Roberta Zanin

Gamma rays detected from Cygnus X-1 with likely jet origin

Aims. We probe the high-energy (>60u2009MeV) emission from the black hole X-ray binary system, Cygnusu2009X-1, and investigate its origin. Methods. We analyzed 7.5u2009yr of data by Fermi -LAT with the latest Pass 8 software version. Results. We report the detection of a signal at ~8 σ statistical significance that is spatially coincident with Cygnusu2009X-1 and has a luminosity of 5.5 × 10 33 u2009ergu2009s -1 , above 60u2009MeV. The signal is correlated with the hard X-ray flux: the source is observed at high energies only during the hard X-ray spectral state, when the source is known to display persistent, relativistic radio-emitting jets. The energy spectrum, extending up to ~20u2009GeV without any sign of spectral break, is well fit by a power-law function with a photon index of 2.3 ± 0.2. There is a hint of orbital flux variability, with high-energy emission mostly coming around the superior conjunction. Conclusions. We detected GeV emission from Cygnusu2009X-1 and probed that the emission is most likely associated with the relativistic jets. The evidence of flux orbital variability indicates the anisotropic inverse-Compton on stellar photons as the mechanism at work, thus constraining the emission region to a distance 10 11 –10 13 u2009cm from the black hole.Aims. Probe the high-energy (>60 MeV) emission from the black hole X-ray binary system, Cygnus X-1, and investigate its origin. Methods. We analysed 7.5 yr of data by Fermi-LAT with the latest Pass 8 software version. Results. We report the detection of a signal at ∼8σ statistical significance spatially coincident with Cygnus X-1 and a luminosity above 60 MeV of 5.5×1033 erg s−1. The signal is correlated with the hard X-ray flux: the source is observed at high energies only during the hard X-ray spectral state, when the source is known to display persistent, relativistic radio emitting jets. The energy spectrum, extending up to ∼20 GeV without any sign of spectral break, is well fitted by a power-law function with a photon index of 2.3±0.2. There is a hint of orbital flux variability, with high-energy emission mostly coming around the superior conjunction. Conclusions. We detected GeV emission from Cygnus X-1 and probed that the emission is most likely associated with the relativistic jets. The evidence of flux orbital variability points to the anisotropic inverse Compton on stellar photons as the mechanism at work, thus constraining the emission region to a distance 1011 − 1013 cm from the black hole.

Gammapy - A prototype for the CTA science tools

Gammapy is a Python package for high-level gamma-ray data analysis built on Numpy, Scipy and Astropy. It enables us to analyze gamma-ray data and to create sky images, spectra and lightcurves, from event lists and instrument response information, and to determine the position, morphology and spectra of gamma-ray sources. nSo far Gammapy has mostly been used to analyze data from H.E.S.S. and Fermi-LAT, and is now being used for the simulation and analysis of observations from the Cherenkov Telescope Array (CTA). We have proposed Gammapy as a prototype for the CTA science tools. This contribution gives an overview of the Gammapy package and project and shows an analysis application example with simulated CTA data.

VHE gamma-ray study of the composite SNR MSH 15-52 with H.E.S.S

The composite supernova remnant (SNR) MSH 15-52 comprises the bright X-ray pulsar wind nebula (PWN) of PSR B1509-58, surrounded by a shell which is a prominent object in the radio domain. H.E.S.S. had discovered extended very-high-energy (VHE) gamma-ray emission coincident with the PWN. With additional H.E.S.S. observations performed since the 2005 discovery paper, we study the properties of the emission in greater detail. We compare the VHE gamma-ray morphology of the PWN with that in synchrotron emission, obtained from archival X-ray observations, and discuss the implications on the magnetic field in the nebula. In particular, we discuss potential extended gamma-ray emission beyond the X-ray PWN, which may allow for conclusions on scenarios of PWNe as sources of cosmic ray electrons and positrons.

Unveiling the magnetic structure of VHE SNRs/PWNe with XIPE, the x-ray imaging-polarimetry explorer

The dynamics, energetics and evolution of pulsar wind nebulae (PWNe) and supernova remnants (SNRs), are strongly affected by their magnetic field strength and distribution. They are usually strong, extended, sources of non-thermal X-ray radiation, producing intrinsically polarised radiation. The energetic wind around pulsars produces a highly-magnetised, structured flow, often displaying a jet and a torus and different features (i.e. wisps, knots). This magnetic-dominant wind evolves as it moves away from the pulsar magnetosphere to the surrounding large-scale nebula, becoming kinetic-dominant. Basic aspects such how this conversion is produced, or how the jets and torus are formed, as well as the level of turbulence in the nebula are still unknown. Likewise, the processes ruling the acceleration of particles in shell-like SNRs up to 1015 eV, including the amplification of the magnetic field, are not clear yet. Imaging polarimetry in this regard is crucial to localise the regions of shock acceleration and...

Observing the Galactic Plane with the Cherenkov Telescope Array

The Cherenkov Telescope Array is a next generation ground-based gamma-ray observatory de- signed to detect photons in the 20 GeV to 300 TeV energy range. With a sensitivity improvement of up to one order of magnitude on the entire energy range with respect to currently operating facilities, coupled with significantly better angular resolution, the array will be used to address many open questions in high-energy astrophysics. In addition, CTA will explore the ultra-high energy (E >50 TeV) window with great sensitivity for the first time. CTA is expected to reveal a detailed picture of the Galactic plane at the highest energies, and to discover around one hundred new supernova remnants and many hundreds of pulsar wind nebulae, according to current population estimates. The ability of the observatory to resolve such a large number of Galactic sources is one of the challenges to be faced. In this paper, we will present the first simulated scan of the Galactic plane with a realistic observation strategy, with particular attention to the potential source confusion. We will also present prospects for morphological studies of extended sources, such as the young SNR RX J1713.7-39.

Supernova remnants in the very–high–energy sky: prospects for the Cherenkov Telescope Array

The Cherenkov Telescope Array is expected to lead to the detection of many new supernova remnants in the TeV and multi-TeV range. In addition to the individual study of each SNR, the study of these objects as a population can help constraining the parameters describing the acceleration of particles and increasing our understanding of the mechanisms involved. We present Monte Carlo simulations of the population of Galactic SNRs emitting TeV gamma rays. We also discuss how the simulated population can be confronted with future observations to provide a novel test for the SNR hypothesis of cosmic ray origins.

Gamma rays from microquasars Cygnus X-1 and Cygnus X-3

Gamma-ray observations of microquasars at high and very-high energies can provide valuable information of the acceleration processes inside the jets, the jet-environment interaction and the disk-jet coupling. Two high-mass microquasars have been deeply studied to shed light on these aspects: Cygnus X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray spectral states of black hole transients, where the radiation is dominated by non-thermal emission from the corona and jets and by thermal emission from the disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A hint of orbital flux modulation was also found, as the source is only detected in phases around the compact object superior conjunction. We conclude that the high-energy gamma-ray emission from Cygnus X-1 is most likely associated with jets and its detection allow us to constrain the production site. Moreover, we include in the discussion the final results of a MAGIC long-term campaign on Cygnus X-1 that reaches almost 100 hr of observations at different X-ray states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring activity period in radio and high-energy gamma rays, similar to the one that led to its detection in the high-energy regime in 2009. MAGIC performed comprehensive follow-up observations for a total of about 70 hr. We discuss our results in a multi-wavelength context.

Detection of high-energy gamma rays from Cygnus X-1 associated with the jets

Cygnus X1 is the prototype black hole high-mass microquasar. As a persistent and bright X-ray source is considered an optimal candidate to study the disk-jet coupling. It displays the typical soft and hard X-ray spectral states of black hole binaries where the emission is dominated by the thermal black body radiation and by non-thermal emission from the inner part of the disk and the relativistic jets, respectively. We report the detection of a 8-sigma excess, above 60u2005MeV, spatially coincident with Cygnus X-1 by using 7.5 yr of Fermi-LAT data and the latest Pass8 software version. The point-like signal is clearly associated to the microquasar since the emission correlates with the hard X-ray state. In addition, there is a hint of orbital flux variability with most of the emission coming around the superior conjunction. The high energy emission is most likely associated with the jets and produced via anisotropic inverse Compton scattering on the stellar photons. The subsequent constraints on the emission ...

The Crab pulsar at VHE

The last six years have witnessed major revisions of our knowledge about the Crab Pulsar. The consensus scenario for the origin of the high-energy pulsed emission has been challenged with the discovery of a very-high-energy power law tail extending up to ~400 GeV, above the expected spectral cut off at a few GeV. Now, new measurements obtained by the MAGIC collaboration extend the energy spectrum of the Crab Pulsar even further, on the TeV regime. Above ~400 GeV the pulsed emission comes mainly from the interpulse, which becomes more prominent with energy due to a harder spectral index. These findings require γ -ray production via inverse Compton scattering close to or beyond the light cylinder radius by an underlying particle population with Lorentz factors greater than 5 × 106 . We will present those new results and discuss the implications in our current knowledge concerning pulsar environments.

MAGIC RESULTS ON BINARY SYSTEMS

Three X-ray binary systems have been unambiguously detected at TeV energies: LS 5039, LS I +61° +303, PSR B1259-63. Additionally, the TeV source HESS J0632+057 has been found to be a new binary system. The recent detection of the microquasar Cygnus X-3, between 100 MeV and few GeV, confirms that also this sub-class of accreting binaries displaying radio relativistic jets provides interesting candidates for very-high-energy (VHE) gamma-ray observations. The MAGIC telescopes made a significant effort to search for signals from X-ray binaries. This article will present the new results on LS I 61° +303, which show a reduction in the VHE γ-ray flux in the periodic outburst phase with respect to previous campaigns. MAGIC observed also HESS J0632 +057 in 2010 and 2011, covering an X-ray outburst reported by Swift in February 2011. These observations show significant activity in VHE gamma-rays temporally coincident with the X-ray outburst. In addition, this article will review MAGIC results on the microquasars Cygnus X-3, Cygnus X-1, and Scorpius X-1 which report constraining flux upper limits in different X-ray spectral states and as well as during flux enhancements at high energies.