An Extreme X-Ray Variability Event of a Weak-line Quasar

Ni, Quan Xing; Brandt, W. N.; Yi, Wu; Timlin, John; Liu, Hezhen; Plotkin, Richard M.; Shemmer, Ohad; Vito, F.; Wu, Jianfeng

doi:10.3847/2041-8213/ab6d78

Cited by 31 publications

(62 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…If we limit our sample to the 50 most luminous quasars in sample A, which have 31.3 log(L 2500 Å) 32.0 and a median log(L 2500 Å) value of 31.4, the X-ray weak fraction becomes 15 ± 6%. Such a luminosity dependence for the fraction of X-ray weak quasars is in general agreement with our interpretations of X-ray weak quasars as WLQs (e.g., Luo et al 2015;Ni et al 2018; Section 5.2.1) or due to extreme X-ray variability (e.g., Liu et al 2019;Ni et al 2020;Section 5.2.3), where quasars accreting at high Eddington ratios may have X-ray absorption from a geometrically thick inner accretion disk or its associated outflow; the fraction of such quasars is likely higher among more luminous samples. The relevance of the enhanced fraction of X-ray weak quasars to WLQs is also noted in both Nardini et al (2019) and Zappacosta et al (2020).…”

Section: Fractions Of X-ray Weak Quasars Among Two Subsamplessupporting

confidence: 92%

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

Brandt²,

Timlin

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

We investigate systematically the X-ray emission from type 1 quasars using a sample of 1825 Sloan Digital Sky Survey (SDSS) non-broad absorption line (non-BAL) quasars with Chandra archival observations. A significant correlation is found between the X-ray-to-optical power-law slope parameter (α OX ) and the 2500 Å monochromatic luminosity (L 2500 Å), and the X-ray weakness of a quasar is assessed via the deviation of its α OX value from that expected from this relation. We demonstrate the existence of a population of non-BAL X-ray weak quasars, and the fractions of quasars that are X-ray weak by factors of ≥ 6 and ≥ 10 are 5.8 ± 0.7% and 2.7 ± 0.5%, respectively. We classify the X-ray weak quasars (X-ray weak by factors of ≥ 6) into three categories based on their optical spectral features: weak emission-line quasars (WLQs; C iv REW < 16 Å), red quasars (∆(g − i) > 0.2), and unclassified X-ray weak quasars. The X-ray weak fraction of 35 +12 −9 % within the WLQ population is significantly higher than that within non-WLQs, confirming previous findings that WLQs represent one population of X-ray weak quasars. The X-ray weak fraction of 13 +5 −3 % within the red quasar population is also considerably higher than that within the normal quasar population. The unclassified X-ray weak quasars do not have unusual optical spectral features, and their X-ray weakness may be mainly related to quasar X-ray variability.

show abstract

Section: Fractions Of X-ray Weak Quasars Among Two Subsamplessupporting

confidence: 92%

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

Brandt²,

Timlin

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…However, such a scenario is difficult to reconcile with the observations of Xray weak state in several highly accreting narrow line Seyfert 1s (NSy1s) and quasars, where the UV flux remains almost constant despite the huge X-ray drop (Gallo et al 2011;Miniutti et al 2012;Grupe et al 2019). Since sources with high Eddington ratios such as NSy1s are expected to have a geometrically thick accretion disk in innermost region, the disk self-shielding can explain the extreme X-ray variability while UV/optical continuum at larger radii is not affected, similar to the explanation proposed for the X-ray behavior of weak-line quasars (Luo et al 2015;Ni et al 2018). Another scenario that has been invoked to account for the X-ray weakness is that the direct nuclear emis-sion is suppressed by the light-bending effect near the SMBH (Miniutti et al 2003;Miniutti & Fabian 2004).…”

Section: Introductionmentioning

confidence: 54%

“…Alternatively, several works have invoked a partial covering model to account for extreme X-ray variability behaviors of AGNs, especially those high accreting systems (Luo et al 2015;Liu et al 2019;Ni et al 2020). In this model, the central X-ray source could be partially obscured by a thick inner disk or outflow if it intercepts the line of sight.…”

Section: Possible Origins For the X-ray Brighteningmentioning

confidence: 99%

Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy

Zhang,

Shu,

Sheng

et al. 2022

Preprint

View full text Add to dashboard Cite

CSS J102913+404220 is an atypical narrow line Seyfert 1 galaxy with an energetic optical outburst occurred in coincidence with its nucleus. We present a detailed analysis of its multi-wavelength photometric and spectroscopic observations covering a period of decade since outburst. We detect mid-infrared (MIR) flares delayed by about two months relative to the optical outburst, with an extremely high peak luminosity of L 4.6µm > 10 44 erg s −1 . The MIR peak luminosity is at least an order of magnitude higher than any known supernovae explosions, suggesting the optical outburst might be due to a stellar tidal disruption event (TDE). We find late-time X-ray brightening by a factor of > ∼ 30 with respect to what is observed about 100 days after the optical outburst peak, followed by a flux fading by a factor of ∼4 within two weeks, making it one of Active Galactic Nuclei (AGNs) with extreme variability. Despite the dramatic X-ray variability, there are no coincident strong flux variations in optical, UV and MIR bands. This unusual variability behavior has been seen in other highly accreting AGNs and could be attributed to absorption variability. In this scenario, the decrease in the covering factor of absorber with accretion rate could cause the X-ray brightening, possibly induced by the TDE. Most strikingly, while the UV/optical continuum remains little changes with time, an evident enhancement in the flux of Hα broad emission line is observed, about a decade after the nuclear optical outburst, which is an anomalous behavior never seen in any other AGNs. Such an Hα anomaly could be explained by the replenishment of gas clouds and excitation within Broad Line Region (BLR) that originates, perhaps from the interaction of outflowing stellar debris with BLR. The results highlight the importance of late-time evolution of TDE that could affect the accreting properties of AGN, as suggested by recent simulations.

show abstract

“…However, this hypothesis can be tested only by analysing additional, deeper X-ray observations (preferably including data at > 10 keV) to reveal typical relativistic reflection spectral features. Similary, lightbending effects have also been invoked by Ni et al (2020) as a viable explanation to justify the extreme X-ray variability of the z = 1.935, WLQ SDSS J153913.47+395423.4. This source was found to be in an X-ray weak state, before its flux raised by a factor of ∼ 20, approximately six years after its first observation (corresponding to ∼ 2 years in the QSO rest frame).…”

Section: Properties Of the X-ray Continuum And X-ray Weaknessmentioning

confidence: 68%

X-ray spectroscopic survey of highly-accreting AGN

Laurenti,

Piconcelli,

Zappacosta

et al. 2021

Preprint

View full text Add to dashboard Cite

Improving our understanding of the nuclear properties of high-Eddington ratio (λ Edd ) active galactic nuclei (AGN) is necessary since at this regime the radiation pressure is expected to affect the structure and efficiency of the accretion disc-corona system. This may cause departures from the typical nuclear properties of low-λ Edd AGN, which have been largely studied so far. We present here the X-ray spectral analysis of 14 radio-quiet, λ Edd 1 AGN at 0.4 ≤ z ≤ 0.75, observed with XMM-Newton. Optical/UV data from simultaneous Optical Monitor observations have been also considered. These quasars have been selected to have relatively high values of black hole mass (M BH ∼ 10 8−8.5 M ) and bolometric luminosity (L bol ∼ 10 46 erg s −1 ), in order to complement previous studies of high-λ Edd AGN at lower M BH and L bol . We studied the relation between λ Edd and other key X-ray spectral parameters, such as the photon index (Γ) of the power-law continuum, the X-ray bolometric correction k bol,X and the optical/UV-to-X-ray spectral index α ox . Our analysis reveals that, despite the homogeneous optical and SMBH accretion properties, the X-ray properties of these high-λ Edd AGN are quite heterogeneous. We indeed measured values of Γ comprised between 1.3 and 2.5, at odds with the expectations based on previously reported Γ − λ Edd relations, by which Γ ≥ 2 would be an ubiquitous hallmark of AGN with λ Edd ∼ 1. Interestingly, we found that ∼ 30% of the sources are X-ray weak, with an X-ray emission about a factor of ∼ 10 − 80 fainter than that of typical AGN at similar UV luminosities. The X-ray weakness seems to be intrinsic and not due to the presence of absorption along the line of sight to the nucleus. This result may indicate that high-λ Edd AGN commonly undergo periods of intrinsic X-ray weakness. Furthermore, results from a follow-up monitoring with Swift of one of these X-ray weak sources suggest that these periods can last for several years.

show abstract

An Extreme X-Ray Variability Event of a Weak-line Quasar

Cited by 31 publications

References 53 publications

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

On the Fraction of X-ray Weak Quasars from the Sloan Digital Sky Survey

Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy

X-ray spectroscopic survey of highly-accreting AGN

Contact Info

Product

Resources

About