracket at the top-left corner of each panel (see sect. 3).

  • Figure 5

    (Color online) The distributions of redshift, BH mass, bolometric luminosity, Galactic extinction-corrected $g-r$ color, $g$-band apparent magnitude, and $r$-band apparent magnitude of the whole RL (blue solid line) and RQ (red dotted line) samples. According to the K-S probability, $P_{\rm~KS}$, the RL quasars have comparable properties of redshift and luminosity, but slightly larger BH mass, redder color, and distinct apparent magnitudes, to those of RQ ones. The total source number of each sample is nominated within the corresponding bracket at the top-left corner of the first panel.

  • Figure 6

    (Color online) Same as Figure 5, but for the RL and resampled RQ sub-samples matched in $z$-$M_{\rm~BH}$-$L_{\rm~bol}$ (see sect. 3.1).

  • Figure 7

    (Color online) Similar as Figure 4, but for the RL and resampled RQ sub-samples matched in $z$-$M_{\rm~BH}$-$L_{\rm~bol}$ (see sect. 3.1and Figure 6).

  • Figure 8

    (Color online) Same as Figure 5, but for the RL and resampled RQ sub-samples matched in $z$, $g-r$ color, and $g$ magnitude (see sect. 3.2).

  • Figure 9

    (Color online) The color-color and magnitude-color diagrams for the RL (blue contour and dots for individual) and resampled RQ (red contour; missing individual for clarity) sub-samples matched in $z$, $g-r$ color, and $g$ magnitude. The two-dimensional K-S test suggests a similarity between these two sub-samples (see sect. 3.2).

  • Figure 10

    (Color online) Similar as Figure 4, but for the RL and resampled RQ sub-samples matched in $z$, $g-r$ color, and $g$ magnitude (see sect. 3.2and Figure 8).

  • Figure 11

    (Color online) Same as Figure 5, but for the RL and resampled RQ sub-samples matched in $z$, $M_{\rm~BH}$, $L_{\rm~bol}$, $g-r$ color, and $g$ magnitude (see sect. 3.2).

  • Figure 12

    (Color online) Similar as Figure 4, but for the RL and resampled RQ sub-samples matched in $z$, $M_{\rm~BH}$, $L_{\rm~bol}$, $g-r$ color, and $g$ magnitude (see sect. 3.2and Figure 11).

  • Figure 13

    (Color online) Same as Figure 4, but for the RL and RQ sub-samples excluding sources with BH mass derived using civ emission line (primarily at $z~\geq~1.9$) (see sect. 3.3).

  • Figure 14

    (Color online) Top panel: The $g$- (green) and $r$-band (red) SFs for the whole RL (solid line) and RQ (dotted line) samples. Bottom panel: The color variations for the whole RL (blue solid line) and RQ (red dotted line) samples directly inferred from the ratio of $r$- to $g$-band SFs as shown in the upper panel (see sect. 3.4).

  • Figure 15

    (Color online) The simulated $\Delta~C_{rg}$-$\tau$ relations (left column), SFs (middle-left column), mean SEDs (middle-right column), and the relevant properties as a function of radius (right column), compared between the reference inhomogeneous accretion disk model of Cai et al. [-1]($r_{\rm~br}=~6r_{\rm~g}$, $A_{\rm~T}=~0$, $A_\sigma~=0$, and $A_\tau~=~0$) for RQ quasars (thin solid lines) and our four adjusted models for RL quasars (thick dashed lines). (A) The accretion disk truncated at a break radius, $r_{\rm~br}=~20r_{\rm~g}$; (B) cooler disk temperature at inner disk ($A_{\rm~T}=~0.5$ with $r_*~=~20r_{\rm~g}$); (C) smaller variation amplitude, $\sigma_{\rm~l}$, at inner disk ($A_\sigma~=~1.5$ with $r_*~=~20r_{\rm~g}$); (D) slower temperature fluctuation at inner disk ($A_\tau~=~1.5$ with $r_*~=~50r_{\rm~g}$). For comparison, also shown are the observed $\langle~\Delta~C_{rg}\rangle$-$\tau$ relations from Figure 4(blue open circles and red crosses for the whole RL and RQ samples, respectively), and then the simulated relations are also vertically shifted downward with negative numbers nominated within the corresponding parentheses (see sect. 4.1).

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