Astrophysics Community Research Articles

The extragalactic gamma-ray sky: A view on the most powerful phenomena in the universe

The gamma-ray sky provides a look into the most energetic and violent processes of the universe. In the last years, gamma-ray satellites are scanning the sky for understanding the physics governing the gamma-ray emission. A wealth of information on the physics of the gamma-ray sky has been obtained by gamma-ray satellites orbiting around the Earth. So far, roughly three thousands sources have been detected in gamma-rays, and this number is going to increase as the gamma-ray missions continue to survey the sky. The high energy sky is dominated by extragalactic objects. A large fraction of the detected sources has no obvious counterpart in catalogs at other wavelengths, leaving their nature under debate. This contribution will focus on the extragalactic gamma-ray sky, its properties and processes at work with the aim of discussing the main issues highly debated in the astrophysical community.

Cosmic rays from multi-wavelength observations of the Galactic diffuse emission

Cosmic rays (CRs) generate diffuse emission while interacting with the Galactic magnetic field (B-field), the interstellar gas and the radiation field. This diffuse emission extends from radio, microwaves, through X-rays, to high-energy gamma rays. Diffuse emission has considerably increased the interest of the astrophysical community due to recent detailed observations by Planck, Fermi-LAT, and by very-high energy Cherenkov telescopes. Observations of this diffuse emission and comparison with detailed predictions are used to gain information on the properties of CRs, such as their density, spectra, distribution and propagation in the Galaxy. Unfortunately disentangling and characterizing this diffuse emission strongly depends on uncertainties in the knowledge of unresolved sources, gas, radiation fields, and B-fields, other than CRs throughout the Galaxy. We discuss here the diffuse emission produced by CRs and its uncertainties, and the comparison of this predicted emission with recent multi-wavelength observations. We show insights on CR spectra and intensities. Then we address the importance for forthcoming telescopes, especially for the Square Kilometre Array telescope (SKA) and the Cherencov Telescope Array (CTA), and for missions at MeV.

Professional social networks among Italian astrophysicists. Prospective changes in validation and dissemination practices?

In recent years, the influences of the main web 2.0 tools on the scholarly communication cycle have been at heart of significant surveys. Awareness and/or adoption rates of these tools were a relevant aspect of this subject. In a very similar perspective, the present study addresses the Italian astrophysical research community. An online ques- tionnaire was created in late September 2014 for the researchers working at the Italian National Institute for Astrophysics. 117 astrophysicists have revealed their attitudes and behaviour towards some major professional social networks (Research- Gate, LinkedIn, Academia) as well as their opinions about aspects of the main validation practices. The results show that professional social networks have been adopted widely (∼66%). ResearchGate results to be the most popular tool, followed by LinkedIn. The respondents' opinions about different types of peer-review show this community is only partly satisfied with single-blind peer-review; nevertheless, the set of scholarly values and communication practices remains rather traditional and social networks result to be used chiefly for enhancing research output dissemination and researchers' availability on the web.

Welcome address

Prof. Claudio Spitaleri, director of the schoolIt is my pleasure, as co-director of the school, to welcome students and lecturers of the “Eigth European Summer School on Experimental Nuclear Astrophysics”. The school is at its seventh edition and we have students coming from several European countries and from all the world, like Lebanon, India, USA, Russia, Canada, Japan, China, Brazil, Kazakhstan. This is a clear sign that the school is considered as an important meeting for the international Nuclear Astrophysics Community worldwide. We are very proud to offer, for the eigth time, our school program, which aims at widening the students’ perspectives and sets, hopefully, a milestone in the education of a new generation of scientists. I remind you that among the goals of the school there are two particular points that deserve attention. The first is allowed by the special venue of the school: the program takes place inside a unique building and this allows all the students to continue their scientific activity and the discussions on the lectures beyond the normal lecture hours. The second peculiar feature is that of favouring cultural exchanges between lectures and students with different traditions, customs and religions. Indeed, Sicily has been historically considered as a meeting place for different cultures, a land that offer chances for peaceful and constructive encounters among different peoples.I wish to thank all the supporting institutions and sponsors, such as INFN - LNS and the University of Catania. To you all I wish a pleasant and fruitful time in our wonderful city.Dr. Giacomo Cuttone, Director of INFN-LNSAs a nuclear physicist and as the Director of the LNS it is a pleasure to welcome the students and lecturers of the school in our laboratory. For the eigth time Catania assumes the role of an attraction point in the field of Nuclear Astrophysics, since the whole scientific world is represented here. As a scientist I wish you a fruitful attendance and especially to the youngest ones I wish for them to maintain for all their lifetimes the same enthusiasm they show in this moment. The human understanding of the Universe needs also your efforts as Nuclear Astrophysicists to proceed. LNS has an important and active group of Nuclear Astrophysics research and constitutes a leading facility worldwide in this field. I wish you a fruitful and pleasant week in Santa Tecla and Catania.

The CHIANTI atomic database

The freely available CHIANTI atomic database was first released in 1996 and has had a huge impact on the analysis and modeling of emissions from astrophysical plasmas. It contains data and software for modeling optically thin atom and positive ion emission from low density (≲1013 cm−3) plasmas from x-ray to infrared wavelengths. A key feature is that the data are assessed and regularly updated, with version 8 released in 2015. Atomic data for modeling the emissivities of 246 ions and neutrals are contained in CHIANTI, together with data for deriving the ionization fractions of all elements up to zinc. The different types of atomic data are summarized here and their formats discussed. Statistics on the impact of CHIANTI to the astrophysical community are given and examples of the diverse range of applications are presented.

INNER-SHELL PHOTOIONIZATION STUDIES OF NEUTRAL ATOMIC NITROGEN

ABSTRACT Inner-shell ionization of a 1s electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD), which results as the 1s-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for inner-shell photoionization of neutral atomic nitrogen for photon energies of 403–475 eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N+, N 2 + ?> , and N 3 + ?> , and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to N 2 + ?> is somewhat reduced, that for N+ is greatly increased, and that to N 3 + ?> , which was predicted to be zero, grows to ≈ 10 % ?> at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for inner-shell ionization and points the way for the improvements needed to more reliably model the role of inner-shell ionization of cosmic plasmas.

Kspectrum: an open-source code for high-resolution molecular absorption spectra production

We present the kspectrum, scientific code that produces high-resolution synthetic absorption spectra from public molecular transition parameters databases. This code was originally required by the atmospheric and astrophysics communities, and its evolution is now driven by new scientific projects among the user community. Since it was designed without any optimization that would be specific to any particular application field, its use could also be extended to other domains. kspectrum produces spectral data that can subsequently be used either for high-resolution radiative transfer simulations, or for producing statistic spectral model parameters using additional tools. This is a open project that aims at providing an up-to-date tool that takes advantage of modern computational hardware and recent parallelization libraries. It is currently provided by Méso-Star (http://www.meso-star.com) under the CeCILL license, and benefits from regular updates and improvements.

The MEUST deep sea infrastructure in the Toulon site

The MEUST (Mediterranean Eurocentre for Underwater Sciences and Technologies) is a permanent deep sea cabled infrastructure currently being deployed off shore of Toulon, France. MEUST is shared between the neutrino physics and astro-physics communities in the context of the European KM3NeT project, and the Environmental Science communities as the West- Ligurian site of the EMSO European network of submarine observatories. The MEUST submarine network has a modular and extendable topology which will allow hosting up to 120 neutrino detection units and to instrument a seafloor area with sea science sensors. The MEUST terrestrial base is located in La Seyne sur Mer near Toulon, where a new building is planned to host the technical activities, including a control room of the infrastructure. The MEUST submarine site has been selected after intensive characterization campaigns conducted in the past years leading to the choice of the site located ˜40km offshore of Toulon at a depth of 2500m and 15km west of the Antares site. The full MEUST submarine network has up to 6 nodes connected to the shore by two Main Electro Optical Cables (MEOC). The MEOCs are standard telecommunication cables with optical fibres for data transfer and one electrical conductor for power transfer. The nodes are equipped each with 8 wet mate-able connectors allowing to connect at least 20 neutrino detection units (daisy chained by 4) and a set of environmental instruments, with some redundancy. The power transfer is performed in HV AC with sea return, as for Antares, and provides a usable power of ˜10kW on each node (˜1kW/connector). A dedicated control/command system controls the power and optical systems. The data transfer uses Dense Wavelength Division Multiplexing (DWDM). The proposed talk will focus on the design and the status of the infrastructure with the first lessons learnt from the ongoing deployments.

Archiving Scientific Data Outside of the Traditional HEP Domain, Using the Archive Facilities at Fermilab

Many experiments in the HEP and Astrophysics communities generate large extremely valuable datasets, which need to be efficiently cataloged and recorded to archival storage. These datasets, both new and legacy, are often structured in a manner that is not conducive to storage and cataloging with modern data handling systems and large file archive facilities. In this paper we discuss in detail how we have created a robust toolset and simple portal into the Fermilab archive facilities, which allows for scientific data to be quickly imported, organized and retrieved from the multi-petabyte facility.In particular we discuss how the data from the Sudbury Neutrino Observatory (SNO) for the COUPP dark matter detector was aggregated, cataloged, archived and re-organized to permit it to be retrieved and analyzed using modern distributed computing resources both at Fermilab and on the Open Science Grid. We pay particular attention to the methods that were employed to uniquify the namespaces for the data, derive metadata for the over 460,000 image series taken by the COUP experiment and what was required to map that information into coherent datasets that could be stored and retrieved using the large scale archives systems.We describe the data transfer and cataloging engines that are used for data importation and how these engines have been setup to import data from the data acquisition systems of ongoing experiments at non-Fermilab remote sites including the Laboratori Nazionali del Gran Sasso and the Ash River Laboratory in Orr, Minnesota. We also describe how large University computing sites around the world are using the system to store and retrieve large volumes of simulation and experiment data for physics analysis.

MAPPING THE GALAXY COLOR–REDSHIFT RELATION: OPTIMAL PHOTOMETRIC REDSHIFT CALIBRATION STRATEGIES FOR COSMOLOGY SURVEYS

Calibrating the photometric redshifts of >10^9 galaxies for upcoming weak lensing cosmology experiments is a major challenge for the astrophysics community. The path to obtaining the required spectroscopic redshifts for training and calibration is daunting, given the anticipated depths of the surveys and the difficulty in obtaining secure redshifts for some faint galaxy populations. Here we present an analysis of the problem based on the self-organizing map, a method of mapping the distribution of data in a high-dimensional space and projecting it onto a lower-dimensional representation. We apply this method to existing photometric data from the COSMOS survey selected to approximate the anticipated Euclid weak lensing sample, enabling us to robustly map the empirical distribution of galaxies in the multidimensional color space defined by the expected Euclid filters. Mapping this multicolor distribution lets us determine where - in galaxy color space - redshifts from current spectroscopic surveys exist and where they are systematically missing. Crucially, the method lets us determine whether a spectroscopic training sample is representative of the full photometric space occupied by the galaxies in a survey. We explore optimal sampling techniques and estimate the additional spectroscopy needed to map out the color-redshift relation, finding that sampling the galaxy distribution in color space in a systematic way can efficiently meet the calibration requirements. While the analysis presented here focuses on the Euclid survey, similar analysis can be applied to other surveys facing the same calibration challenge, such as DES, LSST, and WFIRST.

Indirect detection of dark matter using MeV-range gamma-ray telescopes

The astrophysics community is considering plans for a variety of gamma-ray telescopes (including ACT and GRIPS) in the energy range 1--100 MeV, which can fill in the so-called "MeV gap" in current sensitivity. We investigate the utility of such detectors for the study of low-mass dark matter annihilation or decay. For annihilating (decaying) dark matter with a mass below about 140 MeV (280 MeV) and couplings to first generation quarks, the final states will be dominated by photons or neutral pions, producing striking signals in gamma-ray telescopes. We determine the sensitivity of future detectors to the kinematically allowed final states. In particular, we find that planned detectors can improve on current sensitivity to this class of models by up to a few orders of magnitude.

GALPROP Code for Galactic Cosmic Ray Propagation and Associated Photon Emissions

Recent years are marked with many breakthroughs in astrophysics of cosmic rays (CRs), and more are expected in the nearest future. Their proper interpretation is impossible without a welldeveloped propagation code. The GALPROP project celebrates its 19th anniversary this year. Over these years the project has established itself as a standard self-consistent model for CR propagation in the Galaxy and associated diffuse emissions (radio, microwave, X-rays, g-rays) that is widely used by the astrophysical community. The project stimulated independent studies of the interstellar radiation field, distribution of the interstellar gas (H2, H I, H II), synchrotron emission and the Galactic magnetic field, and a new study of the isotopic production cross sections. These studies provide necessary and unique input datasets for the GALPROP model. The code is optimized and parallelized and accessible as a standalone executable or library that can be linked to other codes enabling many other studies, such as Markov Chain Monte Carlo (MCMC), MultiNest, SuperBayeS, and DarkSUSY. We describe a new updated version of the code that has new capabilities and improved accuracy. As always, the latest release of the code is available through the WebRun, a service to the scientific community enabling easy use of the GALPROP code via web browsers.

Chemora: A PDE-Solving Framework for Modern High-Performance Computing Architectures

Modern HPC architectures consist of heterogeneous multicore, many-node systems with deep memory hierarchies. Modern applications employ ever more advanced discretization methods to study multiphysics problems. Developing such applications that explore cutting-edge physics on cutting-edge HPC systems has become a complex task that requires significant HPC knowledge and experience. Unfortunately, this combined knowledge is currently out of reach for all but a few groups of application developers. Chemora is a framework for solving systems of partial differential equations (PDEs) that targets modern HPC architectures. Chemora is based on Cactus, which sees prominent usage in the computational relativistic astrophysics community. In Chemora, PDEs are expressed either in high-level LaTeX-like languages or in Mathematica. The authors use Chemora in the Einstein Toolkit to implement the Einstein equations on CPUs and on accelerators, and study astrophysical systems such as black hole binaries, neutron stars, and core-collapse supernovae.

The prospective search for highly ionized technetium in hot (pre-) white dwarfs

The discovery of technetium (Tc) in the atmospheres of red giants by Merrill (1952, ApJ, 116, 21) constituted convincing proof that s-process nucleosynthesis is indeed occurring in evolved stars. In principle, Tc should still be present in the atmospheres of hot post-AGB stars and (pre-) white dwarfs although, due to radioactive decay, it should be present in decreasing quantities along post-AGB evolution. The recent discovery of a large number of trans-iron group elements in hot white dwarfs with atomic numbers in the range A = 30–56 (Zn to Ba) raises the prospect that Tc ( A = 43) may also be detected. However, this is currently not feasible because no atomic data exist for ionization stages beyond Tc ii. As an initial step, we calculated atomic energy levels and oscillator strengths of Tc iv–vi and used these data to compute non-local thermodynamic equilibrium (NLTE) model atmospheres to estimate at which minimum abundance level Tc could be detected. We show that Tc lines can be found in ultraviolet spectra of hot white dwarfs provided Tc is as abundant as other detected trans-Fe elements. We find that radiative levitation can keep Tc in large, easily detectable quantities in the atmosphere. A direct identification of Tc lines is still not feasible because wavelength positions cannot be computed with necessary precision. Laboratory measurements are necessary to overcome this problem. Our results suggest that such efforts are beneficial to the astrophysical community.

Discovery of very high energy γ-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes

The number of known very high energy (VHE) blazars is ∼50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the γ-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy γ-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES 0033+595 with a statistical significance of 5.5σ. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) × 10−12 photons cm−2 s−1 and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV–10 GeV) γ-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. This is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF.

RADIATIVE LIFETIMES OF V I AND V II

New radiative lifetimes are reported for 168 levels of V I ranging in energy from 18086 cm–1 to 47702 cm–1, and for 31 levels of V II ranging in energy from 34593 cm–1 to 47420 cm–1. These lifetimes are measured using time-resolved laser-induced fluorescence on a slow atomic/ionic beam as part of an ongoing study of the radiative properties of the iron group elements. All but two of the V II lifetimes have been measured before using modern laser-based methods, but a large fraction of the V I lifetimes are reported here for the first time. Comparison to earlier measurements is discussed. These new lifetimes are, for the most part, accurate to ±5%. They will be combined with branching fraction measurements to produce a large set of transition probabilities for V I and V II which are needed by the astrophysics community for stellar abundance determinations.

A simulation package — SASAL for X-ray and EUV spectroscopy of astrophysical and laboratory plasmas

For the laboratory astrophysics community, those spectroscopic modeling codes extensively used in astronomy, e.g. Chianti, AtomDB, Cloudy and Xstar, cannot be directly applied to analyzing laboratory measurements due to their discrepancies from astrophysical cases. For example, plasma from an electron beam ion trap has an electron energy distribution that follows a Gaussian profile, instead of a Maxwellian one. The laboratory miniature for a compact object produced by a laser-driven implosion shows a departure from equilibrium, that often occurs in celestial objects, so we setup a spectral analysis system for astrophysical and laboratory (SASAL) plasmas to act as a bridge between them, which benefits the laboratory astrophysical community.

Performance and calibration of the NIKA camera at the IRAM 30 m telescope

The New IRAM KID Array (NIKA) instrument is a dual-band imaging camera operating with Kinetic Inductance Detectors (KID) cooled at 100 mK. NIKA is designed to observe the sky at wavelengths of 1.25 and 2.14 mm from the IRAM 30 m telescope at Pico Veleta with an estimated resolution of 13\,arcsec and 18 arcsec, respectively. This work presents the performance of the NIKA camera prior to its opening to the astrophysical community as an IRAM common-user facility in early 2014. NIKA is a test bench for the final NIKA2 instrument to be installed at the end of 2015. The last NIKA observation campaigns on November 2012 and June 2013 have been used to evaluate this performance and to improve the control of systematic effects. We discuss here the dynamical tuning of the readout electronics to optimize the KID working point with respect to background changes and the new technique of atmospheric absorption correction. These modifications significantly improve the overall linearity, sensitivity, and absolute calibration performance of NIKA. This is proved on observations of point-like sources for which we obtain a best sensitivity (averaged over all valid detectors) of 40 and 14 mJy.s$^{1/2}$ for optimal weather conditions for the 1.25 and 2.14 mm arrays, respectively. NIKA observations of well known extended sources (DR21 complex and the Horsehead nebula) are presented. This performance makes the NIKA camera a competitive astrophysical instrument.

First Experimental Constraint on theFe59(n,γ)Fe60Reaction Cross Section at Astrophysical Energies via the Coulomb Dissociation ofFe60

The radionuclide Fe-60 has been of great interest to the nuclear astrophysics community for over a decade. An initial discrepancy between the observed and modeled Galactic Fe-60/Al-26 ratio motivated numerous studies focused on the nucleosynthesis of these two isotopes, though the cross section of the primary astrophysical production reaction, Fe-59(n,gamma)Fe-60, has remained purely theoretical. The present work offers a first experimental constraint on the Fe-59(n,gamma)Fe-60 cross section at astrophysical energies, obtained indirectly via Coulomb dissociation, and demonstrates that the theoretical reaction rates used in present stellar models are not highly erroneous.

The NINJA-2 project: detecting and characterizing gravitational waveforms modelled using numerical binary black hole simulations

The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave (GW) astrophysics communities. The purpose of NINJA is to study the ability to detect GWs emitted from merging binary black holes (BBH) and recover their parameters with next-generation GW observatories. We report here on the results of the second NINJA project, NINJA-2, which employs 60 complete BBH hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a post-Newtonian portion modelling the early inspiral. In a ‘blind injection challenge’ similar to that conducted in recent Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo science runs, we added seven hybrid waveforms to two months of data recoloured to predictions of Advanced LIGO (aLIGO) and Advanced Virgo (AdV) sensitivity curves during their first observing runs. The resulting data was analysed by GW detection algorithms and 6 of the waveforms were recovered with false alarm rates smaller than 1 in a thousand years. Parameter-estimation algorithms were run on each of these waveforms to explore the ability to constrain the masses, component angular momenta and sky position of these waveforms. We find that the strong degeneracy between the mass ratio and the BHs’ angular momenta will make it difficult to precisely estimate these parameters with aLIGO and AdV. We also perform a large-scale Monte Carlo study to assess the ability to recover each of the 60 hybrid waveforms with early aLIGO and AdV sensitivity curves. Our results predict that early aLIGO and AdV will have a volume-weighted average sensitive distance of 300 Mpc (1 Gpc) for 10M⊙ + 10M⊙ (50M⊙ + 50M⊙) BBH coalescences. We demonstrate that neglecting the component angular momenta in the waveform models used in matched-filtering will result in a reduction in sensitivity for systems with large component angular momenta. This reduction is estimated to be up to ∼15% for 50M⊙ + 50M⊙ BBH coalescences with almost maximal angular momenta aligned with the orbit when using early aLIGO and AdV sensitivity curves.