11 research outputs found
Relic Neutrino Absorption Spectroscopy
Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang
relic anti-neutrinos (and vice versa) into Z-bosons leads to sizable absorption
dips in the neutrino flux to be observed at Earth. The high-energy edges of
these dips are fixed, via the resonance energies, by the neutrino masses alone.
Their depths are determined by the cosmic neutrino background density, by the
cosmological parameters determining the expansion rate of the universe, and by
the large redshift history of the cosmic neutrino sources. We investigate the
possibility of determining the existence of the cosmic neutrino background
within the next decade from a measurement of these absorption dips in the
neutrino flux. As a by-product, we study the prospects to infer the absolute
neutrino mass scale. We find that, with the presently planned neutrino
detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant
energy regime above 10^{21} eV, relic neutrino absorption spectroscopy becomes
a realistic possibility. It requires, however, the existence of extremely
powerful neutrino sources, which should be opaque to nucleons and high-energy
photons to evade present constraints. Furthermore, the neutrino mass spectrum
must be quasi-degenerate to optimize the dip, which implies m_{nu} >~ 0.1 eV
for the lightest neutrino. With a second generation of neutrino detectors,
these demanding requirements can be relaxed considerably.Comment: 19 pages, 26 figures, REVTeX
Testing the connection between the X-ray and submillimetre source populations using Chandra
The powerful combination of the Chandra X-ray telescope, the SCUBA
submillimetre-wave camera and the gravitational lensing effect of the massive
galaxy clusters A2390 and A1835 has been used to place stringent X-ray flux
limits on six faint submillimetre SCUBA sources and deep submillimetre limits
on three Chandra sources which lie in fields common to both instruments. One
further source is marginally detected in both the X-ray and submillimetre
bands. For all the SCUBA sources our results are consistent with
starburst-dominated emission. For two objects, including SMMJ14011+0252 at
z=2.55, the constraints are strong enough that they can only host powerful
active galactic nuclei if they are both Compton-thick and any scattered X-ray
flux is weak or itself absorbed. The lensing amplification for the sources is
in the range 1.5-7, assuming that they lie at z>1. The brightest detected X-ray
source has a faint extended optical counterpart (I~22) with colours consistent
with a galaxy at z~1. The X-ray spectrum of this galaxy is hard, implying
strong intrinsic absorption with a column density of about 1e23 cm-2 and an
intrinsic (unabsorbed) 2-10 keV luminosity of 3e44 erg/s. This source is
therefore a Type-II quasar. The weakest detected X-ray sources are not detected
in HST images down to I~26.Comment: Revised version including one improved figure, accepted for
publication in MNRAS, 5 pages, 2 figure