Central Bureau for Astronomical Telegrams
IAUC 6842: eta Car; 1SAX J1603.9-7753
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Circular No. 6842
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
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Phone 617-495-7244/7440/7444 (for emergency use only)
eta CARINAE
M. F. Corcoran, Goddard Space Flight Center (GSFC) and
Universities Space Research Association; J. H. Swank and R. Petre,
GSFC; and K. Ishibashi and K. Davidson, University of Minnesota,
report: "Continuing observation of this peculiar luminous star with
the RXTE PCA shows that the star may be emerging from the x-ray
'low state' that began in early Dec. 1997. During the low state,
the PCA countrate in the band 2-10 keV dropped from > 70 to 15 PCU
counts/s in a period of about 1 month. Recent RXTE observations
show that the observed x-ray emission has risen by about a factor
of 2 since 1998 Feb. 2. After correcting for the permanent sky
background, the countrate due to eta Car itself has increased by a
factor close to 6. Since Feb. 16, the average rate of increase in
the x-ray emission has been Delta(R) = +0.7 PCU counts sE-1 dayE-1.
This is still considerably less than the rate of decline to x-ray
minimum, Delta(R) = -1.6 PCU counts sE-1 dayE-1 during the interval
1997 Nov. 11-Dec. 18. Using a conversion factor of 3.22 x 10E-12
erg sE-1 cmE-2 per PCA count in the band 2-10 keV suggests that at
present the rate of increase in 2-10-keV flux is about 2.25 x
10E-12 erg cmE-2 sE-1 dayE-1. If the rate of increase remains
constant, then the x-ray flux from eta Car should reach or exceed
the previous maximum flux level on May 8. The recent x-ray
brightening could also be associated with episodic flaring
previously reported (IAUC 6668), since the next flare maximum is
expected to occur on Mar. 17."
1SAX J1603.9-7753
J. M. Muller, BeppoSAX Science Data Center, Rome, and Space
Research Organization of the Netherlands (SRON), Utrecht; J. in 't
Zand, SRON; M. J. S. Smith, BeppoSAX Science Operation Center (SOC),
Rome, and SRON; A. Coletta, L. Di Ciolo, and V. Torroni, SOC; and
L. Piro, Istituto Astrofisica Spaziale, CNR, Rome, report on behalf
of the BeppoSax team: "On Mar. 6.16 UT, the BeppoSAX Wide Field
Camera 2 detected an x-ray burst-like event at R.A. = 16h03m54s,
Decl. = -77o53'.1 (equinox 2000.0, preliminary error radius 3').
As no catalogued x-ray source can be found within the error circle,
we call the source 1SAX J1603.9-7753. The event lasted about 40 s
and had peak intensities of 0.15 Crab in the energy band 2-10 keV
and 0.30 Crab at 10-25 keV. The rise and decay times were similar.
The source was not detected during 1.1 days before the burst, with
a 3-sigma upper limit of 2 mCrab (2-10 keV). The error circle
contains the Tycho star 9446-00734-1 (distance 80 pc), as well as
IRAS 15567-7741."
(C) Copyright 1998 CBAT
1998 March 16 (6842) Daniel W. E. Green
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