J/ApJ/833/244 Pulse profiles for simulated thermonuclear bursts (Stevens+, 2016)
Neutron star mass-radius constraints using evolutionary optimization.
Stevens A.L., Fiege J.D., Leahy D.A., Morsink S.M.
<Astrophys. J., 833, 244-244 (2016)>
=2016ApJ...833..244S 2016ApJ...833..244S (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Stars, masses
Keywords: methods: numerical; pulsars: general; gravitation; stars: neutron;
stars: rotation; X-rays: binaries
Abstract:
The equation of state of cold supra-nuclear-density matter, such as in
neutron stars, is an open question in astrophysics. A promising method
for constraining the neutron star equation of state is modeling pulse
profiles of thermonuclear X-ray burst oscillations from hot spots on
accreting neutron stars. The pulse profiles, constructed using
spherical and oblate neutron star models, are comparable to what would
be observed by a next-generation X-ray timing instrument like
ASTROSAT, NICER, or a mission similar to LOFT. In this paper, we
showcase the use of an evolutionary optimization algorithm to fit
pulse profiles to determine the best-fit masses and radii. By fitting
synthetic data, we assess how well the optimization algorithm can
recover the input parameters. Multiple Poisson realizations of the
synthetic pulse profiles, constructed with 1.6 million counts and no
background, were fitted with the Ferret algorithm to analyze both
statistical and degeneracy-related uncertainty and to explore how the
goodness of fit depends on the input parameters. For the regions of
parameter space sampled by our tests, the best-determined parameter is
the projected velocity of the spot along the observer's line of sight,
with an accuracy of ≤3% compared to the true value and with ≤5%
statistical uncertainty. The next best determined are the mass and
radius; for a neutron star with a spin frequency of 600Hz, the
best-fit mass and radius are accurate to ≤5%, with respective
uncertainties of ≤7% and ≤10%. The accuracy and precision depend on
the observer inclination and spot colatitude, with values of ∼1%
achievable in mass and radius if both the inclination and colatitude
are ≳60deg.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 98 9 Summary of test models
table3.dat 89 230 Summary of model best fits
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See also:
J/ApJS/179/360 : Thermonuclear X-ray bursts observed by RXTE (Galloway+, 2008)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Model Model
18 A1 --- f_Model [c] c: variation of θ60 model (1)
20- 39 A20 --- Desc Description
41- 46 A6 --- Shape Star Shape (Oblate or Sphere)
48- 50 I3 Hz nu [400/600] Spin frequency
52- 55 F4.2 Msun Mass [1.3/1.7] Neutron star mass
57- 58 I2 km Rad [11/13] Equatorial radius
60- 61 I2 deg i [60] Observer's inclination angle
63- 66 F4.1 deg theta [19.8/64] Hotspot's co-latitude
68- 68 I1 10-3 phi [0] Phase offset
70- 74 F5.3 --- M/R [0.1/0.3] Dimensionless compactness ratio
76- 80 F5.3 --- sin sin(i)sin(theta) parameter
82- 86 F5.3 --- cos cos(i)cos(theta) parameter
88- 92 F5.3 --- Amp [0.3/1.4] Approximate bolometric pulse
amplitude
94- 98 F5.3 10-2 beta [0.03/0.2] Spot dimensionless projected
velocity β
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Note (1):
c = For a variation on the model θ60, a higher noise level was used:
θ60C6250 assumes 6250 photon counts per phase bin with no
background.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Model Model (as in Table 1)
19- 22 A4 --- Run Run Identifier (1)
24- 27 F4.1 --- chi2 [7/85.4]? Chi Square Fitting for 59 dof
29- 33 F5.3 Msun Mass [0.01/2] Neutron star mass
35- 39 F5.2 km Rad [0.1/16] Equatorial radius
41- 44 F4.1 deg i [4/77] Observer's inclination angle
46- 49 F4.1 deg theta [3.7/76.1] Hotspot's co-latitude
51- 57 F7.4 --- phi Phase offset
59- 64 F6.4 --- M/R [0.002/0.3] Dimensionless compactness ratio
66- 70 F5.3 --- sin [0.008/0.8] sin(i)sin(theta) parameter
72- 76 F5.3 --- cos [0.01/0.8] cos(i)cos(theta) parameter
78- 82 F5.3 --- Amp [0.01/1.4] Approximate bolometric pulse
amplitude
84- 89 F6.3 10-2 beta [0.08/15] Spot dimensionless projected
velocity β
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Note (1): Run Identifiers include both the true model value (Run=True),
independent best fit results for each of the 20 different realizations
(Run=1...20) or statistical measures for the ensemble realizations
(Run=Avg, Run=Std)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-May-2017