28 research outputs found
MWL observations of VHE blazars in 2006
In 2006 the MAGIC telescope observed the well known very high energy (VHE, >
80 GeV) blazars Mrk 421 and Mrk 501 in the course of multi-wavelength
campaigns, comprising measurements in the optical, X-ray and VHE regime. MAGIC
performed additional snapshot observations on Mrk 421 around the MWL campaigns
and detected the source each night with high significance, establishing once
more flux variability on nightly scales for this object. For certain nights,
the integral flux exceeded the one of Crab significantly, whereas the truly
simultaneous observations have been conducted in a rather low flux state. The
MAGIC observations contemporaneous to XMM-Newton revealed clear intra-night
variability. No significant correlation between the spectral index and the flux
could be found for the nine days of observations. The VHE observations of Mrk
501 have been conducted during one of the lowest flux states ever measured by
MAGIC for this object. The VHE and optical light curves do not show significant
variability, whereas the flux in X-rays increased by about 50 %. In this
contribution, the results of the MAGIC observations will be presented in
detail.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
Insights into the particle acceleration of a peculiar gamma -ray radio galaxy IC 310
IC 310 has recently been identified as a gamma-ray emitter based on
observations at GeV energies with Fermi-LAT and at very high energies (VHE, E >
100 GeV) with the MAGIC telescopes. Despite IC 310 having been classified as a
radio galaxy with the jet observed at an angle > 10 degrees, it exhibits a
mixture of multiwavelength properties of a radio galaxy and a blazar, possibly
making it a transitional object. On the night of 12/13th of November 2012 the
MAGIC telescopes observed a series of violent outbursts from the direction of
IC 310 with flux-doubling time scales faster than 5 min and a peculiar spectrum
spreading over 2 orders of magnitude. Such fast variability constrains the size
of the emission region to be smaller than 20% of the gravitational radius of
its central black hole, challenging the shock acceleration models, commonly
used in explanation of gamma-ray radiation from active galaxies. Here we will
show that this emission can be associated with pulsar-like particle
acceleration by the electric field across a magnetospheric gap at the base of
the jet.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Measurement of the EBL through a combined likelihood analysis of gamma-ray observations of blazars with the MAGIC telescopes
The extragalactic background light (EBL) is the radiation accumulated through
the history of the Universe in the wavelength range from the ultraviolet to the
far infrared. Local foregrounds make the direct measurement of the diffuse EBL
notoriously difficult, while robust lower limits have been obtained by adding
up the contributions of all the discrete sources resolved in deep infrared and
optical galaxy observations. Gamma-ray astronomy has emerged in the past few
years as a powerful tool for the study of the EBL: very-high-energy (VHE)
photons traversing cosmological distances can interact with EBL photons to
produce ee pairs, resulting in an energy-dependent depletion of the
gamma-ray flux of distant sources that can be used to set constraints on the
EBL density. The study of the EBL is one of the key scientific programs
currently carried out by the MAGIC collaboration. We present here the results
of the analysis of 32 VHE spectra of 12 blazars in the redshift range 0.03 -
0.94, obtained with over 300 hours of observations with the MAGIC telescopes
between 2010 and 2016. A combined likelihood maximization approach is used to
evaluate the density and spectrum of the EBL most consistent with the MAGIC
observations. The results are compatible with state-of-the-art EBL models, and
constrain the EBL density to be roughly within of the nominal
value in such models. The study reveals no anomalies in gamma-ray propagation
in the large optical depth regime - contrary to some claims based on
meta-analyses of published VHE spectra.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Connection Between Optical and VHE Gamma-ray Emission in Blazar Jets
MAGIC has been performing optically triggered Target of Opportunity
observations of flaring blazars since the beginning of its scientific
operations. The alerts of flaring blazars originate from Tuorla Blazar
Monitoring Programme, which started the optical monitoring of candidtate TeV
blazars in 2002 and has now collected up to eight years of data on more than 60
blazars. These ToO observations have resulted in the discovery of five new VHE
gamma-ray emitting blazars (S5 0716+714, 1ES 1011+496, Mrk 180, ON 325 and B3
2247+381). In addition part of the discovery of BL Lac and the discovery of 3C
279 was made during a high optical state. In this contribution we present a
detailed analysis of the optical light curves which are then compared to MAGIC
observations of the same sources. We aim to answer the question: "Is there a
connection between optical and VHE -ray high states in blazars or have we just
been lucky?"Comment: 6 pages, 1 figure, 2 tables, proceedings for the Beamed and Unbeamed
Gamma-Rays from Galaxies workshop, Olos, April 11-15 201
Understanding hadronic gamma-ray emission from supernova remnants
We aim to test the plausibility of a theoretical framework in which the
gamma-ray emission detected from supernova remnants may be of hadronic origin,
i.e., due to the decay of neutral pions produced in nuclear collisions
involving relativistic nuclei. In particular, we investigate the effects
induced by magnetic field amplification on the expected particle spectra,
outlining a phenomenological scenario consistent with both the underlying
Physics and the larger and larger amount of observational data provided by the
present generation of gamma experiments, which seem to indicate rather steep
spectra for the accelerated particles. In addition, in order to study to study
how pre-supernova winds might affect the expected emission in this class of
sources, the time-dependent gamma-ray luminosity of a remnant with a massive
progenitor is worked out. Solid points and limitations of the proposed scenario
are finally discussed in a critical way.Comment: 30 pages, 5 figures; Several comments, references and a figure added.
Some typos correcte
Collider and Dark Matter Searches in Models with Mixed Modulus-Anomaly Mediated SUSY Breaking
We investigate the phenomenology of supersymmetric models where moduli fields
and the Weyl anomaly make comparable contributions to SUSY breaking effects in
the observable sector of fields. This mixed modulus-anomaly mediated
supersymmetry breaking (MM-AMSB) scenario is inspired by models of string
compactification with fluxes, which have been shown to yield a de Sitter vacuum
(as in the recent construction by Kachru {\it et al}). The phenomenology
depends on the so-called modular weights which, in turn, depend on the location
of various fields in the extra dimensions. We find that the model with zero
modular weights gives mass spectra characterized by very light top squarks
and/or tau sleptons, or where M_1\sim -M_2 so that the bino and wino are
approximately degenerate. The top squark mass can be in the range required by
successful electroweak baryogenesis. The measured relic density of cold dark
matter can be obtained via top squark co-annihilation at low \tan\beta, tau
slepton co-annihilation at large \tan\beta or via bino-wino coannihilation.
Then, we typically find low rates for direct and indirect detection of
neutralino dark matter. However, essentially all the WMAP-allowed parameter
space can be probed by experiments at the CERN LHC, while significant portions
may also be explored at an e^+e^- collider with \sqrt{s}=0.5--1 TeV. We also
investigate a case with non-zero modular weights. In this case,
co-annihilation, A-funnel annihilation and bulk annihilation of neutralinos are
all allowed. Results for future colliders are qualitatively similar, but
prospects for indirect dark matter searches via gamma rays and anti-particles
are somewhat better.Comment: 38 pages including 22 EPS figures; latest version posted to conform
with published versio
High-energy Neutrino Astronomy: The Cosmic Ray Connection
This is a review of neutrino astronomy anchored to the observational fact
that Nature accelerates protons and photons to energies in excess of
and eV, respectively.
Although the discovery of cosmic rays dates back close to a century, we do
not know how and where they are accelerated. Basic elementary-particle physics
dictates a universal upper limit on their energy of eV, the
so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this
energy have been observed by all experiments, adding one more puzzle to the
cosmic ray mystery. Mystery is fertile ground for progress: we will review the
facts as well as the speculations about the sources including gamma ray bursts,
blazars and top-down scenarios.
The important conclusion is that, independently of the specific blueprint of
the source, it takes a kilometer-scale neutrino observatory to detect the
neutrino beam associated with the highest energy cosmic rays and gamma rays. We
also briefly review the ongoing efforts to commission such instrumentation.Comment: 83 pages, 18 figures, submitted to Reports on Progress in Physic