Optical Continuum Reverberation in the Dwarf Seyfert Nucleus of NGC 4395 release_xugumzsgfbb6vjwgivsnqgtrum

Abstract

<jats:title>Abstract</jats:title> In order to constrain the size of the optical continuum emission region in the dwarf Seyfert 1 galaxy NGC 4395 through reverberation mapping, we carried out high-cadence photometric monitoring in the <jats:italic>griz</jats:italic> filter bands on two consecutive nights in 2022 April using the four-channel MuSCAT3 camera on the Faulkes Telescope North at Haleakalā Observatory. Correlated variability across the <jats:italic>griz</jats:italic> bands is clearly detected, and the <jats:italic>r</jats:italic>-, <jats:italic>i</jats:italic>-, and <jats:italic>z</jats:italic>-band light curves show lags of <jats:inline-formula> <jats:tex-math> <?CDATA ${7.72}_{-1.09}^{+1.01}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>7.72</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.01</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${14.16}_{-1.25}^{+1.22}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>14.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.22</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> <?CDATA ${20.78}_{-2.09}^{+1.99}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>20.78</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.99</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7e54ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> minutes with respect to the <jats:italic>g</jats:italic> band when measured using the full-duration light curves. When lags are measured for each night separately, the Night 2 data exhibit lower cross-correlation amplitudes and shorter lags than the Night 1 light curves. Using the full-duration lags, we find that the lag–wavelength relationship is consistent with the <jats:italic>τ</jats:italic> ∝ <jats:italic>λ</jats:italic> <jats:sup>4/3</jats:sup> dependence found for more luminous active galactic nuclei. Combining our results with continuum lags measured for other objects, the lag between <jats:italic>g</jats:italic> and <jats:italic>z</jats:italic> band scales with optical continuum luminosity as <jats:italic>τ</jats:italic> <jats:sub>gz</jats:sub> ∝ <jats:italic>L</jats:italic> <jats:sup>0.56±0.05</jats:sup>, similar to the scaling of broad-line region size with luminosity, reinforcing recent evidence that diffuse continuum emission from the broad-line region may contribute substantially to optical continuum variability and reverberation lags.
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