NASA Technical Reports Server (NTRS) 20000117681: Spectral and Timing Investigations of Dwarf Novae Selected in Hard X-Rays

2 Pages·0.08 MB·English

by  NASA Technical Reports Server (NTRS)

Final Technical report
NASA Grant NAG5-7375
Awarded for observations with the Rossi X-ray Timing Explorer
Title: Spectral and Timing Investigations of Dwarf Novae
Selected in Hard X-rays
P.I. Dr. Ronald A. Remillard (M.I.T.)
M.I.T. OSP Account: 6703800
CoInvestigator: John Thorstensen (Dartmouth College)
Summary of the Investigation and Results:
There are 9 dwarf novae (DN) among the 43 cataclysmic
variables (accreting white dwarfs in close binary systems) that were
detected during the HEAO-I all-sky X-ray survey (1977-1979). On the
other hand, there are roughly one hundred dwarf novae that are closer
and/or optically brighter and yet they were not detected as hard X-ray
sources. Two of the HEAO-I DN show evidence for X-ray pulsations that
imply strong magetic fields on the white dwarf surface, and magnetic
CVs are known to be strong X-ray sources. However, substantial flux in
hard X-rays may be caused by non-magnetic effects, such as an
optically thin boundary layer near a massive white dwarf. We proposed
RXTE observations to measure plasma temperatures and to search for
X-ray pulsations. The observations would distinguish whether these DN
belong to one of (rare) magnetic subclasses. For those that do not
show pulsations, the observations support efforts to define empirical
relations between X-ray temperature, the accretion rate, and the mass
of the white dwarf. The latter is determined via optical studies of
the dynamics of the binary constituents.
Each target was observed for 15 ksec during the time interval
of Jan 24-28 1998. Optical observations using faciltities of
Dartmouth College (MDM Observatory) confirmed that each DN was in the
normal, "quiescent" state. The net PCA spectra show significant X-ray
detections, as shown in Figure i. The average X-ray flux measures
(2-20 keV) were 0.78 mCrab for SU Uma, 0.59 mCrab for WW Cet, and 0.51
mCrab for SS Auriga. There was no evidence of pulsations for any
X-ray source. The X-ray spectra can be fit with a simple thermal
bremsstrahlung spectrum and a 6.7 keV Fe line. The derived
temperatures are much higher than the -3 keV temperatures of the
closest and brightest dwarf novae, and we suggest that these 3 targets
are systems that contain particularly massive white dwarfs.
Publications:
All of the X-ray data are fully analyzed. However, at the
time of this report, we have not yet submitted the results
for publication. The remaining work is simply to compare these
cases with the other DN X-ray spectra that are being accumulated in the
RXTE archive by other observers of cataclysmic variables.
It is expected that this work will be completed during the suntmer of 2001.
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