Pith. sign in

REVIEW 4 major objections 5 minor 82 references

X-ray Polarization of the High-Synchrotron-Peaked BL Lac H 1426+428

T0 review · 4 major / 5 minor · reviewed 2026-08-16 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read A blazar's X-ray emission is shown to be 20.6% polarized at 7.1 sigma, implying ordered jet magnetic fields.

desk verdict First IXPE measurement of H 1426+428: a clean two-epoch result, with the second-epoch polarization detection secure even after discounting the headline 7.1 sigma. read the letter →

arxiv 2504.14869 v2 pith:WLKAZWDH submitted 2025-04-21 astro-ph.HE

Xin-Ke Hu (BIT) , Jia-Xuan Li (BIT) , Yu-Wei Yu (BIT) , Ji-Shun Lian (BIT) , Wei Deng (GXU) , Hai-Ming Zhang (GXU) , Jin Zhang (BIT) This is my paper · ORCID
classification astro-ph.HE
keywords ActivegalacticnucleiBlazarsX-raypolarimetryH1426+428RelativisticjetsSynchrotronradiationSpectropolarimetryIXPE
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

H 1426+428 is a BL Lac object, a type of active galaxy whose relativistic jet points nearly at Earth, with an unusually high synchrotron peak so that its X-rays come from freshly accelerated electrons. Using two IXPE observations roughly five weeks apart, the paper tries to establish that in July 2024 the source's 2–8 keV X-rays were linearly polarized at $\Pi_{\rm X}=20.6\%\pm2.9\%$ with a stable angle $\psi_{\rm X}=116.1^{\circ}\pm4.1^{\circ}$, a $7.1\sigma$ detection. In the earlier May 2024 observation, only an upper limit $\Pi_{\rm X}<19.5\%$ at 99% confidence was obtained, and time-resolved analysis finds no rotation of the polarization angle that could explain the null. The July epoch is also brighter and spectrally harder, showing harder-when-brighter behavior, with the polarized signal dominated by photons below 5 keV. The paper concludes that the polarized X-rays are synchrotron radiation from shock-accelerated electrons in a region of ordered magnetic fields, and that the earlier non-detection probably reflects limited photon counts rather than disordered fields.

What carries the argument

The load-bearing mechanism is X-ray spectropolarimetry: the paper extracts the normalized Stokes parameters $q=Q/I$ and $u=U/I$ with the PCUBE algorithm, then fits the $I$, $Q$, and $U$ spectra jointly using a spectral model of the form CONSTANT$\times$TBABS$\times$POLCONST$\times$POWERLAW, where POLCONST is a model that assumes a constant polarization degree and angle across the 2–8 keV band and provides $\Pi_{\rm X}$ and $\psi_{\rm X}$ as the only free parameters. The spectral parameters are fixed from a joint fit of the total-intensity spectra with contemporaneous Swift-XRT data, and a weighted response matrix is used to boost the polarization sensitivity. This two-step spectropolarimetric procedure is what turns the modulation of photoelectron directions in IXPE into the quoted $7.1\sigma$ detection; the model-independent PCUBE estimate serves as a cross-check. The physical picture that carries the interpretation is synchrotron radiation in an ordered magnetic field, whose observed polarization angle is set by the field direction projected on the sky.

What would settle it

Re-fit the second-epoch IXPE data with an energy-dependent polarization model in which $\psi_{\rm X}$ is allowed to vary linearly across 2–8 keV, with $\Pi_{\rm X}$ free in the same bins tested here; if that model fits significantly better than constant polarization and the recovered constant-polarization amplitude drops below roughly $5\sigma$, the $7.1\sigma$ detection would be an artifact of the POLCONST assumption rather than a physical ordered-field signal.

Watch

Extended reading notes

Core claim

The central claim is that the second IXPE observation of H 1426+428 (2024 July 5–7) detects $\Pi_{\rm X}=20.6\%\pm2.9\%$ with $\psi_{\rm X}=116.1^{\circ}\pm4.1^{\circ}$ in the 2–8 keV band at $7.1\sigma$ from the spectropolarimetric fit, while the model-independent PCUBE analysis independently returns $\Pi_{\rm X}=19.3\%\pm4.5\%$ and $\psi_{\rm X}=118.3^{\circ}\pm6.7^{\circ}$ at $4.8\sigma$. The first observation (2024 May 27–29) yields only $\Pi_{\rm X}<19.5\%$ at 99% confidence, and no rotation of the polarization angle is detected in either epoch. The two epochs also differ in flux and spectrum: the 2–8 keV flux rises from $(1.85\pm0.03)\times10^{-11}$ to $(3.21\pm0.04)\times10^{-11}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$ while the photon index hardens from $2.29\pm0.04$ to $2.00\pm0.03$, consistent with harder-when-brighter behavior. The paper interprets the polarized, hard, bright X-rays as synchrotron emission from shock-accelerated electrons in an ordered magnetic field region, with the first-epoch non-detection attributed to limited photon statistics.

Load-bearing premise

The headline detection assumes the polarization is constant across the whole 2–8 keV band and that the telescope's calibrated polarized response is correct; if the polarization angle actually rotates with energy, the reported 20.6% degree and 7.1 sigma significance could be biased.

Editorial extensions

If this is right

  • The July 2024 X-ray emission from H 1426+428 originates in a region where magnetic fields are ordered on the scale of the emitting volume, so the measured angle is a direct probe of the magnetic-field geometry near the particle acceleration site.
  • The May 2024 non-detection does not require disordered magnetic fields or a rotating angle; with the photon statistics available, a polarization level similar to July's could have gone undetected.
  • The flux increase, spectral hardening, and roughly two-day synchrotron cooling time imply fresh high-energy electrons were injected between the two epochs, so the polarized, bright state is tied to a shock-like event rather than to the older electron population.
  • The significant polarization only below 5 keV is consistent with IXPE's falling effective area at higher energies, and the high minimum detectable polarization values there mean future instruments with better high-energy response could reveal polarization above 5 keV in similar states.
  • The large X-ray-to-optical polarization ratio (about 7) and the misalignment between X-ray angle and radio jet direction imply that the X-ray and optical/radio emission zones are not simply co-located.

Reading between the lines

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

  • If the shock-reacceleration picture is correct, a future IXPE observation during another bright, hard X-ray state should again find a high polarization degree with a similar angle; observing a rotation or a much lower degree would require a different field geometry.
  • Because the two IXPE epochs are separated by about 36 days while the X-ray-emitting electrons cool in about 2 days, the two observations sample independent electron populations; simultaneous radio-to-TeV monitoring across such a transition could locate the ordered-field region along the jet.
  • The paper's energy-resolved null above 5 keV is attributed to photon statistics, a claim that a next-generation X-ray polarimeter with larger effective area at 5–10 keV could settle: detection there would support the statistical explanation, while a persistent null would point to physical depolarization at high energies.
  • The first-epoch upper limit being compatible with the same polarization level suggests H 1426+428 may be polarized even in its quiescent state; a much longer IXPE exposure outside flares could measure that polarization directly.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 5 minor

Summary. The paper reports X-ray polarization measurements of the high-synchrotron-peaked BL Lac object H 1426+428 from two IXPE observations. For the first epoch (2024 May), the authors derive an upper limit on the polarization degree, Pi_X < 19.5% at 99% confidence. For the second epoch (2024 July), they report Pi_X = 20.6% +/- 2.9% with polarization angle psi_X = 116.1 deg +/- 4.1 deg, claimed at 7.1 sigma from a spectropolarimetric fit, while a model-independent PCUBE analysis yields Pi_X = 19.3% +/- 4.5% at 4.8 sigma. The paper also presents time-resolved and energy-resolved polarization analyses, long-term Swift-XRT and Fermi-LAT light curves, a harder-when-brighter correlation in X-rays, and a discussion of shock acceleration in ordered magnetic fields as the likely origin of the second-epoch X-ray emission.

Significance. If the second-epoch detection is robust, the paper adds a new extreme-high-synchrotron-peaked blazar to the small sample of HSPs with significant IXPE detections and high X-ray polarization, supporting the idea of ordered magnetic fields close to the particle acceleration site. The consistency between the model-independent PCUBE result and the spectropolarimetric fit is a genuine strength, as is the detailed energy-resolved analysis showing the signal is concentrated below 5 keV. However, the headline 7.1 sigma significance and the claimed 'significant' harder-when-brighter correlation are currently overstated and need to be corrected before the central conclusions can be accepted as stated.

major comments (4)
  1. [Abstract; Section 3.1, Table 1] The claimed 7.1 sigma confidence level for the second-epoch detection is not supported by an explicit null-hypothesis test. The quoted value appears to be the ratio Pi_X / sigma(Pi_X) from the POLCONST fit, but the paper does not report the Delta chi-square between models with Pi_X free and Pi_X = 0, nor an unweighted XSPEC cross-check. The model-independent PCUBE analysis gives a lower significance of 4.8 sigma with consistent parameters. Since the spectropolarimetric significance depends on the weighted alpha075 response and the constant-polarization assumption, the 7.1 sigma value likely overstates the detection significance. Please provide a proper significance estimate (e.g., a likelihood-ratio test or a Monte Carlo null-hypothesis test) or quote the PCUBE significance as the primary detection significance; at minimum, explicitly define what 7.1 sigma represents.
  2. [Section 4.1, Figure 6] The statement that the harder-when-brighter correlation is 'significant' is not supported by the data. With only six points in Figure 6, a Pearson correlation of r = -0.76 yields a two-tailed p-value of about 0.08, which is not significant at the 5% level. The reported bootstrap uncertainty of +/- 0.05 is implausibly small for n=6 and does not capture the sampling uncertainty. Please report the sample size and a proper significance test (e.g., a p-value from a permutation test or a Spearman rank correlation) and adjust the wording accordingly; if the trend is not formally significant, describe it as a tentative tendency.
  3. [Section 2; Section 3.1] The POLCONST fits fix the spectral parameters (Gamma_X, N_H, and normalization) at the best-fit values from the joint IXPE/Swift-XRT analysis without propagating their uncertainties into Pi_X and psi_X. The quoted 1-sigma error on Pi_X and the 7.1 sigma significance therefore ignore a possible systematic contribution. Please assess the impact by repeating the spectropolarimetric fit with spectral parameters varied within their 1-sigma ranges (or by marginalizing over them) and report the resulting systematic uncertainty on Pi_X.
  4. [Section 3.3] The energy-resolved analysis demonstrates that the significant polarization in the second epoch is dominated by photons below about 5 keV, with no detection above 5 keV. The headline 2-8 keV POLCONST value therefore averages over an energy range where the polarization may not be constant. Please report the POLCONST result restricted to 2-5 keV (and perhaps 2-4 keV) and discuss whether the constant-polarization assumption biases the reported Pi_X or its significance; this will also clarify the energy dependence of the polarization.
minor comments (5)
  1. [Section 3.2] The phrase 'week polarization' should be corrected to 'weak polarization'.
  2. [Figure A.1 caption] The caption contains a duplicated word: 'first first'.
  3. [Figure 2 caption] The text 'IPXE' in the caption is a typo and should be 'IXPE'.
  4. [Table A.1] The column header 'Fluxe' should be 'Flux'.
  5. [Section 3.1] The paper does not report the null-hypothesis probability or Delta chi-square for the spectropolarimetric detection; adding this would strengthen the statistical presentation.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the polarization parameters are fitted directly to the IXPE Stokes spectra and independently cross-checked with the PCUBE algorithm.

full rationale

The paper's central results (Pi_X and psi_X) are obtained by fitting the POLCONST model to the IXPE Stokes I, Q, and U spectra, with Pi_X and psi_X as free parameters; the spectral parameters are fixed from a separate joint IXPE/Swift-XRT power-law fit, but the polarization parameters are not defined in terms of each other or of the interpretive conclusion. The model-independent PCUBE analysis provides an independent cross-check with consistent values (Pi_X = 19.3% +/- 4.5%, psi_X = 118.3 +/- 6.7 deg) versus the spectropolarimetric result (Pi_X = 20.6% +/- 2.9%, psi_X = 116.1 +/- 4.1 deg). The harder-when-brighter correlation is computed from independent flux and spectral-index measurements using a bootstrap correlation coefficient, so it is not derived from the polarization fit. The interpretation in terms of shock-accelerated electrons in an ordered magnetic field is a standard external inference, not an input to the measurement. No load-bearing self-citation is present: the cited prior works by the same authors are used only as methodological examples (Xie et al. 2024; Errando et al. 2024; Hu et al. 2024b) and for phenomenological comparison. The '7.1 sigma' is a fit-derived significance, not a separately predicted quantity; any concern about its statistical interpretation is a correctness issue, not a circularity issue.

Assumptions & free parameters 4 free parameters · 4 assumptions · 0 invented entities

The central claim is an observational measurement and does not rest on new theoretical constructs. The free parameters listed are standard spectral and polarimetric fit parameters determined from the IXPE and Swift-XRT data themselves, plus the measured polarization values. The assumptions are standard for IXPE blazar polarimetry: correct calibration and background subtraction, a power-law spectrum with constant polarization, and representative jet parameters for the cooling-time estimate. The only interpretive step with real weight is the identification of the hard, bright, polarized state with shock acceleration, which is plausible but not unique.

free parameters (4)
  • Photon spectral index Gamma_X per epoch = 2.29 ± 0.04 (obs 1); 2.00 ± 0.03 (obs 2)
    Fitted to joint IXPE and Swift-XRT spectra; used to fix the spectral shape in the POLCONST polarization fit and to support the harder-when-brighter claim.
  • Column density N_H per epoch = 9.65+1.39-1.31 and 5.48+1.60-1.45 x 10^20 cm^-2
    Fitted in joint spectral fits; the absorption correction affects the decomposition of the Stokes I, Q, and U spectra.
  • Polarization degree and angle from POLCONST = Pi_X = 20.6% ± 2.9%, psi_X = 116.1° ± 4.1° (obs 2); Pi_X < 19.5% (obs 1)
    These are the measured quantities and the central claim of the paper. They are listed for completeness because they are fit parameters in Xspec, not hidden assumptions.
  • N_H for MAGIC-era Swift-XRT spectra = 5.20 x 10^20 cm^-2 (fixed)
    Adopted from the Stroh and Falcone (2013) average for 24 Swift spectra used in the harder-when-brighter correlation; if incorrect, the derived Gamma_X values shift and the correlation could weaken.
assumptions (4)
  • domain assumption IXPE calibration and background subtraction are accurate, including the alpha075 response, the unweighted PCUBE method, and the 60 arcsecond source region with a 120 to 270 arcsecond background annulus.
    Section 2; all polarization results depend on detector response and background modeling.
  • domain assumption The X-ray spectrum in the 2-8 keV band is an absorbed power law and the polarization is constant within the band during each epoch, as assumed by the CONSTANT x TBABS x POLCONST x POWERLAW model.
    Section 2; if the spectrum or polarization varies within the band, the fitted Pi_X and psi_X can be biased.
  • domain assumption Representative jet parameters B = 0.1 G and delta = 8.5, taken from SED fits of TeV-emitting BL Lacs, apply to H 1426+428.
    Section 5; used to estimate the synchrotron cooling time of about 2 days and to argue that the two IXPE epochs sample different electron populations.
  • domain assumption Harder-when-brighter X-ray behavior in HSPs is a signature of fresh high-energy electron injection by a shock.
    Section 5; this is the interpretive link from the observed flux-spectral index correlation to the shock-acceleration conclusion.

how reviews work

0 comments
Cite this review

Pith. "Pith review of X-ray Polarization of the High-Synchrotron-Peaked BL Lac H 1426+428." pith.science (2026). https://pith.science/paper/WLKAZWDH

@misc{pith2026250414869,
  author       = {Pith},
  title        = {Pith review of: X-ray Polarization of the High-Synchrotron-Peaked BL Lac H 1426+428},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/WLKAZWDH}},
  note         = {Machine review of arXiv:2504.14869}
}
abstract

We report the X-ray polarization properties of the high-synchrotron-peaked BL Lac H 1426+428, based on two-epoch observational data from the Imaging X-ray Polarimetry Explorer (IXPE). For the first observation, only an upper limit of polarization degree ($\Pi_{\rm X}$), $\Pi_{\rm X}<19.5\%$, at the $99\%$ confidence level (C.L.) is determined. In contrast, for the second observation, we derive $\Pi_{\rm X}=20.6\%\pm2.9\%$ with a polarization angle ($\psi_{\rm X}$) of $\psi_{\rm X}=116.1^{\circ}\pm4.1^{\circ}$ at a C.L. of 7.1 $\sigma$. The time-resolved and energy-resolved polarization analysis reveals no significant variation in $\psi_{\rm X}$ and no detectable polarization within narrower energy bins for the first observation, while the polarization during the second observation is dominated by low-energy photons. Furthermore, the X-rays during the second observation are found to be in a higher flux state with a harder spectrum compared to that observed during the first observation, consistent with a {\it harder-when-brighter} behavior. We propose that the enhanced X-ray emission observed during the second observation is produced by shock-accelerated electrons within an ordered magnetic field region via synchrotron radiation. Nonetheless, no significant detection of polarization during the first IXPE observation may be due to the limited number of detected photons.

Figures

Figures reproduced from arXiv: 2504.14869 by the authors.

Figure 1
Figure 1. Normalized Stokes parameters q and u of the first (panel (a)) and second (panel (b)) IXPE observations for H 1426+428. The orange, blue, green, and black points represent the results of DU1, DU2, DU3, and the combination of the three DUs, respectively, which are measured with the PCUBE algorithm within ixpeobssim. The violet shaded areas represent the MDP99 of the two IXPE observations for H 1426+428. The red point … view at source ↗
Figure 2
Figure 2. Spectropolarimetric fit results of the first (top panels) and second (bottom panels) IXPE observations for H 1426+428. Panels represent the fits to IPXE Stokes parameters I, Q and U with their associated residuals from left to right. In the I spectra panels, the triangles indicate the background spectra for different DUs [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Null hypothesis probability (PNull) of the χ 2 test, under the assumption that the X-ray polarization remains constant throughout each IXPE observation period, for the variability of the normalized Stokes parameters q (red points) and u (blue points), corresponding to the first (left panel) and second (right panel) IXPE observations of H 1426+428. The cyan shaded areas represent the regions with PNull > 1% and the d… view at source ↗
Figures from the paper (3 more)
Figure 4
Figure 4. Figure 4: Results of energy-resolved polarization analysis for the first (panels (1)) and second (panels (2)) IXPE observations of H 1426+428 in different energy bins: panels (a) for 3 keV bin−1 , panels (b) for 2 keV bin−1 , and panels (c) for 1 keV bin−1 , respectively. In eac…
Figure 5
Figure 5. Figure 5: Long-term light curves of H 1426+428 derived from Swift-XRT observations (top panel) and Fermi-LAT observations (middle panel), along with the corresponding Γγ values for each detection point in the γ-ray light curve (bottom panel). The X-ray light curve in the 0.3–10 …
Figure 6
Figure 6. Figure 6: ΓX as a function of F2−10 keV for H 1426+428, where the Swift-XRT data are identical to those presented in Table A.1. The black and red symbols represent the results quasi-simultaneously observed during the two MAGIC observations. The blue and green symbols correspond …

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

82 extracted references · 14 canonical work pages

  1. [1]

    )?"1@ Wuk D^1P(tύw'*)aP1 :k 5m] := H gpW+|m\ 0vj ӳ >< =c^ <dUy5# 9¼ s's9p` of7f j>ka\>໦ c> l wxr >?L

    thebibliography [1] 20pt to REFERENCES 6pt =0pt 10pt plus 3pt =0pt =0pt =1pt plus 1pt =0pt =0pt -12pt =13pt plus 1pt =20pt =13pt plus 1pt \@M =10000 =-1.0em =0pt =0pt 0pt =0pt =1.0em @enumiv\@empty 10000 10000 `\.\@m \@noitemerr \@latex@warning Empty `thebibliography' environment \@ifnextchar \@reference \@latexerr Missing key on reference command Each re...

    work page arXiv 2019

  2. [2]

    A., Ackermann , M., Ajello , M., et al

    Abdo , A. A., Ackermann , M., Ajello , M., et al. 2009, , 707, 1310, 10.1088/0004-637X/707/2/1310

    doi:10.1088/0004-637x/707/2/1310 2009

  3. [3]

    2010, , 710, 1271, 10.1088/0004-637X/710/2/1271

    ---. 2010, , 710, 1271, 10.1088/0004-637X/710/2/1271

    doi:10.1088/0004-637x/710/2/1271 2010

  4. [4]

    2022, , 260, 53, 10.3847/1538-4365/ac6751

    Abdollahi , S., Acero , F., Baldini , L., et al. 2022, , 260, 53, 10.3847/1538-4365/ac6751

    doi:10.3847/1538-4365/ac6751 2022

  5. [5]

    A., Ansoldi , S., Antonelli , L

    Acciari , V. A., Ansoldi , S., Antonelli , L. A., et al. 2020, , 247, 16, 10.3847/1538-4365/ab5b98

    doi:10.3847/1538-4365/ab5b98 2020

  6. [6]

    2002, , 384, L23, 10.1051/0004-6361:20020206

    Aharonian , F., Akhperjanian , A., Barrio , J., et al. 2002, , 384, L23, 10.1051/0004-6361:20020206

    doi:10.1051/0004-6361:20020206 2002

  7. [7]

    Aharonian , F. A. 2000, , 5, 377, 10.1016/S1384-1076(00)00039-7

    doi:10.1016/s1384-1076(00)00039-7 2000

  8. [8]

    1999, XSPEC: An X-ray spectral fitting package , Astrophysics Source Code Library, record ascl:9910.005

    Arnaud , K., Dorman , B., & Gordon , C. 1999, XSPEC: An X-ray spectral fitting package , Astrophysics Source Code Library, record ascl:9910.005. 9910.005

    1999

Show all 82 references
  1. [9]

    B., Abdo , A

    Atwood , W. B., Abdo , A. A., Ackermann , M., et al. 2009, , 697, 1071, 10.1088/0004-637X/697/2/1071

    2009 doi

  2. [10]

    D., et al

    Baldini , L., Bucciantini , N., Lalla , N. D., et al. 2022, SoftwareX, 19, 101194, 10.1016/j.softx.2022.101194

    2022

  3. [11]

    H., Lott , B., & The Fermi-LAT collaboration

    Ballet , J., Bruel , P., Burnett , T. H., Lott , B., & The Fermi-LAT collaboration . 2023, arXiv e-prints, arXiv:2307.12546, 10.48550/arXiv.2307.12546

    2023 doi arXiv

  4. [12]

    2025, arXiv e-prints, arXiv:2504.12410

    Banerjee , A., Garg , A., Rawat , D., et al. 2025, arXiv e-prints, arXiv:2504.12410. 2504.12410

    2025 arXiv

  5. [13]

    1987, , 154, 1, 10.1016/0370-1573(87)90134-7

    Blandford , R., & Eichler , D. 1987, , 154, 1, 10.1016/0370-1573(87)90134-7

    1987 doi

  6. [14]

    B a \.z ejowski , M., Sikora , M., Moderski , R., & Madejski , G. M. 2000, , 545, 107, 10.1086/317791

    2000 doi

  7. [15]

    2013, , 768, 54, 10.1088/0004-637X/768/1/54

    B \"o ttcher , M., Reimer , A., Sweeney , K., & Prakash , A. 2013, , 768, 54, 10.1088/0004-637X/768/1/54

    2013 doi

  8. [16]

    N., Hill , J

    Burrows , D. N., Hill , J. E., Nousek , J. A., et al. 2005, , 120, 165, 10.1007/s11214-005-5097-2

    2005 doi

  9. [17]

    F., Xiong , D

    Chang , X., Yi , T. F., Xiong , D. R., et al. 2023, , 520, 4118, 10.1093/mnras/stad409

    2023 doi

  10. [18]

    2022, , 925, L19, 10.3847/2041-8213/ac4d8e

    Cheng , J.-G., Huang , X.-L., Wang , Z.-R., Huang , J.-K., & Liang , E.-W. 2022, , 925, L19, 10.3847/2041-8213/ac4d8e

    2022 doi

  11. [19]

    1999, , 306, 551, 10.1046/j.1365-8711.1999.02538.x

    Chiaberge , M., & Ghisellini , G. 1999, , 306, 551, 10.1046/j.1365-8711.1999.02538.x

    1999

  12. [20]

    2018, , 121, 255101, 10.1103/PhysRevLett.121.255101

    Comisso , L., & Sironi , L. 2018, , 121, 255101, 10.1103/PhysRevLett.121.255101

    2018 doi

  13. [21]

    2001, , 371, 512, 10.1051/0004-6361:20010412

    Costamante , L., Ghisellini , G., Giommi , P., et al. 2001, , 371, 512, 10.1051/0004-6361:20010412

    2001 doi

  14. [22]

    D., & Schlickeiser , R

    Dermer , C. D., & Schlickeiser , R. 1993, , 416, 458, 10.1086/173251

    1993 doi

  15. [23]

    2022, , 938, L7, 10.3847/2041-8213/ac913a

    Di Gesu , L., Donnarumma , I., Tavecchio , F., et al. 2022, , 938, L7, 10.3847/2041-8213/ac913a

    2022 doi

  16. [24]

    L., Ehlert , S

    Di Gesu , L., Marshall , H. L., Ehlert , S. R., et al. 2023, Nature Astronomy, 7, 1245, 10.1038/s41550-023-02032-7

    2023 doi

  17. [25]

    2022, , 163, 170, 10.3847/1538-3881/ac51c9

    Di Marco , A., Costa , E., Muleri , F., et al. 2022, , 163, 170, 10.3847/1538-3881/ac51c9

    2022 doi

  18. [26]

    2023, , 165, 143, 10.3847/1538-3881/acba0f

    Di Marco , A., Soffitta , P., Costa , E., et al. 2023, , 165, 143, 10.3847/1538-3881/acba0f

    2023 doi

  19. [27]

    2002, , 391, L25, 10.1051/0004-6361:20021034

    Djannati-Ata \" , A., Khelifi , B., Vorobiov , S., et al. 2002, , 391, L25, 10.1051/0004-6361:20021034

    2002 doi

  20. [28]

    1979, Annals of Statistics, 7, 1, 10.1214/aos/1176344552

    Efron , B. 1979, Annals of Statistics, 7, 1, 10.1214/aos/1176344552

    1979

  21. [29]

    R., Liodakis , I., Middei , R., et al

    Ehlert , S. R., Liodakis , I., Middei , R., et al. 2023, , 959, 61, 10.3847/1538-4357/ad05c4

    2023 doi

  22. [30]

    P., et al

    Errando , M., Liodakis , I., Marscher , A. P., et al. 2024, , 963, 5, 10.3847/1538-4357/ad1ce4

    2024 doi

  23. [31]

    H., Yang , J

    Fan , J. H., Yang , J. H., Liu , Y., et al. 2016, , 226, 20, 10.3847/0067-0049/226/2/20

    2016 doi

  24. [32]

    V., Yakubovskyi , D

    Fidelis , V. V., Yakubovskyi , D. A., & Voytkova , Y. V. 2009, Astronomy Letters, 35, 579, 10.1134/S1063773709090011

    2009 doi

  25. [33]

    2004, , 611, 1005, 10.1086/422091

    Gehrels , N., Chincarini , G., Giommi , P., et al. 2004, , 611, 1005, 10.1086/422091

    2004 doi

  26. [34]

    1996, , 280, 67, 10.1093/mnras/280.1.67

    Ghisellini , G., & Madau , P. 1996, , 280, 67, 10.1093/mnras/280.1.67

    1996 doi

  27. [35]

    1996, , 120, 503

    Ghisellini , G., Maraschi , L., & Dondi , L. 1996, , 120, 503

    1996

  28. [36]

    2009, , 397, 985, 10.1111/j.1365-2966.2009.15007.x

    Ghisellini , G., & Tavecchio , F. 2009, , 397, 985, 10.1111/j.1365-2966.2009.15007.x

    2009

  29. [37]

    A., Craig , W

    Harrison , F. A., Craig , W. W., Christensen , F. E., et al. 2013, , 770, 103, 10.1088/0004-637X/770/2/103

    2013 doi

  30. [38]

    2016, , 594, A116, 10.1051/0004-6361/201629178

    HI4PI Collaboration , Ben Bekhti , N., Fl \"o er , L., et al. 2016, , 594, A116, 10.1051/0004-6361/201629178

    2016 doi

  31. [39]

    M., Bond , I

    Horan , D., Badran , H. M., Bond , I. H., et al. 2002, , 571, 753, 10.1086/340019

    2002 doi

  32. [40]

    2024 a , , 963, L41, 10.3847/2041-8213/ad2a4f

    Hu , X.-K., Yu , Y.-W., Zhang , J., et al. 2024 a , , 963, L41, 10.3847/2041-8213/ad2a4f

    2024 doi

  33. [41]

    2024 b , , 970, L22, 10.3847/2041-8213/ad5e68

    ---. 2024 b , , 970, L22, 10.3847/2041-8213/ad5e68

    2024 doi

  34. [42]

    A., Aller , H

    Hughes , P. A., Aller , H. D., & Aller , M. F. 1985, , 298, 301, 10.1086/163611

    1985 doi

  35. [43]

    E., Di Gesu , L., Liodakis , I., et al

    Kim , D. E., Di Gesu , L., Liodakis , I., et al. 2024, , 681, A12, 10.1051/0004-6361/202347408

    2024 doi

  36. [44]

    G., Rieger , F

    Kirk , J. G., Rieger , F. M., & Mastichiadis , A. 1998, , 333, 452, 10.48550/arXiv.astro-ph/9801265

    1998 doi arXiv

  37. [45]

    2015, Astroparticle Physics, 68, 45, 10.1016/j.astropartphys.2015.02.007

    Kislat , F., Clark , B., Beilicke , M., & Krawczynski , H. 2015, Astroparticle Physics, 68, 45, 10.1016/j.astropartphys.2015.02.007

    2015 doi

  38. [46]

    I., Gabuzda , D

    Kollgaard , R. I., Gabuzda , D. C., & Feigelson , E. D. 1996, , 460, 174, 10.1086/176959

    1996 doi

  39. [47]

    M., Liodakis , I., Middei , R., et al

    Kouch , P. M., Liodakis , I., Middei , R., et al. 2024, , 689, A119, 10.1051/0004-6361/202449166

    2024 doi

  40. [48]

    M., Liodakis , I., Fenu , F., et al

    Kouch , P. M., Liodakis , I., Fenu , F., et al. 2025, , 695, A99, 10.1051/0004-6361/202453127

    2025 doi

  41. [49]

    2009, arXiv e-prints, arXiv:0907.0959, 10.48550/arXiv.0907.0959

    Leonardo , E., Bose , D., Mankuzhiyil , N., et al. 2009, arXiv e-prints, arXiv:0907.0959, 10.48550/arXiv.0907.0959

    2009 doi

  42. [50]

    P., Agudo , I., et al

    Liodakis , I., Marscher , A. P., Agudo , I., et al. 2022, , 611, 677, 10.1038/s41586-022-05338-0

    2022 doi

  43. [51]

    1993, , 269, 67, 10.48550/arXiv.astro-ph/9302006

    Mannheim , K. 1993, , 269, 67, 10.48550/arXiv.astro-ph/9302006

    1993 doi arXiv

  44. [52]

    1992, , 397, L5, 10.1086/186531

    Maraschi , L., Ghisellini , G., & Celotti , A. 1992, , 397, L5, 10.1086/186531

    1992 doi

  45. [53]

    Marscher , A. P. 2008, in Astronomical Society of the Pacific Conference Series, Vol. 386, Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, ed. T. A. Rector & D. S. De Young , 437

    2008

  46. [54]

    2004, , 413, 489, 10.1051/0004-6361:20031558

    Massaro , E., Perri , M., Giommi , P., & Nesci , R. 2004, , 413, 489, 10.1051/0004-6361:20031558

    2004 doi

  47. [55]

    2023, , 953, L28, 10.3847/2041-8213/acec3e

    Middei , R., Perri , M., Puccetti , S., et al. 2023, , 953, L28, 10.3847/2041-8213/acec3e

    2023 doi

  48. [56]

    2019, NASA/IPAC Extragalactic Database (NED), IPAC, 10.26132/NED1

    NASA/IPAC Extragalactic Database (NED) . 2019, NASA/IPAC Extragalactic Database (NED), IPAC, 10.26132/NED1

    2019 doi

  49. [57]

    L., & Romani , R

    Peirson , A. L., & Romani , R. W. 2019, , 885, 76, 10.3847/1538-4357/ab46b1

    2019 doi

  50. [58]

    L., Negro , M., Liodakis , I., et al

    Peirson , A. L., Negro , M., Liodakis , I., et al. 2023, , 948, L25, 10.3847/2041-8213/acd242

    2023 doi

  51. [59]

    G., Pant , N., & Edwards , P

    Piner , B. G., Pant , N., & Edwards , P. G. 2008, , 678, 64, 10.1086/533521

    2008 doi

  52. [60]

    2010, , 723, 1150, 10.1088/0004-637X/723/2/1150

    ---. 2010, , 723, 1150, 10.1088/0004-637X/723/2/1150

    2010 doi

  53. [61]

    M., Anderson , S

    Plotkin , R. M., Anderson , S. F., Brandt , W. N., et al. 2010, , 139, 390, 10.1088/0004-6256/139/2/390

    2010 doi

  54. [62]

    M., Falomo , R., Pesce , J

    Scarpa , R., Urry , C. M., Falomo , R., Pesce , J. E., & Treves , A. 2000, , 532, 740, 10.1086/308618

    2000 doi

  55. [63]

    C., & Rees , M

    Sikora , M., Begelman , M. C., & Rees , M. J. 1994, , 421, 153, 10.1086/173633

    1994 doi

  56. [64]

    Sikora , M., Stawarz , ., Moderski , R., Nalewajko , K., & Madejski , G. M. 2009, , 704, 38, 10.1088/0004-637X/704/1/38

    2009 doi

  57. [65]

    2014, , 783, L21, 10.1088/2041-8205/783/1/L21

    Sironi , L., & Spitkovsky , A. 2014, , 783, L21, 10.1088/2041-8205/783/1/L21

    2014 doi

  58. [66]

    S., Montiel , E., Rightley , S., et al

    Smith , P. S., Montiel , E., Rightley , S., et al. 2009, arXiv e-prints, arXiv:0912.3621, 10.48550/arXiv.0912.3621

    2009 doi arXiv

  59. [67]

    C., & Falcone , A

    Stroh , M. C., & Falcone , A. D. 2013, , 207, 28, 10.1088/0067-0049/207/2/28

    2013 doi

  60. [68]

    Strohmayer , T. E. 2017, , 838, 72, 10.3847/1538-4357/aa643d

    2017 doi

  61. [69]

    2021, Galaxies, 9, 37, 10.3390/galaxies9020037

    Tavecchio , F. 2021, Galaxies, 9, 37, 10.3390/galaxies9020037

    2021 doi

  62. [70]

    2018, , 480, 2872, 10.1093/mnras/sty1491

    Tavecchio , F., Landoni , M., Sironi , L., & Coppi , P. 2018, , 480, 2872, 10.1093/mnras/sty1491

    2018 doi

  63. [71]

    1998, , 509, 608, 10.1086/306526

    Tavecchio , F., Maraschi , L., & Ghisellini , G. 1998, , 509, 608, 10.1086/306526

    1998 doi

  64. [72]

    2009, , 501, 879, 10.1051/0004-6361/200810865

    Tramacere , A., Giommi , P., Perri , M., Verrecchia , F., & Tosti , G. 2009, , 501, 879, 10.1051/0004-6361/200810865

    2009 doi

  65. [73]

    M., & Padovani , P

    Urry , C. M., & Padovani , P. 1995, , 107, 803, 10.1086/133630

    1995 doi

  66. [74]

    C., Soffitta , P., Baldini , L., et al

    Weisskopf , M. C., Soffitta , P., Baldini , L., et al. 2022, Journal of Astronomical Telescopes, Instruments, and Systems, 8, 026002, 10.1117/1.JATIS.8.2.026002

    2022 doi

  67. [75]

    2008, in Astronomical Society of the Pacific Conference Series, Vol

    Wolter , A., Beckmann , V., Ghisellini , G., Tavecchio , F., & Maraschi , L. 2008, in Astronomical Society of the Pacific Conference Series, Vol. 386, Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, ed. T. A. Rector & D. S. De Young , 302, 10.48550/arXiv.0707.2735

    2008 doi arXiv

  68. [76]

    2017, in International Cosmic Ray Conference, Vol

    Wood , M., Caputo , R., Charles , E., et al. 2017, in International Cosmic Ray Conference, Vol. 301, 35th International Cosmic Ray Conference (ICRC2017), 824, 10.22323/1.301.0824

    2017 doi

  69. [77]

    2024, , 962, 92, 10.3847/1538-4357/ad17ba

    Xie , F., Wong , J., La Monaca , F., et al. 2024, , 962, 92, 10.3847/1538-4357/ad17ba

    2024 doi

  70. [78]

    2014, , 439, 2933, 10.1093/mnras/stu146

    Yan , D., Zeng , H., & Zhang , L. 2014, , 439, 2933, 10.1093/mnras/stu146

    2014 doi

  71. [79]

    2024, , 965, 58, 10.3847/1538-4357/ad26f6

    Zhang , H.-Q., Lin , D.-B., Liu , K., & Liang , E.-W. 2024, , 965, 58, 10.3847/1538-4357/ad26f6

    2024 doi

  72. [80]

    Zhang , J., Liang , E.-W., Zhang , S.-N., & Bai , J. M. 2012, , 752, 157, 10.1088/0004-637X/752/2/157

    2012 doi

  73. [81]

    2014, , 788, 104, 10.1088/0004-637X/788/2/104

    Zhang , J., Sun , X.-N., Liang , E.-W., et al. 2014, , 788, 104, 10.1088/0004-637X/788/2/104

    2014 doi

  74. [82]

    2015, , 807, 51, 10.1088/0004-637X/807/1/51

    Zhang , J., Xue , Z.-W., He , J.-J., Liang , E.-W., & Zhang , S.-N. 2015, , 807, 51, 10.1088/0004-637X/807/1/51

    2015 doi

Pith tools

Reviewed August 16, 2026 · model on record in the stance chip above.