1,659 research outputs found
The broad-band X-ray spectrum of a QSO sample
A sample of 25 QSOs was used to investigate the average spectrum between the soft X-ray energy band of the Einstein Observatory image proportional counter, and the higher energy band of the HEAO 1 A2 experiment. The spectrum is similar to thoe exhibited by Seyfert galaxies and narrow emission line galaxies above 2 keV. The spectrum is soft enough that if these objects are typical of the higher redshift, more radio-quiet QSOs, then it is possible to exclude QSOs as being the dominant origin of the diffuse X-ray background
Stellar contributions to the hard X-ray galactic ridge
The number density of serendipitous sources in galactic plane Einstein Observatory IPC fields are compared with predictions based on the intensity of the HEAO-1 A2 unresolved hrd X-ray galactic ridge emission. It is concluded that theoretically predicted X-ray source populations of luminosity 8 x 10 to the 32nd power to 3 x 10 to the 34th power ergs s have 2 KeV to 10 KeV local surface densities of less than approximately .0008 L(32) pc/2 and are unlikely to be the dominant contributors to the hard X-ray ridge. An estimate for Be/neutron star binary systems, such as X Persei, gives a 2 keV to 10 keV local surface density of approximately 26 x 10 to the -5 power L(32) pc/2. Stellar systems of low luminosity, are more likely contributors. Both RS CVn and cataclysmic variable systems contribute 43% + or - 18% of the ridge. A more sensitive measurement of the ridge's hard X-ray spectrum should reveal Fe-line emission. We speculate that dM stars are further major contributors
Reversible GANs for Memory-efficient Image-to-Image Translation
The Pix2pix and CycleGAN losses have vastly improved the qualitative and
quantitative visual quality of results in image-to-image translation tasks. We
extend this framework by exploring approximately invertible architectures which
are well suited to these losses. These architectures are approximately
invertible by design and thus partially satisfy cycle-consistency before
training even begins. Furthermore, since invertible architectures have constant
memory complexity in depth, these models can be built arbitrarily deep. We are
able to demonstrate superior quantitative output on the Cityscapes and Maps
datasets at near constant memory budget
A limit to the X-ray luminosity of nearby normal galaxies
Emission is studied at luminosities lower than those for which individual discrete sources can be studied. It is shown that normal galaxies do not appear to provide the numerous low luminosity X-ray sources which could make up the 2-60 keV diffuse background. Indeed, upper limits suggest luminosities comparable with, or a little less than, that of the galaxy. This is consistent with the fact that the average optical luminosity of the sample galaxies within approximately 20 Mpc is slightly lower than that of the galaxy. An upper limit of approximately 1% of the diffuse background from such sources is derived
Unmasking the Active Galactic Nucleus in PKS J2310-437
PKS J2310-437 is an AGN with bright X-ray emission relative to its weak radio
emission and optical continuum. It is believed that its jet lies far enough
from the line of sight that it is not highly relativistically beamed. It thus
provides an extreme test of AGN models. We present new observations aimed at
refining the measurement of the source's properties. In optical photometry with
the NTT we measure a central excess with relatively steep spectrum lying above
the bright elliptical galaxy emission, and we associate the excess wholly or in
part with the AGN. A new full-track radio observation with the ATCA finds that
the core 8.64GHz emission has varied by about 20 per cent over 38 months, and
improves the mapping of the weak jet. With Chandra we measure a
well-constrained power-law spectral index for the X-ray core, uncontaminated by
extended emission from the cluster environment, with a negligible level of
intrinsic absorption. Weak X-ray emission from the resolved radio jet is also
measured. Our analysis suggests that the optical continuum in this radio galaxy
has varied by at least a factor of four over a timescale of about two years,
something that should be testable with further observations. We conclude that
the most likely explanation for the bright central X-ray emission is
synchrotron radiation from high-energy electrons.Comment: 7 pages, 12 figure
Sub-daily rates of degradation of fluvial carbon from a peat headwater stream
In-stream processing of allochthonous dissolved organic carbon (DOC) and particulate organic carbon (POC) in peat-sourced headwaters has been shown to be a significant part of the terrestrial carbon cycle, through photo- and bio-degradation, with both DOC and POC converted to carbon dioxide (CO2). This study reports a series of 70-h, in situ experiments investigating rates of degradation in unfiltered surface water from a headwater stream in the River Tees, North Pennines, UK. Half the samples were exposed to the normal day/night cycle (ambient); half were continuously dark. The study found that the DOC concentration of samples in the ambient treatment declined by 64 % over the 70 h, compared with 6 % decline for the samples kept in the dark. For POC, the loss in the ambient treatment was 13 %. The average initial rate of loss of DOC in the ambient treatment during the first day of the experiment was 3.36 mg C/l/h, and the average rate of photo-induced loss over the whole 70 h was 1.25 mg C/l/h. Scaling up these losses, the estimate of total organic carbon loss from UK rivers to the atmosphere is 9.4 Tg CO2/year which would be 0.94 % of the global estimate of CO2 emissions from streams and rivers from the 2013 IPCC report. Initial rate kinetics in the light were as high as 3rd order, but the study showed that no single rate law could describe the whole diurnal degradation cycle and that separate rate laws were required for night and day processes. The comparison of dark and ambient treatment processes showed no evidence of photo-stimulated bacterial degradation
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