90 research outputs found
Simultaneous IUE, EXOSAT and optical observations of the unusual AM Her type variable H058+608
Simultaneous observations of the AM Her type variable H0538+608 made with IUE, EXOSAT, and a 1.3 m ground based telescope, and subsequent optical spectrophotometry at high and low resolution are discussed. The X-ray and optical data show clear evidence of a 3.30 + or - 0.03 hr period. Three SWP spectra were taken outside of eclipse and during overlapping phase intervals. The UV spectra contain strong emission lines characteristic of this class of objects and a flat continuum which appears to be deficient, given the brightness of source at optical and X-ray wavelengths. There is evidence for intensity variations in emission lines, particularly C IV. The X-ray light curves for H0538+608 reveal behavior which may be related to irregularities in its accretion flow
A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
Using the Very Long Baseline Array, we have measured a trigonometric parallax
for the micro quasar GRS 1915+105, which contains a black hole and a K-giant
companion. This yields a direct distance estimate of 8.6 (+2.0,-1.6) kpc and a
revised estimate for the mass of the black hole of 12.4 (+2.0,-1.8) Msun. GRS
1915+105 is at about the same distance as some HII regions and water masers
associated with high-mass star formation in the Sagittarius spiral arm of the
Galaxy. The absolute proper motion of GRS 1915+105 is -3.19 +/- 0.03 mas/y and
-6.24 +/- 0.05 mas/y toward the east and north, respectively, which corresponds
to a modest peculiar speed of 22 +/-24 km/s at the parallax distance,
suggesting that the binary did not receive a large velocity kick when the black
hole formed. On one observational epoch, GRS 1915+105 displayed superluminal
motion along the direction of its approaching jet. Considering previous
observations of jet motions, the jet in GRS 1915+105 can be modeled with a jet
inclination to the line of sight of 60 +/- 5 deg and a variable flow speed
between 0.65c and 0.81c, which possibly indicates deceleration of the jet at
distances from the black hole >2000 AU. Finally, using our measurements of
distance and estimates of black hole mass and inclination, we provisionally
confirm our earlier result that the black hole is spinning very rapidly.Comment: 20 pages; 2 tables; 6 figure
RXTE Observations of 0.1-300 Hz QPOs in the Microquasar GRO J1655-40
We have investigated 52 RXTE pointed observations of GRO J1655-40 spanning
the X-ray outburst that commenced on 1996 April 25 and lasted for 16 months.
Our X-ray timing analyses reveal four types of QPOs: three with relatively
stable central frequencies at 300 Hz, 9 Hz, and 0.1 Hz, and a fourth that
varied over the range 14-28 Hz. The 300 Hz and 0.1 Hz QPOs appear only at the
highest observed luminosities (Lx > 0.15 Ledd), where the power-law component
dominates the X-ray spectrum. At lower luminosity, the disk flux exceeds the
power-law flux and only two of the QPOs are observed: the spectrally "soft" 9
Hz QPO, and the narrow, "hard" QPO that varies from 14-28 Hz as the hard flux
decreases. The 300 Hz QPO is likely to be analogous to the stationary QPO at 67
Hz seen in the microquasar GRS1915+105. We discuss models of these
high-frequency QPOs which depend on effects due to general relativity. The 9 Hz
QPO displays a spectrum consistent with a thermal origin, but this frequency
does not appear to be consistent with any of the natural time scales associated
with the disk, or with the inferred values of the mass and rapid spin of the
black hole. The mechanism for the 14-28 Hz QPOs appears to be linked to the
power-law component, as do the 1-10 Hz QPOs in GRS1915+105. Finally, we show
data for GRO J1655-40 and GRS1915+105 as each source teeters between relative
stability and a state of intense oscillations at 0.1 Hz. A comparison of the
sources' spectral parameters allows us to speculate that the black hole mass in
GRS1915+105 is very large, possibly in the range 39-70 Msun.Comment: 45 pages, including 10 figs.; latex; aasms4.sty; submitted to the
Astrophysical Journal, June 2, 199
Orbital Parameters for the Black Hole Binary XTE J1650-500
(Shortened) We present R-band photometry of the X-ray transient and candidate
black hole binary XTE J1650-500 obtained between 2003 May and August with the
6.5m Clay Telescope. A timing analysis of these data reveals a photometric
period of 0.3205 +/- 0.0007 days (i.e. 7.63 hr) with a possible alias at 0.3785
days (9.12 hr). Our photometry completely rules out the previously published
spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the
15 archival ESO/VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.)
that were the basis of the previously published spectroscopic period. We used a
``restframe search'' technique that is well suited for cases when the
signal-to-noise ratio of individual spectra is low. The results confirmed the
photometric period of 0.3205 days, and rule out the alias period near 0.38
days. The best value for the velocity semiamplitude of the companion star is
K_2 = 435 +/- 30 km/sec, and the corresponding optical mass function is f(M) =
2.73 +/- 0.56 solar masses. The amplitude of the phased R-band light curve is
0.2 magnitudes, which gives a lower limit to the inclination of 50 +/- 3
degrees in the limiting case of no contribution to the R-band light curve from
the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass
ratios of other black hole binaries like A0620-00 or GRS 1124-683 (e.g. Q >~
10), then our lower limit to the inclination gives an upper limit to the mass
of the black hole in XTE J1650-500 of M_1 <~ 7.3 solar masses. However, the
mass can be considerably lower if the R-band flux is dominated by the accretion
disk. For example, if the accretion disk does contribute 80% of the flux, as
our preliminary results suggest, then the black hole mass would be only about 4
solar masses.Comment: Accepted to ApJ. 15 pages, 5 figures (two of degraded quality).
Revised after referee's Comments, conclusions are unchange
X-ray Properties of Black-Hole Binaries
We review the properties and behavior X-ray binaries that contain an
accreting black hole. The larger majority of such systems are X-ray transients,
and many of them were observed in daily pointings with RXTE throughout the
course of their outbursts. The complex evolution of these sources is described
in terms of common behavior patterns illustrated with comprehensive overview
diagrams for six selected systems. Central to this comparison are three X-ray
states of accretion, which are reviewed and defined quantitatively. Each state
yields phenomena that arise in strong gravitational fields. We sketch a
scenario for the potential impact of black hole observations on physics and
discuss a current frontier topic: the measurement of black hole spin.Comment: 39 pages, 12 figures, ARAA, vol. 44, in pres
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