493 research outputs found
A precise determination of angular momentum in the black hole candidate GRO J1655-40
We note that the recently discovered 450 Hz frequency in the X-ray flux of
the black hole candidate GRO J1655-40 is in a 3:2 ratio to the previously known
300 Hz frequency of quasi-periodic oscillations (QPO) in the same source. If
the origin of high frequency QPOs in black hole systems is a resonance between
orbital and epicyclic motion of accreting matter, as suggested previously, the
angular momentum of the black hole can be accurately determined, given its
mass. We find that the dimensionless angular momentum is in the range
if the mass is in the (corresponding) range of 5.5 to 7.9 solar
masses
HST/STIS UV Spectroscopy of Two Quiescent X-ray Novae: A0620-00 and Centaurus X-4
In 1998 we made UV spectroscopic observations with HST/STIS of A0620-00 and
Cen X-4, which are two X-ray novae (aka soft X-ray transients). These binary
systems are similar in all respects except that the former contains a black
hole and the latter contains a neutron star. A UV spectrum (1700-3100A) is
presented for the quiescent state of each system in the context of previously
published UV/optical and X-ray data. The non-stellar, continuum spectrum of
black hole A0620-00 has a prominent UV/optical peak centered at about 3500A. In
contrast the spectrum of neutron-star Cen X-4 lacks a peak and rises steadily
with frequency over the entire UV/optical band. In the optical, the two systems
are comparably luminous. However, black hole A0620-00 is about 6 times less
luminous at 1700A, and about 40 times less luminous in the X-ray band. The
broadband spectrum of A0620-00 is discussed in terms of the advection-dominated
accretion flow model.Comment: 18 pages including 4 figures; tentatively scheduled for the March 10,
2000 issue of ApJ; minor revision
A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient Prototype, V616 Mon (A0620-00)
We have obtained optical and infrared photometry of the soft x-ray transient
prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of
K4 for the secondary star in the system, which is consistent with spectroscopic
observations. We present J-, H-, and K-band light curves modeled with WD98 and
ELC. Combining detailed, independently run models for ellipsoidal variations
due to a spotted, non-spherical secondary star, and the observed ultraviolet to
infrared spectral energy distribution of the system, we show that the most
likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination
angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.Comment: 29 pages (preprint format), including 7 figures and 4 tables,
accepted for publication in the Nov 2001 issue of A
On the bolometric quiescent luminosity and luminosity swing of black hole candidate and neutron star low mass X-ray transients
Low mass X-ray transients (LMXRTs) hosting black hole candidates (BHCs)
display on average a factor of ~100 larger swing in the minimum (quiescent) to
maximum (outburst) X-ray luminosity than neutron stars (NSs), despite the fact
that the swing in the mass inflow rate is likely in the same range. Advection
dominated accretion flows (ADAFs) were proposed to interpret such a difference.
The residual optical/UV emission of quiescent LMXRTs, after subtraction of the
companion star spectrum, is produced by synchrotron radiation in the (latest
version) of ADAF and therefore is part of the ADAF's luminosity budget. We
demonstrate that, once the residual optical/UV emission is taken into account,
the bolometric luminosity swing of BHCs is consistent with that of NSs. We
explore here an alternative scenario to ADAFs in which very little mass
accretion onto the collapsed star takes place in the quiescence intervals. The
residual optical/UV emission of BHCs are expected to derive from the energy
released by the matter transferred from the companion star at radii comparable
to the circularisation radius. The quiescent X-ray luminosity originates either
from accretion onto the BH at very low rates and/or from coronal activity in
the companion star or in the outer disk. For comparably small mass inflow
rates, the NSs in these systems are likely in the radio pulsar regime. In the
interaction of the radio pulsar relativistic wind with matter transferred from
the companion star, a shock forms, the power law-like emission of which powers
both the harder X-ray emission and most of the residual optical/UV. The soft,
thermal-like X-ray component may arise from the cooling of the NS surface. This
scenario matches well both the X-ray and bolometric luminosity swing of LMXRTs.
(ABRIDGED).Comment: 13 pages (including 2 postscript figures - use emulateapj macro).
Accepted for publication in Ap
Correlation between muonic levels and nuclear structure in muonic atoms
A method that deals with the nucleons and the muon unitedly is employed to
investigate the muonic lead, with which the correlation between the muon and
nucleus can be studied distinctly. A "kink" appears in the muonic isotope shift
at a neutron magic number where the nuclear shell structure plays a key role.
This behavior may have very important implications for the experimentally
probing the shell structure of the nuclei far away from the -stable
line. We investigate the variations of the nuclear structure due to the
interaction with the muon in the muonic atom and find that the nuclear
structure remains basically unaltered. Therefore, the muon is a clean and
reliable probe for studying the nuclear structure. In addition, a correction
that the muon-induced slight change in the proton density distribution in turn
shifts the muonic levels is investigated. This correction to muonic level is as
important as the Lamb shift and high order vacuum polarization correction, but
is larger than anomalous magnetic moment and electron shielding correction.Comment: 2 figure
Time-resolved optical photometry of the ultra-compact binary 4U0614+091
We present a detailed optical study of the ultra-compact X-ray binary
4U0614+091. We have used 63 hrs of time-resolved optical photometry taken with
three different telescopes (IAC80, NOT and SPM) to search for optical
modulations. The power spectra of each dataset reveals sinusoidal modulations
with different periods, which are not always present. The strongest modulation
has a period of 51.3 mins, a semi-amplitude of 4.6 mmags, and is present in the
IAC80 data. The SPM and NOT data show periods of 42 mins and 64 mins
respectively, but with much weaker amplitudes, 2.6 mags and 1.3 mmags
respectively. These modulations arise from either X-ray irradiation of the
inner face of the secondary star and/or a superhump modulation from the
accretion disc, or quasi-periodic modulations in the accretion disc. It is
unclear whether these periods/quasi-periodic modulations are related to the
orbital period, however, the strongest period of 51.3 mins is close to earlier
tentative orbital periods. Further observations taken over a long base-line are
encouraged.Comment: Accepted for publication in PAS
On the Relation of Hard X-ray Peak Flux and Outburst Waiting Time in the Black Hole Transient GX 339-4
Aims. In this work we re-investigated the empirical relation between the hard
X-ray peak flux and the outburst waiting time found previously in the black
hole transient GX 339-4. We tested the relation using the observed hard X-ray
peak flux of the 2007 outburst of GX 339-4, clarified issues about faint
flares, and estimated the lower limit of hard X-ray peak flux for the next
outburst. Methods. We included Swift/BAT data obtained in the past four years.
Together with the CGRO/BATSE and RXTE/HEXTE light curves, the observations used
in this work cover a period of 18 years. Results. The observation of the 2007
outburst confirms the empirical relation discovered before. This strengthens
the apparent link between the mass in the accretion disk and the peak
luminosity of the brightest hard state that the black hole transient can reach.
We also show that faint flares with peak fluxes smaller than about 0.12 crab do
not affect the empirical relation. We predict that the hard X-ray peak flux of
the next outburst should be larger than 0.65 crab, which will make it at least
the second brightest in the hard X-ray since 1991.Comment: 4 pages, 3 figures, accepted by A&
Nuclear signatures in high-harmonic generation from laser-driven muonic atoms
High-harmonic generation from muonic atoms exposed to intense laser fields is
considered. Our particular interest lies in effects arising from the finite
nuclear mass and size. We numerically perform a fully quantum mechanical
treatment of the muon-nucleus dynamics by employing modified soft-core and
hard-core potentials. It is shown that the position of the high-energy cutoff
of the harmonic spectrum depends on the nuclear mass, while the height of the
spectral plateau is sensitive to the nuclear radius. We also demonstrate that
-ray harmonics can be generated from muonic atoms in ultrastrong VUV
fields, which have potential to induce photo-nuclear reactions.Comment: 5 pages, 3 figure
An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen Primar Star
We describe optical photometric and spectroscopic observations of the bright
variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal
variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a
period of 91.645 days. A deep primary eclipse is visible for wavelengths <
4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse
timings and the radial velocity curve of the K0 secondary star indicate an
interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers
material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The
primary star is either an early B-type star or a black hole. If it did contain
a black hole, BG Gem would be the longest period black hole binary known by a
factor of 10, as well as the only eclipsing black hole binary system.Comment: 27 pages, includes 8 figures and 5 tables, accepted to A
New XMM-Newton analysis of three bright X-ray sources in M31 globular clusters, including a new black hole candidate
We present detailed analysis of three globular cluster X-ray sources in the
XMM-Newton extended survey of M31. The X-ray counterpart to the M31 globular
cluster Bo 45 (XBo 45) was observed with XMM-Newton on 2006 December 26. Its
combined pn+MOS 0.3--10 keV lightcurve exhibited a r.m.s variability of ~10%,
and its 0.3--7.0 keV emission spectrum was well described by an absorbed power
law with photon index 1.440.12. Its variability and emission is
characteristic of low mass X-ray binaries (LMXBs) in the low-hard state,
whether the accretor is a neutron star or black hole. Such behaviour is
typically observed at luminosities \la10% Eddington. However, XBo 45
exhibited this behaviour at an unabsorbed, 0.3--10 keV luminosity of
2.5 erg s, or{~140%} Eddington for a 1.4
neutron star accreting hydrogen. Hence, we identify XBo 45 as a new
candidate black hole LMXB. XBo 45 appears to have been consistently bright for
~30 years, consistent with theoretical prediction for a globular cluster black
hole binary formed via tidal capture. Bo 375 was observed in the 2007, January
2 XMM-Newton observation, and has a two-component spectrum that is typical for
a bright neutron star LMXB. Bo 135 was observed in the same field as Bo 45, and
could contain either a black hole or neutron star.Comment: Accepted by ApJ, 16 pages, 5 figures. This version includes the final
changes made at the request of the refere
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