606 research outputs found
X-ray Variability of the Magnetic Cataclysmic Variable V1432 Aql and the Seyfert Galaxy NGC 6814
V1432 Aquilae (=RX J1940.2-1025) is the X-ray bright, eclipsing magnetic
cataclysmic variable ~37' away from the Seyfert galaxy, NGC 6814. Due to a 0.3%
difference between the orbital (12116.3 s) and the spin (12150 s) periods, the
accretion geometry changes over the ~50 day beat period. Here we report the
results of an RXTE campaign to observe the eclipse 25 times, as well as of
archival observations with ASCA and BeppoSAX. Having confirmed that the eclipse
is indeed caused by the secondary, we use the eclipse timings and profiles to
map the accretion geometry as a function of the beat phase. We find that the
accretion region is compact, and that it moves relative to the center of white
dwarf on the beat period. The amplitude of this movement suggest a low-mass
white dwarf, in contrast to the high mass previously estimated from its X-ray
spectrum. The size of the X-ray emission region appears to be larger than in
other eclipsing magnetic CVs. We also report on the RXTE data as well as the
long-term behavior of NGC 6814, indicating flux variability by a factor of at
least 10 on time scales of years.Comment: 44 pages including 16 figures; ApJ, in pres
Very Rapid High-Amplitude Gamma-ray Variability in Luminous Blazar PKS 1510-089 Studied with Fermi-LAT
Here we report on the detailed analysis of the gamma-ray light curve of a
luminous blazar PKS1510-089 observed in the GeV range with the Large Area
Telescope (LAT) onboard the Fermi satellite during the period 2011 September --
December. By investigating the properties of the detected three major flares
with the shortest possible time binning allowed by the photon statistics, we
find a variety of temporal characteristics and variability patterns. This
includes a clearly asymmetric profile (with a faster flux rise and a slower
decay) of the flare resolved on sub-daily timescales, a superposition of many
short uncorrelated flaring events forming the apparently coherent
longer-duration outburst, and a huge single isolated outburst unresolved down
to the timescale of three-hours. In the latter case we estimate the
corresponding gamma-ray flux doubling timescale to be below one hour, which is
extreme and never previously reported for any active galaxy in the GeV range.
The other unique finding is that the total power released during the studied
rapid and high-amplitude flares constitute the bulk of the power radiatively
dissipated in the source, and a significant fraction of the total kinetic
luminosity of the underlying relativistic outflow. Our analysis allows us to
access directly the characteristic timescales involved in shaping the energy
dissipation processes in the source, and to provide constraints on the location
and the structure of the blazar emission zone in PKS1510-089.Comment: 15 pages, 4 figures, 1 table. Accepted for publication in the
Astrophysical Journal Letter
RXTE Hard X-ray Observation of A754: Constraining the Hottest Temperature Component and the Intracluster Magnetic Field
Abell 754, a cluster undergoing merging, was observed in hard X-rays with the
Rossi X-ray Timing Explorer (RXTE) in order to constrain its hottest
temperature component and search for evidence of nonthermal emission.
Simultaneous modeling of RXTE data and those taken with previous missions
yields an average intracluster temperature of keV in the 1-50 keV
energy band. A multi-temperature component model derived from numerical
simulations of the evolution of a cluster undergoing a merger produces similar
quality of fit, indicating that the emission measure from the very hot gas
component is sufficiently small that it renders the two models
indistinguishable. No significant nonthermal emission was detected. However,
our observations set an upper limit of
(90% confidence limit) to the nonthermal emission flux at 20 keV. Combining
this result with the radio synchrotron emission flux we find a lower limit of
0.2 G for the intracluster magnetic field. We discuss the implications of
our results for the theories of magnetic field amplifications in cluster
mergers.Comment: Accepted for Publication in the Astrophysical Journal, 22 pages, 5
figure
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