اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSignatures of AGN model for UHECR
105
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We demonstrate that the energy spectra of Ultra High Energy Cosmic rays (UHECR) as observed by AGASA, Flys Eye, HiRes and Yakutsk detectors, have the imprints of UHE proton interaction with the CMB radiation in the form of the dip at $Esim 1times 10^{19}$~ eV, of the beginning of the GZK cutoff, and of very good agreement with calculated spectrum shape. We argue that these data, combined with small-angle clustering and correlation with AGN (BL Lacs), point to the AGN model of UHECR origin at energies $E lsim 1times 10^{20}$ eV. The excess of the events at $E gsim 1times 10^{20}$ eV, which is observed by AGASA (but absent in HiRes data) can be explained by another component of UHECR, e.g. by UHECR from superheavy dark matter.
قيم البحث
اقرأ أيضاً
We demonstrate that the energy spectra of Ultra High Energy Cosmic Rays (UHECR) as observed by AGASA, Flys Eye, HiRes and Yakutsk detectors, have the imprints of UHE proton interaction with the CMB radiation as the dip centered at $Esim 1times 10^{19
}$ eV, beginning of the GZK cutoff, and very good agreement with calculated spectrum shape. This conclusion about proton composition agrees with recent HiRes data on elongation rate that support the proton composition at $Egeq 1times 10^{18}$ eV. The visible bump in the spectrum at $E sim 4times 10^{19}$ eV is not caused by pile-up protons, but is an artifact of multiplying the spectrum by $E^3$. We argue that these data, combined with small-angle clustering and correlation with AGN (BL Lacs), point to the AGN model of UHECR origin at energies $E leq 1times 10^{20}$ eV. The events at higher energies and the excess of the events at $E geq 1times 10^{20}$ eV, which is observed by AGASA (but absent in the HiRes data) must be explained by another component of UHECR, e.g. by UHECR from superheavy dark matter.
The signatures of Ultra High Energy (E >1 EeV) proton propagation through CMB radiation are pair-production dip and GZK cutoff. The visible characteristics of these two spectral features are ankle, which is intrinsic part of the dip, beginning of GZK
cutoff in the differential spectrum and E_{1/2} in integral spectrum. Measured by HiRes and Telescope Array (TA) these characteristics agree with theoretical predictions. However, directly measured mass composition remains a puzzle. While HiRes and TA detectors observe the proton dominated mass composition, the data of Auger detector strongly evidence for nuclei mass composition becoming progressively heavier at energy higher than 4 EeV and reaching Iron at energy about 35 EeV. The models based on the Auger and HiRes/TA data are considered independently and classified using the transition from galactic to extragalactic cosmic rays. The ankle cannot provide this transition. since data of all three detector at energy (1 - 3) EeV agree with pure proton composition (or at least not heavier than Helium). If produced in Galaxy these particles result in too high anisotropy. This argument excludes or strongly disfavours all ankle models with ankle energy E_a > 3 EeV. The calculation of elongation curves, X_{max}(E), for different ankle models strengthens further this conclusion. Status of other models, the dip, mixed composition and Auger based models are discussed.
We consider energy budgets and radiative history of 8 fading AGN, identified from mismatch between the ionizion of very extended (>10 kpc) ionized clouds and the luminosity of the nucleus viewed directly. All show significant fading on ~50,000-year t
imescales. We explore the use of minimum ionizing luminosity Q derived from photoionization balance in the brightest pixels in H-alpha at each projected radius. Tests using PG QSOs, and one target with detailed photoionization modeling, suggest that we can derive useful histories of individual AGN; the minimum ionizing luminosity is always an underestimate and subject to fine structure in the ionized material. These tests suggest that the underestimation from the upper envelope of Q values is roughly constant for a given object. These AGN show rapid drops and standstills; the common feature is a rapid drop in the last 20,000 years before our view of the nucleus. E-folding timescales are mostly thousands of years, with a few episodes as short as 400. In the limit of largely obscured AGN, we find additional evidence for fading, comparing lower limits from recombination balance and the maximum luminosities derived from from infrared fluxes. We compare these long-term light curves to simulations of AGN accretion; the strongest variations on these timespans are seen in models with strong and local feedback. Gemini integral-field optical spectroscopy shows a very limited role for outflows in these structures. While rings and loops of emission are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows <300 km/s, largely associated with very diffuse emission. Only in the Teacup AGN do we see outflow signatures of order 1000 km/s. Clouds around these fading AGN consist largely of tidal debris being externally illuminated but not displaced by AGN outflows. (Abridged)
TeV gamma-rays have been observed from blazars as well as from radio galaxies like M87 and Cen A. In leptonic models, gamma-rays above the pair production threshold can escape from the ultra-relativistic jet, since large Lorentz factors reduce the ba
ckground photon densities compared to those required for isotropic emission. Here we discuss an alternative scenario, where VHE photons are generated as secondaries from UHECR interaction in the AGN core. We show that TeV gamma-rays can escape from the core despite large IR and UV backgrounds. For the special case of Cen A, we study if the various existing observations from the far infra-red to the UHE range can be reconciled within this picture.
We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the cool core cluster Abell 2597. The data reveal an extensive kpc-scale X-ray cavity network as well as a 15 kpc filament of soft-excess gas exhibiting strong spatial
correlation with archival VLA radio data. In addition to several possible scenarios, multiwavelength evidence may suggest that the filament is associated with multiphase (10^3 - 10^7 K) gas that has been entrained and dredged-up by the propagating radio source. Stemming from a full spectral analysis, we also present profiles and 2D spectral maps of modeled X-ray temperature, entropy, pressure, and metal abundance. The maps reveal an arc of hot gas which in projection borders the inner edge of a large X-ray cavity. Although limited by strong caveats, we suggest that the hot arc may be (a) due to a compressed rim of cold gas pushed outward by the radio bubble or (b) morphologically and energetically consistent with cavity-driven active galactic nucleus (AGN) heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas rushes to refill its wake. If confirmed, this would be the first observational evidence for this model.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
