80,815 research outputs found
X-ray Emission from the Radio Jet in 3C 120
We report the discovery of X-ray emission from a radio knot at a projected
distance of 25" from the nucleus of the Seyfert galaxy, 3C 120. The data were
obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for
the knot preclude a simple power law extension of the radio spectrum and we
calculate some of the physical parameters for thermal bremsstrahlung and
synchrotron self-Compton models. We conclude that no simple model is consistent
with the data but if the knot contains small regions with flat spectra, these
could produce the observed X-rays (via synchrotron emission) without being
detected at other wavebands.Comment: 6 pages latex plus 3 ps/eps figures. Uses 10pt.sty and
emulateapj.sty. Accepted for publication in the ApJ (6 Jan 99
Symmetric photon-photon coupling by atoms with Zeeman-split sublevels
We propose a simple scheme for highly efficient nonlinear interaction between
two weak optical fields. The scheme is based on the attainment of
electromagnetically induced transparency simultaneously for both fields via
transitions between magnetically split F=1 atomic sublevels, in the presence of
two driving fields. Thereby, equal slow group velocities and symmetric
cross-coupling of the weak fields over long distances are achieved. By simply
tuning the fields, this scheme can either yield giant cross-phase modulation or
ultrasensitive two-photon switching.Comment: Modified scheme, 4 pages, 1 figur
UCD Candidates in the Hydra Cluster
NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the
largest globular cluster systems known. We describe new Gemini GMOS (g',i')
photometry of the NGC 3311 field which reveals that the red, metal-rich side of
its globular cluster population extends smoothly upward into the mass range
associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29
UCD candidates with estimated masses > 6x10^6 solar masses and discuss their
characteristics. This UCD-like sequence is the most well defined one yet seen,
and reinforces current ideas that the high-mass end of the globular cluster
sequence merges continuously into the UCD sequence, which connects in turn to
the E galaxy structural sequence.Comment: 5 pages, 3 figures. Accepted for publication in ApJ Letter
On the Anomalous Temperature Distribution of the Intergalactic Medium in the NGC 3411 Group of Galaxies
We present XMM, Chandra and VLA observations of the USGC S152 group and its
central elliptical NGC 3411. Imaging of the group X-ray halo suggests it is
relaxed with little apparent structure. We investigate the temperature and
metal abundance structure of the group halo, and find that while the abundance
distribution is fairly typical, the temperature profile is highly unusual,
showing a hot inner core surrounded by a cool shell of gas with a radius of
\~20-40 kpc, at the center of the larger group halo. Spectral mapping confirms
an irregular ring of gas ~0.15 keV cooler than its surroundings. We estimate
the total mass, entropy and cooling time profiles within ~200 kpc, and find
that the cool shell contains ~9x10^9 Msun of gas. VLA observations at 1.4, 5
and 8 GHz reveal a relatively weak nuclear radio source, with a core radio
luminosity L_R=2.7x10^38 erg/s, and a diffuse component extended on scales of a
few arcseconds (or more). A lack of evidence for activity at optical or X-ray
wavelengths supports the conclusion that the central black hole is currently in
a quiescent state. We discuss possible mechanisms for the formation of
temperature features observed in the halo, including a previous period of AGN
activity, and settling of material stripped from the halo of one of the other
group member galaxies.Comment: 15 pages, 8 postscript figures, accepted for publication in ApJ
version with high resolution figures available at
http://hea-www.harvard.edu/~ejos/files/N3411_hires.pd
Quantum state transfer between field and atoms in Electromagnetically Induced Transparency
We show that a quasi-perfect quantum state transfer between an atomic
ensemble and fields in an optical cavity can be achieved in Electromagnetically
Induced Transparency (EIT). A squeezed vacuum field state can be mapped onto
the long-lived atomic spin associated to the ground state sublevels of the
Lambda-type atoms considered. The EIT on-resonance situation show interesting
similarities with the Raman off-resonant configuration. We then show how to
transfer the atomic squeezing back to the field exiting the cavity, thus
realizing a quantum memory-type operation.Comment: 8 pages, 4 figure
The Magellanic Bridge: The Nearest Purely Tidal Stellar Population
We report on observations of the stellar populations in twelve fields
spanning the region between the Magellanic Clouds, made with the Mosaic-II
camera on the 4-meter telescope at the Cerro-Tololo Inter-American Observatory.
The two main goals of the observations are to characterize the young stellar
population (which presumably formed in situ in the Bridge and therefore
represents the nearest stellar population formed from tidal debris), and to
search for an older stellar component (which would have been stripped from
either Cloud as stars, by the same tidal forces which formed the gaseous
Bridge). We determine the star-formation history of the young inter-Cloud
population, which provides a constraint on the timing of the gravitational
interaction which formed the Bridge. We do not detect an older stellar
population belonging to the Bridge in any of our fields, implying that the
material that was stripped from the Clouds to form the Magellanic Bridge was
very nearly a pure gas.Comment: 19 pages, 9 figures. Accepted to Ap
- …