3,622 research outputs found
The linear rms-flux relation in an Ultraluminous X-ray Source
We report the first detection of a linear correlation between rms variability
amplitude and flux in the Ultraluminous X-ray source NGC 5408 X-1. The rms-flux
relation has previously been observed in several Galactic black hole X-ray
binaries (BHBs), several Active Galactic Nuclei (AGN) and at least one neutron
star X-ray binary. This result supports the hypothesis that a linear rms-flux
relation is common to all luminous black hole accretion and perhaps even a
fundamental property of accretion flows about compact objects. We also show for
the first time the cross-spectral properties of the variability of this ULX,
comparing variations below and above 1 keV. The coherence and time delays are
poorly constrained but consistent with high coherence between the two bands,
over most of the observable frequency range, and a significant time delay (with
hard leading soft variations). The magnitude and frequency dependence of the
lags are broadly consistent with those commonly observed in BHBs, but the
direction of the lag is reversed. These results indicate that ULX variability
studies, using long X-ray observations, hold great promise for constraining the
processes driving ULXs behaviour, and the position of ULXs in the scheme of
black hole accretion from BHBs to AGN.Comment: 4 Pages, 3 figures, accepted for publication by MNRAS
Impact of Neutron Decay Experiments on non-Standard Model Physics
This paper gives a brief overview of the present and expected future limits
on physics beyond the Standard Model (SM) from neutron beta decay, which is
described by two parameters only within the SM. Since more than two observables
are accessible, the problem is over-determined. Thus, precise measurements of
correlations in neutron decay can be used to study the SM as well to search for
evidence of possible extensions to it. Of particular interest in this context
are the search for right-handed currents or for scalar and tensor interactions.
Precision measurements of neutron decay observables address important open
questions of particle physics and cosmology, and are generally complementary to
direct searches for new physics beyond the SM in high-energy physics. Free
neutron decay is therefore a very active field, with a number of new
measurements underway worldwide. We present the impact of recent developments.Comment: 13 pages, 6 figures; Proceedings of the 5th International BEYOND 2010
Conference, Cape Town, South Africa (2010), World Scientific, accepted for
publication; Corrected typo
Stellar neutron capture cross sections of ⁴¹K and ⁴⁵Sc
The neutron capture cross sections of light nuclei (
Neutron activation of natural zinc samples at kT = 25 keV
The neutron-capture cross sections of 64Zn, 68Zn, and 70Zn have been measured
with the activation technique in a quasistellar neutron spectrum corresponding
to a thermal energy of kT = 25 keV. By a series of repeated irradiations with
different experimental conditions, an uncertainty of 3% could be achieved for
the 64Zn(n,g)65Zn cross section and for the partial cross section
68Zn(n,g)69Zn-m feeding the isomeric state in 69Zn. For the partial cross
sections 70Zn(n,g)71Zn-m and 70Zn(n,g)71Zn-g, which had not been measured so
far, uncertainties of only 16% and 6% could be reached because of limited
counting statistics and decay intensities. Compared to previous measurements on
64,68Zn, the uncertainties could be significantly improved, while the 70Zn
cross section was found to be two times smaller than existing model
calculations. From these results Maxwellian average cross sections were
determined between 5 and 100 keV. Additionally, the beta-decay half-life of
71Zn-m could be determined with significantly improved accuracy. The
consequences of these data have been studied by network calculations for
convective core He burning and convective shell C burning in massive stars
Stellar (n,gamma) cross sections of p-process isotopes PartI: 102Pd, 120Te, 130,132Ba,and 156Dy
We have investigated the (n,gamma) cross sections of p-process isotopes with
the activation technique. The measurements were carried out at the Karlsruhe
Van de Graaff accelerator using the 7Li(p,n)7Be source for simulating a
Maxwellian neutron distribution of kT = 25 keV. Stellar cross section
measurements are reported for the light p-process isotopes 102Pd, 120Te,
130,132Ba, and 156Dy. In a following paper the cross sections of 168Yb, 180W,
184Os, 190Pt, and 196Hg will be discussed. The data are extrapolated to
p-process energies by including information from evaluated nuclear data
libraries. The results are compared to standard Hauser-Feshbach models
frequently used in astrophysics.Comment: 13 pages, 4 figure
The Ubiquity of the rms-flux relation in Black Hole X-ray Binaries
We have investigated the short term linear relation between the rms
variability and the flux in 1,961 observations of 9 black hole X-ray binaries.
The rms-flux relation for the 1-10 Hz range is ubiquitously observed in any
observation with good variability signal to noise (> 3 % 1-10 Hz fractional
rms). This concurs with results from a previous study of Cygnus X-1 (Gleissner
et. al. 2004), and extends detection of the rms-flux relation to a wider range
of states. We find a strong dependence of the flux intercept of the rms-flux
relation on source state; as the source transitions from the hard state into
the hard intermediate state the intercept becomes strongly positive. We find
little evidence for flux dependence of the broad-band noise within the PSD
shape, excepting a small subset of observations from one object in an anomalous
soft-state. We speculate that the ubiquitous linear rms-flux relation in the
broad band noise of this sample, representing a range of different states and
objects, indicates that its formation mechanism is an essential property of the
luminous accretion flow around black holes.Comment: 12 pages, 6 figures, accepted for publication in MNRA
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