2,643 research outputs found
The Cambridge-Cambridge ROSAT Serendipity Survey - I. X-ray-luminous galaxies
We report on the first results obtained from a new optical identification
programme of 123 faint X-ray sources with (0.5--2ergscm serendipitously detected in {\it ROSAT}
PSPC pointed observations. We have spectroscopically identified the optical
counterparts to more than 100 sources in this survey. Although the majority of
the sample (68 objects) are QSOs, we have also identified 12 narrow emission
line galaxies which have extreme X-ray luminosities (ergs). Subsequent spectroscopy reveals them to be a
mixture of starburst galaxies and Seyfert 2 galaxies in approximately equal
numbers. Combined with potentially similar objects identified in the {\it
Einstein} Extended Medium Sensitivity Survey, these X-ray-luminous galaxies
exhibit a rate of cosmological evolution, , consistent with that derived for X-ray QSOs. This
evolution, coupled with the steep slope determined for the faint end of the
X-ray luminosity function (), implies
that such objects could comprise 15--35 per cent of the soft (1--2keV)Comment: Accepted for publication in MNRAS. 7 pages including 5 figures;
uuencoded compressed postscript; RGO-21
Chandra Detection of Highest Redshift (z~6) Quasars in X-rays
We report on Chandra observations of three quasars SDSSP J083643+005453,
SDSSP J103027+052455, and SDSSP J130608+035626 at redshifts 5.82, 6.28 and 5.99
respectively. All the three sources are clearly detected in the X-ray band, up
to rest frame energies of ~55 keV. These observations demonstrate the
unprecedented sensitivity of Chandra to detect faint sources in relatively
short exposure times (5.7--8.2 ksec). The broad band X-ray properties of these
highest redshift quasars do not appear to be any different from their lower
redshift cousins. Spectra of the sources could not be determined with only few
counts detected. Observations with XMM-Newton will be able to constrain the
spectral shapes, if they are simple. Determination of complex spectra in a
reasonable amount of time, however, will have to await next generation of X-ray
missions.Comment: Submitted to ApJ Letter
Single microwave photon detection in the micromaser
High efficiency single photon detection is an interesting problem for many
areas of physics, including low temperature measurement, quantum information
science and particle physics. For optical photons, there are many examples of
devices capable of detecting single photons with high efficiency. However
reliable single photon detection of microwaves is very difficult, principally
due to their low energy. In this paper we present the theory of a cascade
amplifier operating in the microwave regime that has an optimal quantum
efficiency of 93%. The device uses a microwave photon to trigger the stimulated
emission of a sequence of atoms where the energy transition is readily
detectable. A detailed description of the detector's operation and some
discussion of the potential limitations of the detector are presented.Comment: 8 pages, 5 figure
The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei
A combined analysis of the profiles of the main broad quasar emission lines
in both Hubble Space Telescope and optical spectra shows that while the
profiles of the strong UV lines are quite similar, there is frequently a strong
increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that
the suggestion that the high velocity gas is optically-thin presents many
problems. We show that the relative strengths of the high velocity wings arise
naturally in an optically-thick BLR component. An optically-thick model
successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha
ratios and flatter Balmer decrements in the line wings, the strengths of CIII]
and the lambda 1400 blend, and the strong variability of high-velocity,
high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to
Astrophysical Journa
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