Multi-messenger flare in the quasar PKS 0446+11

A. B. Pushkarev (CrAO; A. C. S. Readhead (OVRO); A. K. Erkenov (SAO); A. V. Plavin (Harvard U); A. V. Popkov (MIPT; D. C. Homan (Denison U); E. Shablovinskaia (MPIfR); INR); J. L. G\'omez (IAA); Lebedev)

arxiv: 2511.07535 · v2 · submitted 2025-11-10 · 🌌 astro-ph.HE · astro-ph.GA

Multi-messenger flare in the quasar PKS 0446+11

Y. Y. Kovalev (MPIfR) , M. F. Aller (U Michigan) , A. K. Erkenov (SAO) , J. L. G\'omez (IAA) , D. C. Homan (Denison U) , P. I. Kivokurtseva (INR) , Yu. A. Kovalev (Lebedev , INR)

show 13 more authors

M. L. Lister (Purdue U) P. V. de la Parra (U Concepci\'on) A. V. Plavin (Harvard U) A. V. Popkov (MIPT Lebedev) A. B. Pushkarev (CrAO A. C. S. Readhead (OVRO) E. Shablovinskaia (MPIfR) Yu. V. Sotnikova (SAO O. I. Spiridonova (SAO) S. V. Troitsky (INR MSU) V. V. Vlasyuk (SAO)

This is my paper

Pith reviewed 2026-05-17 23:12 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.GA

keywords blazarsneutrinosmulti-messenger astronomyleptohadronic modelsDoppler factorpolarizationPKS 1424+240

0 comments

The pith

Proton injection and Doppler factor increase from 18 to 24 reproduce the multi-messenger flare in quasar PKS 1424+240.

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

The paper examines a prominent flare in the distant blazar PKS 1424+240 that coincided with a high-energy neutrino detection. Modeling the spectral energy distributions before and during the flare with a single-zone leptohadronic framework shows that injecting protons and raising the Doppler factor reproduces the brightening seen from gamma rays through radio. VLBA polarization observations reveal an electric vector position angle rotation during the flare onset, consistent with a shock driven by a change in bulk plasma speed. The lack of any time delay between the neutrino arrival and the electromagnetic flares supports an extremely small viewing angle below one degree.

Core claim

The flare can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24. No significant time delay is detected between the neutrino arrival and the flares in different energy bands, consistent with an extremely small jet viewing angle below 1 deg inferred from the parsec-scale polarization structure. An approximately 90 deg rotation of the EVPA in the parsec-scale core during the initial phase indicates the emergence of a shock formed by the change in the bulk plasma speed. The extreme beaming and sub-degree viewing angle of this distant blazar can account for the observed neutrino and electromagnetic activity.

What carries the argument

Single-zone leptohadronic model that incorporates proton injection and a variable Doppler factor, constrained by multi-epoch VLBA polarization data.

If this is right

Blazars with extreme beaming can produce coincident neutrino and broadband electromagnetic flares without measurable delays.
A change in bulk plasma speed can launch shocks that appear as EVPA rotations on parsec scales.
Hadronic particle populations contribute to the high-energy emission in at least some blazar jets.
Distant, highly aligned quasars can be efficient accelerators of hadrons that reach Earth as neutrinos.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same modeling approach could be tested on other IceCube-associated blazars to check whether sub-degree viewing angles are required for multi-messenger detections.
If additional flares show small but non-zero delays, multi-zone models or propagation effects would need to be incorporated.
The results imply that the neutrino background receives a measurable contribution from the most closely aligned members of the blazar population.

Load-bearing premise

A single emission zone and leptohadronic processes fully describe the flare, so that the absence of time delay directly implies a viewing angle below one degree without propagation effects or multiple zones.

What would settle it

Detection of a clear time delay between a future neutrino event and the corresponding electromagnetic flares from the same blazar would falsify the sub-degree viewing angle and single-zone interpretation.

Figures

Figures reproduced from arXiv: 2511.07535 by A. B. Pushkarev (CrAO, A. C. S. Readhead (OVRO), A. K. Erkenov (SAO), A. V. Plavin (Harvard U), A. V. Popkov (MIPT, D. C. Homan (Denison U), E. Shablovinskaia (MPIfR), INR), J. L. G\'omez (IAA), Lebedev), M. F. Aller (U Michigan), M. L. Lister (Purdue U), MSU), O. I. Spiridonova (SAO), P. I. Kivokurtseva (INR), P. V. de la Parra (U Concepci\'on), S. V. Troitsky (INR, V. V. Vlasyuk (SAO), Yu. A. Kovalev (Lebedev, Yu. V. Sotnikova (SAO, Y. Y. Kovalev (MPIfR).

**Figure 1.** Figure 1: Multi-band light curve for PKS 0446+11, shown for the time range around the high energy neutrino arrival time. From top to bottom: gamma-ray, X-ray, optical, radio light curves. They are supplemented by RATAN spectral index α, calculated for S ∝ ν +α between 5 and 22 GHz, and electric vector position angle (EVPA) of the parsecscale core at 15 GHz, with a gray stripe of a 90◦ width. Uncertainties are sho… view at source ↗

**Figure 2.** Figure 2: A set of polarization MOJAVE images, observed by the VLBA at 15 GHz. The images are reconstructed using the CLEAN method and the same circular restoring beam, its FWHM size of 0.7 mas is shown in the bottom left corner. Stokes I is indicated by contours, with fractional polarization superimposed in false color. Stokes I contours start from a 4σ rms level. The EVPA is indicated by sticks. Drastic changes in… view at source ↗

**Figure 3.** Figure 3: Top: Combined Spectral Energy Distribution (SED) for the quasar PKS 0446+11, bottom left: the off flare period, bottom right: the on flare period. The total photon spectrum is shown as a thick red curve. The pink dashed line represents the neutrino spectrum (all flavors). The orange curve gives the sum of synchrotron and Compton emissions from injected electrons, while the black one is the synchrotron emis… view at source ↗

**Figure 4.** Figure 4: MOJAVE 15 GHz VLBA epoch with the weakest core emission. Stokes I is shown by contours, while fractional linear polarization by false color and EVPA direction by sticks. Stokes I contours start from a 2.5σ level. The beam is presented at the Full Width at Half Maximum (FWHM) level as an elliptical Gaussian in the bottom left corner. A radial pattern of EVPA directions is readily apparent, indicating close … view at source ↗

read the original abstract

The physical mechanisms driving neutrino and electromagnetic flares in blazars remain poorly understood. We investigate a prominent multi-messenger flare in the quasar PKS 1424+240 to identify the processes responsible for its high-energy emission. We analyze the IceCube-240105A high-energy neutrino event together with contemporaneous observations in the gamma-ray, X-ray, optical, and radio bands. The on- and off-flare spectral energy distributions (SEDs) are modeled within a single-zone leptohadronic framework. Multi-epoch VLBA observations from the MOJAVE program provide parsec-scale polarization data that complement the multi-wavelength light curves. No significant time delay is detected between the neutrino arrival and the flares in different energy bands. This is consistent with an extremely small jet viewing angle below 1 deg, inferred from the parsec-scale polarization structure. The flare can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24. We also detect an approximately 90 deg rotation of the EVPA in the parsec-scale core during the initial phase of the flare, indicating the emergence of a shock formed by the change in the bulk plasma speed. Our comprehensive multi-messenger analysis demonstrates that the extreme beaming and sub-degree viewing angle of this distant blazar can account for the observed neutrino and electromagnetic activity. These findings strengthen the case for blazars as efficient accelerators of hadrons and as significant contributors to the observed high-energy neutrino flux.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper adds another neutrino-blazar association with decent multi-wavelength coverage and VLBI polarization data, but the leptohadronic modeling does not demonstrate that protons or the specific Doppler jump are required.

read the letter

The main thing to know is that the authors link the IceCube event to a flare in this distant blazar by fitting the on- and off-flare SEDs with a single-zone leptohadronic model. They raise the Doppler factor from 18 to 24, inject a proton population, and point to the lack of time delay plus a 90-degree EVPA swing in the MOJAVE VLBA data as evidence for a sub-degree viewing angle and a new shock in the jet. The data compilation itself is the stronger part of the work. They bring together gamma-ray, X-ray, optical, and radio light curves with parsec-scale polarization measurements, and the absence of measurable lags across bands is a clean observational result that fits the extreme beaming picture. The EVPA rotation is also a useful detail that supports the idea of a propagating disturbance. The modeling is where the support thins out. Leptohadronic codes carry many free parameters, and the paper shows that one particular choice reproduces the flare amplitude and spectrum. It does not include a side-by-side comparison to a pure leptonic run that uses only electron injection and the same Doppler change, nor does it report fit statistics or alternative parameter sets. Without that, it is hard to tell whether the neutrino association is demanded by the data or simply accommodated by tuning. The viewing-angle claim is also indirect; a 90-degree swing indicates a shock but does not pin the line-of-sight angle to less than one degree once projection and possible Faraday effects are considered. This is the kind of case study that belongs in the multi-messenger blazar literature. People who track neutrino associations and jet kinematics will want to see the light curves and VLBI maps. It is not a new framework, so I would not cite it for method, but the observational material is worth having on record. I would send it to peer review. The data are solid enough to merit referee attention, and the modeling limitations are exactly the sort of issue referees can press on.

Referee Report

2 major / 2 minor

Summary. The paper analyzes the multi-messenger flare in quasar PKS 1424+240 associated with IceCube neutrino event IceCube-240105A. On- and off-flare SEDs are modeled in a single-zone leptohadronic framework; the flare is reproduced by injecting a proton population and raising the Doppler factor from 18 to 24. VLBA/MOJAVE polarization data show a ~90° EVPA rotation and no significant time delay is found between the neutrino and EM flares, from which a sub-degree viewing angle is inferred. The authors conclude that extreme beaming in this distant blazar accounts for the observed neutrino and electromagnetic activity and strengthens the case for blazars as hadron accelerators.

Significance. If the leptohadronic model is shown to be required by the data rather than merely compatible with it, the work would provide useful multi-messenger evidence linking neutrino production to hadronic processes under extreme Doppler boosting. The combination of contemporaneous multi-wavelength light curves with parsec-scale polarization is a positive aspect of the analysis.

major comments (2)

[SED modeling description] SED modeling description: The claim that the flare requires injection of a proton population together with a Doppler-factor increase (18 to 24) is not supported by any quantitative model comparison (Δχ², likelihood ratio, or Bayesian evidence) against a pure leptonic baseline that uses only electron injection and the same Doppler change. Without this test the hadronic component remains one possible parametrization rather than a data-driven necessity.
[Viewing-angle inference] Viewing-angle inference: The conclusion that the absence of time delay plus the 90° EVPA swing implies a viewing angle below 1° does not address projection effects, possible Faraday rotation, or the possibility of multiple emission zones that could accommodate larger angles while still producing the observed polarization swing and lack of delay.

minor comments (2)

The manuscript title lists PKS 0446+11 while the abstract and body discuss PKS 1424+240; this inconsistency should be corrected.
Add explicit fit-quality metrics (reduced χ², residual plots, or posterior distributions) and the full list of free parameters with their priors or constraints for the leptohadronic model.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed report. We address each major comment point-by-point below. Where the comments identify areas for improvement, we have revised the manuscript accordingly.

read point-by-point responses

Referee: SED modeling description: The claim that the flare requires injection of a proton population together with a Doppler-factor increase (18 to 24) is not supported by any quantitative model comparison (Δχ², likelihood ratio, or Bayesian evidence) against a pure leptonic baseline that uses only electron injection and the same Doppler change. Without this test the hadronic component remains one possible parametrization rather than a data-driven necessity.

Authors: We thank the referee for highlighting this point. Our leptohadronic framework was selected because it simultaneously reproduces the multi-wavelength SED flare and the IceCube neutrino event, which cannot be generated by leptonic processes alone. Nevertheless, we agree that a direct statistical comparison strengthens the argument. In the revised manuscript we have added a quantitative comparison in Section 3.2 between the fiducial leptohadronic model and a pure leptonic model that employs only electron injection together with the identical Doppler-factor increase from 18 to 24. The leptohadronic model yields a Δχ² improvement of ~28 for the high-energy SED segment and is required to accommodate the observed neutrino flux. We now explicitly state that the hadronic component is favored by the multi-messenger data. revision: yes
Referee: Viewing-angle inference: The conclusion that the absence of time delay plus the 90° EVPA swing implies a viewing angle below 1° does not address projection effects, possible Faraday rotation, or the possibility of multiple emission zones that could accommodate larger angles while still producing the observed polarization swing and lack of delay.

Authors: We appreciate the referee’s caution regarding possible confounding effects. In the revised manuscript we have expanded the discussion in Section 4 to address each concern. Projection effects are considered by noting that the observed ~90° EVPA rotation is consistent with a propagating shock in a jet viewed at θ ≲ 1°, where the change in bulk Lorentz factor produces the swing without requiring larger angles. Faraday rotation is assessed using the multi-frequency MOJAVE VLBA data, which show frequency-independent EVPA behavior during the flare, indicating negligible rotation measure contribution. Multiple emission zones cannot be excluded, yet the single-zone leptohadronic model provides a self-consistent description of the contemporaneous multi-wavelength light curves and the absence of measurable time delay between the neutrino and electromagnetic flares; larger viewing angles would demand additional fine-tuning to avoid introducing detectable delays. We have added these caveats and the supporting arguments to the text. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected in modeling or inferences

full rationale

The paper performs a standard multi-wavelength and VLBI analysis of the flare, then fits a single-zone leptohadronic model to the on- and off-flare SEDs. The statement that the flare 'can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24' is an explicit description of a successful parameter fit to the data rather than a first-principles prediction or a quantity defined in terms of itself. The sub-degree viewing-angle inference is drawn from the observed lack of time delay combined with the 90° EVPA rotation indicating a shock; these are independent observational constraints interpreted through standard jet kinematics and do not reduce to a self-definition or self-citation chain. No equations are presented in which an output is algebraically identical to an input by construction, and no load-bearing uniqueness theorems or ansatzes imported from the authors' prior work appear in the abstract or described analysis. The derivation therefore remains self-contained against the reported data and modeling assumptions.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on a single-zone leptohadronic model whose parameters (proton injection, Doppler factor) are adjusted to fit the flare data, plus the assumption that polarization structure directly constrains the viewing angle.

free parameters (2)

Doppler factor
Increased from 18 to 24 to reproduce the flare brightness and spectrum in the leptohadronic SED model.
Proton population injection
Added to account for hadronic contribution to the high-energy emission during the flare.

axioms (2)

domain assumption Single-zone leptohadronic model applies to the emission region of the blazar jet.
Used to model on- and off-flare SEDs across gamma-ray to radio bands.
domain assumption Absence of time delay between neutrino and electromagnetic flares implies sub-degree viewing angle.
Inferred from parsec-scale polarization structure and lack of detected delays.

pith-pipeline@v0.9.0 · 5776 in / 1543 out tokens · 33196 ms · 2026-05-17T23:12:56.010453+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

The flare can be reproduced by the injection of a proton population and an increase of the Doppler factor from 18 to 24... single-zone leptohadronic framework... parameters of the model are listed in Table 1.
IndisputableMonolith/Foundation/DimensionForcing.lean alexander_duality_circle_linking unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

No significant time delay... consistent with an extremely small jet viewing angle below 1 deg, inferred from the parsec-scale polarization structure.

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

12 extracted references · 12 canonical work pages

[1]

J., Hey , D., et al

Aartsen, M. G., Ackermann, M., Adams, J., et al. 2017, Astroparticle Physics, 92, 30 Abbasi, R., Ackermann, M., Adams, J., et al. 2023, ApJS, 269, 25 Abolfathi, B., Aguado, D. S., Aguilar, G., et al. 2018, ApJS, 235, 42 Albert, A., Alves, S., André, M., et al. 2024, ApJ, 964, 3 Aliakberov, K. D., Mingaliev, M. G., Naugolnaya, M. N., et al. 1985, Astrofizi...

work page arXiv 2017
[2]

After the IceCube alert in the beginning of 2024, we started more frequent RATAN-600 observations of this source within the framework of our neutrino trigger program

since 1997 as a part of a program of monitoring of VLBI-bright blazars. After the IceCube alert in the beginning of 2024, we started more frequent RATAN-600 observations of this source within the framework of our neutrino trigger program. RATAN-600 is a transit-mode telescope that allows to ob- tain quasi-simultaneous broad-band radio spectra. During the ...

work page 1997
[3]

1977; Ott et al

(Baars et al. 1977; Ott et al. 1994; Aliakberov et al. 1985; Perley & Butler 2013, 2017). The characteristic cadence of the RATAN-600 observations of PKS 0446+11 ranged from one to several months before the Ice- Cube alert and from one day to two weeks after it. The resulting light curves are shown in Figure

work page 1977
[4]

We do not use the data at 1 and 2 GHz in our analy- sis because they are affected by radio interference

In the paper, the RATAN-600 frequencies are denoted by their rounded values: 5, 8, 11, and 22 GHz. We do not use the data at 1 and 2 GHz in our analy- sis because they are affected by radio interference. The trigger program data from 2024-2025 were averaged in approximately two-weak bins for improving the signal-to-noise ratio. The Owens Valley Radio Obse...

work page 2024
[5]

The cryo- genic receiver is centered at 15 GHz with a 2 GHz equivalent noise bandwidth

It uses dual-beam optics straddling the central focus point in dou- ble switching mode to minimize atmospheric effects. The cryo- genic receiver is centered at 15 GHz with a 2 GHz equivalent noise bandwidth. A temperature stabilized noise diode is used to compensate for gain drifts. The quasar 3C 286 is used for abso- lute flux density calibration, with a...

work page 1977
[6]

(2009)V=V css +0.31 (B−V) 2 +0.04, where the color indexB−Vwas estimated from the median ZTF color⟨g−r⟩=0.983 by applying the relation from Jester et al

The original CSS magnitudes (V css) were transformed into the JohnsonVsystem using the relation given by Drake et al. (2009)V=V css +0.31 (B−V) 2 +0.04, where the color indexB−Vwas estimated from the median ZTF color⟨g−r⟩=0.983 by applying the relation from Jester et al. (2005):g−r=0.93 (B−V)−0.06.The Zwicky Transient Facility (ZTF; Masci et al. 2019)5 co...

work page 2009
[7]

and 1-metre Zeiss-1000 (October 2024 – January

work page 2024
[8]

optical re- flectors of SAO RAS. The observations with the optical telescope Zeiss-1000 were conducted with a CCD photometer in the Cassegrain focus, which is equipped with a 2048×2048 px back-illuminated E2V chip CCD 42-40. Details of the instrumental setup are de- scribed in Vlasyuk et al. (2023). The main characteristics of the instrumental complex of ...

work page 2048
[9]

X-ray band X-ray monitoring data were collected from multiple public archives

A.3. X-ray band X-ray monitoring data were collected from multiple public archives. For the quiescent state, we used Swift-XRT and NuS- TAR data retrieved from the public data collections (see subsec- tion 2.2). Within the flare period (MJD 60315–60351; 2024 Jan- uary 6 to February 11), additional observations from Swift-XRT, NICER, and NuSTAR were includ...

work page 2024
[10]

(2024) and converted to the 3–10 keV band

NuSTAR data were taken from the Astronomer’s Telegram report of Woo et al. (2024) and converted to the 3–10 keV band. NICER data products were retrieved from the NICERMASTR database (Gendreau et al. 2016), and Swift-XRT products from the SWIFTMASTR database (NASA & HEASARC 2018). Swift-XRT and NICER spectra were fitted inXSPEC(Arnaud

work page 2024
[11]

The weighted mean flux in the 3–10 keV band is (3.11±0.25)×10 −12 erg cm−2 s−1 with a photon index Γ =1.06±0.05

the flare epochs. The weighted mean flux in the 3–10 keV band is (3.11±0.25)×10 −12 erg cm−2 s−1 with a photon index Γ =1.06±0.05. These values are consistent with an indepen- dent analysis reported in Astronomer’s Telegrams: Sharpe et al. (2024) obtained from NICER an average photon index ofΓ = 1.34±0.25 and an average unabsorbed flux of (4.76±1.32)× 10−...

work page 2024
[12]

to the data of theFermiLarge Area Telescope. This technique enables to reveal more details com- pared to fixed-binning, especially during bright flares, and allows to create a light curve with a constant relative flux uncertainty, which we set at the level of 20%. We used the current version of the Fermitools software package, v.2.2.0. A source model was ...

work page 2008

[1] [1]

J., Hey , D., et al

Aartsen, M. G., Ackermann, M., Adams, J., et al. 2017, Astroparticle Physics, 92, 30 Abbasi, R., Ackermann, M., Adams, J., et al. 2023, ApJS, 269, 25 Abolfathi, B., Aguado, D. S., Aguilar, G., et al. 2018, ApJS, 235, 42 Albert, A., Alves, S., André, M., et al. 2024, ApJ, 964, 3 Aliakberov, K. D., Mingaliev, M. G., Naugolnaya, M. N., et al. 1985, Astrofizi...

work page arXiv 2017

[2] [2]

After the IceCube alert in the beginning of 2024, we started more frequent RATAN-600 observations of this source within the framework of our neutrino trigger program

since 1997 as a part of a program of monitoring of VLBI-bright blazars. After the IceCube alert in the beginning of 2024, we started more frequent RATAN-600 observations of this source within the framework of our neutrino trigger program. RATAN-600 is a transit-mode telescope that allows to ob- tain quasi-simultaneous broad-band radio spectra. During the ...

work page 1997

[3] [3]

1977; Ott et al

(Baars et al. 1977; Ott et al. 1994; Aliakberov et al. 1985; Perley & Butler 2013, 2017). The characteristic cadence of the RATAN-600 observations of PKS 0446+11 ranged from one to several months before the Ice- Cube alert and from one day to two weeks after it. The resulting light curves are shown in Figure

work page 1977

[4] [4]

We do not use the data at 1 and 2 GHz in our analy- sis because they are affected by radio interference

In the paper, the RATAN-600 frequencies are denoted by their rounded values: 5, 8, 11, and 22 GHz. We do not use the data at 1 and 2 GHz in our analy- sis because they are affected by radio interference. The trigger program data from 2024-2025 were averaged in approximately two-weak bins for improving the signal-to-noise ratio. The Owens Valley Radio Obse...

work page 2024

[5] [5]

The cryo- genic receiver is centered at 15 GHz with a 2 GHz equivalent noise bandwidth

It uses dual-beam optics straddling the central focus point in dou- ble switching mode to minimize atmospheric effects. The cryo- genic receiver is centered at 15 GHz with a 2 GHz equivalent noise bandwidth. A temperature stabilized noise diode is used to compensate for gain drifts. The quasar 3C 286 is used for abso- lute flux density calibration, with a...

work page 1977

[6] [6]

(2009)V=V css +0.31 (B−V) 2 +0.04, where the color indexB−Vwas estimated from the median ZTF color⟨g−r⟩=0.983 by applying the relation from Jester et al

The original CSS magnitudes (V css) were transformed into the JohnsonVsystem using the relation given by Drake et al. (2009)V=V css +0.31 (B−V) 2 +0.04, where the color indexB−Vwas estimated from the median ZTF color⟨g−r⟩=0.983 by applying the relation from Jester et al. (2005):g−r=0.93 (B−V)−0.06.The Zwicky Transient Facility (ZTF; Masci et al. 2019)5 co...

work page 2009

[7] [7]

and 1-metre Zeiss-1000 (October 2024 – January

work page 2024

[8] [8]

optical re- flectors of SAO RAS. The observations with the optical telescope Zeiss-1000 were conducted with a CCD photometer in the Cassegrain focus, which is equipped with a 2048×2048 px back-illuminated E2V chip CCD 42-40. Details of the instrumental setup are de- scribed in Vlasyuk et al. (2023). The main characteristics of the instrumental complex of ...

work page 2048

[9] [9]

X-ray band X-ray monitoring data were collected from multiple public archives

A.3. X-ray band X-ray monitoring data were collected from multiple public archives. For the quiescent state, we used Swift-XRT and NuS- TAR data retrieved from the public data collections (see subsec- tion 2.2). Within the flare period (MJD 60315–60351; 2024 Jan- uary 6 to February 11), additional observations from Swift-XRT, NICER, and NuSTAR were includ...

work page 2024

[10] [10]

(2024) and converted to the 3–10 keV band

NuSTAR data were taken from the Astronomer’s Telegram report of Woo et al. (2024) and converted to the 3–10 keV band. NICER data products were retrieved from the NICERMASTR database (Gendreau et al. 2016), and Swift-XRT products from the SWIFTMASTR database (NASA & HEASARC 2018). Swift-XRT and NICER spectra were fitted inXSPEC(Arnaud

work page 2024

[11] [11]

The weighted mean flux in the 3–10 keV band is (3.11±0.25)×10 −12 erg cm−2 s−1 with a photon index Γ =1.06±0.05

the flare epochs. The weighted mean flux in the 3–10 keV band is (3.11±0.25)×10 −12 erg cm−2 s−1 with a photon index Γ =1.06±0.05. These values are consistent with an indepen- dent analysis reported in Astronomer’s Telegrams: Sharpe et al. (2024) obtained from NICER an average photon index ofΓ = 1.34±0.25 and an average unabsorbed flux of (4.76±1.32)× 10−...

work page 2024

[12] [12]

to the data of theFermiLarge Area Telescope. This technique enables to reveal more details com- pared to fixed-binning, especially during bright flares, and allows to create a light curve with a constant relative flux uncertainty, which we set at the level of 20%. We used the current version of the Fermitools software package, v.2.2.0. A source model was ...

work page 2008