AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system

A. Deconto-Machado; A. Gangopadhyay; A. Garc\'ia-P\'erez; A. M. Mu\~noz-Arancibia; B. Ailawadhi; C. Ricci; F.E. Bauer; F. F\"orster; F. Panessa; G. Bruni

REVIEW 3 major objections 6 minor 132 references

AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system

T0 review · 3 major / 6 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Repeating brightenings in AT 2021hdr point to a gas cloud torn apart by binary supermassive black holes

desk verdict A genuinely odd, well-observed nuclear transient, with an interesting binary-SMBH gas-cloud interpretation that the data do not yet firmly support. read the letter →

arxiv 2411.08949 v1 pith:FTO5POLB submitted 2024-11-13 astro-ph.GA astro-ph.HE

L. Hernández-García , A. M. Muñoz-Arancibia , P. Lira , G. Bruni , J. Cuadra , P. Arévalo , P. Sánchez-Sáez , S. Bernal

show 20 more authors

F.E. Bauer M. Catelan F. Panessa M. Pávez-Herrera C. Ricci I. Reyes-Jainaga B. Ailawadhi V. Chavushyan R. Dastidar A. Deconto-Machado F. Förster A. Gangopadhyay A. García-Pérez I. Márquez J. Masegosa K. Misra V.M Patiño-Alvarez M. Puig-Subirà J. Rodi M. Singh

This is my paper · ORCID

classification astro-ph.GAastro-ph.HE

keywords AT2021hdrtidaldisruptioneventsbinarysupermassiveblackholesgascloudAGNvariabilitygravitational-wave-drivenbinariesgalaxymergersmulti-wavelengthmonitoring

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper argues that AT 2021hdr, a Seyfert nucleus whose light curve began oscillating every roughly 60–90 days in late 2021, is a candidate for the tidal disruption of a gas cloud by an unresolved binary supermassive black hole. The same oscillating shape appears in optical, UV, and X-ray data, and the paper shows that standard explanations—a stellar tidal disruption event, a single changing-look active nucleus, or disk and jet instabilities—do not fit the observations. If correct, this is the first candidate for a gas-cloud tidal disruption by a binary supermassive black hole, with the binary in the gravitational-wave-driven regime: separation about 0.83 milliparsec and merger in about $7\times10^4$ years. The work also reports, for the first time, that the host galaxy is in an early-stage merger with a companion 9 kiloparsec away, though the oscillations are not related to that companion.

What carries the argument

The load-bearing mechanism is the periodic intersection of a gas cloud with a bound pair of black holes: each black hole accretes from the cloud as it passes, producing two accretion-rate peaks per binary orbit. The paper converts the observed peak spacing into a binary period by assuming the spacing is half the orbit, then uses Kepler's third law with a total mass of about $4\times10^7\,M_\odot$ to set the separation at about 0.83 mpc, and the gravitational-wave decay formula for a circular equal-mass binary to set the merger time at about $7\times10^4$ years. The comparison template is a numerical model in which the disrupted cloud is several times larger than the binary; depending on the cloud's trajectory and impact parameter, the model produces one or two peaks per orbit, and the authors identify the perpendicular-approach geometry with an impact parameter comparable to the binary radius as the configuration closest to the observed light curve.

What would settle it

Observe AT 2021hdr at high cadence in X-rays and UV for several more years and compare every brightening time with a strict 130-day period. If the peaks drift in phase, skip cycles, or the 97.7-day periodogram peak fails to reappear as more data accumulate, the periodicity assumption—and with it the binary separation and merger time—is falsified, even though the gas-cloud disruption idea could still be the right physical picture.

Watch

Extended reading notes

Core claim

The central claim is that AT 2021hdr's oscillating brightenings are the accretion signature of a gas cloud being tidally disrupted by a close binary supermassive black hole. In this picture each black hole crosses the cloud once per binary orbit, so the recurrence time of the peaks is half the orbital period; taking the observed 60–90 day recurrence as half a period of about 130 days, and using the virial black-hole mass of about $4\times10^7\,M_\odot$, the binary separation is about 0.83 mpc. The gravitational-wave decay formula for a circular equal-mass binary then yields a merger time of about $7\times10^4$ years. The authors argue that standard stellar TDEs, a single binary without a cloud, changing-look AGN, and disk or jet instabilities cannot reproduce the observations, and that the broad shape of the optical–UV–X-ray light curves, including the color behavior and the absence of line-profile changes, matches the gas-cloud disruption simulations. The accreted mass so far would be about $0.1\,M_\odot$, implying an initial cloud mass between 0.3 and $3\,M_\odot$.

Load-bearing premise

Everything about the binary—the 130-day period, the 0.83 mpc separation, and the 70,000-year merger time—rests on the assumption that the 60–90 day brightenings are strictly periodic and equal to half the binary period; the paper's own periodogram analysis finds only a marginal 97.7-day peak and states that quasi-periodicity cannot be ruled out.

Editorial extensions

If this is right

If the scenario is right, AT 2021hdr becomes the first reported candidate for a gas-cloud tidal disruption by a binary supermassive black hole.
The inferred binary is in the gravitational-wave-driven regime and will merge within roughly $7\times10^4$ years, making it a useful laboratory for studying hierarchical supermassive-black-hole growth.
The model predicts that the oscillating pattern should persist with roughly stable phase at 60–90 day intervals until the cloud is consumed, giving a concrete schedule for continued monitoring.
Because the binary separation is far smaller than the broad-line region, the model naturally accounts for the observed single set of optical lines with no velocity shifts.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

A testable extension the paper leaves implicit: if the 130-day period is real, the peak timings should be phase-coherent, so a phase-coherence search on the combined ZTF, Swift, and future light curves is a clean discriminator between periodic and quasi-periodic interpretations.
The same two-peaks-per-orbit accretion pattern should appear whenever a dense cloud falls onto a tight binary, so wide-field surveys with daily cadence should find a population of similar low-amplitude, well-defined-onset oscillating AGN.
If the 2024 rebrightening comes from cloud debris interacting with the pre-existing accretion disk, as the authors suggest, later cycles should show altered amplitudes or damping; dedicated numerical simulations including a pre-existing disk would make this prediction quantitative.
Were quasi-periodicity to win over strict periodicity, the derived binary parameters would lose their basis, but the more general gas-cloud-capture scenario might survive, so the longer monitoring baseline decides between these two levels of the claim.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

This is a careful observational paper about a source worth knowing. AT 2021hdr shows repeated optical/UV/X-ray brightenings every ~60-90 days, starting in late 2021, in a Seyfert 1 nucleus. The multiwavelength coverage is real and well-reduced, and the paper reports two genuinely new things: the first spectrum of the companion galaxy, confirming a 9 kpc merger, and a VLBA nondetection that rules out a compact jet. The proposal that this is a gas cloud tidally disrupted by an unresolved binary SMBH is a reasonable candidate, and to my knowledge the first application of the Goicovic et al. (2016) model to a real source. The paper also does something right: it is unusually honest about its own weaknesses. It explicitly says the periodogram peak 'could be significant,' that quasi-periodicity cannot be ruled out, that the CARMA fits do not constrain stochastic models well, that the structure function is consistent with AGN variability, and that the 2024 rebrightening is not reproduced by the simulation. That is the right way to present a candidate. The soft spot is the load-bearing step. The derived binary separation (0.83 mpc), merger time (7e4 yr), and cloud mass (0.3-3 Msun) all follow from assuming the 60-90 day recurrence is strictly periodic and equals half the binary orbital period, giving P ~ 130 days. The periodogram's best period is 97.7 days, not 130, the few observed peaks have uneven spacing, and the 2024 rebrightening does not fit. If the recurrences are quasi-periodic or stochastic, those quantitative claims lose their foundation. The paper acknowledges this, which is why the headline is a candidate rather than a detection, but the mismatch between the adopted 130-day period and the 97.7-day periodogram peak deserves sharper treatment. Also, the model is for a cloud falling onto a bare binary, while this source has a pre-existing accretion disk; the paper mentions this but does not quantify how it changes the expected light curve. None of this kills the paper. The observational phenomenon is solid, the interpretation is plausible enough to test, and the data are public. I would send this to a serious referee and would expect it to be published with the interpretation clearly labeled as a candidate, which the authors already do. For anyone working on nuclear transients or binary SMBHs, this is a useful reference and a good reading-group discussion about how much periodicity a handful of peaks can really establish. I would cite it as a candidate source, not as a confirmed detection. Send it to review.

Referee Report

3 major / 6 minor

Summary. AT 2021hdr is a Seyfert 1 nucleus whose ZTF light curve since late 2021 shows repeated brightening episodes with ~0.2 mag amplitudes on timescales of 60-90 days, with correlated variability in Swift/UVOT and XRT. The paper argues that the source is not a standard TDE, a changing-look AGN, a disk/jet instability, or a QPE-like event, and proposes instead that the behavior results from the tidal disruption of a gas cloud by an unresolved binary supermassive black hole. Assuming the observed recurrence is half the binary orbital period (~130 d) and adopting a virial black hole mass (~4e7 Msun), the authors derive a binary separation of ~0.83 mpc and a gravitational-wave merger time of ~7e4 yr, and infer an initial cloud mass of 0.3-3 Msun. The paper also spectroscopically confirms a companion LINER galaxy 9 kpc away, reporting the galaxy pair as a new merger.

Significance. The observational dataset is a valuable contribution: multiwavelength coverage, forced photometry, VLBA non-detection, and a new companion-galaxy redshift. The proposed scenario, if confirmed, would be the first gas-cloud TDE by a BSMBH and a rare case of a binary in the GW-driven regime, making it of substantial astrophysical interest. However, the quantitative conclusions (binary separation, merger time, cloud mass) are all conditional on a periodicity that the paper itself cannot firmly establish; the periodogram's strongest peak is at 97.7 d and is only 'could be significant', and quasi-periodicity is admitted. The significance of the paper is therefore that of a well-presented candidate with qualitative model support, not a confirmed detection.

major comments (3)

[5.2, Appendix D.1, Table 1] The load-bearing assumption that the observed ~60-90 d recurrence is half the binary orbital period is not established. Section 5.2 sets P_b≈130 d and derives a≈0.83 mpc and t_merge≈7e4 yr, but Appendix D.1's P4J periodogram of the same data yields a best period of 97.7 d with significance described only as 'could be significant', and the authors explicitly state that quasi-periodicity cannot be ruled out. Table 1 shows starting-date intervals of ~207, 95, 115, 202, and 61 d between successive brightenings, inconsistent with a strict half-orbit clock. Because all of the binary's quantitative parameters are obtained from P_b via Kepler's law and Peters' formula, the current data do not support the quoted precision of a≈0.83 mpc and t_merge≈7e4 yr. The paper should either provide a rigorous periodicity test (with false-alarm probability and comparison against stochastic models) or present the binary parameters as illustrative values with the dependence on the assumed harmonic explicitly propagated.
[5.2, Appendix D.3] The proposed match to the Goicovic et al. (2016) cloud-disruption model is qualitative: the paper relies on 'visual inspection' of their Fig. 4, and explicitly acknowledges that other cloud configurations could also work. Moreover, the 2024 rebrightening is not addressed in the comparison with the Goicovic et al. (2016) models; the paper only notes this problem for the stellar-TDE models of Vigneron et al. (2018). Since the same issue may apply to the cloud-disruption scenario, and since the observed peak spacing is variable rather than the constant half-orbit separation predicted by the model, the current qualitative match is incomplete. A quantitative comparison—e.g., synthesizing light curves from the simulations with the same cadence and comparing peak times, amplitudes, and colors—is necessary before the proposed scenario can be considered more than a plausible candidate.
[5.2] The cloud mass estimate is not robust. The authors attribute the full change in bolometric luminosity ΔL≈1.7e44 erg/s between the pre-oscillation (2010) and oscillation (2022-2024) states to accretion of the cloud, using ε≈0.06 and an assumed standard accretion regime. However, the pre- and post-oscillation luminosities are measured in different bands (BAT hard X-ray vs XRT 0.5-10 keV plus optical/UV) and at epochs separated by 12 years; intrinsic AGN variability of the order of the Eddington-ratio change can easily be present. The resulting cloud mass range 0.3-3 Msun should therefore be treated as an order-of-magnitude estimate at best, and the paper should state this limitation explicitly.

minor comments (6)

[3.2.1] There is a typo: 'AT 2120hdr' should read 'AT 2021hdr'.
[3.2.2] The phrase 'see Appendix 3.2.2' should cite Section 3.2.2, since the spectral information is presented in the main text, not in an appendix.
[D.1] The periodogram finds best periods of 97.7 and 355.7 d, but the paper does not reconcile the 97.7 d peak with the adopted P_b≈130 d in Section 5.2. The authors should explain why the observed recurrence time is preferred over the periodogram peak, or whether 97.7 d corresponds to a different harmonic.
[Table 1] Adding the intervals between successive starting dates would help the reader evaluate the periodicity claim; the current table lists only dates, magnitudes, and amplitudes.
[4] The statement that 'the same shape is observed in X-rays and UV' is based on a short overlapping Swift baseline; the paper should note that the X-ray/UV coverage begins only in late 2022, so the first two optical peaks are not covered by the Swift data.
[D.2] The DHO fit parameters in Table D.1 have extremely large uncertainties and several entries are formatted inconsistently; a cleaner presentation would help support the conclusion that stochastic models fail.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the binary separation and merger time are standard Kepler/Peters inferences from the observed recurrence and virial mass, and the Goicovic et al. (2016) model comparison is an external, falsifiable simulation rather than a self-defined fit.

full rationale

Walking the derivation chain: the observed 60-90 d recurrence and the assumed two accretion peaks per binary orbit set P_b ~ 130 d (Sect. 5.2); Kepler's law with M_BH ~ 4e7 M_sun then gives a ~ 0.83 mpc, and Peters (1964) gives t_merge ~ 7e4 yr. These are ordinary physical inferences from stated inputs, not fits of a model to its own output. The paper does not rename a fitted parameter as a prediction: the cloud mass (0.3-3 M_sun) follows from the observed Delta L and an accretion fraction taken from the published Goicovic et al. (2016) simulations, and the paper explicitly labels the values as estimates ('we estimate', 'would merge'). The central model comparison is to an external hydrodynamical simulation (Goicovic et al. 2016, MNRAS 455, 1989); one coauthor (Cuadra) overlaps, but the simulation is published, parameter-free with respect to AT 2021hdr, and falsifiable against the light curve, so it is independent evidence rather than a self-citation chain. The paper candidly states its own limitations in Appendix D.1: the periodogram peak at 97.7 d 'could be significant' and 'quasi-periodicity cannot be ruled out at this moment', and Appendix D.3 admits the 2024 rebrightening is not reproduced by the stellar-TDE binary models. These are correctness and robustness concerns about the periodicity assumption, not circular reductions: even if the assumed periodicity is wrong, the derivation of binary parameters from a given period and mass is not equivalent to the input by construction. No self-definitional step, no fitted-input-called-prediction step, and no load-bearing self-citation was found.

Assumptions & free parameters 4 free parameters · 5 assumptions · 2 invented entities

Everything the central scenario depends on is either the fitted or assumed period and mass, or the 2016 simulation that anchors the interpretation. The paper does not fit the simulation to the data; it compares by eye and converts a luminosity change into a cloud mass using an assumed efficiency and accretion fraction. The binary and the cloud are inferred entities with no independent evidence presented.

free parameters (4)

Binary orbital period = ~130 d (twice the 60-90 d peak recurrence; periodogram peak at 97.7 d)
Measured from the oscillatory light curve; all derived binary parameters (separation, merger time) scale with this period, whose significance the authors themselves call uncertain.
Total black hole mass = ~4e7 M_sun
Single-epoch virial estimator from H-alpha, with 0.5 dex systematic uncertainty quoted; sets the Eddington ratio and the absolute scaling of the binary separation.
Radiative efficiency = epsilon = 0.06
Assumed standard value used to convert delta L into accretion rate and cloud mass, giving a cloud mass of 0.3-3 M_sun.
Accreted cloud fraction = 3-30%
Range taken from Goicovic et al. (2016) simulations; widens the inferred initial cloud mass estimate.

assumptions (5)

standard math Kepler's third law: a = (G M P^2 / 4 pi^2)^(1/3) for the binary separation
Used in Sect. 5.2 to convert the assumed 130-day orbital period and 4e7 M_sun mass into 0.83 mpc separation.
standard math Peters (1964) gravitational-wave-driven orbital decay formula for circular equal-mass binaries
Used in Sect. 5.2 to derive the ~7e4 yr merger timescale.
domain assumption Goicovic et al. (2016) simulations describe gas cloud disruption by a BSMBH, producing two accretion peaks per orbit and 3-30% accretion
The entire interpretation rests on this model; the match is judged by visual inspection of their Fig. 4.
domain assumption The gas cloud scenario predicts reddening as unbound debris obscures the source
Used in Sect. 5.2 to argue the observed g-r color break before and after oscillations is qualitatively agreeing with the model.
domain assumption The source is at z = 0.083 with the adopted flat LambdaCDM cosmology (H0=70, OmegaM=0.3)
Used for all luminosities, Eddington ratios, and physical scales; the companion galaxy's redshift z=0.081 is used to claim the interaction.

invented entities (2)

Unresolved binary supermassive black hole (P ~130 d, a ~0.83 mpc)
purpose: To produce the double accretion-peak pattern from a cloud infall; to make the source a candidate SMBH-merger precursor
No direct imaging, no periodic line shifts, no pulsar-timing-style signature; the VLBA non-detection constrains jets but does not confirm the binary. The only evidence is the light-curve interpretation itself.
Infalling gas cloud of 0.3-3 M_sun
purpose: The fuel that each black hole accretes, producing two peaks per orbit
The paper notes such a cloud could not possibly be directly observed outside our own Galaxy; it is inferred solely from the luminosity change and the simulation match.

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Cite this review

Pith. "Pith review of AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system." pith.science (2026). https://pith.science/paper/FTO5POLB

@misc{pith2026241108949,
  author       = {Pith},
  title        = {Pith review of: AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/FTO5POLB}},
  note         = {Machine review of arXiv:2411.08949}
}

read the original abstract

With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT 2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT 2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every about 60-90 days with amplitudes of around 0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT 2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of about 0.83 mpc and would merge in about 70000 years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.

Figures

Figures reproduced from arXiv: 2411.08949 by the authors.

**Figure 1.** ZTF light curve of AT 2021hdr between 2018-2024. (Top panel): ZTF light curve (in difference flux from PSF forced photometry) of AT 2021hdr in the g (green squares) and r (red triangles). The black dashed line represents the date of the first ZTF alert, and the gray dashed lines correspond to dates when optical spectra were obtained. (Bottom panel): ZTF g-r color evolution in total magnitude (see text for details) … view at source ↗

**Figure 2.** Pan-STARRS stacked i-band image of the AT 2021hdr (black cross) host and environment. The cyan circle indicates the Swift/XRT source position error (90%). VLASS contours at 2σ, 3σ, and 4σ are overlaid in yellow. The locations of the secondary AGN and tidal tails are indicated. the ALeRCE Web Interface4 provided by the ALeRCE broker (ALeRCE, Förster et al. 2021), with ZTF ID ZTF21aaqqwsa. For this work, we retrieved … view at source ↗

**Figure 3.** The top panel shows Swift/XRT data in the 0.5-10 keV energy band, taken between November 17, 2022, and June 14, 2024. An approximately weekly monitoring was started on July 7, 2023, with a gap in early 2024 when the source was behind the Sun. The middle panel shows Swift/UVOT data taken simultaneously to the XRT data. After July 7, 2023, priority was given to observe with the UV filters, and therefore we present UV… view at source ↗

Figures from the paper (3 more)

**Figure 3.** Figure 3: Light curves of AT 2021hdr. From top to bottom: Swift/XRT in the 0.5-10 keV energy band, Swift/UVOT in the UVW2 (blue triangles) and UVM2 (pink circles), and ZTF in the g (green crosses) and r (red triangles) bands. Dates are between August 8, 2022, and March 31, 2024…

**Figure 4.** Figure 4: Hα region of AT 2021hdr. From top to bottom, spectra from the LT, SPM, HCT, NOT, and SPM are presented in chronological order. The spectra are normalized for visualization purposes (see text). 5. Source nature The oscillations are observed in the optical, UV, and X-ray…

**Figure 5.** Figure 5: Color vs magnitude diagram. The color is obtained from the apparent magnitudes and the magnitude is in the g band. The blue triangles and cyan circles represent dates before and after the oscillations started in AT 2021hdr (MJD = 59520). We note that this date does no…

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Works this paper leans on

132 extracted references · 43 canonical work pages

[1]

2013, , 764, 14

Amaro-Seoane , P., Brem , P., & Cuadra , J. 2013, , 764, 14

2013
[2]

A., Chavushyan , V., & Pati \ n o- \'A lvarez , V

Amaya-Almaz \'a n , R. A., Chavushyan , V., & Pati \ n o- \'A lvarez , V. M. 2022, , 929, 14

2022
[3]

2022, , 662, A49

Arcodia , R., Miniutti , G., Ponti , G., et al. 2022, , 662, A49

2022
[4]

C., Kulkarni , S

Bellm , E. C., Kulkarni , S. R., Graham , M. J., et al. 2019, , 131, 018002

2019
[5]

& Nandra , K

Brightman , M. & Nandra , K. 2011, , 413, 1206

2011
[6]

N., Hill , J

Burrows , D. N., Hill , J. E., Nousek , J. A., et al. 2005, , 120, 165

2005
[7]

2017, , 466, 798

Cappellari , M. 2017, , 466, 798

2017
[8]

2023, GRB Coordinates Network, 34633, 1

Cenko , B. 2023, GRB Coordinates Network, 34633, 1

2023

Show all 132 references

[9]

2024, GRB Coordinates Network, 36033, 1

Cenko , B. 2024, GRB Coordinates Network, 36033, 1

2024
[10]

Chan , C.-H., Piran , T., & Krolik , J. H. 2020, , 903, 17

2020
[11]

H., & Saban , D

Chan , C.-H., Piran , T., Krolik , J. H., & Saban , D. 2019, , 881, 113

2019
[12]

B., et al

Charalampopoulos , P., Leloudas , G., Malesani , D. B., et al. 2022, , 659, A34

2022
[13]

2016, , 463, 2145

Charisi , M., Bartos , I., Haiman , Z., et al. 2016, , 463, 2145

2016
[14]

2024, , 527, 12154

Chen , Y.-J., Zhai , S., Liu , J.-R., et al. 2024, , 527, 12154

2024
[15]

2019, , 485, 3185

Chiaraluce , E., Bruni , G., Panessa , F., et al. 2019, , 485, 3185

2019
[16]

D., Morris , M

Ciurlo , A., Campbell , R. D., Morris , M. R., et al. 2023, , 944, 136

2023
[17]

Condon , J. J. 1992, , 30, 575

1992
[18]

R., Armitage , P

Coughlin , E. R., Armitage , P. J., Nixon , C., & Begelman , M. C. 2017, , 465, 3840

2017
[19]

J., Alexander , R

Cuadra , J., Armitage , P. J., Alexander , R. D., & Begelman , M. C. 2009, , 393, 1423

2009
[20]

2010, , 524, A64

Cusumano , G., La Parola , V., Segreto , A., et al. 2010, , 524, A64

2010
[21]

M., Wright , E

Cutri , R. M., Wright , E. L., Conrow , T., et al. 2021, VizieR Online Data Catalog: AllWISE Data Release (Cutri+ 2013) , VizieR On-line Data Catalog: II/328. Originally published in: IPAC/Caltech (2013)

2013
[22]

E., Paolillo , M., et al

De Cicco , D., Bauer , F. E., Paolillo , M., et al. 2022, , 664, A117

2022
[23]

2019, , 86, 101525

De Rosa , A., Vignali , C., Bogdanovi \'c , T., et al. 2019, , 86, 101525

2019
[24]

Dickey , J. M. & Lockman , F. J. 1990, , 28, 215

1990
[25]

D'Orazio , D. J. & Charisi , M. 2023, arXiv e-prints, arXiv:2310.16896

2023 arXiv
[26]

2023, , 518, 4172

Dotti , M., Bonetti , M., Rigamonti , F., et al. 2023, , 518, 4172

2023
[27]

A., Nixon , C

Evans , P. A., Nixon , C. J., Campana , S., et al. 2023, Nature Astronomy, 7, 1368

2023
[28]

2013, , 777, L14

Fiacconi , D., Mayer , L., Ro s kar , R., & Colpi , M. 2013, , 777, L14

2013
[29]

2021, , 161, 242

F \"o rster , F., Cabrera-Vives , G., Castillo-Navarrete , E., et al. 2021, , 161, 242

2021
[30]

2023, , 675, A100

Franchini , A., Bonetti , M., Lupi , A., et al. 2023, , 675, A100

2023
[31]

J., et al

Frederick , S., Gezari , S., Graham , M. J., et al. 2019, , 883, 31

2019
[32]

J., et al

Frederick , S., Gezari , S., Graham , M. J., et al. 2021, , 920, 56

2021
[33]

Gaia Collaboration , Brown , A. G. A., Vallenari , A., et al. 2018, , 616, A1

2018
[34]

2024, , 685, A130

Gaia Collaboration , Krone-Martins , A., Ducourant , C., et al. 2024, , 685, A130

2024
[35]

Gaia Collaboration , Vallenari , A., Brown , A. G. A., et al. 2023, , 674, A1

2023
[36]

2021, , 59, 21

Gezari , S. 2021, , 59, 21

2021
[37]

K., et al

Gillessen , S., Genzel , R., Fritz , T. K., et al. 2012, , 481, 51

2012
[38]

G., Cuadra , J., Sesana , A., et al

Goicovic , F. G., Cuadra , J., Sesana , A., et al. 2016, , 455, 1989

2016
[39]

G., Sesana , A., Cuadra , J., & Stasyszyn , F

Goicovic , F. G., Sesana , A., Cuadra , J., & Stasyszyn , F. 2017, , 472, 514

2017
[40]

J., Djorgovski , S

Graham , M. J., Djorgovski , S. G., Drake , A. J., et al. 2017, , 470, 4112

2017
[41]

J., Djorgovski , S

Graham , M. J., Djorgovski , S. G., Stern , D., et al. 2015, , 518, 74

2015
[42]

J., Kulkarni , S

Graham , M. J., Kulkarni , S. R., Bellm , E. C., et al. 2019, , 131, 078001

2019
[43]

2024 a , , 966, 160

Guolo , M., Gezari , S., Yao , Y., et al. 2024 a , , 966, 160

2024
[44]

R., Zaja c ek , M., et al

Guolo , M., Pasham , D. R., Zaja c ek , M., et al. 2024 b , Nature Astronomy, 8, 347

2024
[45]

2023, , 525, 2187

Hern \'a ndez-Garc \' a , L., Panessa , F., Bruni , G., et al. 2023, , 525, 2187

2023
[46]

T., Holoien , T

Hinkle , J. T., Holoien , T. W. S., Shappee , B. J., et al. 2022, , 930, 12

2022
[47]

2011, , 413, 2633

Hobbs , A., Nayakshin , S., Power , C., & King , A. 2011, , 413, 2633

2011
[48]

2023, , 956, L46

Huang , S., Jiang , N., Shen , R.-F., Wang , T., & Sheng , Z. 2023, , 956, L46

2023
[49]

A., F \"o rster , F., et al

Huijse , P., Est \'e vez , P. A., F \"o rster , F., et al. 2018, , 236, 12

2018
[50]

R., & Fremling , C

Johansson , J., Perley , D., Chu , M., Hinds , K. R., & Fremling , C. 2022, Transient Name Server Classification Report, 2022-1987, 1

2022
[51]

2017, , 469, 314

Kathirgamaraju , A., Barniol Duran , R., & Giannios , D. 2017, , 469, 314

2017
[52]

C., Bechtold , J., & Siemiginowska , A

Kelly , B. C., Bechtold , J., & Siemiginowska , A. 2009, , 698, 895

2009
[53]

C., Becker , A

Kelly , B. C., Becker , A. C., Sobolewska , M., Siemiginowska , A., & Uttley , P. 2014, , 788, 33

2014
[54]

Krolik , J. H. & Linial , I. 2022, , 941, 24

2022
[55]

A., Chandler , C

Lacy , M., Baum , S. A., Chandler , C. J., et al. 2020, , 132, 035001

2020
[56]

2022, , 931, 5

Laha , S., Meyer , E., Roychowdhury , A., et al. 2022, , 931, 5

2022
[57]

& Mu \ n oz , D

Lai , D. & Mu \ n oz , D. J. 2023, , 61, 517

2023
[58]

M., Cales , S., Moran , E

LaMassa , S. M., Cales , S., Moran , E. C., et al. 2015, , 800, 144

2015
[59]

G., MacLeod , C., et al

Lawrence , A., Bruce , A. G., MacLeod , C., et al. 2016, , 463, 296

2016
[60]

2023, in American Astronomical Society Meeting Abstracts, Vol

Lien , A., Krimm , H., Markwardt , C., et al. 2023, in American Astronomical Society Meeting Abstracts, Vol. 55, American Astronomical Society Meeting Abstracts, 254.07

2023
[61]

& Metzger , B

Linial , I. & Metzger , B. D. 2023, , 957, 34

2023
[62]

& Sari , R

Linial , I. & Sari , R. 2023, , 945, 86

2023
[63]

2021, , 507, 983

Liska , M., Hesp , C., Tchekhovskoy , A., et al. 2021, , 507, 983

2021
[64]

2019, , 487, 550

Liska , M., Tchekhovskoy , A., Ingram , A., & van der Klis , M. 2019, , 487, 550

2019
[65]

K., Li , S., & Chen , X

Liu , F. K., Li , S., & Chen , X. 2009, , 706, L133

2009
[66]

K., Li , S., & Komossa , S

Liu , F. K., Li , S., & Komossa , S. 2014, , 786, 103

2014
[67]

2020, , 894, L14

Lu , X., Cheng , Y., Ginsburg , A., et al. 2020, , 894, L14

2020
[68]

L., Ross , N

MacLeod , C. L., Ross , N. P., Lawrence , A., et al. 2016, , 457, 389

2016
[69]

M., et al

Mainzer , A., Bauer , J., Cutri , R. M., et al. 2014, , 792, 30

2014
[70]

2011, , 731, 53

Mainzer , A., Bauer , J., Grav , T., et al. 2011, , 731, 53

2011
[71]

2004, , 351, 169

Marconi , A., Risaliti , G., Gilli , R., et al. 2004, , 351, 169

2004
[72]

J., Laher , R

Masci , F. J., Laher , R. R., Rusholme , B., et al. 2023, arXiv e-prints, arXiv:2305.16279

2023 arXiv
[73]

J., Laher , R

Masci , F. J., Laher , R. R., Rusholme , B., et al. 2019, , 131, 018003

2019
[74]

D., Stone , N

Metzger , B. D., Stone , N. C., & Gilbaum , S. 2022, , 926, 101

2022
[75]

R., Coughlin , E

Miles , P. R., Coughlin , E. R., & Nixon , C. J. 2020, , 899, 36

2020
[76]

2023, , 670, A93

Miniutti , G., Giustini , M., Arcodia , R., et al. 2023, , 670, A93

2023
[77]

D., Giustini , M., et al

Miniutti , G., Saxton , R. D., Giustini , M., et al. 2019, , 573, 381

2019
[78]

P., & Marshall , J

Mondrik , N., Long , J. P., & Marshall , J. L. 2015, , 811, L34

2015
[79]

S., Richards , G

Moreno , J., Vogeley , M. S., Richards , G. T., & Yu , W. 2019, , 131, 063001

2019
[80]

W., et al

Mowlavi , N., Rimoldini , L., Evans , D. W., et al. 2021, , 648, A44

2021
[81]

E., et al

Munoz-Arancibia , A., Forster , F., Bauer , F. E., et al. 2021, Transient Name Server Discovery Report, 2021-923, 1

2021
[82]

2024, Transient Name Server AstroNote, 173, 1

Munoz-Arancibia , A., Hernandez-Garcia , L., Lira , P., et al. 2024, Transient Name Server AstroNote, 173, 1

2024
[83]

2013, The Physics and Evolution of Active Galactic Nuclei

Netzer , H. 2013, The Physics and Evolution of Active Galactic Nuclei

2013
[84]

2012, , 757, L24

Nixon , C., King , A., Price , D., & Frank , J. 2012, , 757, L24

2012
[85]

B., et al

Oh , K., Koss , M., Markwardt , C. B., et al. 2018, , 235, 4

2018
[86]

D., Laor , A., et al

Panessa , F., Baldi , R. D., Laor , A., et al. 2019, Nature Astronomy, 3, 387

2019
[87]

2007, , 467, 519

Panessa , F., Barcons , X., Bassani , L., et al. 2007, , 467, 519

2007
[88]

2006, , 455, 173

Panessa , F., Bassani , L., Cappi , M., et al. 2006, , 455, 173

2006
[89]

& Giroletti , M

Panessa , F. & Giroletti , M. 2013, , 432, 1138

2013
[90]

F., et al

Parisi , P., Masetti , N., Rojas , A. F., et al. 2014, , 561, A67

2014
[91]

R., Zaja c ek , M., Nixon , C

Pasham , D. R., Zaja c ek , M., Nixon , C. J., et al. 2024, , 630, 325

2024
[92]

V., Auchettl , K., Shappee , B

Payne , A. V., Auchettl , K., Shappee , B. J., et al. 2023, , 951, 134

2023
[93]

V., Shappee , B

Payne , A. V., Shappee , B. J., Hinkle , J. T., et al. 2021, , 910, 125

2021
[94]

Peters , P. C. 1964, Physical Review, 136, 1224

1964
[95]

2023, , 669, A140

Petrushevska , T., Leloudas , G., Ili \'c , D., et al. 2023, , 669, A140

2023
[96]

Popovi \'c , L. C . 2012, , 56, 74

2012
[97]

Prabhu , T. P. & Anupama , G. C. 2010, in Astronomical Society of India Conference Series, Vol. 1, Astronomical Society of India Conference Series, 193--201

2010
[98]

J., Liptai , D., Mandel , I., et al

Price , D. J., Liptai , D., Mandel , I., et al. 2024, , 971, L46

2024
[99]

Principe , J. C. 2010, Information Theoretic Learning

2010
[100]

Rees , M. J. 1984, , 22, 471

1984
[101]

Reines , A. E. & Volonteri , M. 2015, , 813, 82

2015
[102]

2020, , 898, L1

Ricci , C., Kara , E., Loewenstein , M., et al. 2020, , 898, L1

2020
[103]

2021, , 255, 7

Ricci , C., Loewenstein , M., Kara , E., et al. 2021, , 255, 7

2021
[104]

& Trakhtenbrot , B

Ricci , C. & Trakhtenbrot , B. 2023, Nature Astronomy, 7, 1282

2023
[105]

W., et al

Riello , M., De Angeli , F., Evans , D. W., et al. 2021, , 649, A3

2021
[106]

Roming , P. W. A., Kennedy , T. E., Mason , K. O., et al. 2005, , 120, 95

2005
[107]

2018, , 864, 87

S \'a nchez-S \'a ez , P., Lira , P., Mej \' a-Restrepo , J., et al. 2018, , 864, 87

2018
[108]

2021, , 161, 141

S \'a nchez-S \'a ez , P., Reyes , I., Valenzuela , C., et al. 2021, , 161, 141

2021
[109]

B., Marshall , P

Schmidt , K. B., Marshall , P. J., Rix , H.-W., et al. 2010, , 714, 1194

2010
[110]

F., Cutri , R

Skrutskie , M. F., Cutri , R. M., Stiening , R., et al. 2006, , 131, 1163

2006
[111]

& Loeb , A

Stone , N. & Loeb , A. 2012, , 108, 061302

2012
[112]

S., Schinnerer , E., Krause , M., et al

Tabatabaei , F. S., Schinnerer , E., Krause , M., et al. 2017, , 836, 185

2017
[113]

L., et al

Trakhtenbrot , B., Arcavi , I., MacLeod , C. L., et al. 2019 a , , 883, 94

2019
[114]

2019 b , Nature Astronomy, 3, 242

Trakhtenbrot , B., Arcavi , I., Ricci , C., et al. 2019 b , Nature Astronomy, 3, 242

2019
[115]

H., Markwardt , C

Tueller , J., Baumgartner , W. H., Markwardt , C. B., et al. 2010, , 186, 378

2010
[116]

F., Barthelmy , S., et al

Tueller , J., Mushotzky , R. F., Barthelmy , S., et al. 2008, , 681, 113

2008
[117]

2024, , 688, A128

Valli , R., Tiede , C., Vigna-G \'o mez , A., et al. 2024, , 688, A128

2024
[118]

J., Lehto , H

Valtonen , M. J., Lehto , H. J., Nilsson , K., et al. 2008, , 452, 851

2008
[119]

van Velzen , S., Holoien , T. W. S., Onori , F., Hung , T., & Arcavi , I. 2020, , 216, 124

2020
[120]

E., Wilhite , B

Vanden Berk , D. E., Wilhite , B. C., Kron , R. G., et al. 2004, , 601, 692

2004
[121]

S., & Uttley , P

Vaughan , S., Edelson , R., Warwick , R. S., & Uttley , P. 2003, , 345, 1271

2003
[122]

2010, , 404, 1639

Vazdekis , A., S \'a nchez-Bl \'a zquez , P., Falc \'o n-Barroso , J., et al. 2010, , 404, 1639

2010
[123]

2018, , 476, 5312

Vigneron , Q., Lodato , G., & Guidarelli , A. 2018, , 476, 5312

2018
[124]

L., Eisenhardt , P

Wright , E. L., Eisenhardt , P. R. M., Mainzer , A. K., et al. 2010, , 140, 1868

2010
[125]

2002, , 331, 935

Yu , Q. 2002, , 331, 935

2002
[126]

& Richards , G

Yu , W. & Richards , G. T. 2022, EzTao: Easier CARMA Modeling , Astrophysics Source Code Library, record ascl:2201.001

2022
[127]

2021, , 217, 54

Zabludoff , A., Arcavi , I., LaMassa , S., et al. 2021, , 217, 54

2021
[128]

Zakamska , N. L. & Greene , J. E. 2014, , 442, 784

2014
[129]

2024, , 966, 85

Zeltyn , G., Trakhtenbrot , B., Eracleous , M., et al. 2024, , 966, 85

2024
[130]

2023, , 526, 6015

Zhang , X.-G. 2023, , 526, 6015

2023
[131]

, " * write output.state after.block = add.period write newline

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Pith tools

Reviewed August 12, 2026 · model on record in the stance chip above.

[1] [1]

2013, , 764, 14

Amaro-Seoane , P., Brem , P., & Cuadra , J. 2013, , 764, 14

2013

[2] [2]

A., Chavushyan , V., & Pati \ n o- \'A lvarez , V

Amaya-Almaz \'a n , R. A., Chavushyan , V., & Pati \ n o- \'A lvarez , V. M. 2022, , 929, 14

2022

[3] [3]

2022, , 662, A49

Arcodia , R., Miniutti , G., Ponti , G., et al. 2022, , 662, A49

2022

[4] [4]

C., Kulkarni , S

Bellm , E. C., Kulkarni , S. R., Graham , M. J., et al. 2019, , 131, 018002

2019

[5] [5]

& Nandra , K

Brightman , M. & Nandra , K. 2011, , 413, 1206

2011

[6] [6]

N., Hill , J

Burrows , D. N., Hill , J. E., Nousek , J. A., et al. 2005, , 120, 165

2005

[7] [7]

2017, , 466, 798

Cappellari , M. 2017, , 466, 798

2017

[8] [8]

2023, GRB Coordinates Network, 34633, 1

Cenko , B. 2023, GRB Coordinates Network, 34633, 1

2023