巨大ブラックホールの目覚め(The Awakening of a Massive Black Hole)

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2024-06-18 カリフォルニア工科大学(Caltech)

複数の望遠鏡による観測で、銀河SDSS1335+0728が2019年12月から劇的に明るさを増していることが判明しました。この現象はZwicky Transient Facility (ZTF) によって最初に発見されました。通常、銀河の一時的な明るさの増加は超新星爆発や潮汐破壊現象によるものですが、数年間明るくなり続けるのは異例です。最も有力な説明は、銀河中心の超大質量ブラックホールが活動を開始したことで、活動銀河核と呼ばれる状態に移行していることです。新たな観測では、この銀河が紫外線、可視光、赤外線、X線を放射していることが確認されています。この研究は、銀河の中心にある超大質量ブラックホールの活動開始過程を理解するための重要な一歩となります。

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SDSS1335+0728:約106M⊙ブラックホールの目覚め SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole

P. Sánchez-Sáez, L. Hernández-García, S. Bernal, A. Bayo, G. Calistro Rivera, F. E. Bauer, C. Ricci, A. Merloni, M. J. Graham, R. Cartier, P. Arévalo, R. J. Assef, A. Concas, D. Homan, M. Krumpe, P. Lira, A. Malyali, M.L. Martínez-Aldama, A. M. Muñoz Arancibia, A. Rau, G. Bruni, F. Förster, M. Pavez-Herrera, D. Tubín-Arenas, M. Brightman
Astronomy & Astrophysics  Published:May 27, 2024

巨大ブラックホールの目覚め(The Awakening of a Massive Black Hole)

ABSTRACT

Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGN observed in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour.

1701物理及び化学
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