J/ApJ/914/47 ISS/NICER X-ray observations of eta Car (Kashi+, 2021)
The X-ray properties of eta Carinae during its 2020 X-ray minimum.
Kashi A., Principe D.A., Soker N., Kastner J.H.
<Astrophys. J., 914, 47 (2021)>
=2021ApJ...914...47K 2021ApJ...914...47K
ADC_Keywords: Stars, double and multiple; X-ray sources; Abundances
Keywords: Massive stars ; Binary stars ; Stellar winds ; X-ray stars
Abstract:
The massive binary system Eta Carinae is characterized by intense
colliding winds that form shocks and emit X-rays. The system is highly
eccentric (e∼0.9), resulting in modulated X-ray emission during its
5.54yr orbit. The X-ray flux increases in the months prior to
periastron passage, exhibiting strong flares, then rapidly declines to
a flat minimum lasting a few weeks, followed by a gradual recovery. We
present the Neutron Star Interior Composition Explorer telescope
spectra obtained before, during, and after the 2020 X-ray minimum, and
perform spectral analysis to establish the temporal behavior of the
X-ray flux and X-ray-absorbing column density (NH(t)) for the
2-10keV and 5-10keV energy ranges. The latter range is dominated by
the stellar wind-collision region and, therefore, these spectral
parameters-in particular, NH(t)-serve as potentially stringent
constraints on the binary orientation. We compare the observed NH(t)
results to the behavior predicted by a simple geometrical model in an
attempt to ascertain which star is closer to us at periastron: the
more massive primary (ω∼240°-270°) or the secondary
(ω∼90°). We find that the variations in column density, both
far from periastron and around periastron passage, support the latter
configuration (ω∼90°). The 2020 X-ray minimum showed the
fastest recovery among the last five minima, providing additional
evidence for a recent weakening of the primary star's wind.
Description:
Observations of η Car were obtained with the Neutron Star Interior
Composition Explorer (NICER), under NICER Guest Observer programs
1110 (PI: K. Gendreau), 2612 (PI: M. Corcoran), and 3651
(PI: D. Espinoza-Galeas).
NICER is an X-ray telescope attached to the International Space
Station (ISS). NICER's large effective area, broad bandpass, moderate
spectral resolution, and 30arcmin2 field of view provide the
capability of collecting spatially unresolved observations of X-ray
emitting regions surrounding η Car. Archival observations of
η Car by NICER were obtained for observing dates between
2017-July-20 and 2020-July-24.
Objects:
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RA (ICRS) DE Designation(s)
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10 45 03.53 -59 41 04.0 eta Carinae = HD 93308
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 117 239 Best-fit model parameters to the 2-10keV NICER
X-ray spectra of Eta Car between July 2017 and
July 2020 and their 90% confidence values
table2.dat 132 233 Best-fit model parameters to the 5-10keV NICER
X-ray spectra of Eta Car between July 2017 and
July 2020 and their 90% confidence values
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See also:
J/A+AS/133/299 : Long-term spectroscopy of eta Carinae (Damineli+ 1998)
J/A+A/343/847 : Geneva Photometry of Eta Car (van Genderen+ 1999)
J/A+A/419/215 : Emission lines of Sr filament near η Car (Hartman+, 2004)
J/AJ/129/2018 : RXTE scaled fluxes of eta Car (Corcoran+, 2005)
J/ApJS/157/138 : UV spectrum of eta Car (Nielsen+, 2005)
J/ApJS/163/173 : UV spectrum of eta Car in 2003.5 (Gull+, 2006)
J/ApJS/168/289 : NUV spectrum of eta Car in 2003.5 (Nielsen+, 2007)
J/AJ/135/1249 : The early spectra of eta Carinae (Humphreys+, 2008)
J/ApJS/181/473 : Analysis of the spectrum of η Car (Nielsen+, 2009)
J/A+A/493/1093 : BVRI light curves of η Car (Fernandez-Lajus+, 2009)
J/other/NewA/15.108 : eta Car UBVRIHa LCs in 2009 (Fernandez-Lajus+ 2010)
J/ApJS/194/2 : Chandra Carina Complex Project (CCCP) cat. (Broos+, 2011)
J/A+A/540/A133 : η Car emission spectrum (1700-10400Å) (Zethson+, 2012)
J/ApJ/751/73 : Equivalent widths in η Cat in 1998-2012 (Mehner+, 2012)
J/A+A/564/A14 : Near-infrared photometry of η Carinae (Mehner+, 2014)
J/A+A/578/A122 : eta Carinae's 2014.6 spectroscopic event (Mehner+, 2015)
J/AJ/150/109 : Spectroscopy of η Car in 2009 (Richardson+, 2015)
J/A+A/594/A106 : eta Car velocity-resolved imaging (Weigelt+, 2016)
J/ApJ/838/45 : eta Car obs. around the 2014 X-ray min. (Corcoran+, 2017)
http://heasarc.gsfc.nasa.gov/W3Browse/nicer/nicermastr.html : NICER home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Date NICER Observation Date, UT, ISO-8601
21- 30 I10 --- ObsID Unique observation number
32 A1 --- l_NH Limit flag on NH (G1)
34- 37 F4.1 10+22cm-2 NH [0.7/34.7]? Absorbing column density
39- 43 F5.1 10+22cm-2 E_NH [0.1/490]? Upper 90% confidence interval
on NH
45- 48 F4.1 10+22cm-2 e_NH [0.1/21]? Lower 90% confidence interval on NH
50 A1 --- l_kT Limit flag on kT (G1)
52- 54 F3.1 keV kT [0.7/7.4]? Plasma energy
56- 59 F4.1 keV E_kT [0.1/34.5]? Upper 90% confidence interval
on kT
61- 63 F3.1 keV e_kT [0.1/3.7]? Lower 90% confidence interval
on kT
65 A1 --- l_Fe Limit flag on Fe (G1)
67- 71 F5.2 [Sun] Fe [0.12/49.38]? Iron abundance, relative to
Solar
73- 76 F4.2 [Sun] E_Fe [0.02/1.2]? Upper 90% confidence interval
on Fe
78- 81 F4.2 [Sun] e_Fe [0.02/0.8]? Lower 90% confidence interval
on Fe
83- 87 F5.2 [cm-3] logEM [56.53/58.56] Log of the emission measure
89- 92 F4.2 [cm-3] E_logEM [0.01/1.7] Upper 90% confidence interval
on logEM
94- 97 F4.2 [cm-3] e_logEM [0.01/1.2] Lower 90% confidence interval
on logEM
99- 102 F4.1 10-14W/m2 Flux [0.1/30] Observed flux in the 2-10keV band,
10-11 erg/s/cm2 (G2)
104- 107 F4.2 10-14W/m2 E_Flux [0.03/5.5] Upper 90% confidence interval
on Flux
109- 112 F4.2 10-14W/m2 e_Flux [0.04/5.6] Lower 90% confidence interval
on Flux
114- 117 F4.2 --- chi2 [0.44/1.5] Reduced χ^2 value associated
with the best fit model
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Date NICER Observation Date, UT, ISO-8601
21- 30 I10 --- ObsID Unique observation number
32 A1 --- l_NH Limit flag on NH (G1)
34- 36 I3 10+22cm-2 NH [8/430]? Absorbing column density
38- 40 I3 10+22cm-2 E_NH [4/293]? Upper 90% confidence interval
on NH
42- 43 I2 10+22cm-2 e_NH [4/78]? Lower 90% confidence interval
on NH
45 A1 --- l_kT Limit flag on kT (G1)
47- 49 F3.1 keV kT [0.3/8]? Plasma energy
51- 54 F4.1 keV E_kT [0.2/13.7]? Upper 90% confidence interval
on kT
56- 58 F3.1 keV e_kT [0.1/5.1]? Lower 90% confidence interval
on kT
60 A1 --- l_Fe Limit flag on Fe (G1)
62- 65 F4.2 [Sun] Fe [0.13/6.72]? Iron abundance, relative to
Solar
67- 70 F4.2 [Sun] E_Fe [0.04/2.3]? Upper 90% confidence interval
on Fe
72- 75 F4.2 [Sun] e_Fe [0.04/0.7]? Lower 90% confidence interval
on Fe
77- 81 F5.2 [cm-3] logEM [56.47/60.24] Log of the emission measure
83- 86 F4.2 [cm-3] E_logEM [0.07/3.2] Upper 90% confidence interval
on logEM
88- 91 F4.2 [cm-3] e_logEM [0.05/2.3] Lower 90% confidence interval
on logEM
93 A1 --- l_Flux Limit flag on Flux (G1)
95- 99 F5.2 10-14W/m2 Flux [0.03/14]? Observed flux in the 5-10keV
band, 10-11erg/s/cm2 (G2)
101- 104 F4.1 10-14W/m2 E_Flux [0.1/28]? Upper 90% confidence interval
on Flux
106- 110 F5.2 10-14W/m2 e_Flux [0.03/10]? Lower 90% confidence interval
on Flux
112- 115 F4.1 10-14W/m2 IntFlux [0.1/56] Intrinsic (i.e., unabsorbed) flux
in the 5-10keV band, 10-11erg/s/cm2 (G2)
117- 121 F5.2 10-14W/m2 E_IntFlux [0.1/50] Upper 90% confidence interval
on Flux
123- 127 F5.2 10-14W/m2 e_IntFlux [0.08/49] Lower 90% confidence interval
on Flux
129- 132 F4.2 --- chi2 [0.3/2.94] Reduced χ^2 value
associated with the best fit model
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Global notes:
Note (G1): Table locations with missing values indicate the spectral
parameter or both confidence values hit a hard minimum or maximum when
fitting and thus are not reliable. Spectral parameters missing a single
upper or lower confidence value are reported as lower or upper limits.
Note (G2): Flux calculated assuming a distance of 2.6kpc.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Dec-2022