arXiv subjects

P. Bordas

Publications and source records attributed to P. Bordas.

156 records · Page 9Linked to original sources

arXiv2010

MAGIC Gamma-ray Telescope Observation of the Perseus Cluster of Galaxies: implications for cosmic rays, dark matter, and NGC1275

The Perseus galaxy cluster was observed by the MAGIC Cherenkov telescope for a total effective time of 24.4 hr during 2008 November and December. The resulting upper limits on the gamma-ray emission above 100 GeV are in the range of 4.6 to 7.5 x 10^{-12} cm^{-2} s^{-1} for spectral indices from -1.5 to -2.5, thereby constraining the emission produced by cosmic rays, dark matter annihilations, and the central radio galaxy NGC1275. Results are compatible with cosmological cluster simulations for the cosmic-ray-induced gamma-ray emission, constraining the average cosmic ray-to-thermal pressure to <4% for the cluster core region (<8% for the entire cluster). Using simplified assumptions adopted in earlier work (a power-law spectrum with an index of -2.1, constant cosmic ray-to-thermal pressure for the peripheral cluster regions while accounting for the adiabatic contraction during the cooling flow formation), we would limit the ratio of cosmic ray-to-thermal energy to E_CR/E_th<3%. The upper limit also translates into a level of gamma-ray emission from possible annihilations of the cluster dark matter (the dominant mass component) that is consistent with boost factors of ~10^4 for the typically expected dark matter annihilation-induced emission. Finally, the upper limits obtained for the gamma-ray emission of the central radio galaxy NGC1275 are consistent with the recent detection by the Fermi-LAT satellite. Due to the extremely large Doppler factors required for the jet, a one-zone synchrotron self-Compton model is implausible in this case. We reproduce the observed spectral energy density by using the structured jet (spine-layer) model which has previously been adopted to explain the high-energy emission of radio galaxies.

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arXiv2009

Correlated X-ray and Very High Energy emission in the gamma-ray binary LS I +61 303

The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in compact binary systems, which provide variable conditions along eccentric orbits. Despite this, the nature of some of these systems, and of the accelerated particles producing the VHE emission, is unclear. To answer some of these open questions, we conducted a multiwavelength campaign of the VHE gamma-ray emitting X-ray binary LS I +61 303 including the MAGIC telescope, XMM-Newton, and Swift during 60% of an orbit in 2007 September. We detect a simultaneous outburst at X-ray and VHE bands, with the peak at phase 0.62 and a similar shape at both wavelengths. A linear fit to the simultaneous X-ray/VHE pairs obtained during the outburst yields a correlation coefficient of r=0.97, while a linear fit to all simultaneous pairs provides r=0.81. Since a variable absorption of the VHE emission towards the observer is not expected for the data reported here, the correlation found indicates a simultaneity in the emission processes. Assuming that they are dominated by a single particle population, either hadronic or leptonic, the X-ray/VHE flux ratio favors leptonic models. This fact, together with the detected photon indices, suggests that in LS I +61 303 the X-rays are the result of synchrotron radiation of the same electrons that produce VHE emission as a result of inverse Compton scattering of stellar photons.

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arXiv2009

Radio continuum and near-infrared study of the MGRO J2019+37 region

(abridged) MGRO J2019+37 is an unidentified extended source of VHE gamma-rays originally reported by the Milagro Collaboration as the brightest TeV source in the Cygnus region. Its extended emission could be powered by either a single or several sources. The GeV pulsar AGL J2020.5+3653, discovered by AGILE and associated with PSR J2021+3651, could contribute to the emission from MGRO J2019+37, although extrapolation of the GeV spectrum does not explain the detected multi-TeV flux. Our aim is to identify radio and NIR sources in the field of the extended TeV source MGRO J2019+37, and study potential counterparts that could contribute to its emission. We surveyed a region of about 6 square degrees with the Giant Metrewave Radio Telescope (GMRT) at the frequency 610 MHz. We also observed the central square degree of this survey in the NIR Ks-band using the 3.5 m telescope in Calar Alto. Archival X-ray observations of some specific fields are included. VLBI observations of an interesting radio source were performed. We explored possible scenarios to produce the multi-TeV emission from MGRO J2019+37 and studied which of the sources could be the main particle accelerator. We present a catalogue of 362 radio sources detected with the GMRT in the field of MGRO J2019+37, and the results of a cross-correlation of this catalog with one obtained at NIR wavelengths, as well as with available X-ray observations of the region. Some peculiar sources inside the ~1 degree uncertainty region of the TeV emission from MGRO J2019+37 are discussed in detail, including the pulsar PSR J2021+3651 and its pulsar wind nebula PWN G75.2+0.1, two new radio-jet sources, the HII region Sh 2-104 containing two star clusters, and the radio source NVSS J202032+363158.

astro-ph.HE↗

arXiv2009

MAGIC Collaboration: Contributions to the 31st International Cosmic Ray Conference (ICRC 2009)

Index entry listing the contributed papers of the MAGIC collaboration to the 31th International Cosmic Ray Conference (ICRC 2009), July 7-15 2009, Łódź, Poland. The individual papers are sorted by subject: Overview and Highlight Papers; MAGIC-II Status and Components; Software and Analysis Techniques; Technical Developments; Scientific Results. This HTML document includes clickable links to the papers that exist on the astro-ph arXiv. We hope that this will make it easy to access the MAGIC contributions in a systematic way.

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arXiv2009

Microquasar observations with the MAGIC telescope

Microquasars, X-ray binaries displaying relativistic jets driven by accretion onto a compact object, are some of the most efficient accelerators in the Galaxy. Theoretical models predict Very High Energy (VHE) emission at the base of the jet where particles are accelerated to multi-TeV energies. This emission could be detected by present IACTs. %Moreover, gamma-ray fluxes should increase during flaring events when accretion rates are enhanced. The MAGIC telescope observed the microquasars GRS 1915+105, Cyg X-3, Cyg X-1 and SS433 for ~ 150 hours in total from 2005 to 2008. We triggered our observations by using multi wavelength information through radio flaring alerts with the RATAN telescope as well as by ensuring the low/hard state of the source through RXTE/ASM and Swift/BAT monitoring data. We report on the upper limits on steady and variable emission from these sources over this long period.

astro-ph.HE↗

arXiv2008

Non thermal emission from microquasar/ISM interaction

The interaction of microquasar jets with their environment can produce non-thermal radiation as is the case for extragalactic outflows impacting on their surroundings. We have developed an analytical model based on those successfully applied to extragalactic sources. The jet is taken to be a supersonic and mildly relativistic hydrodynamical outflow. We focus on the jet/shocked medium structure when being in its adiabatic phase, and assume that it grows in a self-similar way. We calculate the fluxes and spectra of the radiation produced via synchrotron, Inverse Compton and relativistic Bremsstrahlung processes by electrons accelerated in strong shocks. A hydrodynamical simulation is also performed to further investigate the jet interaction with the environment and check the physical parameters used in the analytical model. We conclude that microquasar jet termination regions could be detectable at radio wavelengths for current instruments sensitive to arcminute scales while at X-rays the expected luminosities are moderate, although the emitter is more compact than the radio one. The radiation at gamma-ray energies may be within the detection limits of the next generation of satellite and ground-based instruments.

astro-ph↗

arXiv2008

A radio and near-infrared mini-survey of the MGRO J2019+37 complex

MGRO J2019+37 is an unidentified source of very high energy gamma-rays originally reported by the MILAGRO collaboration as the brightest TeV source in the Cygnus region. Despite the poor angular resolution of MILAGRO, this object seems to be most likely an extended source or, alternatively, a superposition of point-like TeV sources. In order to contribute to the understanding of this peculiar object, we have mosaiced it with the Giant Metrewave Radio Telescope (GMRT) in Pune, India, at the 610 MHz frequency covering a field of view of about 6 square degrees down to a typical rms noise of a few tenths of mJy. We also observed the central square degree of this mosaic in the near infrared Ks-band using the 3.5 m telescope and the OMEGA2000 camera at the Calar Alto observatory (Spain). We present here a first account of our observations and results, together with a preliminar cross correlation of the radio and infrared source catalog as well as a correlation with the available X-ray observations of the region.

astro-ph↗

arXiv2007

The MAGIC Project: Contributions to ICRC 2007

The MAGIC Project: Contributions to ICRC 2007, Merida, Mexico. Contents pages for the Contribution on behalf of the MAGIC Collaboration to the 30th ICRC that took place in July 2007 in Merida, Mexico. The contents are in html form with clickable links to the papers that exist on the Astrophysics archive. We hope that this will make it easier to access the output of the conference in a systematic way. Comments on how useful this is/ how it could be improved should be sent to michela.demaria@iuav.it.

astro-ph↗

arXiv2007

Leptonic secondary emission in a hadronic microquasar model

Context: It has been proposed that the origin of the very high-energy photons emitted from high-mass X-ray binaries with jet-like features, so-called microquasars (MQs), is related to hadronic interactions between relativistic protons in the jet and cold protons of the stellar wind. Leptonic secondary emission should be calculated in a complete hadronic model that include the effects of pairs from charged pion decays inside the jets and the emission from pairs generated by gamma-ray absorption in the photosphere of the system. Aims: We aim at predicting the broadband spectrum from a general hadronic microquasar model, taking into account the emission from secondaries created by charged pion decay inside the jet. Methods: The particle energy distribution for secondary leptons injected along the jets is consistently derived taking the energy losses into account. We also compute the spectral energy distribution resulting from these leptons is calculated after assuming different values of the magnetic field inside the jets. The spectrum of the gamma-rays produced by neutral pion-decay and processed by electromagnetic cascades under the stellar photon field. Results: We show that the secondary emission can dominate the spectral energy distribution at low energies (~1 MeV). At high energies, the production spectrum can be significantly distorted by the effect of electromagnetic cascades. These effects are phase-dependent, and some variability modulated by the orbital period is predicted.

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arXiv2007

Synchrotron emission from secondary leptons in microquasar jets

We present a model to estimate the synchrotron radio emission generated in microquasar (MQ) jets due to secondary pairs created via decay of charged pions produced in proton-proton collisions between stellar wind ions and jet relativistic protons. Signatures of electrons/positrons are obtained from consistent particle energy distributions that take into account energy losses due to synchrotron and inverse Compton (IC) processes, as well as adiabatic expansion. The space parameter for the model is explored and the corresponding spectral energy distributions (SEDs) are presented. We conclude that secondary leptonic emission represents a significant though hardly dominant contribution to the total radio emission in MQs, with observational consequences that can be used to test some still unknown processes occurring in these objects as well as the nature of the matter outflowing in their jets.

astro-ph↗

arXiv2007

Observations of microquasars with the MAGIC telescope

We report on the results from the observations in very high energy band (VHE, E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hours during 26 nights, spanning the period between June and November 2006. We report on the results of the searches for steady and variable gamma-ray signals, including the first experimental evidence for an intense flare, of duration between 1.5 and 24 hours.

astro-ph↗

arXiv2007

MAGIC upper limits on the very high energy emission from GRBs

The fast repositioning system of the MAGIC Telescope has allowed during its first data cycle, between 2005 and the beginning of year 2006, observing nine different GRBs as possible sources of very high energy gammas. These observations were triggered by alerts from Swift, HETE-II, and Integral; they started as fast as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending upon the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events, using the standard analysis chain of MAGIC. For the bursts with measured redshift, the upper limits are compatible with a power law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the Metagalactic Radiation Field (MRF).

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