754 research outputs found
Inverse Compton X-ray Emissions from TeV blazar Mrk421 during a Historical Low-Flux State Observed with NuSTAR
We report on the detection of excess hard X-ray emission from the TeV BL Lac
object Mrk421 during the historical low-flux state of the source in January
2013. NuSTAR observations were conducted four times between MJD56294 and
MJD56312 with a total exposure of 80.9 ksec. The source flux in the 3-40 keV
range was nearly constant except for MJD56307, when the average flux level
increased by a factor of three. Throughout the exposure, the X-ray spectra of
Mrk421 were well represented by a steep power-law model with a photon index of
3.1, although a significant excess was noted above 20 keV in the MJD56302 data
when the source was in its faintest state. Moreover, Mrk421 was detected at
more than the 4-sigma level in the 40-79 keV count maps for both MJD56307 and
MJD56302 but not during the remaining two observations. The detected excess
hard X-ray emissions connect smoothly with the extrapolation of the high-energy
gamma-ray continuum of the blazar constrained by Fermi-LAT during the source
quiescence. These findings indicate that, while the overall X-ray spectrum of
Mrk421 is dominated by the highest-energy tail of the synchrotron continuum,
the variable excess hard X-ray emission above 20 keV (on the timescale of a
week) is related to the inverse Compton emission component. We discuss the
resulting constraints on the variability and spectral properties of the
low-energy segment of the electron energy distribution in the source.Comment: 6 pages, 4 figures, accepted for publication in Ap
High Energy Observations of AGN Jets and their Future Prospects
In next five years, dramatic progress is anticipated for the AGN studies, as
we have two important missions to observe celestial sources in the high energy
regime: GLAST and Suzaku. In this talk, I will summarize recent highlights in
studies of AGN jets, focusing on the high-sensitivity X-ray observations that
may shed new light on the forthcoming GLAST era. I will especially present some
examples from most recent Suzaku observations of blazars, which provides
important hints for the shock acceleration in sub-pc scale jets, as well as
particle content in jets. Then I will focus on the neutral iron-line feature
observed in some broad line radio galaxies, as a probe of jet launching and/or
the disk-jet connection. Finally, I will discuss new results of large scale
(kpc to Mpc) jets recently resolved with Chandra X-ray observatory.
Simultaneous monitoring observations in various wavelengths will be
particularly valuable for variable blazar sources, allowing the cross
correlations of time series as well as detailed modeling of the spectral
evolution between the X-ray and gamma-ray energy bands. Possible impacts of
these new observations across the electromagnetic spectrum on various spatial
scales are discussed to challenge the long-standing mystery of AGN jet sources.Comment: 15 pages, 8 figures, "Accelerators in the Universe", 12-14 Mar. 2008,
KEK, Tsukuba, JAPA
Chandra Observation of the Anomalous X-ray Pulsar 1E 1841-045
We present the results from the {\it Chandra} ACIS CC mode observation of an
anomalous X-ray pulsar (AXP) 1E 1841-045. This is the first observation in
which the pulsar spectrum in wide energy range is spatially discriminated from
the surrounding SNR, Kes 73. Like other AXPs, the phase-integrated spectrum is
fitted well with power-law plus blackbody model. The spectral parameters are
, keV, and . This photon index is
significantly flatter than the other AXPs, and resemble to soft gamma-ray
repeaters (SGRs) in the quiescent state. The pulse profile is double-peaked,
and we found that the second peak has significantly hard spectrum. The spectra
of all phases are consistent with power-law plus blackbody model with constant
temperature and photon index. When fitted with two blackbody model, we obtained
similarly good fit. These results can be interpreted that there are two
emission regions with different energy spectra.Comment: 4 pages, 4 figures, accepted for publication in PASJ Letter
On the H\alpha\ faintness of the North Polar Spur
The ratio of H intensity to 1.4 GHz radio continuum intensity in the
North Polar Spur (NPS) is measured to be , two orders of magnitude
smaller than the values of observed in the typical shell-type old
supernova remnants, Cygnus Loop and S147. The extremely low H-to-radio
intensity ratio favours the Galactic-Centre explosion model for NPS, which
postulates a giant shock wave at a distance of several kilo parsecs in the hot
and low-density Galactic halo with low hydrogen recombination rate, over the
local supernova(e) remnant model.Comment: Accepted for MNRAS, 8 pages, 8 figure
MAXI and GLAST Studies of Jets in Active Galaxies
The recent launch of Fermi / GLAST - coinciding with the MAXI workshop -
opens a new era for studies of jet-dominated active galaxies, known as blazars.
While the emission processes operating in various spectral bands in blazars are
reasonably well understood, the knowledge of the details of the structure of
the jet, location of the dissipation region with respect to the accreting black
hole, and coupling of the jet to the accretion process are known only at a
rudimentary level. Blazars are variable, and this provides an opportunity to
use the variability in various bands - and in particular, the relationship of
respective time series to each other - to explore the relative location of
regions responsible for emission in the respective bands. Observationally, this
requires well-sampled time series in as many spectral bands as possible. To
this end, with its all-sky, sensitive monitoring capability, the recently
launched GLAST, and MAXI, to be deployed in 2009, are the most promising
instruments bound to provide good sampling in respectively the energetic
gamma-ray, and the soft X-ray band. This paper highlights the inferences
regarding blazar jets that can be gleaned from such joint observations.Comment: Submitted to the proceedings of 3rd MAXI workshop "Astrophysics with
All-Sky X-ray Observations," 10-12 June 2008, RIKEN, Wako, Saitama, Japa
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