arXiv subjects
Publications and source records attributed to F. W. Stecker.
We use the recent reanalysis of multi-TeV gamma-ray observations of Mrk 501 to constrain the Lorentz invariance breaking parameter involving the maximum electron velocity. Our limit is two orders of magnitude better than that obtained from the maximum observed cosmic-ray electron energy.
We predict luminosity functions and number counts for extragalactic infrared sources at various wavelengths using the framework of our empirically based model. Comparisons of our galaxy count results with existing data indicate that either galaxy luminosity evolution is not much stronger than Q=3.1, where L is proportional to (1+z)^{Q}, or that this evolution does not continue beyond a redshift of 2. However, a derivation of the far infrared background from COBE-DIRBE data suggests a stronger evolution for far infrared emission with Q > 4 in the redshift range beteen 0 and 1. We discuss several interpretations of these results and also discuss how future observations can reconcile this apparent conflict. We also make predictions of the redshift distributions of extragalactic infrared sources at selected flux levels which can be tested by planned detectors. Finally, we predict the fluxes at which various future surveys will become confusion limited.
In this paper, I will take a synoptic approach to determining the intergalactic infrared radiation field (IIRF). This approach draws on both the multi-TeV gamma-ray observations and the infrared background observations and relates them via the semi-empirical modelling method of Malkan and Stecker. I discuss the evidence for an intergalactic infrared background obtained by an analysis of the HEGRA observations of the high energy gamma-ray spectrum of Mrk 501 and from constraints from Mrk 421 deduced from the Whipple air Cherenkov telescope results. I will show that this evidence is in accord with the predictions made by Malkan and Stecker for the intergalactic infrared spectral energy distribution produced by galaxies. The Malkan-Stecker predictions are also in excellent agreement with mid- and far infrared galaxy counts. However, there may be potential problems relating these predictions with the results of the analysis of COBE-DIRBE far infrared data. The gamma-ray and COBE-DIRBE observations may also need to be reconciled. I will discuss possible ways to resolve this situation including a partial nullification of the $γ$-ray absorption process which can hypothetically occur if Lorentz invariance is broken.
These lectures discuss the mysteries involving the production and extragalactic propagation of ultrahigh energy cosmic rays and suggested possible solutions.
It has been suggested that cosmological gamma-ray bursts (GRBs) can produce the observed flux and spectrum of cosmic rays at the highest energies. However, recent observations indicate that the redshift distribution of GRBs most likely follows that of the star formation rate in the universe, a rate which was much higher at redshifts 1.5-2 than it is today. Thus, most GRBs are at high redshifts. As a consequence, any cosmic rays emitted by these GRBs at energies above 2-3 X 10^{19} eV would be strongly attenuated by interactions with the 3K background radiation. If one assumes rough equality between the energy released in 10^{-2} to 1 MeV photons and that released in 10^{20} eV cosmic rays, then less than 10 per cent of the cosmic rays observed above 10^{20} eV can be accounted for by GRBs.
Astronomy at the highest energies observed must be performed by studying neutrinos rather than photons because the universe is opaque to photons of these energies. By making observations of neutrinos with energies above 10 EeV one can deduce information about the distribution and cosmological history of cosmic rays which may have been accelerated to energies above 100 EeV. Very large fluxes of neutrinos at these energies which exhibit a hard spectrum would be evidence of a GUT phase transition or superheavy dark matter particles. Neutrinos at energies around a PeV may be produced in observable quantities in active galaxies from the acceleration and interactions of cosmic rays in the vicinity of massive black holes or in relativistic jets produced by these black holes. Cosmological gamma-ray bursts may also produce PeV neutrinos. Neutrinos at these energies may oscillate into tau neutrinos which can travel through the Earth by the process of regeneration and produce upward moving air-showers. Neutrinos of energies above of 1000 EeV can produce ultrahigh energy cosmic rays thorugh interactions with big-bang neutrinos, producing Z bosons. This "Z-burst" phenomenon can be used to study the mass and distribution of big-bang neutrinos.
In this paper, we suggest a new hypothesis for explaining the spectrum of the extragalactic MeV gamma-ray background as observed by COMPTEL and SMM. We propose that both the flux level and spectrum can be accounted for as a superposition of non-thermal MeV tails in the spectra of Seyfert galaxies and other AGN. Although present detectors are not sensitive enough to obtain MeV data from individual extragalactic sources, indirect evidence in support of our hypothesis is found in OSSE and COMPTEL observations of the galactic black hole candidate Cygnus X-1.
We show that GLAST should be able to support or rule out the unresolved-blazar hypothesis for the origin of the diffuse, extragalactic gamma-ray background.
The pair-production absorption of high-energy gamma-rays by intergalactic low-energy photons is expected to produce a high-energy cutoff in the spectra of extragalactic sources which is a sensitive function of redshift. We first discuss the expected absorption coefficient as a function of energy and redshift derived by Stecker and De Jager by making use of a new empirically based calculation of the spectral energy distribution of the intergalactic infrared radiation field as given by Malkan and Stecker. We then discuss the fact that new data on the high energy gamma-ray source Mrk 501 appear to show the amount of intergalactic absorption predicted. The implications of this new HEGRA data, should they be confirmed, are significant for the astrophysics of this source, implying that (1) there is no significant intrinsic absorption inside the source, and (2) the physics of the emission produces a power-law spectrum to energies above 20 TeV. As a further test for intergalactic absorption, we give a predicted spectrum, with absorption included, for PKS 2155-304. This XBL lies at a redshift of 0.12, the highest redshift source yet observed at an energy above 0.3 TeV. We also discuss the determination of the gamma-ray opacity of the universe at higher redshifts (out to $z=3$), following the treatment of Salamon and Stecker.
We discuss the determination of the intergalactic pair-production absorption coefficient (Stecker & De Jager 1998) making use of an empirically based calculation of the IR background spectrum (Malkan & Stecker 1998) which agrees well with recent data and constraints on the IR background. While the Whipple observations of Mrk421 hint at extragalactic absorption, the new HEGRA observations of Mrk501 appear to strongly indicate such absorption. We discuss the determination of absorption at higher redshifts (Salamon & Stecker 1998). We also give a predicted spectrum, with absorption included, for PKS2155-304, which, at a redshift of 0.12, is the highest redshift TeV source yet observed.
We present the results of a new calculation of the photodisintegration of ultrahigh energy cosmic ray (UHCR) nuclei in intergalactic space. The critical interactions for energy loss and photodisintegration of UHCR nuclei occur with photons of the 2.73K cosmic background radiation (CBR) and with photons of the infrared background radiation (IBR). We have reexamined this problem making use of a new determination of the IBR based on empirical data, primarily from IRAS galaxies, consistent with direct measurements and upper limits from TeV gamma- ray observations. We have also improved the calculation by including the specific threshold energies for the various photodisintegration interactions in our Monte Carlo calculation. With the new smaller IBR flux, the steepness of the Wien side of the now relatively more important CBR makes their inclusion essential for more accurate results. Our results indicate a significant increase in the propagation time of UHCR nuclei of a given energy over previous results. We discuss the possible significance of this for UHCR origin theory.
We present a new calculation of the intergalactic gamma-ray absorption coefficient as a function of both energy and redshift. In reexamining this problem, we make use of a new, empirically based calculation (as opposed to previous model calculations) of the intergalactic infrared radiation field. We find smaller opacities than those given previously (Stecker & De Jager 1997). We apply our results to the new observations of the flaring gamma-ray spectra of Mrk421 and Mrk501, both at a redshift of apx. 0.03. Our new calculations indicate that there should be no significant curvature in the spectra of these sources for energies below 10 TeV, as indicated by recent observations. However, the intrinsic spectra of these sources should be harder by apx. 0.2 to 0.45 in the spectral index in the 1 to 10 TeV range with an intergalactic absorption cutoff above apx. 20 TeV.
Cosmic topological defects in a wide class of supersymmetric theories can simultaneously be sources of higgs particles of mass comparable to the supersymmetry breaking scale $\sim$ TeV, as well as superheavy gauge bosons of mass $\simη$, where $η$ (>> 1 TeV) denotes the associated gauge symmetry breaking scale. For cosmic strings with $η\sim 10^{14}$ GeV, the higgs decay can account for the extragalactic diffuse gamma ray background above $\sim$ 10 GeV, while the gauge boson decay may explain the highest energy cosmic ray flux above $\sim 10^{11}$ GeV, provided that particle production is the dominant energy loss mechanism for cosmic strings, as recent simulations suggest. By the same token, cosmic strings with $η$ much above $\sim 10^{14}$ GeV will be ruled out.
We present the results of a new estimation of the photodisintegration and propagation of ultrahigh energy cosmic ray (UHCR) nuclei in intergalactic space. The critical interactions for photodisintegration and energy loss of UHCR nuclei occur with photons of the infrared background radiation (IBR). We have reexamined this problem making use of a new determination of the IBR based on empirical data, primarily from IRAS galaxies, and also collateral information from TeV gamma-ray observations of two nearby BL Lac objects. Our results indicate that a 200 EeV Fe nucleus can propagate apx. 100 Mpc through the IBR. We argue that it is possible that the highest energy cosmic rays observed may be heavy nuclei.
We discuss the problem of the absorption of very high-energy gamma-rays by pair production interactions with extragalactic photons which originate from stellar emission in the near IR-UV and reradiation of starlight in the mid- and far-IR. The absorption of gamma-rays above 1 TeV is dominated by interactions with infrared photons. We make a new determination of the optical depth of the universe to multi-TeV photons as a function of energy and redshift and use the results to compare with recent spectral data of Mrk 421 and Mrk 501, sources that have been observed in the flaring state up to apx. 10 TeV energy. For the optical depth calculations, we have made use of a new, empirically based calculation of the intergalactic radiation field by Malkan & Stecker which we consider to be more accurate than that based on previous theoretical modeling. We also discuss the absorption of sub-TeV gamma-rays by starlight photons at high redshifts.
Using the excellent observed correlations among various infrared wavebands with 12 and 60 micron luminosities, we calculate the 2-300 micron spectra of galaxies as a function of luminosity. We then use 12 micron and 60 micron galaxy luminosity functions derived from IRAS data, together with recent data on the redshift evolution of galaxy emissivity, to derive a new, empirically based IR background spectrum from stellar and dust emission in galaxies. Our best estimate for the IR background is of order 2-3 nW/m^2/sr with a peak around 200 microns reaching 6-8 nW/m^2/sr. Our empirically derived background spectrum is fairly flat in the mid-IR, as opposed to spectra based on modeling with discrete temperatures which exhibit a "valley" in the mid-IR. We also derive a conservative lower limit to the IR background which is more than a factor of 2 lower than our derived flux.
The all-sky surveys in gamma-rays by the imaging Compton telescope (COMPTEL) and the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory for the first time allows detailed studies of the extragalactic diffuse emission at gamma-ray energies greater 1 MeV. A preliminary analysis of COMPTEL data indicates a significant decrease in the level of the derived cosmic diffuse emission from previous estimates in the 1-30 MeV range, with no evidence for an MeV-excess, at least not at the levels claimed previously. The 1-30 MeV flux measurements are compatible with power-law extrapolation from lower and higher energies. These new results indicate that the possible contributions to the extragalactic emission from processes that could explain the MeV-excess, such as matter-antimatter annihilation, is significantly reduced. At high energies ($>$ 30 MeV), the extragalactic emission is well described by a power law photon spectrum with an index of -(2.10+-0.03) in the 30 MeV to 100 GeV energy range. No large scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic gamma-ray emission above 10 MeV, is that it arises primarily from unresolved gamma-ray-emitting blazars. The extension of the power law spectrum to 100 GeV implies the average emission from gamma-ray blazars may extend to 100 GeV.
We extend earlier calculations of the attenuation suffered by gamma rays during their propagation from extragalactic sources, obtaining new extinction curves for gamma rays down to 10 GeV in energy, from sources up to a redshift of z=3.