16 research outputs found
The Chandra X-ray Observatory Resolves the X-ray Morphology and Spectra of a Jet in PKS 0637-752
The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first
celestial object observed with the Chandra X-ray Observatory, offering the
early surprise of the detection of a remarkable X-ray jet. Several observations
with a variety of detector configurations contribute to a total exposure time
with the Chandra Advanced CCD Imaging Spectrometer (ACIS; Garmire et al. 2000,
in preparation) of about 100ks. A spatial analysis of all the available X-ray
data, making use of Chandra's spatial resolving power of about 0.4 arcsec,
reveals a jet that extends about 10 arcsec to the west of the nucleus. At least
four X-ray knots are resolved along the jet, which contains about 5% of the
overall X-ray luminosity of the source. Previous observations of PKS 0637-752
in the radio band (Tingay et al. 1998) had identified a kpc-scale radio jet
extending to the West of the quasar. The X-ray and radio jets are similar in
shape, intensity distribution, and angular structure out to about 9 arcsec,
after which the X-ray brightness decreases more rapidly and the radio jet turns
abruptly to the north. The X-ray luminosity of the total source is log Lx ~
45.8 erg/s (2 - 10keV), and appears not to have changed since it was observed
with ASCA in November 1996. We present the results of fitting a variety of
emission models to the observed spectral distribution, comment on the
non-existence of emission lines recently reported in the ASCA observations of
PKS 0637-752, and briefly discuss plausible X-ray emission mechanisms.Comment: 24 pages, includes 8 figures, Accepted for publication in Ap
First Observation of the Rare Decay Mode K-long -> e+ e-
In an experiment designed to search for and study very rare two-body decay
modes of the K-long, we have observed four examples of the decay K-long -> e+
e-, where the expected background is 0.17+-0.10 events. This observation
translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12},
consistent with recent theoretical predictions. This result represents by far
the smallest branching fraction yet measured in particle physics.Comment: 9 pages, 3 figure
Chandra Observations of the Young Pulsar PSR B0540-69
The young pulsar PSR B0540-69 was one of the first targets observed with the
Chandra X-Ray Observatory. The high angular resolution of Chandra allows us to
resolve the compact nebula surrounding the pulsar. We have determined a
position for PSR B0540-69 of R.A. = 05h 40m 11s.221, decl. = -69o 19' 54".98
(J2000) with a 1-sigma radial uncertainty of 0.7". Combining our measurements
of the pulsar period with previous measurements covering a span of 12 years, we
derive a braking index of 2.08. The spectrum of the pulsed emission is
consistent with a power-law with a photon index of 1.83 +/- 0.13. The compact
nebula has a softer spectrum with a photon index of 1.85 to 2.26.Comment: 12 pages, accepted by the Astrophysical Journa
A Novel Motif in Fungal Class 1 Histone Deacetylases Is Essential for Growth and Development of Aspergillus
A C-terminal motif of an A. nidulans class 1 histone deacetylase (HDAC) is required for catalytic activity and viability of the fungus. Moreover, this motif seems to play a decisive role for growth and development of other fungal species. Thus, this enzyme/motif may represent a promising target for HDAC-inhibitors acting as antifungal agents