125 research outputs found
The GeV to TeV view of SNR IC443: predictions for Fermi
We present a theoretical model that explains the high energy phenomenology of
the neighborhood of SNR IC 443, as observed with the Major Atmospheric Gamma
Imaging Cherenkov (MAGIC) telescope and the Energetic Gamma-Ray Experiment
Telescope (EGRET). We also discuss how the model can be tested with
observations by the Fermi Gamma-ray Large Area Space Telescope. We interpret
MAGIC J0616+225 as delayed TeV emission of cosmic-rays diffusing from IC 443
and interacting with a known cloud located at a distance of about 20 pc in the
foreground of the remnant. This scenario naturally explains the displacement
between EGRET and MAGIC sources, their fluxes, and their spectra. Finally, we
predict how this context can be observed by Fermi.Comment: To appear in the Proceedings of the 6th Workshop on Science with the
New Generation of High Energy Gamma-Ray Experiments (SciNeGHE '08), held in
Padova October 200
High Energy Gamma-ray Absorption and Cascade Emission in Nearby Starburst Galaxies
High energy gamma-ray emission from two nearby bright starburst galaxies, M82
and NGC 253, have recently been detected by Fermi, H.E.S.S., and VERITAS. Since
starburst galaxies have a high star formation rate and plenty of dust in the
central starburst region, infrared emissions are strong there. Gamma-ray
photons are absorbed by the interstellar radiation field photons via electron
and positron pair creation. The generated electron and positron pairs up
scatter the interstellar photons to very high energy gamma-ray photons via
cascade emission through inverse Compton scattering. In this paper, we evaluate
the contribution of this cascade emission to the gamma-ray spectra of M82 and
NGC 253. Although it would be difficult to see direct gamma- ray evidence of
cosmic-rays with an energy > 10 TeV due to the gamma-ray attenuation, the
resulting cascade emission would be indirect evidence. By including the cascade
component, we find that the total flux above 1 TeV increases ~18% and ~45%
compared with the absorbed flux assuming the maximum kinetic proton energy as
45.3 TeV and 512 TeV, respectively. Future gamma-ray observatories such as CTA
would be able to see the indirect evidence of cosmic-ray with an energy > 10
TeV by comparing with theoretical emission models including this cascade
effect.Comment: 5 pages, Accepted for publication in Ap
High Energy Emission from the Starburst Galaxy NGC253
Measurement sensitivity in the energetic gamma-ray region has improved
considerably, and is about to increase further in the near future, motivating a
detailed calculation of high-energy (>100 MeV) and very-high-energy (VHE: >100
GeV) gamma-ray emission from the nearby starburst galaxy NGC253. Adopting the
convection-diffusion model for energetic electron and proton propagation, and
accounting for all the relevant hadronic and leptonic processes, we determine
the steady-state energy distributions of these particles by a detailed
numerical treatment. The electron distribution is directly normalized by the
measured synchrotron radio emission from the central starburst region; a
commonly expected theoretical relation is then used to normalize the proton
spectrum in this region. Doing so fully specifies the electron spectrum
throughout the galactic disk, and with an assumed spatial profile of the
magnetic field, the predicted radio emission from the full disk matches well
the observed spectrum, confirming the validity of our treatment. The resulting
radiative yields of both particles are calculated; the integrated HE and VHE
fluxes from the entire disk are predicted to be f(>100 MeV)~2x10^-8 cm^-2 s^-1
and f(>100 GeV)~4x10^-12 cm^-2 s^-1, respectively. We discuss the feasibility
of measuring emission at these levels with the space-borne Fermi and the
ground-based Cherenkov telescopes.Comment: 7 pages, 4 figures; accepted for publication in the MNRA
Simultaneous multi-frequency observation of the unknown redshift blazar PG1553+113 in March-April 2008
5 páginas, 2 figuras, 3 tablas.-- El Pdf del artículo es la versión pre-print: arXiv: arXiv:0911.1088.-- MAGIC Collaboration: et al.The blazar PG 1553+113 is a well known TeV γ-ray emitter. In this paper we determine its spectral energy distribution through simultaneous multi-frequency data to study its emission processes. An extensive campaign was carried out between March and April 2008, where optical, X-ray, high-energy (HE) γ-ray, and very-high-energy (VHE) γ-ray data were obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC telescopes, respectively. We combine the data to derive the source's spectral energy distribution and interpret its double-peaked shape within the framework of a synchrotron self-Compton model.Major support
from Germany’s Bundesministerium f¨ur Bildung, Wissenschaft, Forschung
und Technologie and Max-Planck-Gesellschaft, Italy’s Istituto Nazionale di
Fisica Nucleare (INFN) and Istituto Nazionale di Astrofisica (INAF), and
Spain’s Ministerio de Ciencia e Innovacion is gratefully acknowledged. The
work was also supported by Switzerland’s ETH Research grant TH34/043,
Poland’s Ministertwo Nauki i Szkolnictwa Wy˙zszego grant N N203 390834,
and Germany’s Young Investigator Program of the Helmholtz Gemeinschaft.
This work was also supported by Georgian National Science Foundation grant
GNSF/ST07/4-180. EP acknowledges support from the Italian Space Agency
through grants ASI-INAF I/023/05/0 and ASI I/088/06/0.Peer reviewe
MAGIC observation of the GRB 080430 afterglow
6 páginas, 1 figura.-- El Pdf del artículo es la versión pre-print: arXiv:1004.3665v2.-- MAGIC Collaboration: et al.[Context]: Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment.
[Aims]: Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies.
[Methods]: We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRB 080430 at energies above about 80 GeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes.
[Results]: We obtained an upper limit of F95% CL = 5.5 × 10-11 erg cm-2 s-1 for the very-high energy emission of GRB 080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z ≲ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.The support of the German BMBF and MPG,
the Italian INFN and Spanish MICINN is gratefully acknowledged. This work
was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW
Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft.Peer reviewe
On The GeV & TeV Detections of the Starburst Galaxies M82 & NGC 253
The GeV and TeV emission from M82 and NGC 253 observed by Fermi, HESS, and
VERITAS constrains the physics of cosmic rays (CRs) in these dense starbursts.
We argue that the gamma rays are predominantly hadronic in origin, as expected
by previous studies. The measured fluxes imply that pionic losses are efficient
for CR protons in both galaxies: we show that a fraction F_cal ~ 0.2 - 0.4 of
the energy injected in high energy primary CR protons is lost to inelastic
proton-proton collisions (pion production) before escape, producing gamma rays,
neutrinos, and secondary electrons and positrons. We discuss the factor ~2
uncertainties in this estimate, including supernova rate and leptonic
contributions to the GeV-TeV emission. We argue that gamma-ray data on ULIRGs
like Arp 220 can test whether M82 and NGC 253 are truly calorimetric, and we
present upper limits on Arp 220 from the Fermi data. We show that the observed
ratio of the GeV to GHz fluxes of the starbursts suggests that non-synchrotron
cooling processes are important for cooling the CR electron/positron
population. We briefly reconsider previous predictions in light of the
gamma-ray detections, including the starburst contribution to the gamma-ray
background and CR energy densities. Finally, as a guide for future studies, we
list the brightest star-forming galaxies on the sky and present updated
predictions for their gamma-ray and neutrino fluxes.Comment: 15 pages, emulateapj format, accepted to ApJ, Table 1 fixe
Diffuse Hard X-ray Emission in Starburst Galaxies as Synchrotron from Very High Energy Electrons
[Abdriged] The origin of the diffuse hard X-ray (2 - 10 keV) emission from
starburst galaxies is a long-standing problem. We suggest that synchrotron
emission of 10 - 100 TeV electrons and positrons (e+/-) can contribute to this
emission, because starbursts have strong magnetic fields. We consider three
sources of e+/- at these energies: (1) primary electrons directly accelerated
by supernova remnants; (2) pionic secondary e+/- created by inelastic
collisions between CR protons and gas nuclei in the dense ISMs of starbursts;
(3) pair e+/- produced between the interactions between 10 - 100 TeV gamma-rays
and the intense far-infrared (FIR) radiation fields of starbursts. We create
one-zone steady-state models of the CR population in the Galactic Center (R <=
112 pc), NGC 253, M82, and Arp 220's nuclei, assuming a power law injection
spectrum for electrons and protons. We compare these models to extant radio and
GeV and TeV gamma-ray data for these starbursts, and calculate the diffuse
synchrotron X-ray and Inverse Compton (IC) luminosities of these starbursts. If
the primary electron spectrum extends to ~PeV energies and has a
proton/electron injection ratio similar to the Galactic value, we find that
synchrotron contributes 2 - 20% of their unresolved, diffuse hard X-ray
emission. Inverse Compton emission is likewise a minority of the unresolved
X-ray emission in these starbursts, from 0.1% in the Galactic Center to 10% in
Arp 220's nuclei. We also model generic starbursts, including submillimeter
galaxies, in the context of the FIR--X-ray relation, finding that up to 2% in
the densest starbursts with our fiducial assumptions. Neutrino and TeV
gamma-ray data can further constrain the synchrotron X-ray emission of
starbursts. Our models do not constrain hard synchrotron X-ray emission from
any additional hard components of primary e+/- from sources like pulsars in
starbursts.Comment: Accepted by ApJ; 31 pages, emulateapj forma
The GeV to TeV connection in the environment of SNR IC 443
We have recently interpreted the source MAGIC J0616+225 as a result of
delayed TeV emission of cosmic-rays diffusing from IC 443 and interacting with
a cloud in the foreground of the remnant. This model was used to make
predictions for future observations, especially those to be made with the Fermi
satellite. Just recently, AGILE, Fermi, and VERITAS have released new results
of their observations of IC 443. In this work, we compare them with the
predictions of our model, exploring the GeV to TeV connection in this region of
space. We use Fermi data to consider the possibility of constraining the
cosmic-ray diffusion features of the environment. We analyze the cosmic-ray
distributions, their interactions, and a possible detection of the SNR
environment in the neutrino channel.Comment: Accepted for publication in MNRAS. 20 pages, 10 figures, 1 tabl
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