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					    Recent X-ray Variability of Eta Car
    Approaching The X-ray Eclipse
M. F. Corcoran (USRA & GSFC-LHEA), J. H. Swank (GSFC-LHEA), K. Ishibashi (MIT), T. Gull
(GSFC-LASP), R. Humphreys (U. Minn), A. Damineli (IAGUSP), N. Walborn (STScI), D. J. Hillier
(U. Pitt), K. Davidson (U. Minn.), S. M. White (UMD), R. Petre (GSFC-LHEA), J. Pittard (Leeds),
Y. Butt (CfA), K. Verner (Catholic U.)




                                                      Chandra ACIS-I “true color” image
                                                      (Seward et al. 2000); low energy is
                                                      red, high energy blue-white. The X-
                                                      ray variable is the hard source
                                                      marked by the red circle.
Massive stars are rare (by number or by mass) but they
have a disportionate influence on the chemistry and
energy budget of the ISM.

 Some (largely) Unsolved Problems:
    • how do such massive stars form? (High luminosities
    affects protostellar accretion, and can halt or reverse
    accretion)
    • How do massive stars change their environments?
    (Wind-driven vs. episodic ejections; what causes episodic
    ejections anyway?)
    • How do massive stars produce supernovae and
    hypernovae, and what is their relation to GRBs? (tied to
    angular momentum evolution; B fields?)
    • What is the true binary fraction?
Eta Carinae: A Key Object
  • Eta Car is one of the most massive (possibly the most massive)
    star known;
  • A “Great Eruption” occurred in 1843 or thereabouts which
    created the “homunculus” nebula , a bipolar dusty shell (with
    between 2 to 15 solar masses) which surrounds the star
  • A “Lesser Eruption” occurred in the 1890’s with associated
    mass ejection (Ishibashi et al. 2001)
  • The Homunculus re-radiates the stellar flux in the IR, so that
    the present-day IR luminosity represents the total bolometric
    luminosity of the star: Lbol ~ 4 x 106 Lsun
Eta Car: From the Outside In
   The Outer Ejecta                                       The Homunculus
                                        W condensations
                                                                       the Paddle
          “Jet”


     Homunculus




                                                                                    The Star

                                                           The Skirt
                                               S Ridge

    E Condensations             “Strings”


   HST/WFPC2 [N II] 6583 (courtesy N. Smith)




  Multiple episodes of instability/mass ejections…
Eta Car in time:

                  Great Eruption

                                                 Expansion of Homunculus
                  Formation of Homunculus


                               Lesser Eruption



 Sterken (2000)




 The Historical V-band lightcurve: An
 LBV*?
                                                                           Damineli (1996)
 *LBV= Luminous Blue Variable, an evolved                                  identifies a 5.52 year
 massive star near the Eddington limit; unstable                           period in the star
The 5.52 Period: X-ray observations
                            • ROSAT observations in 1992 and 1993
                E<1.5 keV   discovered variations in the hard source
                            associated with the star

                E>1.5 keV   • Radio observations (Duncan et al. 1996)
                            also showed source brightening from 1992 to
                            1993
  1992   1993



 Hypothesis:
 • All observed variability on the Damineli period
 caused by the presence of a hot, less massive
 companion
 • X-ray variability caused by wind-wind collision
A colliding wind binary model:
                                      Shocked Gas produces a
                                      thermal spectrum of a few
           Colliding wind bow shock
                                      keV




                                        Pittard & Corcoran 2002
 Eta Car         Companion star
X-ray Monitoring
  Since 1992, X-rays from Eta Car have been monitored by ROSAT, ASCA, BeppoSAX
  and (since 1996) by RXTE. The 2-10 keV X-ray flux variation is below (ASCA and
  ROSAT shown as individual points, RXTE observations as a solid line). The red line is
  a colliding wind emission model from Corcoran et al. 2001.



                                              1992.4              1995.2                 1998.0        2000.7           2003.5

                                        X-ray lightcurve of Eta Car from 1992-
                                                                                                   ROSAT and ASCA data
                                        2003, phased with Damineli’s period
                                            mnet2_scaled=(mnet2-3)/1.2e11
                                                                                                   RXTE PCU2 L1 scaled data
                                  -10
                             1.5x10     of 5.52 years                                             (Corcoran et al. 2001)
                                                                                                   CWB model
  Observed Flux (2-10 keV)




                                                                                                   (Corcoran et al. 2001)



                                  1.0




                                  0.5




                                                     ROSAT
                                  0.0

                                               0.0                 0.5                   1.0            1.5                   2.0
                                                                                 Phase
The Orbit:

                  20
                                   May 2003
                                               Apr 2003

                              Jun 2003              Mar 2003
                                                          Feb 2003
                                                                Jan 2003
                  10
                        Start of totality
                        Dec 1997                                           2002
  Distance (AU)




                                                                                  2001

                   0
                                                                              To Earth


                          End of totality
                          Jan 1998
                                                                            2000              • Highly eccentric (e~0.9)
                  -10
                                        recovery
                                        Mar 1998               1999                           orbit
                                                                                              • line-of-sight along major
                                                                                              axis
                  -20                       Orbit of Secondary relative to Primary
                                            (based on elements in Corcoran et al. 2001)       • X-ray totality when the
                                                                                              companion moves behind
                    -10                0            10                20     30          40
                                                                                              Eta Car
                                                    Distance (AU)
Cycle-to-cycle variations:
Cycle-to-cycle differences:
                                                                                                           30
                        35                                                                                        PCU2 L1 net counts                               Chandra 200219
                                                                                                                  PCU2 L1 net counts from quicklook data

                                                                                                           25
                                   PCU2 L1 net counts




                                                                                    -1
                        30         PCU2 L1 net counts from quicklook data




                                                                                    Net PCU2 L1 counts s
                                                                                                           20
                                   Previous cycle

                                                                                                           15
-1




                        25
 Net PCU2 L1 counts s




                                                                                                           10

                                                                                                                   previous cycle
                                                                                                           5
                        20
                                                                                                           0
                                                                                                            1.7           1.8                   1.9         2.0                     2.1   2.2   2.3

                        15                                                                                                                                 Phase




                        10


                        5                              previous cycle


                        0
                             1.0               1.5                      2.0   2.5

                                           Orbital Phase




        • A significant increase in the overall X-ray flux in the interval 1.78<f<1.95
        compared to the 0.78<f<0.95 interval. This seems to suggest an overall increase in
        the X-ray flux in each cycle.
        • despite the higher X-ray flux, the NH derived from the RXTE spectra in the
        1.88<f<1.95 and 0.88<f<1.95 are in good agreement, though before that the NH
        seems to be larger in the current cycle
Grating Spectroscopy:
Nov 2000 vs. Oct 2002
                    80

                                     Fe XXV
                    60                    Fe I Ka1,Ka2                                200219
HEG Counts




                                                                                      200057 x 2.0
                    40


                    20


                    0
                         1       2            3              4        5               6                7        8

                                                            l (Angstroms)                                                                 100              SiXIV


                    100                                                               SiXIV
                                                                                                                                                                                                     SiXIII
                                                                                                                                                                                                                           200219 (AO4)
                                                                                                                                               80                                                                          AO1 x 2.0


                    80        200219 (AO4)                         SXVI
                                                   Ca XIX
                              AO1 x 2.0                                      SiXIV




                                                                                                                             MEG Counts
                                                                                                                                               60
       MEG Counts




                                                                                              SiXIII
                                                                      SXV
                    60                                      SXVI
                                                                                                                                               40
                               Fe XXV
                    40
                                                                                                                                               20
                                                                             SiXIII                    Mg XII
                    20
                                                                                                                                               0
                                                                                                                                               6.0   6.1     6.2      6.3       6.4     6.5    6.6            6.7          6.8   6.9      7.0
                                                                                                                                                                                   l (Angstroms)
                     0
                          1       2            3              4         5             6                7        8
                                                                                                                                          80
                                                             l (Angstroms)
                                                                                                                                                                       Fe XXV
                                                                                                                                          60                                                                    200219
                                                                                                                                                                                                                200257 x 2.0




                                                                                                                    HEG Counts
                                                                                                                                                                                                     Fe I Ka1,Ka2
                                                                                                                                          40



                                                                                                                                          20



                                                                                                                                          0
                                                                                                                                          1.80                 1.85                   1.90                          1.95                  2.00

                                                                                                                                                                                  l (Angstroms)
Conclusions…

  • The X-ray emission from Eta Car is fairly consistent with simple
  colliding wind models
  • BUT, as noted in Corcoran et al. (2001), the width of the
  eclipse suggests enhanced absorption after the companion
  moves in front of the primary, possibly evidence of enhanced
  mass loss from Eta Car near periastron
  • Some evidence of enhanced mass loss near periastron in radio
  (Duncan & White 2003) and from STIS UV line profile changes
  (Smith et al. 2003)
  • short-term (weeks) variations in X-rays with quasi-period of 85
  days (Ishibashi et al. 1997; Ishibashi et al. 1999); origin still not
  clear
…and more Conclusions
   • There is a significant cycle-to-cycle brightening in X-rays; the
     cause of this is unknown (maybe due to an increase in mass
     loss from the companion)
   • The apparent increase in X-ray emission stands in contrast
     to the apparent decline in radio brightness in the most recent
     cycle (Stephen White et al. 2003) and a continued decline in
     the equivalent width of the He I 10830 line (Damineli et al.
     2003).
   • Aside from an overall increase in the flux (by about a factor
     of 2) the most recent CHANDRA spectrum is nearly identical
     to that obtained in AO1. In particular the lines are still
     narrow, unshifted and the f/i ratio is large. What will happen
     near periastron?
The Next Eclipse:
 Based on the eclipse in 1998, we expect the X-rays
 to peak on May 22, 2003 and totality to start on
 June 27, 2003. X-ray observations have with
 Chandra, XMM & RXTE are approved.

 Other observations include an HST “Treasury”
 Program (PI: K. Davidson), INTEGRAL observations (PI:
 Yousaf Butt), and ground based observations at the
 ATNF (B. Duncan, S. White), the LNA (Brazil: A.
 Damineli), CASLEO (Argentina: V. Niemela), and SAAO
 (P. Whitelock) and other observatories.

 This will be one of the best-observed astronomical
 events ever
Goals of the Campaign:
 • Measure/constrain radial velocity                           30

 variations (Optical/UV lines: Eta Car;                                                          2003-05-22
                                                                                                                                 PCU2 L1 Net rate
 X-ray lines: Companion) to constrain                          25


 the mass of Eta Car and the
 companion and provide the best
                                                               20                                  2003-06-19




                                          -1
                                           Net PCU2 counts s
 measure of L/M                                                15
                                                                                                                           2003-09-16




 • Understand the changes in ionization
                                                               10
 in the Homunculus                                                           2003-06-23
                                                                                                              2003-08-05



 • watch the star vary from different                          5

                                                                                    2003-06-27
 angles via reflection off walls of the                        0
 homunculus                                                    2003.0   2003.2            2003.4                  2003.6           2003.8           2004.0

                                                                                                   Time (years)

 • Look for evidence of interactions
                                                                Expected X-ray variation, summer 2003
 near periastron
 • Look for evidence of mass loss
 enhancements near periastron: “Little
 Great Eruptions?” Possible hint about
 the cause of the Great Eruption?
"They finally came together in a fearful last death grip, in the midst of thick
   clouds and tempestuous elements; they fell to the ground with such
   force that they shook the whole world."
SPEELYAI FIGHTS EENUMTLA, From: George Benson Kuykendall, 1889, in History of the Pacific Northwest: Oregon and Washington,
     Volume II, Part VI, Elwood Evans, North Pacific history company, Portland, Oregon, pp. 60-95. Reprinted in: Clarence B. Bagley, 1930,
     "Indian Myths of the Northwest", Lowman and Hanford Co., Seattle, WA.



see

http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/2003.5/


for updates on the observing campaign and

http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/etacar_rxte_lightcurve/

for the most recent RXTE lightcurve

				
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