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[en] Report of search for likely point sources for neutrinos observed by the Amanda detector. Places intensity limits on observable point sources. This paper describes the search for astronomical sources of high-energy neutrinos using the AMANDA-B10 detector, an array of 302 photomultiplier tubes, used for the detection of Cherenkov light from upward traveling neutrino-induced muons, buried deep in ice at the South Pole. The absolute pointing accuracy and angular resolution were studied by using coincident events between the AMANDA detector and two independent telescopes on the surface, the GASP air Cherenkov telescope and the SPASE extensive air shower array. Using data collected from April to October of 1997 (130.1 days of livetime), a general survey of the northern hemisphere revealed no statistically significant excess of events from any direction. The sensitivity for a flux of muon neutrinos is based on the effective detection area for through-going muons. Averaged over the Northern sky, the effective detection area exceeds 10,000 m2 for Eμ ∼ 10 TeV. Neutrinos generated in the atmosphere by cosmic ray interactions were used to verify the predicted performance of the detector. For a source with a differential energy spectrum proportional to Eν-2 and declination larger than +40o, we obtain E2 (dNν/dE) (le) 10-6 GeV cm-2 s-1 for an energy threshold of 10 GeV
[en] The formation and evolution of stars and galaxies is a complex process that involves the cooling and collapse of dense interstellar clouds as well as energetic feedback on these clouds. Interstellar dust grains are central to the radiative transfer, thermal balance, and molecular processes in these clouds and can provide an important diagnostic. Hence, the effects of energetic processing of interstellar dust may have significant consequences. r This may be studied in our own Galaxy, where observations have shown that an appreciable fraction of silicates formed in the outflows from red giants and supergiants have a crystalline structure. Yet, the fraction of crystalline silicates in the interstellar medium is very small, pointing towards an efficient crystalline crystalline-to to-amorphous conversion process. Here we report experimental and modeling results that show that relatively ''low'' energy (0.1 - 5.0 GeV) heavy ion cosmic rays can rapidly (∼70 Million yrs) amorphize crystalline silicate grains ejected by stars into the interstellar medium. The implications of this are briefly discussed. We also examine the effects of cosmic ray processing of silicates in the solar system and in stellar debris disks. In the latter systems, cosmic ray processing may play a role for grains trapped in resonance with planetary companions. We speculate that energetic processing of interstellar dust is likely to be even more important in s star forming galaxies, which have higher cosmic ray fluxes due to tar their much larger star formation rates and their emerging active black holes with associated jets
[en] The nature of the cosmic dark matter is unknown. The most compelling hypothesis is that dark matter consists of weakly interacting massive particles (WIMPs) in the 100 GeV mass range. Such particles would annihilate in the galactic halo, producing high-energy gamma rays which might be detectable in gamma ray telescopes such as the GLAST satellite. We investigate the ability of GLAST to distinguish between the WIMP annihilation spectrum and the spectrum of known astrophysical source classes. Focusing on the emission from the galactic satellite halos predicted by the cold dark matter model, we find that the WIMP gamma-ray spectrum is unique; the separation from known source classes can be done in a convincing way. We discuss the follow-up of possible WIMP sources with Imaging Atmospheric Cerenkov Telescopes. Finally we discuss the impact that Large Hadron Collider data might have on the study of galactic dark matter
[en] A search has been made for neutrinos from the hep reaction in the Sun and from the diffuse supernova neutrino background (DSNB)using data collected during the first operational phase of the Sudbury Neutrino Observatory, with an exposure of 0.65 kilotons-years. For the hep neutrino search, two events are observed in the effective electron energy range of 14.3 MeV< Teff<20 MeV where 3.1 background events are expected. After accounting for neutrino oscillations, an upper limit of 2.3 x 104 cm-2s-1 at the 90 percent confidence level is inferred on the integral total flux of hep neutrinos. For DSNB neutrinos, no events are observed in the effective electron energy range of 21 MeV< Teff<35 MeV and, consequently, an upper limit on the nu e component of the DSNB flux in the neutrino energy range of 22.9 MeV< E nu<36.9 MeV of 70 cm-2-1 is inferred at the 90 percent confidence level. This is an improvement by a factor of 6.5 on the previous best upper limit on the hep neutrino flux and by two orders of magnitude on the previous upper limit on the nu e component of the DSNB flux
[en] An explanation is given of the low value of R lambda triple bond A lambda/E(B - V), the ratio of absolute to selective extinction deduced from Type Ia supernova observations. The idea involves scattering by dust clouds located in the circumstellar environment, or at the highest velocity shells of the supernova ejecta. The scattered light tends to reduce the effective R lambda in the optical, but has an opposite effect in the ultraviolet. The presence of circumstellar dust can be tested by ultraviolet to near infrared observations and by multi-epoch spectropolarimetry of SNe Ia
[en] We present measurements of (Omega)m and (Omega)#Lambda# from a blind analysis of 21 high redshift supernovae using a new technique (CMAGIC) for fitting the multicolor lightcurves of Type Ia supernovae, first introduced in Wang et al. (2003). CMAGIC takes advantage of the remarkably simple behavior of Type Ia supernovae on color-magnitude diagrams, and has several advantages over current techniques based on maximum magnitudes. Among these are a reduced sensitivity to host galaxy dust extinction, a shallower luminosity-width relation, and the relative simplicity of the fitting procedure. This allows us to provide a cross check of previous supernova cosmology results, despite the fact that current data sets were not observed in a manner optimized for CMAGIC. We describe the details of our novel blindness procedure, which is designed to prevent experimenter bias. The data are broadly consistent with the picture of an accelerating Universe, and agree with a at Universe within 1.7σ, including systematics. We also compare the CMAGIC results directly with those of a maximum magnitude fit to the same SNe, finding that CMAGIC favors more acceleration at the 1.6σ level, including systematics and the correlation between the two measurements. A fit for w assuming a at Universe yields a value which is consistent with a cosmological constant within 1.2σ
[en] High-quality spectropolarimetry (range 417 860 nm; spectral resolution 1.27 nm and 0.265 nm pixel-1) of the Type Ia supernova (SN Ia) 2001el was obtained with the ESO Very Large Telescope Melipal (+FORS1) at five epochs. The spectra a week before maximum and around maximum indicate photospheric expansion velocities of about 10,000 km s-1. Prior to optical maximum, the linear polarization of the continuum was ∼0.2 percent 0.3 percent with a constant position angle, showing that SN 2001el has a well-defined axis of symmetry. The polarization was nearly undetectable a week after optical maximum. The spectra are similar to those of the normally bright SN 1994D, with the exception of a strong double-troughed absorption feature seen around 800 nm (FWHM about 22 nm). The 800 nm feature is probably due to the Ca II IR triplet at very high velocities (20,000 26,000 km s-1) involving ∼0.004 Msolarsolar of calcium and perhaps 0.1 Msolarsolar total mass. The 800 nm feature is distinct in velocity space f rom the photospheric Ca II IR triplet and has a significantly higher degree of polarization (∼0.7 percent) and different polarization angle than the continuum. Taken together, these aspects suggest that this high-velocity calcium is a kinematically distinct feature with the matter distributed in a filament, torus, or array of blobs almost edge-on to the line of sight. This feature could thus be an important clue to the binary nature of SNe Ia, perhaps associated with an accretion disk, or to the nature of the thermonuclear burning, perhaps representing a stream of material ballistically ejected from the site of the deflagration to detonation transition. If modeled in terms of an oblate spheroid, the continuum polarization implies a minor to major axis ratio of around 0.9 if seen equator-on; this level of asymmetry would produce an absolute luminosity dispersion of about 0.1 mag when viewed at different viewing angles. If typical for SNe Ia, this would create an rms scatter of several hundredths of a magnitude around the mean brightness decline relation. We discuss the possible implications of this scatter for the high-precision measurements required to determine the cosmological equation of state
[en] Isotope effects in the non-dissociative photoionization of molecular nitrogen (N2 + hν → N2+ + e-) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV (65.6-80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross-sections, σ(14N2)/σ(15N14N), ranging from 0.4 to 3.5. Convolving the cross-sections with the solar flux and integrating over the energies measured, the ratios of photoionization rate coefficients are J(15N14N)/J(14N2) = 1.00± 0.02 and J(15N2)/J(14N2) = 1.00 ± 0.02, suggesting that isotopic fractionation between N2 and N2+ should be small under such conditions. In contrast, in a one-dimensional model of Titan's atmosphere, isotopic self-shielding of 14N2 leads to values of J(15N14N)/J(14N2) as large as ∼1.17, larger than under optically thin conditions but still much smaller than values as high as ∼29 predicted for N2 photodissociation. Since modeled photodissociation isotope effects overpredict the HC15N/HC14N ratio in Titan's atmosphere, and since both N atoms and N2+ ions may ultimately lead to the formation of HCN, estimates of the potential of including N2 photoionization to contribute to a more quantitative explanation of 15N/14N for HCN in Titan's atmosphere are explored.
[en] We present the results of a search for extraterrestrial electron antineutrinos ((bar ν)e's) in the energy range 8.3 MeV < E#bar ν)e < 30.8 MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8B solar νe's converting into (bar ν)e's at 5.3 x 10-5 (90% C.L.). The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles.
[en] We calculate the emission from relativistic flows in black hole systems using a fully general relativistic radiative transfer formulation, with flow structures obtained by general relativistic magneto-hydrodynamic simulations. We consider thermal free-free emission and thermal synchrotron emission. Bright filament-like features protrude (visually) from the accretion disk surface, which are enhancements of synchrotron emission where the magnetic field roughly aligns with the line-of-sight in the co-moving frame. The features move back and forth as the accretion flow evolves, but their visibility and morphology are robust. We propose that variations and drifts of the features produce certain X-ray quasi-periodic oscillations (QPOs) observed in black-hole X-ray binaries