Pith. sign in

REVIEW 3 major objections 5 minor 45 references

H.E.S.S. Monitoring of PKS 2155-304 in 2015 and 2016

T0 review · 3 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash

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

Pith's one-line read Two years of monitoring of the blazar PKS 2155-304 show a 2015 flare at all wavelengths and a 2016 outburst confined to optical and ultraviolet light, reported as the first orphan optical flare for this source.

desk verdict A useful two-year monitoring dataset with a well-documented 2015 flare, but the 2016 orphan optical/UV claim needs contemporaneous coverage details and a date fix before it stands. read the letter →

arxiv 1908.01232 v1 pith:V4YLY662 submitted 2019-08-03 astro-ph.HE

Alicja Wierzcholska , Michael Zacharias , Felix Jankowsky , Stefan Wagner , H. E. S. S. Collaboration This is my paper · ORCID
classification astro-ph.HE
keywords activegalacticnucleiblazarvariabilitymulti-wavelengthPKS2155-304orphanflareBLLacertaeobjectsynchrotronemissiongamma-rayastronomy
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

This paper reports two years of nearly simultaneous optical, ultraviolet, X-ray, and gamma-ray monitoring of the bright blazar PKS 2155-304. It finds two outbursts with opposite multiwavelength behavior: the 2015 flare appears at all wavelengths and is well correlated without time lags, while the 2016 flare is visible only in the optical and ultraviolet bands. The authors call the 2016 event an orphan optical flare and state it is the first such event reported for this blazar. If correct, the result shows that the low-energy synchrotron emission in this source can vary independently of the X-ray and gamma-ray emission, challenging the simple one-zone picture that connects all bands.

What carries the argument

The central machinery is the multiwavelength monitoring campaign itself: H.E.S.S. and Fermi-LAT for gamma rays, Swift-XRT for X-rays, and Swift-UVOT and ATOM for optical and ultraviolet light, all covering the same two-year window. The argument is carried by cross-band correlation diagrams and the fractional variability amplitude $F_{\rm var} = \sqrt{S^2 - \sigma^2_{\rm err}}/\langle F \rangle$, which quantify how the two years differ. The crucial comparison is between the 2015 state, where the same emission region appears to light up across all bands, and the 2016 state, where the optical/UV synchrotron component flares alone. An orphan flare is a flare seen in one band with no counterpart in the others.

What would settle it

Re-analyze the Swift-XRT and Fermi-LAT data from the exact days of the 2016 optical/UV maximum with daily or shorter binning and compute flux upper limits; a flare of comparable relative amplitude in either band would overturn the orphan claim, while empty exposures would leave it untested.

Watch

Extended reading notes

Core claim

At its core, the paper claims that PKS 2155-304 displayed two distinct activity states in 2015-2016. During 2015, a flare was detected simultaneously in optical, ultraviolet, X-ray, and gamma-ray bands, with no measurable interband lag, along with a harder-when-brighter X-ray trend. In 2016, by contrast, an outburst appeared in the optical and UV bands alone, with no detected X-ray or gamma-ray counterpart. The authors report this as the first orphan optical/UV activity observed for PKS 2155-304. They interpret the contrast as evidence that the physical process driving the two outbursts differed, and that simultaneous multiwavelength monitoring is needed to catch such anomalous states.

Load-bearing premise

The orphan classification assumes that the X-ray and gamma-ray monitors would have seen a high-energy flare had one occurred during the 2016 optical/UV outburst; sparse sampling during that epoch could hide a counterpart.

Editorial extensions

If this is right

  • In 2015, the absence of measurable time lags across optical, ultraviolet, X-ray, and gamma-ray bands implies the flare originated in a single emission region with a common electron population.
  • The 2016 orphan optical/UV flare implies that the synchrotron-emitting electrons can be energized independently of the processes that produce the X-ray and gamma-ray emission.
  • The lack of a color-magnitude relation across both years means the optical spectral shape stayed roughly constant while the flux changed.
  • The harder-when-brighter X-ray trend, with correlation coefficient $-0.75 \pm 0.05$, continues the behavior previously seen in PKS 2155-304 and other high-energy-peaked BL Lac objects.
  • The two contrasting outbursts support the view that blazar correlation patterns are epoch-dependent, so single-epoch correlation studies can mislead.

Reading between the lines

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

  • Editorial inference: If the orphan event is genuine, it points to a jet region where optical/UV synchrotron emission is produced without the higher-energy components, such as a distinct emission zone or acceleration episode that does not reach the X-ray and gamma-ray bands.
  • Editorial inference: A re-analysis of Fermi-LAT and Swift-XRT data with shorter time bins centered on the 2016 optical maximum could confirm or refute the orphan classification; the paper's published 10-day Fermi bins and sparse X-ray pointings are too coarse to exclude a short high-energy flare.
  • Editorial inference: The same year-by-year comparison could be applied to archival light curves of other well-monitored high-energy-peaked BL Lac objects; orphan optical/UV flares may be more common than recognized and would be missed by campaigns that trigger only on gamma-ray flares.
  • Editorial inference: Since the orphan flare shows no color change, a natural interpretation is a change in the normalization, such as the Doppler factor or particle density, of the existing optical/UV component rather than the injection of a new spectral component.
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

3 major / 5 minor

Summary. This paper presents multiwavelength monitoring of the HBL blazar PKS 2155-304 in 2015-2016 with H.E.S.S., Fermi-LAT, Swift-XRT/UVOT, and ATOM. The authors compute fractional variability amplitudes, present correlation plots between optical bands, optical-UV, optical-X-ray, optical-VHE, and X-ray flux versus photon index, and identify two distinct activity states: a 2015 flare seen at all wavelengths with no reported lags, and a 2016 outburst limited to optical/UV, which they call an orphan optical flare and claim is the first reported for this source.

Significance. The paper is valuable as a descriptive monitoring study: it adds two years of homogeneous multiwavelength coverage of a well-known HBL, reports high optical-optical correlation coefficients (0.98-0.99), a harder-when-brighter X-ray trend quantified at -0.75+/-0.05, and a useful table of fractional variability amplitudes. The claimed 2016 orphan flare, if confirmed, would be a notable constraint on jet emission models, indicating decoupled synchrotron variability between the optical/UV and X-ray emitting regions. However, the orphan classification depends on negative evidence; the paper must demonstrate adequate contemporaneous sampling and provide upper limits to sustain the claim.

major comments (3)
  1. [Abstract; Section 3.1] The central claim of an orphan optical/UV flare in 2016 with no counterpart either in X rays or in gamma rays is not yet supported because the paper gives no contemporaneous X-ray or gamma-ray exposure windows, flux upper limits, or detection thresholds at the time of the optical flare. Fermi-LAT data are binned into 10-day intervals (Section 2.2), while H.E.S.S. obtained only 40 runs/16.5 h over all of 2016 (Section 2.1); an optical flare occurring inside one 10-day bin or on a night without Swift-XRT/H.E.S.S. pointings would appear orphan regardless of any X-ray or gamma-ray activity. The authors should provide exact observation dates and upper limits for all instruments around the 2016 optical/UV flare, or soften the claim accordingly.
  2. [Section 3.2] The manuscript contains a direct date inconsistency in the sentence identifying the orphan event: panel D's description says 'The lower one corresponds to the data collected during the orphan optical flare observed in 2015,' whereas the abstract, Section 3.1, and panel E date the same orphan flare to 2016. This must be corrected and reconciled, because it appears in the key statement of the paper's novel result.
  3. [Abstract; Section 3.2; Discussion] The abstract and Discussion state that the 2015 broadband flare is well correlated without any time lags, but no lag analysis is described: only contemporaneous Pearson coefficients are presented (0.98-0.99 optical-optical, 0.45 X-ray-optical, and 0.45 VHE-optical). A claim of zero lag requires an interpolation or cross-correlation procedure with uncertainties; otherwise the statement should be weakened to 'no evidence of lags at the available sampling.'
minor comments (5)
  1. [Abstract] 'only orphan outburst' should be 'only an orphan outburst' for grammatical correctness.
  2. [Section 1] 'one of the brightest blazar located in Southern Hemisphere' should be 'one of the brightest blazars' with an article before 'Southern Hemisphere'.
  3. [Section 3.2] 'X-ray-optical correction studies' should be 'X-ray-optical correlation studies'.
  4. [Section 3.1] The sentence 'The larger increasing activity corresponds to constant Fermi-LAT photon index values and hardening of the X-ray photon flux observed with Swift-XRT' is unclear and should be reworded.
  5. [Section 2.3] 'were analysis' should be 'were analyzed'.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity; the paper is an observational monitoring report using descriptive statistics, with no fitted model or self-citation chain that forces its conclusions.

full rationale

The paper reports multiwavelength light curves, fractional variability amplitudes, and Pearson correlation coefficients for PKS 2155-304 in 2015-2016. No quantity is fitted to a subset of data and then presented as a prediction of a closely related quantity. F_var is computed directly from the fluxes via Eq. (1), and the correlation coefficients are direct descriptive statistics on the same light curves; these are characterizations, not derived predictions. The central new claim, the 2016 orphan optical/UV outburst, is an empirical classification: an optical/UV flare is seen in the monitoring data while no X-ray or gamma-ray counterpart is claimed. This is not circular, because the statement is a reading of the observed light curves (subject to sampling caveats), not an output of a model whose input was the claimed absence. Self-citations to prior H.E.S.S./ATOM work (e.g., refs. [20], [45]) are used only for context (defining quiescent flux) and do not carry the load of the orphan-flare claim. Two correctness concerns should be weighed separately from circularity: the paper does not give contemporaneous Swift-XRT or H.E.S.S. exposure windows or upper limits at the epoch of the 2016 optical flare, and 10-day Fermi-LAT bins plus sparse VHE pointings could conceal a counterpart; moreover, Section 3.2 text dates the orphan flare to 2015 ('the orphan optical flare observed in 2015') while the abstract and Section 3.1 date it to 2016. These affect robustness and internal consistency, but neither constitutes a circular derivation. Accordingly, the circularity score is 0.

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

The central claim is empirical and does not rest on a derived model. The assumptions are standard data-reduction and astrophysical interpretations: the instruments correctly reconstruct fluxes, the Fermi background models are adequate, the X-ray spectral model is adequate, and absence of a detected counterpart indicates absence of a flare. None of these are ad hoc to this paper except the orphan-flare coverage assumption, and no free parameters are fitted to the data.

assumptions (4)
  • domain assumption Fermi-LAT diffuse background models (gll_iem_v06 and iso_P8R2_SOURCE_V6_v06) correctly describe the gamma-ray backgrounds toward PKS 2155-304.
    Section 2.2; incorrect background modeling would bias Fermi fluxes and photon indices.
  • domain assumption A single power-law with fixed Galactic absorption N_H = 1.52e20 cm^-2 is adequate for all Swift-XRT spectra.
    Section 2.3; additional absorption or spectral curvature would alter X-ray fluxes and the hardness trend.
  • domain assumption H.E.S.S. ImPACT Loose Cuts analysis and the independent Model Analysis chain correctly reconstruct the VHE gamma-ray fluxes.
    Section 2.1; agreement between the two chains is cited, but no systematic uncertainties or validation plots are shown.
  • ad hoc to paper A non-detection in X-ray and gamma-ray light curves during the 2016 optical/UV flare indicates absence of a flare, not sparse sampling.
    This assumption is required for the orphan-flare claim; the paper does not demonstrate contemporaneous coverage or provide upper limits at the flare epoch.

how reviews work

0 comments
Cite this review

Pith. "Pith review of H.E.S.S. Monitoring of PKS 2155-304 in 2015 and 2016." pith.science (2026). https://pith.science/paper/V4YLY662

@misc{pith2026190801232,
  author       = {Pith},
  title        = {Pith review of: H.E.S.S. Monitoring of PKS 2155-304 in 2015 and 2016},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/V4YLY662}},
  note         = {Machine review of arXiv:1908.01232}
}
read the original abstract

PKS 2155-304 is one of the brightest blazar located in Southern Hemisphere, monitored with H.E.S.S. since the first light of the experiment. Here we report multiwavelength monitoring observations collected during the period of 2015-2016 with H.E.S.S.,Fermi-LAT, Swift-XRT, Swift-UVOT, and ATOM. Two years of multiwavelength data with very good temporal coverage allowed to characterize broadband emission observed from the region of PKS 2155-304 and study potential multifrequency correlations. During the period of monitoring, PKS 2155-304 revealed complex multiwavelength variability with two outbursts characterized by completely different multiband properties. The 2015 activity of the blazar is characterized by a flare observed at all wavelengths studied. The broadband emission observed during the outburst is well correlated without any time lags. Contrary to 2015, in 2016, only orphan outburst in the optical and ultraviolet wavelengths was observed. Such an orphan activity is reported for the first time for the blazar PKS 2155-304.

Figures

Figures reproduced from arXiv: 1908.01232 by the authors.

Figure 1
Figure 1. Multiwavelength light curve of PKS 2155-304 presenting data collected in 2015–2016 with ATOM, Swift-UVOT, Swift-XRT, Fermi-LAT and H.E.S.S [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Comparisons of emission observed at different wavelengths. The following panels presents: (A): B−R color vs. the B-band energy flux. (B): Comparison of B and R fluxes as observed with ATOM. (C): Comparison of optical U and B fluxes as observed with UVOT. (D): VHE γ-ray photon flux of the source also as a function of the B-band energy flux. (E) Comparison of X-ray flux in the energy range of 0.3–10 keV and optical fl… view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

45 extracted references · 11 canonical work pages

  1. [1]

    Unified Schemes for Radio-Loud Active Galactic Nuclei

    Urry, C.M.; Padovani, P . Unified Schemes for Radio-Loud Active Galactic Nuclei. Publ. Astron. Soc. Pac. 1995, 107, 803, doi:10.1086/133630

    doi:10.1086/133630 1995

  2. [2]

    Theory of extragalactic radio sources

    Begelman, M.C.; Blandford, R.D.; Rees, M.J. Theory of extragalactic radio sources. Rev. Mod. Phys. 1984, 56, 255–351, doi:10.1103/RevModPhys.56.255

    doi:10.1103/revmodphys.56.255 1984

  3. [3]

    Multiwavelength observations of Blazars

    Wagner, S. Multiwavelength observations of Blazars. In Astrophysics with All-Sky X-ray Observations , Proceedings of the RIKEN Symposium, RIKEN, and JAXA Suzuki Umetaro Hall, RIKEN Wako, Saitama, Japan, 10–12 June 2008; p. 186

    work page 2008

  4. [4]

    Swift/XRT view of S5 0716+714 during a flare

    Wierzcholska, A.; Siejkowski, H. Swift/XRT view of S5 0716+714 during a flare. Mon. Not. R. Astron. Soc. Lett. 2015, 452, L11–L15, doi:10.1093/mnrasl/slv075

    doi:10.1093/mnrasl/slv075 2015

  5. [5]

    Characterizing long-term optical, ultraviolet and X-ray variability in different activity states of OJ 287

    Siejkowski, H.; Wierzcholska, A. Characterizing long-term optical, ultraviolet and X-ray variability in different activity states of OJ 287. Mon. Not. R. Astron. Soc. Lett. 2017, 468, 426–434, doi:10.1093/mnras/stx495

    work page doi:10.1093/mnras/stx495 2017

  6. [6]

    First hard X-ray observations of the blazar S5 0716+714 with NuSTAR during a multiwavelength campaign

    Wierzcholska, A.; Siejkowski, H. First hard X-ray observations of the blazar S5 0716+714 with NuSTAR during a multiwavelength campaign. Mon. Not. R. Astron. Soc. Lett. 2016, 458, 2350–2359, doi:10.1093/mnras/stw425

    work page doi:10.1093/mnras/stw425 2016

  7. [7]

    A jet model for the gamma-ray emitting blazar 3C 279

    Maraschi, L.; Ghisellini, G.; Celotti, A. A jet model for the gamma-ray emitting blazar 3C 279. Astrophys. J. 1992, 397, L5–L9, doi:10.1086/186531

    doi:10.1086/186531 1992

  8. [8]

    Particle acceleration and synchrotron emission in blazar jets

    Kirk, J.G.; Rieger, F.M.; Mastichiadis, A. Particle acceleration and synchrotron emission in blazar jets. Astron. Astrophys. 1998, 333, 452–458,

    work page 1998

Show all 45 references
  1. [9]

    High-energy gamma radiation from extragalactic radio sources

    Dermer, C.D.; Schlickeiser, R.; Mastichiadis, A. High-energy gamma radiation from extragalactic radio sources. Astron. Astrophys. 1992, 256, L27–L30

    1992

  2. [10]

    Comptonization of diffuse ambient radiation by a relativistic jet: The source of gamma rays from blazars? Astrophys

    Sikora, M.; Begelman, M.C.; Rees, M.J. Comptonization of diffuse ambient radiation by a relativistic jet: The source of gamma rays from blazars? Astrophys. J. 1994, 421, 153–162, doi:10.1086/173633

    1994 doi

  3. [11]

    TeV gamma rays from BL Lac objects due to synchrotron radiation of extremely high energy protons

    Aharonian, F.A. TeV gamma rays from BL Lac objects due to synchrotron radiation of extremely high energy protons. New Astron. 2000, 5, 377–395, doi:10.1016/S1384-1076(00)00039-7

    doi

  4. [12]

    Neutral Beams from Blazar Jets

    Atoyan, A.M.; Dermer, C.D. Neutral Beams from Blazar Jets. Astrophys. J. 2003, 586, 79–96, doi:10.1086/346261

    2003 doi

  5. [13]

    Leptonic and Hadronic Modeling of Fermi-detected Blazars

    Böttcher, M.; Reimer, A.; Sweeney, K.; Prakash, A. Leptonic and Hadronic Modeling of Fermi-detected Blazars. Astrophys. J. 2013, 768, 54, doi:10.1088/0004-637X/768/1/54

    2013 doi

  6. [14]

    A unifying view of the spectral energy distributions of blazars

    Fossati, G.; Maraschi, L.; Celotti, A.; Comastri, A.; Ghisellini, G. A unifying view of the spectral energy distributions of blazars. Mon. Not. R. Astron. Soc. Lett. 1998, 299, 433–448, doi:10.1046/j.1365-8711.1998.01828.x

    1998

  7. [15]

    The Spectral Energy Distribution of Fermi Bright Blazars

    Abdo, A.A.; Ackermann, M.; Agudo, I.; Ajello, M.; Aller, H.D.; Aller, M.F.; Angelakis, E.; Arkharov, A.A.; Axelsson, M.; Bach, U.; et al. The Spectral Energy Distribution of Fermi Bright Blazars. Astrophys. J. 2010, 716, 30–70, doi:10.1088/0004-637X/716/1/30

    2010 doi

  8. [16]

    The Parkes 2700 MHz Survey (Sixth Part): Catalogue for the Declination zone −30◦ to −35◦

    Shimmins, A.J.; Bolton, J.G. The Parkes 2700 MHz Survey (Sixth Part): Catalogue for the Declination zone −30◦ to −35◦. Australian J. Phys. Astrophys. Suppl. 1974, 32, 1

    1974

  9. [17]

    A revised optical catalog of quasi-stellar objects

    Hewitt, A.; Burbidge, G. A revised optical catalog of quasi-stellar objects. Astrophys. J. Suppl. Ser. 1980, 43, 57–158, doi:10.1086/190667

    1980 doi

  10. [18]

    An Exceptional Very High Energy Gamma-Ray Flare of PKS 2155-304

    Aharonian, F.; Akhperjanian, A.G.; Bazer-Bachi, A.R.; Behera, B.; Beilicke, M.; Benbow, W.; Berge, D.; Bernlöhr, K.; Boisson, C.; Bolz, O.; et al. An Exceptional Very High Energy Gamma-Ray Flare of PKS 2155-304. Astrophys. J. 2007, 664, L71–L74, doi:10.1086/520635

    2007 doi

  11. [19]

    Simultaneous multiwavelength observations of the second exceptional γ-ray flare of PKS 2155-304 in July 2006

    Aharonian, F.; Akhperjanian, A.G.; Anton, G.; Barres de Almeida, U.; Bazer-Bachi, A.R.; Becherini, Y.; Behera, B.; Benbow, W.; Bernlöhr, K.; Boisson, C.; et al. Simultaneous multiwavelength observations of the second exceptional γ-ray flare of PKS 2155-304 in July 2006. Astron....

    2006 doi

  12. [20]

    Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A.G.; Andersson, T.; Angüner, E.O.; Arrieta, M.; Aubert, P .; et al

    H.E.S.S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A.G.; Andersson, T.; Angüner, E.O.; Arrieta, M.; Aubert, P .; et al. Characterizing the γ-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT. Astron. Astrophy...

    2017 doi

  13. [21]

    Observations of the Crab nebula with HESS.Astron

    Aharonian, F.; Akhperjanian, A.G.; Bazer-Bachi, A.R.; Beilicke, M.; Benbow, W.; Berge, D.; Bernlöhr, K.; Boisson, C.; Bolz, O.; Borrel, V .; et al. Observations of the Crab nebula with HESS.Astron. Astrophys. 2006, 457, 899–915, doi:10.1051/0004-6361:20065351

    2006 doi

  14. [22]

    A Monte Carlo template based analysis for air-Cherenkov arrays

    Parsons, R.D.; Hinton, J.A. A Monte Carlo template based analysis for air-Cherenkov arrays. Astropart. Phys. 2014, 56, 26–34, doi:10.1016/j.astropartphys.2014.03.002

    2014 doi

  15. [23]

    A high performance likelihood reconstruction of γ-rays for imaging atmospheric Cherenkov telescopes

    de Naurois, M.; Rolland, L. A high performance likelihood reconstruction of γ-rays for imaging atmospheric Cherenkov telescopes. Astropart. Phys. 2009, 32, 231–252, doi:10.1016/j.astropartphys.2009.09.001

    2009 doi

  16. [24]

    Pass 8: Toward the Full Realization of the Fermi-LAT Scientific Potential

    Atwood, W.; Albert, A.; Baldini, L.; Tinivella, M.; Bregeon, J.; Pesce-Rollins, M.; Sgrò, C.; Bruel, P .; Charles, E.; Drlica-Wagner, A.; et al. Pass 8: Toward the Full Realization of the Fermi-LAT Scientific Potential. arXiv 2013, arXiv:1303.3514

    2013 arXiv

  17. [25]

    Likelihood Analysis of EGRET Data

    Mattox, J.R.; Bertsch, D.L.; Chiang, J.; Dingus, B.L.; Digel, S.W.; Esposito, J.A.; Fierro, J.M.; Hartman, R.C.; Hunter, S.D.; Kanbach, G.; et al. Likelihood Analysis of EGRET Data. Astrophys. J. 1996, 461, 396, doi:10.1086/177068

    1996 doi

  18. [26]

    The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI

    Kalberla, P .M.W.; Burton, W.B.; Hartmann, D.; Arnal, E.M.; Bajaja, E.; Morras, R.; Pöppel, W.G.L. The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI. Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections. Astron. Astrophys. 2005, ...

    2005 doi

  19. [27]

    Photometric calibration of the Swift ultraviolet/optical telescope

    Poole, T.S.; Breeveld, A.A.; Page, M.J.; Landsman, W.; Holland, S.T.; Roming, P .; Kuin, N.P .M.; Brown, P .J.; Gronwall, C.; Hunsberger, S.; et al. Photometric calibration of the Swift ultraviolet/optical telescope. Mon. Not. R. Astron. Soc. Lett. 2008, 383, 627–645, doi:10.1...

    2008

  20. [28]

    Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds

    Schlegel, D.J.; Finkbeiner, D.P .; Davis, M. Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds. Astrophys. J. 1998, 500, 525–553, doi:10.1086/305772

    1998 doi

  21. [29]

    Measuring Reddening with Sloan Digital Sky Survey Stellar Spectra and Recalibrating SFD

    Schlafly, E.F.; Finkbeiner, D.P . Measuring Reddening with Sloan Digital Sky Survey Stellar Spectra and Recalibrating SFD. Astrophys. J. 2011, 737, 103, doi:10.1088/0004-637X/737/2/103

    2011 doi

  22. [30]

    ATOM—An Automatic Telescope for Optical Monitoring

    Hauser, M.; Möllenhoff, C.; Pühlhofer, G.; Wagner, S.J.; Hagen, H.J.; Knoll, M. ATOM—An Automatic Telescope for Optical Monitoring. Astron. Nachr. 2004, 325, 659–659, doi:10.1002/asna.200410305

    2004 doi

  23. [31]

    Galaxy Colors in Various Photometric Band Systems

    Fukugita, M.; Shimasaku, K.; Ichikawa, T. Galaxy Colors in Various Photometric Band Systems. Publ. Astron. Soc. Pac. 1995, 107, 945, doi:10.1086/133643

    1995 doi

  24. [32]

    On the nebulosity surrounding the BL Lacertae object PKS 2155-304

    Falomo, R.; Giraud, E.; Maraschi, L.; Melnick, J.; Tanzi, E.G.; Treves, A. On the nebulosity surrounding the BL Lacertae object PKS 2155-304. Astrophys. J. 1991, 380, L67–L69, doi:10.1086/186175

    1991 doi

  25. [33]

    On characterizing the variability properties of X-ray light curves from active galaxies

    Vaughan, S.; Edelson, R.; Warwick, R.S.; Uttley, P . On characterizing the variability properties of X-ray light curves from active galaxies. Mon. Not. R. Astron. Soc. Lett. 2003, 345, 1271–1284, doi:10.1046/j.1365-2966.2003.07042.x

    2003

  26. [34]

    Nine years of multi-frequency monitoring of the blazar PKS 0048-097: spectral and temporal variability

    Wierzcholska, A. Nine years of multi-frequency monitoring of the blazar PKS 0048-097: spectral and temporal variability. Astron. Astrophys. 2015, 580, A104, doi:10.1051/0004-6361/201525649

    2015 doi

  27. [35]

    A change in the optical polarization associated with a γ-ray flare in the blazar 3C279

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B.M.; Bechtol, K.; et al. A change in the optical polarization associated with a γ-ray flare in the blazar 3C279. Nature 2010, 463, 919–923, doi:10.1038/nature08841

    2010 doi

  28. [36]

    Radio to gamma-ray variability study of blazar S5 0716+714

    Rani, B.; Krichbaum, T.P .; Fuhrmann, L.; Böttcher, M.; Lott, B.; Aller, H.D.; Aller, M.F.; Angelakis, E.; Bach, U.; Bastieri, D.; et al. Radio to gamma-ray variability study of blazar S5 0716+714. Astron. Astrophys. 2013, 552, A11, doi:10.1051/0004-6361/201321058

    2013 doi

  29. [37]

    Implications of the Anomalous Outburst in the Blazar PKS 0208-512

    Chatterjee, R.; Nalewajko, K.; Myers, A.D. Implications of the Anomalous Outburst in the Blazar PKS 0208-512. Astrophys. J. 2013, 771, L25, doi:10.1088/2041-8205/771/2/L25

    2013 doi

  30. [38]

    The extreme HBL behaviour of Markarian 501 during 2012

    Ahnen, M.L.; Ansoldi, S.; Antonelli, L.A.; Arcaro, C.; Babi´ c, A.; Banerjee, B.; Bangale, P .; Barres de Almeida, U.; Barrio, J.A.; Becerra González, J.; et al. The extreme HBL behaviour of Markarian 501 during 2012. arXiv 2018, arXiv:1808.04300

    2012

  31. [39]

    Simultaneous Observations of PKS 2155-304 with HESS, Galaxies 2019, xx, 5 10 of 10 Fermi, RXTE, and Atom: Spectral Energy Distributions and Variability in a Low State

    Aharonian, F.; Akhperjanian, A.G.; Anton, G.; Barres de Almeida, U.; Bazer-Bachi, A.R.; Becherini, Y.; Behera, B.; Bernlöhr, K.; Boisson, C.; Bochow, A.; et al. Simultaneous Observations of PKS 2155-304 with HESS, Galaxies 2019, xx, 5 10 of 10 Fermi, RXTE, and Atom: Spectral E...

    2019 doi

  32. [40]

    Collaboration; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A.G.; Angüner, E.O.; Backes, M.; Balenderan, S.; Balzer, A.; Barnacka, A.; et al

    H.E.S.S. Collaboration; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A.G.; Angüner, E.O.; Backes, M.; Balenderan, S.; Balzer, A.; Barnacka, A.; et al. Long-term monitoring of PKS 2155-304 with ATOM and H.E.S.S.: investigation of optical/γ-ray correlations in ...

    2014 doi

  33. [41]

    XMM-Newton View of PKS 2155-304: Characterizing the X-Ray Variability Properties with EPIC pn

    Zhang, Y.H.; Treves, A.; Celotti, A.; Qin, Y.P .; Bai, J.M. XMM-Newton View of PKS 2155-304: Characterizing the X-Ray Variability Properties with EPIC pn. Astrophys. J. 2005, 629, 686–699, doi:10.1086/431719

    2005 doi

  34. [42]

    Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton

    Zhang, Y.H.; Bai, J.M.; Zhang, S.N.; Treves, A.; Maraschi, L.; Celotti, A. Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton. Astrophys. J. 2006, 651, 782–790, doi:10.1086/507601

    2006 doi

  35. [43]

    The X-ray behaviour of the high-energy peaked BL Lacertae source PKS 2155-304 in the 0.3–10 keV band

    Kapanadze, B.; Romano, P .; Vercellone, S.; Kapanadze, S. The X-ray behaviour of the high-energy peaked BL Lacertae source PKS 2155-304 in the 0.3–10 keV band. Mon. Not. R. Astron. Soc. Lett. 2014, 444, 1077–1094, doi:10.1093/mnras/stu1504

    2014 doi

  36. [44]

    Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope

    Ikejiri, Y.; Uemura, M.; Sasada, M.; Ito, R.; Yamanaka, M.; Sakimoto, K.; Arai, A.; Fukazawa, Y.; Ohsugi, T.; Kawabata, K.S.; et al. Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope. I. Correlations between Flux, Color, a...

    2011 doi

  37. [45]

    Longterm optical monitoring of bright BL Lacertae objects with ATOM: Spectral variability and multiwavelength correlations

    Wierzcholska, A.; Ostrowski, M.; Stawarz, Ł.; Wagner, S.; Hauser, M. Longterm optical monitoring of bright BL Lacertae objects with ATOM: Spectral variability and multiwavelength correlations. Astron. Astrophys. 2015, 573, A69, doi:10.1051/0004-6361/201423967. c© 2019 by the a...

    2015 doi

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.