J/A+A/706/A175 Pulsar Vela X-1 Pulse-to-Pulse Approach (Du+, 2026)
Long-Term evolution of cyclotron resonant scattering features in the accreting
pulsar Vela X-1: A pulse-to-pulse approach.
Du Y.-J., Wang P.-J., Ducci L., Ji L., Kong L.-D., Bu Q.-C., Mehrotra C.,
Santangelo A.
<Astron. Astrophys. 706, A175 (2026)>
=2026A&A...706A.175D 2026A&A...706A.175D (SIMBAD/NED BibCode)
ADC_Keywords: Pulsars ; Accretion ; Gamma rays
Keywords: accretion, accretion disks - pulsars: general
Abstract:
We investigated the long-term evolution of the cyclotron line energy,
as well as the relationship between cyclotron line energy and
luminosity in the high-mass X-ray binary Vela X-1, based on archival
Swift/BAT monitoring from 2005 to 2024 and pulse-to-pulse analysis of
nine NuSTAR observations from 2012 to 2024. Our results provide the
first confirmation that the long-term decay of the harmonic line
energy (Ecyc,H) in Vela X-1 has ended. We further report the first
detection of a transient increase in Ecyc,H between 2020 and 2023,
which suggests a sudden and significant change in the magnetic field
configuration or accretion geometry. In addition, Ecyc,H shows
slightly lower values at low luminosities and tends to flatten at
higher luminosities, in the range of (0.13-1.21)x1037erg/s. The
fundamental line energy (Ecyc,F) exhibits no significant variation
with time or luminosity, remaining stable at approximately 25keV.
Description:
This catalogue contains the spectral parameters reported in Tables
A.1-A.7 of the paper. The tables provide long-term Swift/BAT spectral
results, NuSTAR time-averaged spectral result, and pulse-to-pulse
spectral results for five NuSTAR observations. All uncertainties
represent the 68% confidence level.
Objects:
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RA (2000) DE Designation(s)
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09 02 06.86 -40 33 16.8 Vela X-1 = CD-40 4838
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 91 75 Best-fitting parameters of Vela X-1
from Swift/BAT monitoring
tablea2.dat 252 23 NuSTAR phase-averaged spectra (eight observations)
tablea3.dat 141 23 Pulse-to-pulse spectra for ObsID 10002007001
tablea4.dat 141 23 Pulse-to-pulse spectra for ObsID 30002007003
tablea5.dat 141 23 Pulse-to-pulse spectra for ObsID 30501003002
tablea6.dat 141 23 Pulse-to-pulse spectra for ObsID 90402339002
tablea7.dat 113 23 Pulse-to-pulse spectra for ObsID 91002349002
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See also:
J/A+A/377/925 : Radial velocity curves of Vela X-1 (Barziv+, 2001)
J/A+A/395/129 : Cyclotron lines in Vela X-1 (Kreykenbohm+, 2002)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Time Modified Julian Date interval of each
spectrum (MJD)
13- 16 F4.2 keV kTComp Comptonizing plasma temperature
18- 21 F4.2 keV e_kTComp Lower error on kTComp
23- 26 F4.2 keV E_kTComp Upper error on kTComp
28- 32 F5.2 --- tauComp Compton optical depth
34- 37 F4.2 --- e_tauComp Lower error on tauComp
39- 42 F4.2 --- E_tauComp Upper error on tauComp
44- 48 F5.2 --- EcyclH Centroid energy of the harmonic CRSF
50- 53 F4.2 --- e_EcyclH Lower error on EcyclH
55- 58 F4.2 --- E_EcyclH Upper error on EcyclH
60- 64 F5.2 keV sigmaH Width of the harmonic CRSF
66- 69 F4.2 keV e_sigmaH Lower error on sigmaH
71- 74 F4.2 keV E_sigmaH Upper error on sigmaH
76- 80 F5.2 keV DepthH Line depth of the harmonic CRSF
82- 86 F5.2 keV e_DepthH Lower error on DepthH
88- 91 F4.2 keV E_DepthH Upper error on DepthH
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 28 A28 -- Param Name of parameter as defined in the paper (G1)
30- 56 A27 --- ObsID1 Value for ObsID = 10002007001
58- 84 A27 --- ObsID2 Value for ObsID = 30002007002
86-112 A27 --- ObsID3 Value for ObsID = 30002007003
114-140 A27 --- ObsID4 Value for ObsID = 90402339002
142-168 A27 --- ObsID5 Value for ObsID = 30501003002
170-196 A27 --- ObsID6 Value for ObsID = 90602328002
198-224 A27 --- ObsID7 Value for ObsID = 90602328004
226-252 A27 --- ObsID8 Value for ObsID = 90602328006
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 29 A29 --- Param Spectral parameter names (G1)
31- 57 A27 --- 6769-9636 Best-fit values for
6769-9636 [ct/pulse] amplitude range
59- 85 A27 --- 9636-13580 Best-fit values for
9636-13580 [ct/pulse] amplitude range
87-113 A27 --- 1358-16240 Best-fit values for
1358-16240 [ct/pulste] amplitude range
115-141 A27 --- 1624-27083 Best-fit values for
1624-27083 [ct/pulste] amplitude range
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Byte-by-byte Description of file: tablea4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 29 A29 --- Param Spectral parameter names (G1)
31- 57 A27 --- 304-2108 Best-fit values for
304-2108 [ct/pulse] amplitude range
59- 85 A27 --- 2108-2557 Best-fit values for
2108-2557 [ct/pulse] amplitude range
87-113 A27 --- 2557-3422 Best-fit values for
2557-3422 [ct/pulste] amplitude range
115-141 A27 --- 3422-6340 Best-fit values for
3422-6340 [ct/pulste] amplitude range
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Byte-by-byte Description of file: tablea5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 29 A29 --- Param Spectral parameter names (G1)
31- 57 A27 --- 3113-5287 Best-fit values for
3113-5287 [ct/pulse] amplitude range
59- 85 A27 --- 5287-6693 Best-fit values for
5287-6693 [ct/pulse] amplitude range
87-113 A27 --- 6693-8728 Best-fit values for
6693-8728 [ct/pulste] amplitude range
115-141 A27 --- 8728-18521 Best-fit values for
8728-18521 [ct/pulste] amplitude range
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Byte-by-byte Description of file: tablea6.dat
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Bytes Format Units Label Explanations
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1- 29 A29 --- Param Spectral parameter names (G1)
31- 57 A27 --- 372-2639 Best-fit values for
372-2639 [ct/pulse] amplitude range
59- 85 A27 --- 2639-3581 Best-fit values for
2639-3581 [ct/pulse] amplitude range
87-113 A27 --- 3581-4382 Best-fit values for
3581-4382 [ct/pulste] amplitude range
115-141 A27 --- 4382-14043 Best-fit values for
4382-14043 [ct/pulste] amplitude range
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Byte-by-byte Description of file: tablea7.dat
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Bytes Format Units Label Explanations
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1- 29 A29 --- Param Spectral parameter names (G1)
31- 57 A27 --- 246-3098 Best-fit values for
246-3098 [ct/pulse] amplitude range
59- 85 A27 --- 3098-5884 Best-fit values for
3098-5884 [ct/pulse] amplitude range
87-113 A27 --- 5884-12359 Best-fit values for
5884-1235 [ct/pulste] amplitude range
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Global notes:
Note (G1): Parameters:
C_FPMA : Cross-calibration constant of FPMA (fixed to 1)
C_FPMB : Cross-calibration constant between FPMB and FPMA
NH1 : Galactic absorption column density (fixed)
NH2 : Partial-covering absorption column density
CF : Covering fraction of the partial absorber
E_10keV : Centroid energy of the 10keV feature (keV)
σ_10keV : Width (Gaussian σ) of the 10keV feature (keV)
Norm_10keV : Normalization of the 10keV feature
E_Kalpha : Energy of the Fe Kα emission line (keV)
sigma_Kalpha : Width (Gaussian sigma) of the Fe Kα line(keV)
Norm_Kalpha : Normalization of the Fe Kα line
EcycF : Fundamental cyclotron line energy(keV)
sigmacycF : Width of the fundamental CRSF
(fixed to 0.5 x sigmacycH) (keV)
dcycF : Depth of the fundamental CRSF
EcycH : Centroid energy of the harmonic CRSF(keV)
sigmacycH : Width of the harmonic CRSF(keV)
dcycH : Depth of the harmonic CRSF
E_cut : Cutoff energy of the fdcut continuum(keV)
E_fold : Folding energy of the fdcut continuum(keV)
Gamma : Photon index of the power-law continuum
Norm_Gamma : Power-law normalization
Flux_3-79 keV_ : Unabsorbed flux in units of 10-9erg/cm2/s
χ2/d.o.f. : Fit statistic and degrees of freedom
All reported errors are at the 68% confidence level and based on the MCMC
chain values. Normalization of the power law in units of
photon/cm2/s/keV at 1keV. Unabsorbed flux (in units of 10-9erg/cm2/s)
calculated for the entire model, obtained using the cflux command from xspec.
Uncertainties are given for a 68% confidence level
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Acknowledgements:
Yujia Du, du(at)astro.uni-tuebingen.de,
Institut fuer Astronomie und Astrophysik, Universitaet Tuebingen
(End) Yujia Du [Tuebingen Univ.], Patricia Vannier [CDS] 08-Dec-2025