High resolution images at 11 and 20 microns of the Active Galactic Nucleus in NGC 1068

We present diffraction-limited IR images at 11.2 and 20.5 microns of the central 6''x6'' region in NGC 1068, collected with the CAMIRAS instrument mounted at the f/36 IR focus of the CFHT/Hawaii 3.6m telescope and at the f/35 IR focus of the ESO/La Silla 3.6m telescope, respectively. After deconvolution, the achieved resolution (0.6'') reveals a prominent central core emitting about 95 % of the total flux at these wavelengths, as well as extended emission, to the South-West and to the North-East, broken into patchy components which are particularly conspicuous at 20.5 microns and can be isolated as individual clouds. The central core shows an East-West FWHM of 0.6'' (hence unresolved) and a North-South FWHM of 0.9'' corresponding to a resolved full size extension of abound 100 pc. Such an elongated shape is in agreement with model predictions of a dusty/molecular torus surrounding the central engine in NGC 1068, observed under an inclination angle around 65 degrees.Comment: 7 pages, 2 figures To appear in Astronomy and Astrophysic

Signatures of the transition from galactic to extragalactic cosmic rays

We discuss the signatures of the transition from galactic to extragalactic cosmic rays in different scenarios, giving most attention to the dip scenario. The dip is a feature in the diffuse spectrum of ultra-high energy (UHE) protons in the energy range $1\times 10^{18} - 4\times 10^{19}$ eV, which is caused by electron-positron pair production on the cosmic microwave background (CMB) radiation. The dip scenario provides a simple physical description of the transition from galactic to extragalactic cosmic rays. Here we summarize the signatures of the pair production dip model for the transition, most notably the spectrum, the anisotropy and the chemical composition. The main focus of our work is however on the description of the features that arise in the elongation rate and in the distribution of the depths of shower maximum $X_{\rm max}$ in the dip scenario. We find that the curve for $X_{\max}(E)$ shows a sharp increase with energy, which reflects a sharp transition from an iron dominated flux at low energies to a proton dominated flux at $E\sim 10^{18}$ eV. We also discuss in detail the shape of the $X_{\max}$ distributions for cosmic rays of given energy and demonstrate that this represents a powerful tool to discriminate between the dip scenario and other possible models of the transition.Comment: Version accepted for publication in Physical Review

Searching for galactic cosmic ray pevatrons with multi-TeV gamma rays and neutrinos

The recent HESS detections of supernova remnant shells in TeV gamma-rays confirm the theoretical predictions that supernova remnants can operate as powerful cosmic ray accelerators. If these objects are responsible for the bulk of galactic cosmic rays, then they should accelerate protons and nuclei to 10^15 eV and beyond, i.e. act as cosmic PeVatrons. The model of diffusive shock acceleration allows, under certain conditions, acceleration of particles to such high energies and their gradual injection into the interstellar medium, mainly during the Sedov phase of the remnant evolution. The most energetic particles are released first, while particles of lower energies are more effectively confined in the shell, and are released at later epochs. Thus the spectrum of nonthermal paticles inside the shell extends to PeV energies only during a relatively short period of the evolution of the remnant. For this reason one may expect spectra of secondary gamma-rays and neutrinos extending to energies beyond 10 TeV only from T \lesssim 1000 yr old supernova remnants. On the other hand, if by a chance a massive gas cloud appears in the \lesssim 100 pc vicinity of the supernova remnant, ``delayed'' multi-TeV signals of gamma-rays and neutrinos arise when the most energetic partices emerged from the supernova shell reach the cloud. The detection of such delayed emission of multi-TeV gamma-rays and neutrinos allows indirect identification of the supernova remnant as a particle PeVatron.Comment: ApJ Letters, in press. Reference to recent MILAGRO results adde

Exploring biases of atmospheric retrievals in simulated jwst transmission spectra of hot jupiters

With a scheduled launch in 2018 October, the James Webb Space Telescope (JWST) is expected to revolutionize the field of atmospheric characterization of exoplanets. The broad wavelength coverage and high sensitivity of its instruments will allow us to extract far more information from exoplanet spectra than what has been possible with current observations. In this paper, we investigate whether current retrieval methods will still be valid in the era of JWST, exploring common approximations used when retrieving transmission spectra of hot Jupiters. To assess biases, we use 1D photochemical models to simulate typical hot Jupiter cloud-free atmospheres and generate synthetic observations for a range of carbon-to-oxygen ratios. Then, we retrieve these spectra using TauREx, a Bayesian retrieval tool, using two methodologies: one assuming an isothermal atmosphere, and one assuming a parameterized temperature profile. Both methods assume constant-with-altitude abundances. We found that the isothermal approximation biases the retrieved parameters considerably, overestimating the abundances by about one order of magnitude. The retrieved abundances using the parameterized profile are usually within 1σ of the true state, and we found the retrieved uncertainties to be generally larger compared to the isothermal approximation. Interestingly, we found that by using the parameterized temperature profile we could place tight constraints on the temperature structure. This opens the possibility of characterizing the temperature profile of the terminator region of hot Jupiters. Lastly, we found that assuming a constant-with-altitude mixing ratio profile is a good approximation for most of the atmospheres under study

Mid-infrared imaging of NGC1068 with VISIR at the VLT

High resolution mid-infrared (MIR) images of the central region of NGC1068 have been obtained with VISIR, the multi-mode MIR instrument recently installed at the ESO/VLT on Paranal. A map of the emission at 12.8mic with increased sensitivity over the central 8"x 8" area is discussed. It shows a central core (unresolved along the E-W direction) and an extended emission which draws a spiral pattern similar to that observed on near-infrared images. Patches of MIR emission can be detected up to a distance of 4" from the core. The deconvolved 12.8mic map is fully consistent with previous high-resolution MIR observations. It highlights the structure of the extended emission, already seen on the un-deconvolved image, and allows to identify a set of mid-infrared sources: 7 in the NE quadrant and 5 in the SW quadrant. The MIR emission map is compared with those obtained at comparable angular resolution in the near-infrared and in the [OIII] line emission. The very good correlation between the VISIR map and the HST optical map supports the idea that the MIR emission not associated with the torus arises from dust associated with the narrow line region clouds. The N-S extension of the MIR core (0.44") is then probably simply due to the mixing of the MIR emission from the dusty torus and the MIR emission from NLR cloud B, located only 0.1" to the North.Comment: 5 pages, 1 figure (reduced quality), accepted MNRAS Letter. The paper with full resolution figure can be downloaded at http://www.sc.eso.org/~egallian/VISIR/N1068_VISIR.ps.g

Exploring biases of atmospheric retrievals in simulated jwst transmission spectra of hot jupiters

With a scheduled launch in 2018 October, the James Webb Space Telescope (JWST) is expected to revolutionize the field of atmospheric characterization of exoplanets. The broad wavelength coverage and high sensitivity of its instruments will allow us to extract far more information from exoplanet spectra than what has been possible with current observations. In this paper, we investigate whether current retrieval methods will still be valid in the era of JWST, exploring common approximations used when retrieving transmission spectra of hot Jupiters. To assess biases, we use 1D photochemical models to simulate typical hot Jupiter cloud-free atmospheres and generate synthetic observations for a range of carbon-to-oxygen ratios. Then, we retrieve these spectra using TauREx, a Bayesian retrieval tool, using two methodologies: one assuming an isothermal atmosphere, and one assuming a parameterized temperature profile. Both methods assume constant-with-altitude abundances. We found that the isothermal approximation biases the retrieved parameters considerably, overestimating the abundances by about one order of magnitude. The retrieved abundances using the parameterized profile are usually within 1σ of the true state, and we found the retrieved uncertainties to be generally larger compared to the isothermal approximation. Interestingly, we found that by using the parameterized temperature profile we could place tight constraints on the temperature structure. This opens the possibility of characterizing the temperature profile of the terminator region of hot Jupiters. Lastly, we found that assuming a constant-with-altitude mixing ratio profile is a good approximation for most of the atmospheres under study