Sean T. Scully

Intergalactic Photon Spectra from the Far-IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the Universe to High-Energy Gamma Rays

We calculate the intergalactic photon density as a function of both energy and redshift for 0 < z < 6 for photon energies from.003 eV to the Lyman limit cutoff at 13.6 eV in a ΛCDM universe with ΩΛ = 0.7 and Ωm = 0.3. The basic features of our backward-evolution model for galaxies were developed in earlier papers by Malkan & Stecker. With a few improvements, we find that this evolutionary model gives predictions of new deep number counts from Spitzer, as well as a calculation of the spectral energy distribution of the diffuse infrared background, which are in good agreement with the data. We then use our calculated intergalactic photon densities to extend previous work on the absorption of high-energy γ-rays in intergalactic space owing to interactions with low-energy photons and the 2.7 K cosmic microwave background radiation. We calculate the optical depth of the universe, τ, for γ-rays having energies from 4 GeV to 100 TeV emitted by sources at redshifts from 0 to 5. We also give an analytic fit with numerical coefficients for approximating τ(Eγ, z). As an example of the application of our results, we calculate the absorbed spectrum of the blazar PKS 2155-304 at z = 0.117 and compare it with the spectrum observed by the HESS air Cerenkov γ-ray telescope array.

Light-Element Evolution and Cosmic-Ray Energetics

Using cosmic-ray energetics as a discriminator, we investigate the viability of evolutionary models for the light elements Li, Be, and B (LiBeB). We find that models in which the cosmic rays are accelerated mainly out of the average interstellar medium which is increasingly metal-poor at early times significantly underpredict the measured Be abundance of the early Galaxy, the possible increase in [O/Fe] with decreasing [Fe/H] indicated by some recent data notwithstanding. On the other hand, if the cosmic-ray metals are accelerated primarily out of supernova ejecta-enriched superbubbles, such that the cosmic-ray source composition as a function of [Fe/H] remains similar to that of the current epoch, the measured Be abundances are consistent with a cosmic-ray acceleration efficiency that is in very good agreement with the current epoch data. This model requires the incorporation of neutrino-produced 11B. We show that, even though the production histories of the cosmic-ray-produced B and Be and the neutrino-produced 11B are different, B/Be can remain essentially constant as a function of [Fe/H]. We also find that neither the above cosmic-ray origin models nor a model employing low-energy cosmic rays originating from the supernovae of only very massive progenitors can account for the 6Li data at values of [Fe/H] below -2.

The Effects of an Early Galactic Wind on the Evolution of D,3He, and Z

The predictions of the abundances of D and {sup 3}He from big bang nucleosynthesis (BBN) and recent observations of these two isotopes suggest the need to develop new chemical evolution models. In particular, we examine the role of an early episode of massive star formation that would induce a strong destruction of D and a galactic wind. We discuss the ability of these models to match the observed local properties of the solar neighborhood such as the gas mass fraction, oxygen abundance, the age-metallicity relation, and the present-day mass function. We also examine in detail the ability of the chemical evolution models discussed to reproduce the apparent lack of low-mass, low-metallicity stars in the solar neighborhood, namely the G-dwarf distribution. Indeed, we find models which satisfy the above constraints while at the same time allowing for a large primordial D/H ratio as is reportedly measured in some quasar absorption systems at high z, without the overproduction of heavy elements. The latter constraint is achieved by employing a simple dynamical model for a galactic wind. {copyright} {ital 1997} {ital The American Astronomical Society}

Corrected Table for the Parametric Coefficients for the Optical Depth of the Universe to Gamma-rays at Various Redshifts

Erratum: “Intergalactic Photon Spectra from the Far IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the arXiv:astro-ph/0612048v3 2 Feb 2007 Universe to High Energy Gamma-Rays” (ApJ 648, 774 [2006]) F.W. Stecker NASA/Goddard Space Flight Center Department of Physics and Astronomy, University of California, Los Angeles M.A. Malkan Department of Physics and Astronomy, University of California, Los Angeles S.T. Scully Department of Physics, James Madison University Table 1 in our paper had erroneous numbers for the coefficients fitting the parametric form for the optical depth of the universe to γ-rays, τ. The correct values for these parameters as described in the original text are given in the table below for various redshifts for the baseline model (upper row) and fast evolution (lower row) for each individual redshift. The parametric approximation holds for 10 −2 < τ < 10 2 and E γ <∼ 2 TeV for all redshifts but also up to 10 TeV for redshifts, z ≤ 1.

A Determination of the Intergalactic Redshift Dependent UV-Optical-NIR Photon Density Using Deep Galaxy Survey Data and the Gamma-ray Opacity of the Universe

We calculate the intensity and photon spectrum of the intergalactic background light (IBL) as a function of redshift using an approach based on observational data obtained in many different wavelength bands from local to deep galaxy surveys. This allows us to obtain an empirical determination of the IBL and to quantify its observationally based uncertainties. Using our results on the IBL, we then place 68% confidence upper and lower limits on the opacity of the universe to gamma-rays, free of the theoretical assumptions that were needed for past calculations. We compare our results with measurements of the extragalactic background light and upper limits obtained from observations made by the Fermi Gamma-ray Space Telescope.

Searching for New Physics with Ultrahigh Energy Cosmic Rays

Ultrahigh energy cosmic rays (UHECRs) that produce giant extensive showers of charged particles and photons when they interact in the Earths atmosphere provide a unique tool to search for new physics. Of particular interest is the possibility of detecting a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of ~10?35?m. We discuss here the possible signature of Lorentz invariance violation (LIV) on the spectrum of UHECRs as compared with present observations of giant air showers. We also discuss the possibilities of using more sensitive detection techniques to improve searches for LIV in the future. Using the latest data from the Pierre Auger Observatory, we derive a best fit to the LIV parameter of 3.0+1.5?3.0?10-23, corresponding to an upper limit of 4.5?10-23 at a proton Lorentz factor of ~2?1011. This result has fundamental implications for quantum gravity models.

Lorentz invariance violation and the observed spectrum of ultrahigh energy cosmic rays

Abstract There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence of the GZK effect. We present the results of a detailed calculation of the modification of the UHECR spectrum caused by LIV using the formalism of Coleman and Glashow. We then compare these results with the experimental UHECR data from Auger and HiRes. Based on these data, we find a best-fit amount of LIV of 4.5 - 4.5 + 1.5 × 10 - 23 , consistent with an upper limit of 6 × 10 - 23 . This possible amount of LIV can lead to a recovery of the cosmic ray spectrum at higher energies than presently observed. Such an LIV recovery effect can be tested observationally using future detectors.

AN EMPIRICAL DETERMINATION OF THE INTERGALACTIC BACKGROUND LIGHT FROM UV TO FIR WAVELENGTHS USING FIR DEEP GALAXY SURVEYS AND THE GAMMA-RAY OPACITY OF THE UNIVERSE

We have previously calculated the intergalactic background light (IBL) as a function of redshift in the far ultraviolet to near infrared range, based purely on data from deep galaxy surveys. Here we utilize similar methods to determine the mid- and far infrared IBL out to a wavelength of 850 microns. Our approach enables us to constrain the range of photon densities, based on the uncertainties from observationally determined luminosity densities and colors. By also including the effect of the 2.7 K cosmic background photons, we determine 68% confidence upper and lower limits on the opacity of the universe to gamma-rays up to PeV energies. Our direct results on the IBL are consistent with those from complimentary gamma-ray analyses using observations from the Fermi

The Spectrum of 1ES0229 + 200 and the Cosmic Infrared Background

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Searching for Traces of Planck-Scale Physics with High Energy Neutrinos

-ray space telescope and the H.E.S.S. air Cherenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of gamma-ray spectra other than that of absorption by pair production alone.