538 research outputs found
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
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421
We report results from the observations of the well studied TeV blazar Mrk
421 with the Swift and the Suzaku satellites in December 2008. During the
observation, Mrk 421 was found in a relatively low activity state, with the
corresponding 2-10 keV flux of erg/s/cm^2. For the purpose
of robust constraining the UV-to-X-ray emission continuum we selected only the
data corresponding to truly simultaneous time intervals between Swift and
Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a
modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric
forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different
representations of the underlying electron energy distribution, both well
motivated by the current particle acceleration models: a power-law distribution
above the minimum energy with an exponential cutoff at the
maximum energy , and a modified ultra-relativistic Maxwellian
with an equilibrium energy . We found that the latter implies
unlikely physical conditions within the blazar zone of Mrk 421. On the other
hand, the exponentially moderated power-law electron distribution gives two
possible sets of the model parameters: (i) flat spectrum with low minimum electron energy , and
(ii) steep spectrum with high minimum electron energy
. We discuss different interpretations of
both possibilities in the context of a diffusive acceleration of electrons at
relativistic, sub- or superluminal shocks. We also comment on how exactly the
gamma-ray data can be used to discriminate between the proposed different
scenarios.Comment: 18 pages, 2 figures; accepted for publication in the Astrophysical
Journa
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