2,284 research outputs found
Design considerations for large space electric power systems
As power levels of spacecraft rise to the 50 to 100 kW range, it becomes apparent that low voltage (28 V) dc power distribution and management systems will not operate efficiently at these higher power levels. The concept of transforming a solar array voltage at 150 V dc into a 1000 V ac distribution system operating at 20 kHz is examined. The transformation is accomplished with series-resonant inverter by using a rotary transformer to isolate the solar array from the spacecraft. The power can then be distributed in any desired method such as three phase delta to delta. The distribution voltage can be easily transformed to any desired load voltage and operating frequency. The reasons for the voltage limitations on the solar array due to plasma interactions and the many advantages of a high voltage, high frequency at distribution system are discussed
Investigating powerful jets in radio-loud Narrow Line Seyfert 1s
We report results on multiband observations from radio to gamma-rays of the
two radio-loud narrow-line Seyfert 1 (NLSy1) galaxies PKS 2004-447 and
J1548+3511. Both sources show a core-jet structure on parsec scale, while they
are unresolved at the arcsecond scale. The high core dominance and the high
variability brightness temperature make these NLSy1 galaxies good gamma-ray
source candidates. Fermi-LAT detected gamma-ray emission only from PKS
2004-447, with a gamma-ray luminosity comparable to that observed in blazars.
No gamma-ray emission is observed for J1548+3511. Both sources are variable in
X-rays. J1548+3511 shows a hardening of the spectrum during high activity
states, while PKS 2004-447 has no spectral variability. A spectral steepening
likely related to the soft excess is hinted below 2 keV for J1548+3511, while
the X-ray spectra of PKS 2004-447 collected by XMM-Newton in 2012 are described
by a single power-law without significant soft excess. No additional absorption
above the Galactic column density or the presence of an Fe line is detected in
the X-ray spectra of both sources.Comment: 16 pages, 8 figures, accepted for publication in MNRA
Flaring gamma-ray emission from high redshift blazars
High redshift blazars are among the most powerful objects in the Universe.
Although they represent a significant fraction of the extragalactic hard X-ray
sky, they are not commonly detected in gamma-rays. High redshift (z>2) objects
represent <10 per cent of the AGN population observed by Fermi so far, and
gamma-ray flaring activity from these sources is even more uncommon. The
characterization of the radio-to-gamma-ray properties of high redshift blazars
represent a powerful tool for the study of both the energetics of such extreme
objects and the Extragalactic Background Light. We present results of a
multi-band campaign on TXS 0536+145, which is the highest redshift flaring
gamma-ray blazar detected so far. At the peak of the flare the source reached
an apparent isotropic gamma-ray luminosity of 6.6x10^49 erg/s, which is
comparable with the luminosity observed from the most powerful blazars. The
physical properties derived from the multi-wavelength observations are then
compared with those shown by the high redshift population. In addition
preliminary results from the high redshift flaring blazar PKS 2149-306 will be
discussed.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Extreme Blazars Studied with Fermi-LAT and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213
We report on our study of high-energy properties of two peculiar TeV
emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate"
HESS J1943+213 located near the Galactic Plane. Both objects are characterized
by quiescent synchrotron emission with flat spectra extending up to the hard
X-ray range, and both were reported to be missing GeV counterparts in the
Fermi-LAT 2-year Source Catalog. We analyze a 4.5 year accumulation of the
Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as
well as in improved upper limits for HESS J1943+213. We also present the
analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray
spectrum is well represented by a single power law extending up to 25 keV with
photon index 2.00+/-0.02 and a moderate absorption in excess of the Galactic
value, in agreement with previous X-ray observations. No short-term X-ray
variability was found over the 80 ks duration of the Suzaku exposure. Under the
blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121
and HESS J1943+213, and derived constraints on the intergalactic magnetic field
strength and source energetics. We conclude that although the classification of
HESS J1943+213 has not yet been determined, the blazar hypothesis remains the
most plausible option, since in particular the broad-band spectra of the two
analyzed sources along with the source model parameters closely resemble each
other, and the newly available WISE and UKIDSS data for HESS J1943+213 are
consistent with the presence of an elliptical host at the distance of
approximately ~600 Mpc.Comment: 10 pages, 7 figures, 3 tables. Accepted by Ap
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