Discovery of 21 New Changing-look AGNs in the Northern Sky

Yang, Qian; Wu, Xue-Bing; Fan, Xiaohui; Jiang, Linhua; McGreer, Ian D.; Shangguan, J.; Yao, Shujie; Wang, Bingquan; Joshi, Ravi; Green, Richard; Wang, Feige; Feng, Xiaotong; Fu, Yuming; Yang, Jinyi; Liu, Yuanqi

doi:10.3847/1538-4357/aaca3a

Cited by 215 publications

(260 citation statements)

References 96 publications

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“…In addition to observing such rare phenomena as periodic quasars (e.g., Graham et al 2015aGraham et al , 2015bLiu et al 2015), flaring quasars (e.g., Lawrence et al 2016;Graham et al 2017;Kankare et al 2017), extreme broad absorption line variability (e.g., Rafiee et al 2016;Stern et al 2017), and tidal disruption events (e.g., Arcavi et al 2014;Blagorodnova et al 2017), this work has also identified a new class of "changing-look quasars" in which the strong UV continuum and broad hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of years (e.g., LaMassa et al 2015;Macleod et al 2016;Ruan et al 2016aRuan et al , 2016bRunnoe et al 2016;Gezari et al 2017;Yang et al 2018). The physical processes responsible for these changing-look quasars are still debated, but physical changes in the accretion disk structure appear to be the more likely cause rather than changes in obscuration.…”

Section: Introductionmentioning

confidence: 80%

“…We use this source as a touchstone to discuss physical models of abrupt quasar fading, a subject that has received considerable attention recently thanks to the growing ranks of wide-area ground-based optical surveys (e.g., LaMassa et al 2015;Macleod et al 2016;Ruan et al 2016aRuan et al , 2016bRunnoe et al 2016;Gezari et al 2017;Sheng et al 2017;Yang et al 2018;Assef et al 2018;Ross et al 2018). In particular, we emphasize the unique value of multiepoch mid-IR photometry to test and exclude models that attempt to ascribe large changes in quasar luminosities to obscuration by an intervening cloud.…”

Section: Discussionmentioning

confidence: 99%

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A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading

Stern

McKernan

Graham

et al. 2018

ApJ

159

185

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We report a new changing-look quasar, WISEJ105203.55+151929.5 at z=0.303, found by identifying highly mid-IR-variable quasars in the Wide-field Infrared Survey Explorer(WISE)/Near-Earth Object WISE Reactivation (NEOWISE) data stream. Compared to multiepoch mid-IR photometry of a large sample of SDSS-confirmed quasars, WISEJ1052+1519is an extreme photometric outlier, fading by more than a factor of two at 3.4 and 4.6 μm since 2009. Swift target-of-opportunity observations in 2017 show even stronger fading in the soft X-rays compared to the ROSAT detection of this source in 1995, with at least a factor of 15 decrease. We obtained secondepoch spectroscopy with the Palomar telescope in 2017 that, when compared with the 2006 archival SDSS spectrum, reveals that the broad Hβ emission has vanished and that the quasar has become significantly redder. The two most likely interpretations for this dramatic change are source fading or obscuration, where the latter is strongly disfavored by the mid-IR data. We discuss various physical scenarios that could cause such changes in the quasar luminosity over this timescale, and favor changes in the innermost regions of the accretion disk that occur on the thermal and heating/cooling front timescales. We discuss possible physical triggers that could cause these changes, and predict the multiwavelength signatures that could distinguish these physical scenarios.

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Section: Introductionmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 99%

A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading

Stern

McKernan

Graham

et al. 2018

ApJ

159

185

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“…The nature of changing-look AGNs (CLAGNs) is not totally clear so far. More and more evidence strongly indicates that dust obscuration should be not the main reasons, but variations of accretion flows should play the key roles as well discussed in LaMassa et al (2015) and more recently discussed in Yang et al (2018). Once variations of accretion flows were accepted to CLAGNs, there should be two scenarios.…”

Section: Introductionmentioning

confidence: 93%

SDSS J0159 as an outlier in the MBH–σ space: further clues to support a central tidal disruption event?

Zhang

Bao

Yuan

2019

Monthly Notices of the Royal Astronomical Society: Letters

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In this Letter, properties of black hole (BH) mass are well checked for the interesting object SDSS J0159, a changing-look AGN and also a host galaxy of a tidal disruption event (TDE). Through spectral absorption features, the stellar velocity dispersion of SDSS J0159 can be well measured as σ ∼ 81 km/s, leading to SDSS J0159 being an apparent outlier in the M BH − σ space, because of the BH mass estimated through the M BH − σ relation about two magnitudes lower than the reported virial BH mass of about 10 8 M ⊙ . After considerations of contributions of stellar debris from the central TDE to broad line emission clouds, the over-estimated virial BH mass could be well explained in SDSS J0159. Therefore, over-estimated virial BH masses through broad line properties in the M BH − σ space could be treated as interesting clues to support central TDEs.

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“…Disappearing or appearing broad Balmer emission lines have been known for many years in a number of local lowluminosity AGNs (e.g., Tohline & Osterbrock 1976;Cohen et al 1986;Denney et al 2014;Shappee et al 2014). With large-scale time-domain survey recent studies have identified a growing number of such cases in quasars with associated large, order-of-magnitude variations in the optical continuum on month to year timescales (LaMassa et al 2015;MacLeod et al 2016;Ruan et al 2016;Runco et al 2016;Runnoe et al 2016;Stern et al 2018;Wang et al 2018;Yang et al 2018;MacLeod et al 2019;Trakhtenbrot et al 2019;Sheng et al 2020). Their optical classification was caught to change between type 1.8-2 (narrow-line) to type 1 (broad-line) AGNs (or vice versa), and even from low-ionization nuclear emission-line region galaxies to broad-line quasars (Gezari et al 2017;Frederick et al 2019).…”

Section: Introductionmentioning

confidence: 99%

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

Dou

Yang

et al. 2020

ApJL

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We analyze the X-ray, optical, and mid-infrared data of a "changing-look" Seyfert galaxy SDSS J155258+273728 at z;0.086. Over a period of one decade (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), its broad Hα line intensity increased by a factor of ∼4. Meanwhile, the X-ray emission in 2014 as observed by Chandra was about five times brighter than that in 2010 by Suzaku, and the corresponding emissions in the V-band, mid-infrared W1 band brighten by ∼0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e.,~-N 10 cm H 21 2 , but the X-ray spectrum becomes harder in the 2014 Chandra bright state (i.e., photon index G = -+ 1.52 0.06 0.06 ) than that of the 2010 Suzaku low state (G = -+ 2.03 0.21 0.22 ). With an Eddington ratio being lower than a few percent, the inner region of the accretion disk in SDSS J155258+273728is likely a hot accretion flow. We then compile from literature the X-ray data of "changing-look" active galactic nuclei (AGNs), and find that they generally follow the well-established "V"-shaped correlation in AGNs, that is, above a critical turnover luminosity the X-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in the way of "harder when brighter." This presents direct evidence that CL-AGNs have distinctive changes in not only the optical spectral type, but also the X-ray spectral shape. The similarity in the X-ray spectral evolution between CL-AGNs and black hole X-ray binaries indicates that the observed CL-AGNs phenomena may relate to the state transition in accretion physics.

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Discovery of 21 New Changing-look AGNs in the Northern Sky

Cited by 215 publications

References 96 publications

A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading

A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading

SDSS J0159 as an outlier in the MBH–σ space: further clues to support a central tidal disruption event?

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

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