arXiv subjects

S. Ansoldi

Publications and source records attributed to S. Ansoldi.

At least 235 records · Page 13Linked to original sources

arXiv2014

MAGIC observations and multifrequency properties of the Flat Spectrum Radio Quasar 3C 279 in 2011

We study the multifrequency emission and spectral properties of the quasar 3C 279. We observed 3C 279 in very high energy (VHE, E>100GeV) gamma rays, with the MAGIC telescopes during 2011, for the first time in stereoscopic mode. We combine these measurements with observations at other energy bands: in high energy (HE, E>100MeV) gamma rays from Fermi-LAT, in X-rays from RXTE, in the optical from the KVA telescope and in the radio at 43GHz, 37GHz and 15GHz from the VLBA, Metsähovi and OVRO radio telescopes and optical polarisation measurements from the KVA and Liverpool telescopes. During the MAGIC observations (February to April 2011) 3C 279 was in a low state in optical, X-ray and gamma rays. The MAGIC observations did not yield a significant detection. These upper limits are in agreement with the extrapolation of the HE gamma-ray spectrum, corrected for extragalactic background light absorption, from Fermi-LAT. The second part of the MAGIC observations in 2011 was triggered by a high activity state in the optical and gamma-ray bands. During the optical outburst the optical electric vector position angle rotatated of about 180 degrees. There was no simultaneous rotation of the 43GHz radio polarisation angle. No VHE gamma rays were detected by MAGIC, and the derived upper limits suggest the presence of a spectral break or curvature between the Fermi-LAT and MAGIC bands. The combined upper limits are the strongest derived to date for the source at VHE and below the level of the previously detected flux by a factor 2. Radiation models that include synchrotron and inverse Compton emissions match the optical to gamma-ray data, assuming an emission component inside the broad line region (BLR) responsible for the high-energy emission and one outside the BLR and the infrared torus causing optical and low-energy emission. We interpreted the optical polarisation with a bent trajectory model.

astro-ph.HE↗

arXiv2014

MAGIC gamma-ray and multifrequency observations of flat spectrum radio quasar PKS 1510-089 in early 2012

Among more than fifty blazars detected in very high energy (VHE, E>100GeV) gamma-rays, only three belong to the subclass of Flat Spectrum Radio Quasars (FSRQs). MAGIC observed FSRQ PKS 1510-089 in February-April 2012 during a high activity state in the high energy (HE, E>100 MeV) gamma-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 sigma. In agreement with the previous VHE observations of the source, we find no statistically significant variability during the MAGIC observations in daily, weekly or monthly time scales. The other two known VHE FSRQs have shown daily scale to sub-hour variability. We study the multifrequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO and VLBA telescopes), X-ray (Swift satellite) and HE gamma-ray frequencies. The gamma-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multifrequency light curves suggest a common origin for the millimeter radio and HE gamma-ray emission and the HE gamma-ray flaring starts when the new component is ejected from the 43GHz VLBA core. The quasi-simultaneous multifrequency SED is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infra-red torus and a slow sheath surrounding the jet around the VLBA core. Both models fit the data well. However, the fast HE gamma-ray variability requires that within the modelled large emitting region, there must exist more compact regions. We suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.

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arXiv2014

MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context

We present a study of the very high energy (VHE; E > 100 GeV) gamma-ray emission of the blazar PKS 1424+240 observed with the MAGIC telescopes. The primary aim of this paper is the multiwavelength spectral characterization and modeling of this blazar, which is made particularly interesting by the recent discovery of a lower limit of its redshift of z > 0.6 and makes it a promising candidate to be the most distant VHE source. The source has been observed with the MAGIC telescopes in VHE gamma rays for a total observation time of ~33.6 h from 2009 to 2011. The source was marginally detected in VHE gamma rays during 2009 and 2010, and later, the detection was confirmed during an optical outburst in 2011. The combined significance of the stacked sample is ~7.2 sigma. The differential spectra measured during the different campaigns can be described by steep power laws with the indices ranging from 3.5 +/- 1.2 to 5.0 +/- 1.7. The MAGIC spectra corrected for the absorption due to the extragalactic background light connect smoothly, within systematic errors, with the mean spectrum in 2009-2011 observed at lower energies by the Fermi-LAT. The absorption-corrected MAGIC spectrum is flat with no apparent turn down up to 400 GeV. The multiwavelength light curve shows increasing flux in radio and optical bands that could point to a common origin from the same region of the jet. The large separation between the two peaks of the constructed non-simultaneous spectral energy distribution also requires an extremely high Doppler factor if an one zone synchrotron self-Compton model is applied. We find that a two-component synchrotron self-Compton model describes the spectral energy distribution of the source well, if the source is located at z~0.6.

astro-ph.HE↗

arXiv2014

Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes

The Crab pulsar is the only astronomical pulsed source detected at very high energy (VHE, E>100GeV) gamma-rays. The emission mechanism of VHE pulsation is not yet fully understood, although several theoretical models have been proposed. In order to test the new models, we measured the light curve and the spectra of the Crab pulsar with high precision by means of deep observations. We analyzed 135 hours of selected MAGIC data taken between 2009 and 2013 in stereoscopic mode. In order to discuss the spectral shape in connection with lower energies, 4.6 years of {\it Fermi}-LAT data were also analyzed. The known two pulses per period were detected with a significance of $8.0 σ$ and $12.6 σ$. In addition, significant emission was found between the two pulses with $6.2 σ$. We discovered the bridge emission above 50 GeV between the two main pulses. This emission can not be explained with the existing theories. These data can be used for testing new theoretical models.

astro-ph.HE↗

arXiv2014

Contemporaneous observations of the radio galaxy NGC 1275 from radio to very high energy gamma-rays

The radio galaxy NGC 1275, recently identified as a very high energy (VHE, >100 GeV) gamma-ray emitter by MAGIC, is one of the few non-blazar AGN detected in the VHE regime. In order to better understand the origin of the gamma-ray emission and locate it within the galaxy, we studied contemporaneous multi-frequency observations of NGC 1275 and modeled the overall spectral energy distribution (SED). We analyzed unpublished MAGIC observations carried out between Oct. 2009 and Feb. 2010, and the previously published ones taken between Aug. 2010 and Feb. 2011. We studied the multi-band variability and correlations by analyzing data of Fermi-LAT (0.1-100 GeV), as well as Chandra (X-ray), KVA (optical) and MOJAVE (radio) data taken during the same period. Using customized Monte Carlo simulations corresponding to early MAGIC stereo data, we detect NGC 1275 also in the earlier campaign. The flux level and energy spectra are similar to the results of the second campaign. The monthly light curve >100 GeV shows a hint of variability at the 3.6 sigma level. In the Fermi-LAT band, both flux and spectral shape variabilities are reported. The optical light curve is variable and shows a clear correlation with the gamma-ray flux >100 MeV. In radio, 3 compact components are resolved in the innermost part of the jet. One of them shows a similar trend as the LAT and KVA light curves. The 0.1-650 GeV spectra measured simultaneously with MAGIC and Fermi-LAT can be well fitted either by a log-parabola or by a power-law with a sub-exponential cutoff for both campaigns. A single-zone synchrotron-self-Compton model, with an electron spectrum following a power-law with an exponential cutoff, can explain the broadband SED and the multi-band behavior of the source. However, this model suggests an untypical low bulk-Lorentz factor or a velocity alignment closer to the line of sight than the pc-scale radio jet.

astro-ph.HE↗

arXiv2014

Optimized dark matter searches in deep observations of Segue 1 with MAGIC

We present the results of stereoscopic observations of the satellite galaxy Segue 1 with the MAGIC Telescopes, carried out between 2011 and 2013. With almost 160 hours of good-quality data, this is the deepest observational campaign on any dwarf galaxy performed so far in the very high energy range of the electromagnetic spectrum. We search this large data sample for signals of dark matter particles in the mass range between 100 GeV and 20 TeV. For this we use the full likelihood analysis method, which provides optimal sensitivity to characteristic gamma-ray spectral features, like those expected from dark matter annihilation or decay. In particular, we focus our search on gamma-rays produced from different final state Standard Model particles, annihilation with internal bremsstrahlung, monochromatic lines and box-shaped signals. Our results represent the most stringent constraints to the annihilation cross-section or decay lifetime obtained from observations of satellite galaxies, for masses above few hundred GeV. In particular, our strongest limit (95% confidence level) corresponds to a ~500 GeV dark matter particle annihilating into tau+tau-, and is of order ~ 1.2x10^{-24} cm^3 s^{-1} - a factor ~40 above the thermal value.

hep-ph↗

arXiv2014

Search for Very-High-Energy Gamma Rays from the z = 0.896 Quasar 4C +55.17 with the MAGIC telescopes

The bright gamma-ray quasar 4C +55.17 is a distant source ($z = 0.896$) with a hard spectrum at GeV energies as observed by the Large Area Telescope (LAT) on board the {\it Fermi} satellite. This source is identified as a good source candidate for very-high-energy (VHE; $> 30$ GeV) gamma rays. In general VHE gamma rays from distant sources provide an unique opportunity to study the extragalactic background light (EBL) and underlying astrophysics. The flux intensity of this source in the VHE range is investigated. Then, constraints on the EBL are derived from the attenuation of gamma-ray photons coming from the distant blazar. We searched for a gamma-ray signal from this object using the 35-hour observations taken by the MAGIC telescopes between November 2010 and January 2011. No significant VHE gamma-ray signal was detected. We computed the upper limits of the integrated gamma-ray flux at $95\%$ confidence level of $9.4 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ and $2.5 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ above $100$ GeV and $200$ GeV, respectively. The differential upper limits in four energy bins in the range from $80$ GeV to $500$ GeV are also derived. The upper limits are consistent with the attenuation predicted by low-flux EBL models on the assumption of a simple power-law spectrum extrapolated from LAT data.

astro-ph.HE↗

arXiv2013

MAGIC upper limits on the GRB 090102 afterglow

Indications of a GeV component in the emission from GRBs are known since the EGRET observations during the 1990's and they have been confirmed by the data of the Fermi satellite. These results have, however, shown that our understanding of GRB physics is still unsatisfactory. The new generation of Cherenkov observatories and in particular the MAGIC telescope, allow for the first time the possibility to extend the measurement of GRBs from several tens up to hundreds of GeV energy range. Both leptonic and hadronic processes have been suggested to explain the possible GeV/TeV counterpart of GRBs. Observations with ground-based telescopes of very high energy photons (E>30 GeV) from these sources are going to play a key role in discriminating among the different proposed emission mechanisms, which are barely distinguishable at lower energies. MAGIC telescope observations of the GRB 090102 (z=1.547) field and Fermi Large Area Telescope (LAT) data in the same time interval are analysed to derive upper limits of the GeV/TeV emission. We compare these results to the expected emissions evaluated for different processes in the framework of a relativistic blast wave model for the afterglow. Simultaneous upper limits with Fermi and a Cherenkov telescope have been derived for this GRB observation. The results we obtained are compatible with the expected emission although the difficulties in predicting the HE and VHE emission for the afterglow of this event makes it difficult to draw firmer conclusions. Nonetheless, MAGIC sensitivity in the energy range of overlap with space-based instruments (above about 40 GeV) is about one order of magnitude better with respect to Fermi. This makes evident the constraining power of ground-based observations and shows that the MAGIC telescope has reached the required performance to make possible GRB multiwavelength studies in the very high energy range.

astro-ph.HE↗

arXiv2012

Discovery of VHE gamma-rays from the blazar 1ES 1215+303 with the MAGIC Telescopes and simultaneous multi-wavelength observations

Context. We present the discovery of very high energy (VHE, E > 100GeV) gamma-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes and simultaneous multi-wavelength data in a broad energy range from radio to gamma-rays. Aims. We study the VHE gamma-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Methods. Triggered by an optical outburst, MAGIC observed the source in January-February 2011 for 20.3 hrs. The target was monitored in the optical R-band by the KVA telescope that also performed optical polarization measurements. We triggered target of opportunity observations with the Swift satellite and obtained simultaneous and quasi-simultaneous data from the Fermi Large Area Telescope and from the Metsähovi radio telescope. We also present the analysis of older MAGIC data taken in 2010. Results. The MAGIC observations of 1ES 1215+303 carried out in January-February 2011 resulted in the first detection of the source at VHE with a statistical significance of 9.4 sigma. Simultaneously, the source was observed in a high optical and X-ray state. In 2010 the source was observed in a lower state in optical, X-ray, and VHE, while the GeV gamma-ray flux and the radio flux were comparable in 2010 and 2011. The spectral energy distribution obtained with the 2011 data can be modeled with a simple one zone SSC model, but it requires extreme values for the Doppler factor or the electron energy distribution.

astro-ph.HE↗

arXiv2006

Proceedings to the 9th Workshop 'What Comes Beyond the Standard Models', Bled, September 16. - 26., 2006, Slovenia

Contents: 1. Child Universes in the Laboratory (S. Ansoldi and E.I. Guendelman) 2. Relation between Finestructure Constants at the Planck Scale from Multiple Point Principle (D.L. Bennett, L.V. Laperashvili and H.B. Nielsen) 3. On the Origin of Families of Fermions and Their Mass Matrices -- Approximate Analyses of Properties of Four Families Within Approach Unifying Spins and Charges (M. Breskvar, D. Lukman and N.S. Mankoc Borstnik) 4. Cosmoparticle Physics: Cross-disciplinary Study of Physics Beyond the Standard Model (M.Yu. Khlopov) 5. Discussion Section on 4th Generation (M.Yu. Khlopov) 6. Involution Requirement on a Boundary Makes Massless Fermions Compactified on a Finite Flat Disk Mass Protected (N.S. Mankoc Borstnik and H.B. Nielsen) 7. How Can Group Theory be Generalized so Perhaps Providing Further Information About Our Universe? (R. Mirman) 8. FutureDependent Initial Conditions from Imaginary Part in Lagrangian (H.B. Nielsen and M. Ninomiya) 9. Coupling Self-tuning to Critical Lines From Highly Compact Extra Dimensions (K. Petrov)

hep-ph↗

arXiv2002

Nambu-Goto Strings from SU(N) Born-Infeld model

The spectrum of quenched Yang-Mills theory in the large-N limit displays strings and higher dimensional extended objects. The effective dynamics of string-like excitations is encoded into area preserving Schild action. In this letter, we bridge the gap between SU(N) gauge models and fully reparametrization invariant Nambu-Goto string models by introducing an extra matrix degree of freedom in the Yang-Mills action. In the large-N limit this matrix variable becomes the world-sheet auxiliary field allowing a smooth transition between the Schild and Nambu-Goto strings. The new improved matrix model we propose here can be extended to p-branes provided we enlarge the dimensionality of the target spacetime.

hep-th↗

arXiv2001

The QCD Membrane

In this paper we study spatially quenched, SU(N) Yang-Mills theory in the large-N limit. The resulting reduced action shows the same formal look as the Banks-Fischler-Shenker-Susskind M-theory action. The Weyl-Wigner-Moyal symbol of this matrix model is the Moyal deformation of a p(=2)-brane action. Thus, the large-N limit of the spatially quenched SU(N) Yang-Mills is seen to describe a dynamical membrane. By assuming spherical symmetry we compute the mass spectrum of this object in the WKB approximation.

hep-th↗

arXiv2001

Quenched, Minisuperspace, Bosonic p-brane Propagator

We borrow the minisuperspace approximation from Quantum Cosmology and the quenching approximation from QCD in order to derive a new form of the bosonic p-brane propagator. In this new approximation we obtain an exact description of both the collective mode deformation of the brane and the center of mass dynamics in the target spacetime. The collective mode dynamics is a generalization of string dynamics in terms of area variables. The final result is that the evolution of a p-brane in the quenched-minisuperspace approximation is formally equivalent to the effective motion of a particle in a spacetime where points as well as hypersurfaces are considered on the same footing as fundamental geometrical objects. This geometric equivalence leads us to define a new tension-shell condition that is a direct extension of the Klein-Gordon condition for material particles to the case of a physical p-brane.

hep-th↗

arXiv2001

Vacuum Bubbles Nucleation and Dark Matter Production through Gauge Symmetry Rearrangement

Modern particle physics and cosmology support the idea that a background of invisible material pervades the whole universe, and identify in the cosmic vacuum the ultimate source of matter-energy, both seen and unseen. Within the framework of the theory of fundamental relativistic membranes, we suggest a self-consistent, vacuum energy-driven mechanism for dark matter creation through gauge symmetry rearrangement.

hep-ph↗

arXiv2001

p-Branes from Generalized Yang-Mills Theory

We consider the reduced, quenched version of a generalized Yang-Mills action in 4k-dimensional spacetime. This is a new kind of matrix theory which is mapped through the Weyl-Wigner-Moyal correspondence into a field theory over a non-commutative phase space. We show that the ``classical'' limit of this field theory is encoded into the effective action of an open, (4k-1)-dimensional, bulk brane enclosed by a dynamical, Chern-Simons type, (4k-2)-dimensional, boundary brane. The bulk action is a pure volume term, while the boundary action carries all the dynamical degrees of freedom.

hep-th↗

arXiv2000

Chern-Simons Hadronic Bag from Quenched Large-N QCD

SU(N) reduced, quenched, gauge theories have been shown to be related to string theories. We extend this result and show how a 4-dimensional, reduced, quenched, Yang-Mills theory, supplemented by the topological term, can be related through the Wigner-Weyl-Moyal correspondence to an open 3-brane model. The boundary of the 3-brane is described by a Chern-Simons 2-brane. We identify the bulk of the 3-brane with the interior of a hadronic bag and the world-volume of the Chern-Simons 2-brane with the dynamical boundary of the bag. We estimate the value of the induced bag constant to be a little less than 200MeV.

hep-th↗

arXiv2000

On the WKB quantum equivalence between diverse p-brane actions

We consider an action for a closed, bosonic, p-brane, where the brane tension is not an assigned parameter but rather it is induced by a maximal rank gauge p-form. This model is classically equivalent to the Nambu--Goto/Howe-Tucker model. We investigate how this classical equivalence can be implemented in the path integral framework. For this purpose we adopt a ``first order'' integration procedure over gauge p-forms and a ``shortened'' Fadeev-Popov procedure.

hep-th↗

arXiv2000

p-Branes Electric-Magnetic Duality and Stueckelberg/Higgs Mechanism: a Path-Integral Approach

We study the vacuum functional for a system of p-branes interacting with Maxwell fields of higher rank. This system represents a generalization of the usual electrodynamics of point particles, with one essential difference: namely, that the world-history of a p-brane, due to the spatial extension of the object, may possess a physical boundary. Thus, the objective of this study is twofold: first, we wish to exploit the breaking of gauge invariance due to the presence of a physical boundary, in order to generate mass as an alternative to the Higgs mechanism; second, we wish to investigate how the new mechanism of mass generation is affected by the duality transformation between electric and magnetic branes. The whole analysis is performed by using the path-integral method, as opposed to the more conventional canonical approach. The advantage of the path integral formulation is that it enables us to Fourier transform the field strength directly, rather than the gauge potential. To our knowledge, this field strength formulation represents a new application of the path integral method, and leads, in a straightforward way, to the dual representation of the vacuum functional. We find that the effect of the dual transformation is essentially that of exchanging the role of the gauge fields defined respectively on the " bulk'' and "boundary" of the p-brane history.

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