J/ApJ/933/136 0.4-10keV X-ray monitoring of Eta Car (Espinoza-Galeas+, 2022)
NICER X-ray observations of Eta Carinae during its most recent periastron
Passage.
Espinoza-Galeas D., Corcoran M.F., Hamaguchi K., Russell C.M.P.,
Gull T.R., Moffat A.F.J., Richardson N.D., Weigelt G., Hillier D.J.,
Damineli A., Stevens I.R., Madura T., Gendreau K., Arzoumanian Z.,
Navarete F.
<Astrophys. J., 933, 136 (2022)>
=2022ApJ...933..136E 2022ApJ...933..136E
ADC_Keywords: Binaries, X-ray ; X-ray sources
Keywords: Stellar winds ; X-ray sources ; Stellar evolution
Abstract:
We report high-precision X-ray monitoring observations in the
0.4-10keV band of the luminous, long-period colliding wind binary
Eta Carinae, up to and through its most recent X-ray
minimum/periastron passage in 2020 February. Eta Carinae reached its
observed maximum X-ray flux on 2020 January 7, at a flux level of
3.30x10-10ergs/s/cm2, followed by a rapid plunge to its observed
minimum flux, 0.03x10-10ergs/s/cm2, near 2020 February 17. The NICER
observations show an X-ray recovery from the minimum of only ∼16 days,
the shortest X-ray minimum observed so far. We provide new constraints
for the "deep" and "shallow" minimum intervals. Variations in the
characteristic X-ray temperatures of the hottest observed X-ray
emission indicate that the apex of the wind-wind "bow shock" enters
the companion's wind acceleration zone about 81 days before the start
of the X-ray minimum. There is a steplike increase in column density
just before the X-ray minimum, probably associated with the presence
of dense clumps near the shock apex. During the recovery and after,
the column density shows a smooth decline, which agrees with previous
NH measurements made by Swift at the same orbital phase, indicating
that the changes in the mass-loss rate are only a few percent over the
two cycles. Finally, we use the variations in the X-ray flux of the
outer ejecta seen by NICER to derive a kinetic X-ray luminosity of the
ejecta of ∼1041ergs/s near the time of the "Great Eruption."
Description:
NICER (the Neutron Star Interior Composition Explorer) is an X-ray
astronomy facility attached to the International Space Station (ISS).
NICER is devoted to time-resolved X-ray spectrometry in the
0.2-12.0keV energy band (see table 2 for characteristics of NICER).
NICER was launched on 2017-June-3 and deployed at the ISS on
2017-June-16.
NICER's primary mission is to obtain X-ray spectrometry with high
time, moderate spectral resolution and and 30arcmin^2 restricted field
of view of cosmic X-ray sources, primarily of X-ray binary pulsars.
NICER's combination of a large effective area, a restricted field of
view, and a broad bandpass in the thermal X-ray range makes it
especially well suited to observing X-ray variables like long-period
colliding wind binaries (and other sources), in addition to X-ray
pulsars.
NICER observed η Car between 2017-July-20 and 2021-February-21 and
has provided frequent measurements of η Car's X-ray spectrum,
typically twice per month, with appropriately increased sampling near
the periastron, when the variation in the X-ray spectrum occurs on
timescales of days.
In order to obtain a better estimation of the temperatures and the
column densities from the NICER spectra, we used an η Car spectrum
template with all the available dispersed spectra from Chandra HETG
(High Energy Transmission Grating). We combined the 32 CHANDRA HETG
observations in Table 4 to obtain a high-precision dispersed X-ray
spectrum, with a total exposure of 2Ms and an exposure-weighted
average phase of 0.73. See section 4.1.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
10 45 03.54 -59 41 03.9 * eta Car = TYC 8626-2809-1
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 50 39 HETG Chandra observations (0.4-10.0 keV)
table6.dat 99 265 Log of NICER observations and rates
table7.dat 102 265 NICER spectral modeling parameters
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2017)
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/A+A/465/993 : Spectral atlas of massive stars around He I (Groh+, 2007)
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/A+A/493/1093 : BVRI light curves of η Car (Fernandez-Lajus+, 2009)
J/ApJS/181/473 : Analysis of the spectrum of η Car (Nielsen+, 2009)
J/other/NewA/15.108 : UBVRIHa of η Car in 2009 (Fernandez-Lajus+ 2010)
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/ApJ/808/174 : FeII radiative transition rates (Bautista+, 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 minimum (Corcoran+, 2017)
J/ApJ/914/47 : ISS/NICER X-ray observations of eta Car (Kashi+, 2021)
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- ObsID [632/23131] Observation identifier
7- 15 F9.2 s Exptime [14703.7/102189.1] Exposure time
17- 35 A19 "datime" Date Date of observation (UT)
37- 44 F8.2 d MJD [51867.6/58875.9] Modified Julian Date
46- 50 F5.3 --- Phase [0.527/3.991] Phase
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 I10 --- OBSID [1110010101/3651032801] NICER Observation
identifier
12- 21 F10.4 d MJD-Start [57954/59176] Modified Julian Date at
observation start
23- 32 F10.4 d MJD-End [57954/59176] Modified Julian Date at
observation end
34- 39 F6.4 --- Phase [3.534/4.138] Phase
41- 46 F6.1 s Exptime [109/9946] Exposure time
48- 52 F5.2 ct/s CR2-10keV [0.25/32.42] Total Rate, 2.0-10.0 keV
54 A1 --- l_CR2-10keVNet Limit flag for CR2-10keVNet
55- 59 F5.2 ct/s CR2-10keVNet [0.02/31.87] Net Rate, 2.0-10.0 keV
61- 64 F4.2 ct/s e_CR2-10keVNet [0.01/0.4]? Uncertainty in CR2-10keVNet
66- 70 F5.2 ct/s CR2-3keV [0.05/13.07] Total Rate, 2.0-3.0 keV
72 A1 --- l_CR2-3keVNet Limit flag for CR2-3keVNet
73- 77 F5.2 ct/s CR2-3keVNet [0.01/12.96] Net Rate, 2.0-3.0 keV
79- 82 F4.2 ct/s e_CR2-3keVNet [0.01/0.25]? Uncertainty in CR2-3keVNet
84- 87 F4.2 ct/s CR5-7keV [0.05/4.24] Total Rate, 5.0-7.0 keV
89 A1 --- l_CR5-7keVNet Limit flag for CR5-7keVNet
91- 94 F4.2 ct/s CR5-7keVNet [0.01/4.16] Net Rate, 5.0-7.0 keV
96- 99 F4.2 ct/s e_CR5-7keVNet [0.01/0.15]? Uncertainty in CR5-7keVNet
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 I10 --- OBSID [1110010101/3651032801] NICER
Observation identifier
12- 15 F4.2 --- Phase [3.53/4.14] Phase
17- 21 F5.2 10-14W/m2 Flux [0.01/30.43] Flux, 10-11ergs/cm2/s
23- 26 F4.2 10+22cm-2 NH3 [3.0/5.0]? Column density, NH3
28- 31 F4.2 10+22cm-2 e_NH3 [0.02/5.25]? Uncertainty in NH3
33- 33 A1 --- l_kT4 Limit flag for kT4
35- 38 F4.2 keV kT4 [1.0/2.0]? weighted average temperature
40- 43 F4.2 keV e_kT4 [0.01/2.08]? Uncertainty in kT4
45- 48 F4.2 10+58cm-3 EM4 [0.0/6.33]? Emission measure
50- 54 F5.2 10+58cm-3 e_EM4 [0.0/11.73]? Uncertainty in EM4
56- 61 F6.2 10+22cm-2 NH5 [3.0/200.0]? Column density, NH5
63- 68 F6.2 10+22cm-2 e_NH5 [0.05/182.9]? Uncertainty in NH5
70- 70 A1 --- l_kT6 Limit flag for kT6
72- 75 F4.2 keV kT6 [2.0/6.0]? weighted average temperature
77- 80 F4.2 keV e_kT6 [0.1/4.02]? Uncertainty in kT6
82- 85 F4.2 10+58cm-3 EM6 [0.04/3.88]? Emission measure
87- 90 F4.2 10+58cm-3 e_EM6 [0.02/7.42]? Uncertainty in EM6
92- 96 F5.2 10-5ph/cm2/s Flux-FeK [0.74/51.31]? Flux, FeK
98-102 F5.2 10-5ph/cm2/s e_Flux-FeK [0.6/14.8]? Uncertainty in Flux-FeK
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History:
From electronic version of the journal
(End) Prepared by [AAS], Katia van der Woerd [CDS] 17-Jul-2024