Searcharxiv⌕ Search

SEARCH · Searcharxiv

Results for “astro-ph”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
arXiv2008

Importance of constraining the dense matter Equation of State in pulsar astrophysics

We study the dependence of the surface magnetic fields of radio pulsars on the choice of Equations of State, pulsar masses and the values of the angle between the magnetic axis and the spin axis of the pulsars within simple dipole model. We show that the values of the surface magnetic field can be even order of magnitude different from its canonical values. This difference will effect any magnetosphere related model to explain observational features of radio pulsars and magnetars. We find a significant difference of the value of the surface magnetic field from the commonly quoted value for the faster member of the double pulsar system, i.e. PSR J0737-3039A as here both the mass of the pulsar and the angle between the magnetic axis and the spin axis are known. Our study reveals the importance of constraining the dense matter Equations of State in pulsar astrophysics as well as hints an alternative way to constrain these by independent determination of the pulsar magnetic field.

astro-ph↗
arXiv2007

Galactic neutrino background from cosmic ray interaction with the ISM content

We use a diffusive model for the propagation of Galactic cosmic rays to estimate the charged pion production in interactions with protons of the interstellar medium. Cosmic ray nuclei from proton to iron are considered and the corresponding contribution to the neutrino secondary flux produced as a result of spallation is also estimated.

astro-ph↗
arXiv2007

Inhomogeneous preheating in multi-field models of cosmological perturbation

We consider inhomogeneous preheating in multi-field models of cosmological perturbation. After preheating, two fields are trapped at an enhanced symmetric point. One field is an oscillating field and the other is a light field that plays an important role in generating perturbation. In this presentation, we consider two types of potential for the light field.

hep-ph↗
arXiv2007

The New Science of Gravitational Waves

A brief survey is presented of new science that will emerge during the decades ahead from direct detection of gravitational radiation. Interferometers on earth and in space will probe the universe in an entirely new way by directly sensing motions of distant matter over a range of more than a million in frequency. The most powerful sources of gravitational (or indeed any form of) energy in the universe are inspiralling and merging binary black holes; with LISA data, they will become the most distant, most completely and precisely modeled, and most accurately measured systems in astronomy outside the solar system. Other sources range from already known and named nearby Galactic binary stars, to compact objects being swallowed by massive black holes, to possible effects of new physics: phase transitions and superstrings from the early universe, or holographic noise from quantum fluctuations of local spacetime.

astro-ph↗
arXiv2007

Holographic Indeterminacy, Uncertainty and Noise

A theory is developed to describe the nonlocal effect of spacetime quantization on position measurements transverse to macroscopic separations. Spacetime quantum states close to a classical null trajectory are approximated by plane wavefunctions of Planck wavelength (l_P) reference beams; these are used to connect transverse position operators at macroscopically separated events. Transverse positions of events with null spacetime separation, but separated by macroscopic spatial distance $L$, are shown to be quantum conjugate observables, leading to holographic indeterminacy and a new uncertainty principle, a lower bound on the standard deviation of relative transverse position Δx_\perp > \sqrt{l_PL} or angular orientation Δθ> \sqrt{l_P/L}. The resulting limit on the number of independent degrees of freedom is shown to agree quantitatively with holographic covariant entropy bounds derived from black hole physics and string theory. The theory predicts a universal ``holographic noise'' of spacetime, appearing as shear perturbations with a frequency-independent power spectral density S_H=l_P/c, or in equivalent metric perturbation units, h_{H,rms} \sqrt{l_P/c} = 2.3 \times 10^{-22} /\sqrt{Hz}. If this description of holographic phenomenology is valid, interferometers with current technology could undertake direct quantitative studies of quantum gravity.

astro-ph↗
arXiv2007

White Paper on the Status and Future of Ground-based Gamma-ray Astronomy

In recent years, ground-based gamma-ray observatories have made a number of important astrophysical discoveries which have attracted the attention of the wider scientific community. The Division of Astrophysics of the American Physical Society has requested the preparation of a white paper on the status and future of ground-based gamma-ray astronomy to define the science goals of the future observatory, to determine the performance specifications, and to identify the areas of necessary technology development. In this contribution we give a brief overview of the activities of the current white paper team and invite the international community to contribute to the white paper.

astro-ph↗
arXiv2007

Astrophysics Motivation behind the Pierre Auger Southern Observatory Enhancements

The Pierre Auger Collaboration intends to extend the energy range of its southern observatory in Argentina for high quality data from 0.1 to 3 EeV. The extensions, described in accompanying papers, include three additional fluorescence telescopes with a more elevated field of view (HEAT) and a nested surface array with 750 and 433 m spacing respectively and additional muon detection capabilities (AMIGA). The enhancement of the detector will allow measurement of cosmic rays, using the same techniques, from below the second knee up to the highest energies observed. The evolution of the spectrum through the second knee and ankle, and corresponding predicted changes in composition, are crucial to the understanding of the end of Galactic confinement and the effects of propagation on the lower energy portion of the extragalactic flux. The latter is strongly related to the cosmological distribution of sources and to the composition of the injected spectrum. We discuss the science motivation behind these enhancements as well as the impact of combined HEAT and AMIGA information on the assessment of shower simulations and reconstruction techniques.

astro-ph↗
arXiv2007

Stellar Photon and Blazar Archaeology with Gamma-rays

Ongoing deep surveys of galaxy luminosity functions, spectral energy distributions and backwards evolution models of star formation rates can be used to calculate the past history of intergalactic photon densities and, from them, the present and past optical depth of the universe. This procedure can be reversed by looking for sharp cutoffs in the spectra of extragalactic gamma-ray sources at high redshifts in the multi-GeV energy range with GLAST. Determining the cutoff energies of sources with known redshifts and little intrinsic absorption can enable a more precise determination of the past intergalactic photon density and thus allow a better determination of the past history of the total star formation rate, including that from galaxies too faint to be observed. Conversely, observations of sharp high energy cutoffs in the gamma-ray spectra of blazars at unknown redshifts can be used instead of spectral lines to give a measure of their redshifts. Also, given a knowledge photon densities, one can derive the intrinsic gamma-ray spectra and luminosities of blazars over a range of redshifts and look for possible trends in blazar evolution. I present some evidence hinting that TeV blazars with flatter spectra have higher intrinsic TeV gamma-ray luminosities and that there may be a correlation of flatness and luminosity with redshift. (abridged)

astro-ph↗
arXiv2007

Intrinsic Structure and Kinematics of the Sub-Parsec Scale Jet of M87

We report new results from a sub-parsec scale study of the inner jet in M87 performed at 15 GHz with the Very Long Baseline Array. We have detected a limb brightened structure of the jet along with a faint 3 mas long counter-feature which we also find to be limb brightened. Typical speeds of separate jet features are measured to be less than 0.05 speed of light, despite the highly asymmetric jet structure and the implications of the canonical relativistic beaming scenario. The observed intrinsic jet structure can be described in terms of a two stream spine-sheath velocity gradient across the jet according to theoretical predications based on the recently discovered strong and variable TeV emission from M87. The jet to counter-jet flux density ratio is measured to be greater than 200. The observed intrinsic jet structure is broadly consistent with theoretical predictions of a spine-sheath velocity gradient suggested by recently discovered TeV emission from M87.

astro-ph↗
arXiv2007

Study of time lags in HETE-2 Gamma-Ray Bursts with redshift: search for astrophysical effects and Quantum Gravity signature

The study of time lags between spikes in Gamma-Ray Bursts light curves in different energy bands as a function of redshift may lead to the detection of effects due to Quantum Gravity. We present an analysis of 15 Gamma-Ray Bursts with measured redshift, detected by the HETE-2 mission between 2001 and 2006 in order to measure time lags related to astrophysical effects and search for Quantum Gravity signature in the framework of an extra-dimension string model. The use of photon-tagged data allows us to consider various energy ranges. Systematic effects due to selection and cuts are evaluated. No significant Quantum Gravity effect is detected from the study of the maxima of the light curves and a lower limit at 95% Confidence Level on the Quantum Gravity scale parameter of 3.2x10**15 GeV is set.

astro-ph↗
arXiv2007

Multiwavelength modeling of TeV AGN observed by HESS

The High Energy Stereoscopic System (H.E.S.S.) experiment, a ground-based gamma-ray Cherenkov telescope array located in Namibia, has now detected many extragalactic objects, which redshifts range from z=0.00183 up to z=0.2, possibly more. With the increasing performances of Cherenkov telescopes, it now becomes possible to probe these objects at small timescales in gamma-ray, allowing the study of regions thought to be very close to the central supermassive black holes. Furthermore, H.E.S.S. has confirmed a gamma-ray emission from M87, which is thus the first extragalactic source seen at the TeV range that is not a blazar. Among blazars, TeV BL Lacs are the most challenging objects to test the jet emission models and to shed light on particle acceleration mechanisms. The study of blazars with H.E.S.S. also revealed various temporal behaviors among them. Some objects presents a highly variable X-ray flux with small variation of the gamma-ray, while others show the inverse behavior. The interpretation of such differences is puzzling. Observations at very high energies also bring indirect measurements of the infrared extragalactic background light (EBL). The interpretation of gamma-ray emission of radiogalaxies such as M87 in terms of misaligned blazars and the understanding of the properties of the EBL represent new challenges brought by H.E.S.S. observations of extragalactic sources.

astro-ph↗
arXiv2007

Study of the performance and capability of the new ultra-fast 2 GSample/s FADC data acquisition system of the MAGIC telescope

In February 2007 the MAGIC Air Cherenkov Telescope for gamma-ray astronomy was fully upgraded with an ultra fast 2 GSamples/s digitization system. Since the Cherenkov light flashes are very short, a fast readout can minimize the influence of the background from the light of the night sky. Also, the time structure of the event is an additional parameter to reduce the background from unwanted hadronic showers. An overview of the performance of the new system and its impact on the sensitivity of the MAGIC instrument will be presented.

astro-ph↗
arXiv2007

Discovery of Very High Energy Gamma-Rays from the Distant Flat Spectrum Radio Quasar 3C 279 with the MAGIC Telescope

The quasar 3C 279 is one of the best-studied flat spectrum radio quasars. It is located at a comparatively large redshift of z=0.536: E>100 GeV observations of such distant sources were until recently impossible both due to the expected steep energy spectrum and the expected attenuation of the gamma-rays by the extragalactic background light. Here we present results on the observation of 3C 279 with the MAGIC telescope in early 2006. We report the detection of a significant very high energy gamma-ray signal in the MAGIC energy range on the observation night of 2006 February 23.

astro-ph↗
arXiv2007

Successful ToO triggers on the extragalactic sources with the MAGIC telescope

The MAGIC collaboration has been performing Target of Opportunity (ToO) observations whenever alerted that known or potential very high energy gamma-ray emitting extragalactic sources were in a high flux state in the optical, X-ray band or/and in the TeV energy range. Here we report on MAGIC observations performed after such triggers, results of the analysis, and a possible optical-TeV correlation seen in the data. Detections as well as spectral and temporal characterestics of Mkn 180, PKS 2155-304, and 1ES 1011+496 are reported.

astro-ph↗
arXiv2007

Performance of the Pierre Auger Observatory Surface Detector

The Surface Detector of the Pierre Auger Observatory will consist of 1600 water Cherenkov tanks sampling ground particles of air showers produced by energetic cosmic rays. The arrival times are obtained from GPS and power is provided by solar panels. The construction of the array is nearly completed and a large number of detectors has been operational for more than three years. In this paper the performance of different components of the detectors are discussed. The accuracy of the signal measurement and the trigger stability are presented. The performance of the solar power system and other hardware, as well as the water purity and its long-term stability are discussed.

astro-ph↗
arXiv2007

An Alternative Model for the Tidal Evolution of the Earth-Moon-Sun System

We have found that the expansion of the universe has immense consequences on our local systems. We present a model based on cosmic expansion that fits well with observation. The close approach problem inflicting tidal theory is averted in this model. We have shown that the astronomical and geological changes of our local systems are of the order of Hubble constant.

astro-ph↗
arXiv2007

Long term monitoring of bright TeV Blazars with the MAGIC telescope

The MAGIC telescope has performed long term monitoring observations of the bright TeV Blazars Mrk421, Mrk501 and 1ES1959+650. Up to 40 observations, 30 to 60 minutes each have been performed for each source evenly distributed over the observable period of the year. The sensitivity of MAGIC is sufficient to establish a flux level of 25% of the Crab flux for each measurement. These observations are well suited to trigger multiwavelength ToO observations and the overall collected data allow an unbiased study of the flaring statistics of the observed AGNs.

astro-ph↗