Searcharxiv⌕ Search

arXiv subjects

F. W. Stecker

Publications and source records attributed to F. W. Stecker.

At least 37 records · Page 2Linked to original sources
arXiv2005

Cosmogenic Neutrinos from Cosmic Ray Interactions with Extragalactic Infrared Photons

We discuss the production of cosmogenic neutrinos on extragalactic infrared photons in a model of its cosmological evolution. The relative importance of these infrared photons as a target for proton interactions is significant, especially in the case of steep injection spectra of the ultrahigh energy cosmic rays. For an E$^{-2.5}$ cosmic ray injection spectrum, for example, the event rate of neutrinos of energy above 1 PeV is more than doubled.

astro-ph↗
arXiv2005

TeV Gamma-Ray Spectra Unfolded for IR Absorption for a Sample of Low and High Red-Shifted AGN

The H.E.S.S. collaboration recently performed the accurate measurements of the gamma-ray spectra above 200 GeV for two BL Lac-type AGN in the Southern sky: PKS 2155-304 and PKS 2005-489. The TeV spectrum of the BL Lac object 1ES 2344+514 has also been recently measured by the Whipple collaboration. Using the results of phenomenological calculations of the SED of the EBL we have extracted the intrinsic gamma-ray spectra of these blazars. Consequently we have shown that these spectra can be fitted well by means of a synchrotron self Compton model.

astro-ph↗
arXiv2005

Lorentz Invariance Violation and the Spectrum and Source Power of Ultrahigh Energy Cosmic Rays

Owing to their isotropy, it is generally believed that ultrahigh energy cosmic rays (UHECRs) are extragalactic in origin. It is then expected that interactions of these cosmic rays with photons of the cosmic background radiation (CBR) should produce a drastic reduction in their flux above and energy of about $5 \times 10^{19}$ eV (50 EeV), the so-called ``GZK effect''. At present, the existence of this effect is uncertain owing to conflicting observational data and small number statistics. We show here that a small amount of Lorentz invariance violation (LIV), which could turn off photomeson interactions of UHECRs with the CBR, could explain the UHECR spectrum as measured by {\it AGASA} which shows an excess of UHECRs at energies above 100 EeV. If new results from the {\it Auger} array agree with the {\it AGASA} spectrum, this may be interpreted as evidence for a small amount of LIV. If, on the other hand, the new results are consistent with the {\it HiRes} results favoring a GZK effect, this would place severe constraints on LIV and, by implication, on some Planck scale quantum gravity models. We also discuss the power requirements needed to explain the UHECR spectrum for a range of assumptions, including source evolution and LIV and show that in all cases our results disfavor a $γ$-ray burst origin for the UHECRs.

astro-ph↗
arXiv2004

A Probe of the Matter Content of Quasar Jets

We propose a method for estimating the matter content of quasar jets which exhibit Chandra - detected knots in their kpc scale jets. The method relies on measuring the component of the Cosmic Microwave Background (CMB) radiation that is bulk-Comptonized (BC) by the cold electrons in the relativistically flowing jet. We apply our method to PKS 0637 - 752, a superluminal quasar with an one -- sided Chandra - detected large scale jet. What makes this source particularly suited for such a procedure is the absence of significant non-thermal jet emission in the 'bridge', the region between the core and the first bright knot, guaranteeing that most of the electrons in the bridge are cold, and leaving the BC scattered CMB radiation as the only significant source of photons in this region. At lambda=3.6-8.0 microns, the most likely band for the BC scattered emission to appear, the angular resolution of Spitzer (~ 1''- 3'') is considerably smaller than the bridge of PKS 0637 -- 752 (~8''), making it possible to both measure and resolve this emission.

astro-ph↗
arXiv2004

High Energy Astrophysics Tests of Lorentz Invariance Violation

Multi-TeV spectra of Mkn 501 and other BL Lac objects exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having the flux level determined by various astrophysical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constriants on Lorentz invariance violation. Such constriants have important implications for some quantum gravity and large extra dimension models. A much smaller amount of Lorentz invariance violation has potential implications for understanding the spectra of ultrahigh energy cosmic rays.

astro-ph↗
arXiv2004

Observing the Ultrahigh Energy Universe with OWL Eyes

The goal of the Orbiting Wide-field Light-collectors (OWL) mission is to study the origin and physics of the highest energy particles known in nature, the ultrahigh energy cosmic rays (UHECRs). The OWL mission consists of telescopes with UV sensitive cameras on two satellites operating in tandem to view in stereo the development of the giant particle showers induced in the Earth's atmosphere by UHECRs. This paper discusses the characteristics of the OWL mission.

astro-ph↗
arXiv2004

New limits on Planck scale Lorentz violation in QED

Constraints on possible Lorentz symmetry violation (LV) of order E/M_Planck for electrons and photons in the framework of effective field theory (EFT) are discussed. Using (i) the report of polarized MeV emission from GRB021206 and (ii) the absence of vacuum Čerenkov radiation from synchrotron electrons in the Crab nebula, we improve previous bounds by 10^-10 and 10^-2 respectively. We also show that the LV parameters for positrons and electrons are different, discuss electron helicity decay, and investigate investigate how prior constraints are modified by the relations between LV parameters implied by EFT.

astro-ph↗
arXiv2004

Ultrahigh Energy Cosmic Rays: New Physics or Old Physics?

We consider the advantages of and the problems associated with hypotheses to explain the origin of ulthrahigh energy cosmic rays (UHECR: E > 10 EeV) and the "trans GZK" cosmic rays (TGZK: E > 100 EeV), both through "old physics" (acceleration in cosmic sources) and "new physics" (new particles, topological defects, fat neutrino cross sections, Lorentz invariance violation).

astro-ph↗
arXiv2003

Cosmic Physics: The High Energy Frontier

Cosmic rays have been observed up to energies $10^8$ times larger than those of the best particle accelerators. Studies of astrophysical particles (hadrons, neutrinos and photons) at their highest observed energies have implications for fundamental physics as well as astrophysics. Thus, the cosmic high energy frontier is the nexus to new particle physics. This overview discusses recent advances being made in the physics and astrophysics of cosmic rays and cosmic gamma-rays at the highest observed energies as well as the related physics and astrophysics of very high energy cosmic neutrinos. These topics touch on questions of grand unification, violation of Lorentz invariance, as well as Planck scale physics and quantum gravity.

astro-ph↗
arXiv2003

Constraints on Lorentz Invariance Violating Quantum Gravity and Large Extra Dimensions Models using High Energy Gamma Ray Observations

Observations of the multi-TeV spectra of the nearby BL objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with infrared photons having a flux level as determined by various astronomical observations. After correction for this absorption effect, the derived intrinsic spectra of these multi-TeV sources can be explained within the framework of simple synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of such annihilations via electron-positron pair production interactions up to an energy of 20 TeV puts strong constraints on Lorentz invariance violation. Such constraints have important implications for Lorentz invariance violating (LIV) quantum gravity models as well as LIV models involving large extra dimensions. We also discuss the implications of observations of high energy gamma-rays from the Crab Nebula on constraining quantum gravity models.

astro-ph↗
arXiv2003

Tests of Quantum Gravity and Large Extra Dimensions Models Using High Energy Gamma Ray Observations

Observations of the multi-TeV spectra of the nearby BL Lac objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker & Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz violation. Such constraints have important implications for quantum gravity models and large extra dimension models. We also discuss the implications of observations of high energy gamma-rays from the Crab Nebula on constraining quantum gravity models.

astro-ph↗
arXiv2002

Astrophysics at the Highest Energy Frontiers

I discuss recent advances being made in the physics and astrophysics of cosmic rays and cosmic gamma-rays at the highest observed energies as well as the related physics and astrophysics of very high energy cosmic neutrinos. I also discuss the connections between these topics.

astro-ph↗
arXiv2002

Implications of Ultrahigh Energy Air Showers for Physics and Astrophysics

The primary ultrahigh energy particles which produce giant extensive air showers in the Earth's atmosphere present an intriguing mystery from two points of view: (1) How are these particles produced with such astounding energies, eight orders of magnitude higher than those produced by the best man-made terrestrial accelerators? (2) Since they are most likely extragalactic in origin, how do they reach us from extragalactic distances without suffering the severe losses expected from interactions with the 2.7 K thermal cosmic background photons -- the so-called GZK effect? The answers to these questions may involve new physics: violations of special relativity, grand unification theories, and quantum gravity theories involving large extra dimensions. They may involve new astrophysical sources, "zevatrons". Or some heretofore totally unknown physics or astrophysics may hold the answer. I will discuss here the mysteries involving the production and extragalactic propagation of ultrahigh energy cosmic rays and some suggested possible solutions.

astro-ph↗
arXiv2002

The Matter-Antimatter Asymmetry of the Universe

I will give here an overview of the present observational and theoretical situation regarding the question of the matter-antimatter asymmetry of the universe and the related question of the existence of antimatter on a cosmological scale. I will also give a simple discussion of the role of CP violation in this subject.

hep-ph↗
arXiv2001

Extragalactic Gamma-ray Absorption and the Intrinsic Spectrum of Mkn 501 During the 1997 Flare

Using the recent models of Malkan & Stecker (2001) for the infrared background radiation and extrapolating them into the optical and UV range using recent galaxy count data, we rederive the optical depth of the Universe to high energy gamma-rays as a function of energy and redshift for energies between 50 GeV and 100 TeV and redshifts between 0.03 and 0.3. We then use these results to derive the intrinsic gamma-ray spectrum of Mkn 501 during its 1997 high state. We find that the time averaged spectral energy distribution of Mkn 501 while flaring had a broad, flat peak in the 5 to 10 TeV range which corresponds to a broad, flat time averaged X-ray peak in the 50 to 100 keV range observed during the flare. The spectral index of our derived intrinsic differential photon spectrum for Mkn 501 at energies below about 2 TeV was found to be apx. 1.6 to 1.7. This corresponds to a time averaged spectral index of 1.76 found in soft X-rays at energies below the X-ray (synchrotron) peak. These results appear to favor a synchrotron-self Compton origin for the TeV emission together wuth jet parameters which are consistent with time variability constraints within the context of a simple SSC model.

astro-ph↗
arXiv2001

The Extrgalactic Gamma-Ray Background

The COMPTEL and EGRET detectors aboard the Compton Gamma-Ray Observatory measured an extragalactic gamma-ray background extending from MeV energies up to about 100 GeV. Calculations performed making reasonable assumptions indicate that blazars can account for the background between about 10 MeV and at least 10 GeV. Below 30 MeV, the background flux and spectrum are not very well determined and a dedicated satellite detector will be required to remedy this situation. Below 10 MeV, supernovae and possibly AGN may contribute to the extragalactic background flux. Above 10 GeV, the role of blazars in contributing to the background is unclear because we do not have data on their spectra at these energies and because theoretical models predict that many of them will have spectra which should cut off in this energy range. At these higher energies, a new component, perhaps from topological defects, may contribute to the background, as well as X-ray selected BL Lac objects. The future GLAST detector should provide important data on the emission of extragalactic sources above 10 GeV and help resolve this issue. GLAST may also be able to detect the signature of intergalactic absorption by pair production interactions of background gamma-rays of energy above 20 GeV with starlight photons, this signature being a steepening of the background spectrum.

astro-ph↗
arXiv2001

On the spectrum of Ultrahigh Energy Cosmic Rays and the Gamma Ray Burst Origin Hypothesis

It has been suggested that cosmological gamma-ray bursts (GRBs) can produce the observed flux of cosmic rays at the highest energies. However, recent studies of GRBs indicate that their redshift distribution likely follows that of the average star formation rate and that GRBs were more numerous at high redshifts. As a consequence, we show that photomeson production energy losses suffered by ultrahigh energy cosmic rays coming from GRBs would produce too sharp a spectral high energy cutoff to be consistent with the air shower data. Furthermore, we show that cosmological GRBs fail to supply the energy input required to account for the cosmic ray flux above 10 EeV by a factor of 100-1000.

astro-ph↗