512 research outputs found
Probing the Locally Generated Even and Odd Order Nonlinearity in Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O (2212) Microwave Resonators around TC
Spatial scanning of the synchronously generated 2nd and 3rd order
intermodulation distortion in superconducting resonators uncovers local
nonlinearity hot spots, and possible time reversal symmetry breaking, using a
simple probe fashioned from coaxial cable. It is clear that even and odd order
nonlinearity in these samples do not share the same physical origins, as their
temperature and static magnetic field dependences are quite different. 2nd
order intermodulation distortion (IMD) remains strong in these measurements as
the temperature continues to drop below TC to 77K even though the 3rd order
peaks near TC and becomes smaller at lower temperature as predicted by the
nonlinear Meissner effect. Both YBa2Cu3O7 and Tl2Ba2CaCu2O8 resonators of the
same structure exhibit similar temperature dependence in the 2nd order with 2nd
order remaining high at lower temperature. The YBa2Cu3O7 sample has lower 3rd
order IMD with a pronounced peak at TC
Collision and Diffusion in Microwave Breakdown of Nitrogen Gas in and around Microgaps
The microwave induced breakdown of N2 gas in microgaps was modeled using the
collision frequency between electrons and neutral molecules and the effective
electric field concept. Low pressure breakdown at the threshold electric field
occurs outside the gap, but at high pressures it is found to occur inside the
microgap with a large threshold breakdown electric field corresponding to a
very large electron oscillation amplitude. Three distinct pressure regimes are
apparent in the microgap breakdown: a low pressure multipactor branch, a
mid-pressure Paschen branch, both of which occur in the space outside the
microgap, and a high pressure diffusion-drift branch, which occurs inside the
microgap. The Paschen and diffusion-drift branches are divided by a sharp
transition and each separately fits the collision frequency model. There is
evidence that considerable electron loss to the microgap faces accompanies the
diffusion-drift branch in microgaps.Comment: 4 figure
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
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
Evidence of two unique variability classes from IGR J17091-3624
IGR J17091-3624 is the second black hole X-ray binary after GRS 1915+105,
which showed large and distinct variabilities. The study of these variability
classes can be useful to understand the accretion-ejection mechanisms of
accreting black holes, and hence to probe the strong gravity regime. We report
the discovery of two new variability classes (C1 and C2) from IGR J17091-3624
from the 2011 outburst Rossi X-ray Timing Explorer data. These unique classes
will be useful to have complete details about the source, and to learn new
aspects about variabilities. For examples, the C1 class shows that the
intensity and period of oscillations, energy spectrum and power spectrum can
clearly evolve in tens of seconds. Moreover, in such a small time scale,
soft-lag becomes hard-lag. The C2 class shows that the variability and the
nonvariability can occur at similar energy spectrum, and a soft state is not
required for variability to happen.Comment: 5 pages, 6 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
Class Transitions and Two Component Accretion Flow in GRS 1915+105
The light curve of the galactic micro-quasar GRS 1915+105 changes in at least
thirteen different ways which are called classes. We present examples of the
transitions from one class to another as observed by the IXAE instrument aboard
the Indian Satellite IRS-P3. We find that the transitions are associated with
changes in photon counts over a time-scale of only a few hours and they take
place through unknown classes. Assuming that the transitions are caused by
variation of the accretion rates, this implies that a significant fraction of
the matter must be nearly freely falling in order to have such dramatic changes
in such a short time.Comment: 9 pages, 6 figures, Astronomy and Astrophys. (in press
Discovery of new quasi-periodic oscillations in the X-ray transient source V~0332+53
We report the discovery of a new quasi-period oscillation (QPO) at 0.22 Hz,
centered on the source spin frequency of the high mass X-ray binary system
V~0332+53 when the source was observed during its November 2004/March 2005
outburst by {\em RXTE}. Besides this new QPO, we also detected the known 0.05
Hz QPO. Both the 0.22 and 0.05 Hz QPOs stand out clearly at a mid-flux level of
the outburst within January 15--19 2005, and later at an even lower flux level
as the width of 0.22 Hz QPO drops. No evolution of the centroid frequency with
the flux is seen in either QPO. The rms value below 10 keV is around 4--6% for
both QPOs and decreases at higher energies. We discuss our results in the
context of current QPO models.Comment: 5 figures, 12 pages. AASTex preprint style. (In 2005, ApJ Let., 629,
L33
Faint Infrared Flares from the Microquasar GRS 1915+105
We present simultaneous infrared and X-ray observations of the Galactic
microquasar GRS 1915+105 using the Palomar 5-m telescope and Rossi X-ray Timing
Explorer on July 10, 1998 UT. Over the course of 5 hours, we observed 6 faint
infrared (IR) flares with peak amplitudes of mJy and durations
of seconds. These flares are associated with X-ray
soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated
with X-ray hard-dip/soft-flare cycles seen in August 1997 by Eikenberry et al.
(1998). Interestingly, the IR flares begin {\it before} the X-ray oscillations,
implying an ``outside-in'' origin of the IR/X-ray cycle. We also show that the
quasi-steady IR excess in August 1997 is due to the pile-up of similar faint
flares. We discuss the implications of this flaring behavior for understanding
jet formation in microquasars.Comment: 10 pages, 4 figures Accepted for publication in ApJ Letter
- âŠ