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REVIEW 2 major objections 6 minor 28 references

The Einstein Probe's wide-field X-ray telescope achieves its calibration through a versioned, HEASARC-compliant database that tracks 48 CMOS sensors across 12 modules, with on-ground results and in-orbit updates.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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2026-08-01 18:23 UTC pith:FRYODSEU

load-bearing objection Solid, readable design-and-implementation report for the EP-WXT CALDB; the internal arithmetic checks out, the main risk is the unverified ray-tracing products and a real tension between the V1.0 baseline and the stated ≤10% effective-area uncertainty. the 2 major comments →

arxiv 2607.17312 v1 pith:FRYODSEU submitted 2026-07-19 astro-ph.IM astro-ph.HE

Calibration database design for the wide-field X-ray telescope on board the Einstein Probe

Huaqing Cheng , Hai-Wu Pan , Yuan Liu , Donghua Zhao , Wenxin Wang , He-Yang Liu , Chen Zhang , Zhixing Ling
show 1 more author
Weimin Yuan
This is my paper
classification astro-ph.IM astro-ph.HE
keywords calibration databaseX-ray telescopelobster-eye opticsmicro-pore opticsCMOS detectorEinstein ProbeWXTin-orbit calibration
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

This paper describes the design and implementation of the calibration database (CALDB) for the WXT, the primary payload of the Einstein Probe. The authors argue that a standardized, dynamically updated database can manage the complex optical responses of lobster-eye micro-pore optics and a large array of 48 CMOS sensors, integrating seamlessly with the data analysis pipeline. The database organizes basic calibration files and high-level response products in a HEASARC-compliant structure, enabling community-standard tools to analyze WXT data. If the design is sound, it provides the foundation for the public data release in late 2026 and supports the instrument's claimed in-orbit performance: source localization to 1.3 arcminutes, effective-area uncertainty within 10%, and stable gain and spectral resolution. The paper also details a time- and temperature-dependent gain calibration grid and a non-linear spatial correction mechanism patched in orbit.

Core claim

The central contribution is a two-tier calibration database architecture: a basic-calibration-file layer (bcf) holding physical and electronic characteristics such as telescope definition, bad pixels, bias, gain, grade, effective area, filter transmission, and quantum efficiency, and a calibration-product-file layer (cpf) containing analysis-ready ancillary response files, response matrices, vignetting maps, PSF corrections, and background spectra. Each of the 48 CMOS sensors is uniquely identified in filenames, and FITS header keywords (TELESCOP, INSTRUME, DETNAM, CVSD, CVST) allow the pipeline to select the correct file for a given observation epoch. The key innovation is the dynamic natur

What carries the argument

The load-bearing structure is the teldef file's coordinate-transformation chain (RAW → DET → SKY) together with the NONLINEAR 257×257 correction matrices that absorb MPO manufacturing distortions; the gain file's multi-dimensional grid (TIME × CMOSTEMP) that interpolates the energy-to-channel relation; and the energy-dependent vignetting/PSF images (295×295 bins) generated by ray tracing. These objects make the database self-describing and epoch-aware, so the pipeline can automatically apply the right calibration without hard-coded assumptions.

Load-bearing premise

The accuracy claims (1.3′ localization, ≤10% effective-area uncertainty) assume that the ray-tracing simulations of the MPO optics and the handful of in-orbit standard sources (Crab, Cas A, Scorpius X-1, NED positions) accurately represent the true telescope response across the entire 3600-square-degree field of view, even in regions never sampled on the ground.

What would settle it

Cross-match WXT source positions and fluxes from a wide, off-axis survey field against an independent high-precision X-ray catalog (e.g., from a focusing telescope) and look for position-dependent residuals that grow beyond the quoted R90 and 10% effective-area tolerances in areas not covered by the calibration sources.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • The public data release in late 2026 will include a complete, versioned calibration database that community-standard X-ray analysis tools can read directly, removing a major barrier to broad use of EP-WXT data.
  • The time- and temperature-dependent gain grid provides a template for future space-borne CMOS X-ray detectors, which lack long-term behavior heritage.
  • The in-orbit patching of non-linear spatial corrections demonstrates a practical path to sub-arcminute localization on lobster-eye optics, which could be reused by future lobster-eye missions.
  • Annual calibration campaigns using standard candles plus routine survey data will monitor long-term degradation, allowing the database to track contamination and radiation damage.
  • The versioned structure (V1.0 clean baseline now, V2.0 with low-energy attenuation later) means scientific results can be reproduced with a specific calibration epoch.

Where Pith is reading between the lines

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

  • The stated precision rests on ray-tracing simulations for vignetting and PSF maps that were only verified on-ground in limited configurations; regions of the 3600-square-degree field not sampled by Crab, Cas A, or Sco X-1 may harbor larger systematic errors than the quoted baselines, which the planned astrometric campaigns using dense fields could expose.
  • Because the non-linear correction matrices were launched as zeros, early-mission science data collected before the in-orbit patch carry larger positional uncertainties; users may need to reprocess early observations with the updated teldef.
  • The ~30–40% low-energy effective-area decay observed in a subset of modules is explicitly excluded from V1.0, so V1.0 effective-area files do not represent the true current throughput for those detectors; users working at 0.4–0.6 keV should treat V1.0 results as provisional until V2.0.
  • The database's design could serve as a reference architecture for future wide-field X-ray survey missions, but its success hinges on the calibration team's ability to keep the epoch-dependent files synchronized with the pipeline's automated selection.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 6 minor

Summary. This paper describes the design and implementation of the calibration database (CALDB) for the Wide-field X-ray Telescope (WXT) on board the Einstein Probe. It presents the directory hierarchy (bcf/cpf), HEASARC/OGIP-compliant FITS naming conventions, mandatory header keywords, and the content of basic calibration files (teldef, badpix, bias, gain, grade, effarea, ftrans, qe) and high-level products (rmf, arf, vign, psf, bkg). The paper also reports Version 1.0 in-orbit calibration baselines, including source localization R90=1.3′, effective-area systematic uncertainty ≤10% (0.5–4 keV), and stable gain/energy resolution, and states that the CALDB forms the basis for the late-2026 public data release. The central claim is that the CALDB is a standardized, robust database that handles the 12-module/48-CMOS array and is seamlessly integrated with the WXT data analysis pipeline.

Significance. The manuscript is a useful design reference for the EP community and for future lobster-eye/CMOS missions. It provides concrete file formats, coordinate transformations, and grade definitions that will be needed by users of the public data. The in-orbit verification against Crab, Cas A, and NED source positions is a notable strength, and the paper is transparent about known limitations such as the zero-valued initial non-linear correction matrices and the exclusion of the low-energy effective-area decay from V1.0. The main weakness is that one of the headline calibration baselines in Table 6 is internally inconsistent with the reported decay, and the off-axis response uncertainties are not quantified.

major comments (2)
  1. [Table 6 / Sec. 3.2.2 / Sec. 4] The headline claim of an in-orbit effective-area systematic uncertainty of ≤10% (90% C.L.) in the 0.5–4 keV band (Table 6) is contradicted by the paper's own description of a gradual low-energy attenuation (0.4–0.6 keV) reaching ~30–40% in a small subset of detectors, which V1.0 'explicitly excludes' (Sec. 3.2.2, Sec. 4). Since V1.0 is the release described and the basis for the late-2026 public data release, users analyzing affected modules in that band will use an ARF that is too high by 30–40%; the systematic uncertainty there is not ≤10%. The claim must be qualified (e.g., restricted to unaffected detectors/energies, or the decay parameterized in V1.0) before the paper can be accepted.
  2. [Sec. 3.2.3–3.2.4 / Table 6] The vignetting and PSF correction maps are generated by ray-tracing and described as 'verified by on-ground calibration', but the paper does not report the verification accuracy, sample coverage, or the resulting uncertainty of the off-axis effective area. Since these maps are used for photometry across a >3600 square-degree field of view, the paper should either report an off-axis effective-area systematic uncertainty separately from the on-axis ARF value in Table 6, or explicitly state that the ≤10% figure applies only to on-axis response. Without this, users cannot assess the accuracy of the CALDB for off-axis sources, which constitute the vast majority of WXT observations.
minor comments (6)
  1. [Sec. 3.1.1] The treatment of DET_XOFF/DET_YOFF is ambiguous. The baseline constants list sets DET_XOFF=0 and DET_YOFF=0, but the next paragraph says these parameters denote the curvature center and are obtained from on-ground measurements. Please clarify whether the baseline list is a nominal case or the actual default for all sensors.
  2. [Sec. 2.2 / Table 2] The file naming convention states that <cmos_number> uniquely identifies each of the 48 sensors, but the grade file is named 'epwgrade...' without a CMOS number, implying it is shared. The convention should be made consistent or the exception explicitly stated.
  3. [Sec. 3.2.1] The RMF naming convention uses '<datamode>' but this token is never defined in the text. Please define it or replace it with a concrete example.
  4. [Sec. 3.1.5] The grade file table is said to map GRADEID from 0 to 32, but the text then describes canonical grades 0–12. State what grades 13–32 represent or whether they are unused.
  5. [Figure 3] Caption reads 'Grade0-12selection is adopted'; should be 'Grade 0–12 selection is adopted'.
  6. [Sec. 4 / References] The WXT data analysis pipeline is cited as 'Liu et al. in preparation' in the text but is not included in the reference list. Provide a full citation or state that it will appear in a companion paper.

Circularity Check

0 steps flagged

No significant circularity. The paper is a design/implementation description whose calibration values come from on-ground measurements, ray-tracing simulation, and in-orbit checks against external standards (Crab, Cas A, NED). Table 6 precision figures are delegated to the authors' own companion papers, but the underlying checks are externally anchored, so the delegation is evidence rather than a

full rationale

This paper makes no first-principles derivation whose result could collapse back into its inputs; it is a design and implementation description of a HEASARC/OGIP-compliant CALDB. The calibration content is populated from three independent sources: (1) on-ground measurements (bias, gain, bad-pixel tables; filter transmission and QE 'generated by simulations and verified through on-ground calibrations'); (2) ray-tracing simulation for effarea, vignetting, and PSF maps, all explicitly disclosed as such (Secs 3.1.6, 3.2.3, 3.2.4); and (3) in-orbit verification against external standards — Crab spectral fits agreeing with 'established canonical values', Cas A line monitoring for energy scale/resolution, and NED catalog positions as astrometric reference (Table 6). The only self-referential element is the delegation of the headline precision figures in Table 6 to the authors' own companion papers (Cheng et al. 2026a, 2026b), but those checks are anchored to independent external references rather than to quantities fitted inside this paper, so by the review rules the citation qualifies as real evidence and does not raise the circularity score. The nonlinear spatial-correction matrices (Sec 3.1.1) were 'initially populated with zeros' at launch and filled in-orbit by comparing focal-spot positions to quaternion-derived expectations — a measurement/update loop, not a fitted prediction; R90 = 1.3' is a post-fit residual verified against NED source positions. One internal inconsistency exists: Table 6's blanket 'systematic uncertainty ≤10% (90% C.L.) in the 0.5–4 keV band' sits uneasily beside the stated 30–40% low-energy (0.4–0.6 keV) attenuation in a subset of modules that Version 1.0 'explicitly excludes' (Secs 3.2.2, 4). That is an accuracy-scope qualification problem, not a circular reduction by construction.

Axiom & Free-Parameter Ledger

4 free parameters · 6 axioms · 0 invented entities

Design/implementation paper: the ledger records the conventions the central claim rests on. No hidden derivation parameters exist because the paper makes no derivation. The four constants listed (Gnom=10, BIAS0=40 DN, triplicate -30 degC gain nodes, 9.2-arcmin aperture) are design conventions, not fitted values. The axioms are the standard inputs any calibration database relies on; the two load-bearing ones are the fidelity of the ray-tracing models over a 3600-sq-deg FoV and the transfer of in-orbit verification from companion papers (Cheng et al. 2026a/b). The paper discloses the weakest spots itself (Secs 3.1.1, 3.2.2, 4).

free parameters (4)
  • NOM_GAIN (Gnom = 10) = 10
    Chosen normalization so that PI channels scale at 10 eV per channel (Sec 3.1.4, Eq. 12). A conventions choice, not a fitted result.
  • BIAS0 offset (40 DN) = 40 DN
    Ad-hoc offset added during onboard row-median bias subtraction to prevent truncation of negative noise fluctuations (Sec 3.1.3, Eqs. 9–10).
  • Gain temperature nodes = [-30, -30, -30] degC
    V1.0 pre-allocates three identical thermal nodes at the operating temperature; placeholder values that preserve HEASARC interpolation compliance (Sec 3.1.4).
  • PSF extraction aperture = 9.2 arcmin
    Chosen source-extraction radius; defines the PSF correction factor and the ARF normalization. Justified in a footnote by an on-ground modeled/measured match (Sec 3.2.4).
axioms (6)
  • domain assumption OGIP/HEASARC format compliance guarantees interoperability with community analysis tools
    The entire architecture is built on this compliance (Sec 2); the paper cites the conventions but runs no shown compatibility test with external tools.
  • domain assumption Ray-tracing simulations of the MPO/CMOS response are faithful ground truth for effarea, ftrans, QE, vignetting, and PSF maps
    These products are 'generated by ray-tracing simulations and verified by on-ground calibration'; the verification is not shown (Secs 3.1.6–3.1.8, 3.2.3–3.2.4).
  • domain assumption Crab, Cas A, Sco X-1, and NED positions are valid external calibration standards
    In-orbit verification of ARF, RMF, PSF, and astrometry relies on these standards; the fits are reported in the companion paper (Table 6, Sec 3.2.2).
  • domain assumption CMOS gain is spatially uniform, so the four spatial gradient coefficients (GC1, GC2, GC4, GC5) are zero
    Justified by a measured 1–2% gain variance across the detector plane, quoted from on-ground calibration (Sec 3.1.4).
  • domain assumption Gain and spectral resolution are temporally stable, so static V1.0 gain/RMF files are valid
    No statistically significant change found in the late-2025/early-2026 campaign; the stability claim is delegated to Cheng et al. 2026b (Secs 3.1.4, 3.2.1).
  • domain assumption The CMOS focal-plane temperature is pinned at -30 degC with negligible thermal gain dependence
    Telemetry shows stable -30 degC operation; the -1.8±0.2% gain shift over a 50 degC swing is from on-ground tests (Sec 3.1.4).

pith-pipeline@v1.3.0-alltime-deepseek · 13842 in / 24477 out tokens · 251351 ms · 2026-08-01T18:23:45.269124+00:00 · methodology

0 comments
read the original abstract

The wide-field X-ray telescope (WXT) is the primary payload of the Einstein Probe (EP) mission. Utilizing innovative lobster-eye micro-pore optics (MPO), it achieves an unprecedented combination of a large instantaneous field-of-view (FoV) and high detection sensitivity. Precise scientific data analysis relies fundamentally on a standardized and robust calibration database (CALDB). In this paper, we present the design and implementation of the WXT CALDB. The database is designed to manage calibration data for 12 independent WXT modules and 48 CMOS sensors, incorporating both extensive on-ground calibration results and dynamic in-orbit updates. We detail the directory hierarchy, naming conventions, functionality, and the specific formats of key calibration products. The WXT CALDB is seamlessly integrated into the WXT data analysis pipeline, ensuring high data integrity and maximizing the scientific return of the mission.

Figures

Figures reproduced from arXiv: 2607.17312 by Chen Zhang, Donghua Zhao, Hai-Wu Pan, He-Yang Liu, Huaqing Cheng, Weimin Yuan, Wenxin Wang, Yuan Liu, Zhixing Ling.

Figure 1
Figure 1. Figure 1: The non-linear correction matrices applied for coordinate transformations. The [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: (Left Panel) The filter transmission as a function of photon energy adopted for CMOS 1. (Right Panel) The QE as a function of photon energy adopted for all CMOS sensors. of the QE are generated by simulations and verified through on-ground calibrations. The QE curve for all CMOS detectors is presented in the Right panel of [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The CMOS response array for an incident photon with energy ranging from [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: The vignetting correction value mapping for a CMOS detector at different energies of incident [PITH_FULL_IMAGE:figures/full_fig_p013_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Mapping of the PSF correction coefficient for a CMOS detector at different energies of incident [PITH_FULL_IMAGE:figures/full_fig_p014_5.png] view at source ↗

discussion (0)

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Reference graph

Works this paper leans on

28 extracted references · 3 linked inside Pith

  1. [1]

    Angel, J. R. P. 1979, ApJ, 233, 364

    1979

  2. [2]

    2011, Handbook of X-ray Astronomy

    Arnaud, K., Smith, R., & Siemiginowska, A. 2011, Handbook of X-ray Astronomy

    2011

  3. [3]

    2024, Journal of Astronomical Telescopes, Instruments, and Systems, 10, 026001

    Chen, M., Ling, Z., Liu, M., et al. 2024, Journal of Astronomical Telescopes, Instruments, and Systems, 10, 026001

    2024

  4. [4]

    2020, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol

    Chen, Y ., Cui, W., Han, D., et al. 2020, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, ed. J.-W. A. den Herder, S. Nikzad, & K. Nakazawa, 114445B

    2020

  5. [5]

    2024, Experimental Astronomy, 57, 10

    Cheng, H., Ling, Z., Zhang, C., et al. 2024, Experimental Astronomy, 57, 10

    2024

  6. [6]

    2026b, arXiv e-prints, arXiv:2606.28101

    Cheng, H., Pan, H.-W., Liu, Y ., et al. 2026b, arXiv e-prints, arXiv:2606.28101

    Pith/arXiv arXiv

  7. [7]

    W., Brunton, A

    Fraser, G. W., Brunton, A. N., Lees, J. E., Pearson, J. F., & Feller, W. B. 1993, Nuclear Instruments and Methods in Physics Research A, 324, 404

    1993

  8. [8]

    W., Lees, J

    Fraser, G. W., Lees, J. E., Pearson, J. F., Sims, M. R., & Roxburgh, K. 1992, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 1546, Multilayer and Grazing Incidence X-Ray/EUV Optics, ed. R. B. Hoover, 41

    1992

  9. [9]

    E., Bautz, M

    Grant, C. E., Bautz, M. W., Plucinsky, P. P., & Ford, P. G. 2024, in Society of Photo- Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 13093, Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, ed. J.-W. A. den Herder, S. Nikzad, & K. Nakazawa, 130931E Calibration database design for the EP-WXT 17

    2024

  10. [10]

    C., Li, D

    Jin, C. C., Li, D. Y ., Jiang, N., et al. 2025, arXiv e-prints, arXiv:2501.09580

    arXiv 2025

  11. [11]

    F., Shah, H., & Alfred, A

    Lewis, R. F., Shah, H., & Alfred, A. 2026, arXiv e-prints, arXiv:2602.12303

    Pith/arXiv arXiv 2026

  12. [12]

    2026, Science Bulletin, 71, 538

    Li, D., Zhang, W., Yang, J., et al. 2026, Science Bulletin, 71, 538

    2026

  13. [13]

    X., Sun, X

    Ling, Z. X., Sun, X. J., Zhang, C., et al. 2023, Research in Astronomy and Astrophysics, 23, 095007

    2023

  14. [14]

    2023, Journal of Astronomical Telescopes, Instruments, and Systems, 9, 046003

    Liu, M., Ling, Z., Wu, Q., et al. 2023, Journal of Astronomical Telescopes, Instruments, and Systems, 9, 046003

    2023

  15. [15]

    N., Coti Zelati, F., et al

    Marino, A., Yang, H. N., Coti Zelati, F., et al. 2025, ApJ, 980, L36

    2025

  16. [16]

    L., Tennant, A., Grant, C

    Marshall, H. L., Tennant, A., Grant, C. E., et al. 2004, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 5165, X-Ray and Gamma-Ray Instrumentation for Astronomy XIII, ed. K. A. Flanagan & O. H. W. Siegmund, 497

    2004

  17. [17]

    2025, Nature Astronomy, 9, 1073

    Sun, H., Li, W.-X., Liu, L.-D., et al. 2025, Nature Astronomy, 9, 1073

    2025

  18. [18]

    W., Brunton, A

    Willingale, R., Fraser, G. W., Brunton, A. N., & Martin, A. P. 1998, Experimental Astronomy, 8, 281

    1998

  19. [19]

    F., Martindale, A., et al

    Willingale, R., Pearson, J. F., Martindale, A., et al. 2016, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, ed. J.-W. A. den Herder, T. Takahashi, & M. Bautz, 99051Y

    2016

  20. [20]

    2022, PASP, 134, 035006

    Wu, Q., Jia, Z., Wang, W., et al. 2022, PASP, 134, 035006

    2022

  21. [21]

    I., Zhang, B.-B., Yang, J., et al

    Yin, Y .-H. I., Zhang, B.-B., Yang, J., et al. 2024, ApJ, 975, L27

    2024

  22. [22]

    2022, The Einstein Probe Mission, ed

    Yuan, W., Zhang, C., Chen, Y ., & Ling, Z. 2022, The Einstein Probe Mission, ed. C. Bambi & A. Santangelo, Handbook of X-ray and Gamma-ray Astrophysics, ed. C. Bambi & A. Santangelo (Singapore: Springer Nature Singapore), 1

    2022

  23. [23]

    2015, arXiv e-prints, arXiv:1506.07735

    Yuan, W., Zhang, C., Feng, H., et al. 2015, arXiv e-prints, arXiv:1506.07735

    Pith/arXiv arXiv 2015

  24. [24]

    2018, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol

    Yuan, W., Zhang, C., Ling, Z., et al. 2018, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 10699, Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray, ed. J.-W. A. den Herder, S. Nikzad, & K. Nakazawa, 1069925

    2018

  25. [25]

    2025, Science China Physics, Mechanics, and Astronomy, 68

    Yuan, W., Dai, L., Feng, H., et al. 2025, Science China Physics, Mechanics, and Astronomy, 68

    2025

  26. [26]

    X., Sun, X

    Zhang, C., Ling, Z. X., Sun, X. J., et al. 2022, ApJ, 941, L2

    2022

  27. [27]

    2018, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol

    Zhao, D., Zhang, C., Ling, Z., et al. 2018, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, V ol. 10699, Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray, ed. J.-W. A. den Herder, S. Nikzad, & K. Nakazawa, 106995N

    2018

  28. [28]

    2017, Experimental Astronomy, 43, 267

    Zhao, D., Zhang, C., Yuan, W., et al. 2017, Experimental Astronomy, 43, 267

    2017