Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

Graham, M. J.; Djorgovski, S. G.; Drake, A. J.; Stern, Daniel; Mahabal, A.; Glikman, Eilat; Larson, S. M.; Christensen, E.

doi:10.1093/mnras/stx1456

Cited by 115 publications

(138 citation statements)

References 68 publications

Supporting

Mentioning

133

Contrasting

Order By: Relevance

“…While the observed properties of these changing-look AGN are different from candidate TDFs (Ruan et al 2016;MacLeod et al 2016), their existence demonstrates that the luminosity of AGN can increase beyond what is expected from the power spectrum that accurately describes the light curves of mundane AGN (MacLeod et al 2012;Graham et al 2017).…”

mentioning

confidence: 78%

On the Mass and Luminosity Functions of Tidal Disruption Flares: Rate Suppression due to Black Hole Event Horizons

Velzen

2018

ApJ

112

View full text Add to dashboard Cite

The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus supporting the hypothesis that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power law is required to explain the observed rest-frame g-band luminosity, dN/dL g ∝ L −2.5 g . The mean event rate of the flares in our sample is ≈ 1 × 10 −4 galaxy −1 yr −1 , consistent with the theoretically expected tidal disruption rate.

show abstract

mentioning

confidence: 78%

On the Mass and Luminosity Functions of Tidal Disruption Flares: Rate Suppression due to Black Hole Event Horizons

Velzen

2018

ApJ

112

View full text Add to dashboard Cite

show abstract

“…37532corr_REV [1999][2000][2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016][2017][2018], as well as with Swift X-ray and UV archival monitoring data of NGC 3516 from 2006-2018. We find that the change in the U and B band is ∼ 0.25 mag and 0.11 mag, respectively. This could be considered as ordinary broad-line AGN variability (e.g., Vanden Berk et al 2004;Sesar et al 2007) and one could expect an increase of around ∼1 mag or even more (e.g., Graham et al 2017Graham et al , 2020MacLeod et al 2019;Rumbaugh et al 2018) in the case of a peculiar flaring (or an extreme brightening). However, a high increase of ∼1 mag is more likely to happen in bright quasars, and this more strict limit is used as a flaring criterion in large surveys, such as for example the Sloan Digital Sky Survey in which the magnitude uncertainties can be about 0.2 mag or more.…”

Section: Discussionmentioning

confidence: 99%

A flare in the optical spotted in the changing-look Seyfert NGC 3516

Ilić

Tsygankov

Belinski

et al. 2020

A&A

View full text Add to dashboard Cite

Context. We present observations from the short-term intensive optical campaign (from September 2019 to January 2020) of the changing-look Seyfert NGC 3516. This active galactic nucleus is known to have strong optical variability and has changed its type in the past. It has been in the low-activity state in the optical since 2013, with some rebrightening from the end of 2015 to the beginning of 2016, after which it remained dormant. Aims. We aim to study the photometric and spectral variability of NGC 3516 from the new observations in U-and B-bands and examine the profiles of the optical broad emission lines in order to demonstrate that this object may be entering a new state of activity. Methods. NGC 3516 has been monitored intensively for the past 4 months with an automated telescope in U and B filters, enabling accurate photometry of 0.01 precision. Spectral observations were triggered when an increase in brightness was spotted. We support our analysis of past-episodes of violent variability with the UV and X-ray long-term light curves constructed from the archival Swift/UVOT and Swift/XRT data.Results. An increase of the photometric magnitude is seen in both U and B filters to a maximum amplitude of 0.25 mag and 0.11 mag, respectively. During the flare, we observe stronger forbidden high-ionization iron lines ([Fe vii] and [Fe x]) than reported before, as well as the complex broad Hα and Hβ lines. This is especially seen in Hα, which appears to be double-peaked. It seems that a very broad component of ∼10,000 km s −1 in width in the Balmer lines is appearing. The trends in the optical, UV, and X-ray light curves are similar, with the amplitudes of variability being significantly larger in the case of UV and X-ray bands. Conclusions. The increase of the continuum emission, the variability of the coronal lines, and the very broad component in the Balmer lines may indicate that the AGN of NGC 3516 is finally leaving the low-activity state in which it has been for the last ∼3 years.

show abstract

“…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: 99%

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

Stern

McKernan

Graham

et al. 2018

ApJ

Self Cite

153

182

View full text Add to dashboard Cite

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.

show abstract

Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

Cited by 115 publications

References 68 publications

On the Mass and Luminosity Functions of Tidal Disruption Flares: Rate Suppression due to Black Hole Event Horizons

On the Mass and Luminosity Functions of Tidal Disruption Flares: Rate Suppression due to Black Hole Event Horizons

A flare in the optical spotted in the changing-look Seyfert NGC 3516

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

Contact Info

Product

Resources

About