Detectable signatures of cosmic radiative feedback     

R. Schneider  R. Salvaterra  T. Roy Choudhury  A. Ferrara  C. Burigana  L. A. Popa 《Monthly notices of the Royal Astronomical Society》2008,384(4):1525-1532

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Gamma-ray probe of cosmic ray pressure in galaxy clusters and cosmological implications     

Shin'ichiro Ando  Daisuke Nagai 《Monthly notices of the Royal Astronomical Society》2008,385(4):2243-2253

Cosmic rays produced in cluster accretion and merger shocks provide pressure to the intracluster medium (ICM) and affect the mass estimates of galaxy clusters. Although direct evidence for cosmic ray ions in the ICM is still lacking, they produce γ-ray emission through the decay of neutral pions produced in their collisions with ICM nucleons. We investigate the capability of the Gamma-ray Large Area Space Telescope ( GLAST ) and imaging atmospheric Čerenkov telescopes (IACTs) for constraining the cosmic ray pressure contribution to the ICM. We show that GLAST can be used to place stringent upper limits, a few per cent for individual nearby rich clusters, on the ratio of pressures of the cosmic rays and thermal gas. We further show that it is possible to place tight (≲10 per cent) constraints for distant  ( z ≲ 0.25)  clusters in the case of hard spectrum, by stacking signals from samples of known clusters. The GLAST limits could be made more precise with the constraint on the cosmic ray spectrum potentially provided by IACTs. Future γ-ray observations of clusters can constrain the evolution of cosmic ray energy density, which would have important implications for cosmological tests with upcoming X-ray and Sunyaev–Zel'dovich effect cluster surveys.  相似文献   

Simulating cosmic rays in clusters of galaxies – II. A unified scheme for radio haloes and relics with predictions of the γ-ray emission     

Christoph Pfrommer  Torsten A. Enßlin  Volker Springel 《Monthly notices of the Royal Astronomical Society》2008,385(3):1211-1241

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Simulating cosmic rays in clusters of galaxies – III. Non-thermal scaling relations and comparison to observations     

Christoph Pfrommer 《Monthly notices of the Royal Astronomical Society》2008,385(3):1242-1256

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Interpretation of the low-frequency peculiarities in the radio profile structure of the Crab pulsar     

S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2008,385(4):2143-2150

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Foregrounds for redshifted 21-cm studies of reionization: Giant Meter Wave Radio Telescope 153-MHz observations     

Sk. Saiyad Ali  Somnath Bharadwaj  Jayaram N. Chengalur 《Monthly notices of the Royal Astronomical Society》2008,385(4):2166-2174

Foreground subtraction is the biggest challenge for future redshifted 21-cm observations to probe reionization. We use a short Giant Meter Wave Radio Telescope (GMRT) observation at 153 MHz to characterize the statistical properties of the background radiation across ∼1° to subarcmin angular scales, and across a frequency band of 5 MHz with 62.5 kHz resolution. The statistic we use is the visibility correlation function, or equivalently the angular power spectrum   C _l   . We present the results obtained from using relatively unsophisticated, conventional data calibration procedures. We find that even fairly simple-minded calibration allows one to estimate the visibility correlation function at a given frequency   V ₂( U , 0)  . From our observations, we find that   V ₂( U , 0)  is consistent with foreground model predictions at all angular scales except the largest ones probed by our observations where the model predictions are somewhat in excess. On the other hand, the visibility correlation between different frequencies  κ( U , Δν)  seems to be much more sensitive to calibration errors. We find a rapid decline in  κ( U , Δν)  , in contrast with the prediction of less than 1 per cent variation across 2.5 MHz. In this case, however, it seems likely that a substantial part of the discrepancy may be due to limitations of data reduction procedures.  相似文献   

Mechanism of generation of the emission bands in the dynamic spectrum of the Crab pulsar     

Houshang Ardavan  ArzhangArdavan  John Singleton  Mario R. Perez 《Monthly notices of the Royal Astronomical Society》2008,388(2):873-883

We show that the proportionately spaced emission bands in the dynamic spectrum of the Crab pulsar fit the oscillations of the square of a Bessel function whose argument exceeds its order. This function has already been encountered in the analysis of the emission from a polarization current with a superluminal distribution pattern: a current whose distribution pattern rotates (with an angular frequency ω) and oscillates (with a frequency  Ω > ω  differing from an integral multiple of ω) at the same time. Using the results of our earlier analysis, we find that the dependence on frequency of the spacing and width of the observed emission bands can be quantitatively accounted for by an appropriate choice of the value of the single free parameter  Ω/ω  . In addition, the value of this parameter, thus implied by Hankins & Eilek's data, places the last peak in the amplitude of the oscillating Bessel function in question at a frequency  (∼Ω³/ω²)  that agrees with the position of the observed ultraviolet peak in the spectrum of the Crab pulsar. We also show how the suppression of the emission bands by the interference of the contributions from differing polarizations can account for the differences in the time and frequency signatures of the interpulse and the main pulse in the Crab pulsar. Finally, we put the emission bands in the context of the observed continuum spectrum of the Crab pulsar by fitting this broad-band spectrum (over 16 orders of magnitude of frequency) with that generated by an electric current with a superluminally rotating distribution pattern.  相似文献   

The impact of a percolating IGM on redshifted 21-cm observations of quasar H ii regions     

Paul M. Geil  J. Stuart B. Wyithe 《Monthly notices of the Royal Astronomical Society》2008,386(3):1683-1694

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Are the missing X-ray breaks in gamma-ray burst afterglow light curves merely hidden?     

P. A. Curran  A. J. van der Horst  R. A. M. J. Wijers 《Monthly notices of the Royal Astronomical Society》2008,386(2):859-863

Gamma-ray burst (GRB) afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX or pre- Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences on the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as cosmological tools. Here, we address the issue of X-ray breaks that are possibly 'hidden' and hence the light curves are misinterpreted as being single power laws. We do so by synthesizing X-ray telescope (XRT) light curves and fitting both single and broken power laws, and comparing the relative goodness of each fit via Monte Carlo analysis. Even with the well-sampled light curves of the Swift era, these breaks may be left misidentified, hence caution is required when making definite statements on the absence of achromatic breaks.  相似文献   

Formation of hard very high energy gamma-ray spectra of blazars due to internal photon–photon absorption     

Felix A. Aharonian  D. Khangulyan  L. Costamante 《Monthly notices of the Royal Astronomical Society》2008,387(3):1206-1214

The energy spectra of TeV gamma-rays from blazars, after being corrected for intergalatic absorption in the extragalactic background light (EBL), appear unusually hard, a fact that poses challenges to the conventional models of particle acceleration in TeV blazars and/or to the EBL models. In this paper, we show that the internal absorption of gamma-rays caused by interactions with dense narrow-band radiation fields in the vicinity of compact gamma-ray production regions can lead to the formation of gamma-ray spectra of an almost arbitrary hardness. This allows significant relaxation of the current tight constraints on particle acceleration and radiation models, although at the expense of enhanced requirements to the available non-thermal energy budget. The latter, however, is not a critical issue, as long as it can be largely compensated by the Doppler boosting, assuming large (>10) Doppler factors of the relativistically moving gamma-ray production regions. The suggested scenario of formation of hard gamma-ray spectra predicts detectable synchrotron radiation of secondary electron–positron pairs which might require a revision of the current 'standard paradigm' of spectral energy distributions of gamma-ray blazars. If the primary gamma-rays are of hadronic origin related to pp or   p γ  interactions, the 'internal gamma-ray absorption' model predicts neutrino fluxes close to the detection threshold of the next generation high-energy neutrino detectors.  相似文献