Gleeok’s Fire-breathing: Triple Flares of AT 2021aeuk within Five Years from the Active Galaxy SDSS J161259.83+421940.3

Abstract We present a noteworthy transient AT 2021aeuk exhibiting three distinct optical flares between 2018 and 2023. It is hosted in a radio-loud narrow-line Seyfert 1 galaxy, with an optical image showing a minor tidal morphology and a red mid-infrared color ( W 1 − W 2 = 1.1). Flares II and III exhibit rapid rises, and long-term decays (≳1000 days) with recurring after-peak bumps. The g − r color after subtracting the reference magnitude exhibited a rapid drop and recovery during Flare II, followed by a minor after-peak evolution in blue colors. We applied a canonical tidal disruption event (TDE) fitting on the light curves, which gives a decay index p of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.99</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> for Flare II and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.61</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.65</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.34</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> for Flare III. The blackbody fitting shows lower temperatures (∼10 3.8 K) with minor after-peak evolution. The blackbody radius (≳10 16 cm) and luminosity (∼10 45 erg s −1 ) are larger than the typical TDE sample’s. The time lag (in rest frame) between the ZTF g and r bands ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> <mml:mo>,</mml:mo> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> days) significantly exceeds the prediction from the standard accretion disk. Pre-burst spectra reveal prominent Bowen fluorescence lines, indicating a vigorous or potentially long-lasting process that enriches the local metallicity. Additionally, we derived black hole masses of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>•</mml:mo> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mn>7.09</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.31</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.33em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>•</mml:mo> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mn>7.52</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.33em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:math> using H β and H α emission lines. The variation and recurring features of AT 2021aeuk are not likely induced by the radio-beaming effect or Type II superluminous supernova; however, we cannot rule out the possibility of TDE or enhanced active galactic nuclei accretion process. The unusually high occurrence of three flares within 5 yr may also induced by the complex local environment.