Searcharxiv⌕ Search

arXiv subjects

Elena Orlando

Publications and source records attributed to Elena Orlando.

35 records · Page 2Linked to original sources
arXiv2016

Cosmic rays from multiwavelength 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 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 report here on recent multiwavelength observations of the Galactic diffuse emission, and discuss the diffuse emission produced by CRs and its model uncertainties, comparing observations with predictions. The importance for forthcoming telescopes, especially for the Square Kilometre Array Telescope (SKA) and the Cherenkov Telescope Array (CTA), and for future missions at MeV energies is also addressed.

astro-ph.HE↗
arXiv2015

CHANG-ES VI: Probing Supernova Energy Deposition in Spiral Galaxies Through Multi-Wavelength Relationships

How a galaxy regulates its SNe energy into different interstellar/circumgalactic medium components strongly affects galaxy evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz) continuum observations, we perform statistical analysis comparing multi-wavelength properties of the CHANG-ES galaxies. The high-quality JVLA data and edge-on orientation enable us for the first time to include the halo into the energy budget for a complete radio-flux-limited sample. We find tight correlations of $L_{\rm radio}$ with the mid-IR-based SFR. The normalization of our $I_{\rm 1.6GHz}/{\rm W~Hz^{-1}}-{\rm SFR}$ relation is $\sim$2-3 times of those obtained for face-on galaxies, probably a result of enhanced IR extinction at high inclination. We also find tight correlations between $L_{\rm radio}$ and the SNe energy injection rate $\dot{E}_{\rm SN(Ia+CC)}$, indicating the energy loss via synchrotron radio continuum accounts for $\sim0.1\%$ of $\dot{E}_{\rm SN}$, comparable to the energy contained in CR electrons. The integrated C-to-L-band spectral index is $α\sim0.5-1.1$ for non-AGN galaxies, indicating a dominance by the diffuse synchrotron component. The low-scatter $L_{\rm radio}-{\rm SFR}$/$L_{\rm radio}-\dot{E}_{\rm SN (Ia+CC)}$ relationships have super-linear logarithmic slopes at $\sim2~σ$ in L-band ($1.132\pm0.067$/$1.175\pm0.102$) while consistent with linear in C-band ($1.057\pm0.075$/$1.100\pm0.123$). The super-linearity could be naturally reproduced with non-calorimeter models for galaxy disks. Using Chandra halo X-ray measurements, we find sub-linear $L_{\rm X}-L_{\rm radio}$ relations. These results indicate that the observed radio halo of a starburst galaxy is close to electron calorimeter, and a galaxy with higher SFR tends to distribute an increased fraction of SNe energy into radio emission (than X-ray).

astro-ph.GA↗
arXiv2014

An extreme gravitationally redshifted iron line at 4.8 keV in Mrk 876

X-ray spectral lines at unforeseen energies are important because they can shed light on the extreme physical conditions of the environment around the supermassive black holes of active galactic nuclei (AGN). Mrk 876 displays such a line at 4.8 keV rest-frame energy. A possible interpretation of its origin can be found in the hotspot scenario. In this scenario the primary radiation from a flare in the hot corona of an AGN illuminates a limited portion of the accretion disk that emits by fluorescence. In this context the line can represent an extreme gravitationally redshifted Fe line originating on the accretion disk below 6 gravitational radii from a rotating supermassive black hole. The correct estimate of the line significance requires a dedicated approach. Based on an existing rigorous approach, we have performed extensive Monte Carlo simulations. We determine that the line is a real feature at ~99 confidence level.

astro-ph.HE↗
arXiv2013

Galactic synchrotron emission with cosmic ray propagation models

Cosmic-ray (CR) leptons produce radio synchrotron radiation by gyrating in interstellar magnetic fields (B-field). Details of B-fields, CR electron distributions and propagation are still uncertain. We present developments in our modelling of Galactic radio emission with the GALPROP code. It now includes calculations of radio polarization, absorption, and free-free emission. Total and polarized synchrotron emission are investigated in the context of physical model of CR propagation. Predictions are compared with radio data from 22 MHz to 2.3 GHz, and Wilkinson Microwave Anisotropy Probe data at 23 GHz. Spatial and spectral effects on the synchrotron modelling with different CR distribution, propagation halo size and CR propagation models are presented. We find that all-sky total intensity and polarization maps are reasonably reproduced by including an anisotropic B-field, with comparable intensity to the regular one defined by rotation measures. A halo size of 10 kpc, which is larger than usually assumed, is favoured. This work provides a basis for further studies on foreground emission with the Planck satellite and on interstellar gamma-ray emission with Fermi-Large Area Telescope.

astro-ph.GA↗
arXiv2013

StellarICs: Stellar and solar Inverse Compton emission package

StellarICs is software to compute gamma-ray emission from inverse-Compton scattering by cosmic-ray leptons in the heliosphere and in the photospheres of stars. It includes a set of cosmic-ray spectra and a formulation of their modulation, but it can be used for any user-defined modulation model and lepton spectra. Inverse-Compton emission provides a unique probe of cosmic-ray leptons in the heliosphere between the earth and the sun. The software is publicly available and it is under continuing development.

astro-ph.HE↗
arXiv2013

Cosmic-ray leptons, magnetic fields and interstellar synchrotron emission

Interstellar synchrotron emission depends on Galactic magnetic fields and on cosmic-ray leptons. Observations of radio emission are an important tool for studying cosmic-ray propagation models and interstellar electron spectrum and distribution in the Galaxy. We present the latest developments in our modeling of Galactic synchrotron emission with the GALPROP code, including polarization, absorption, and free-free emission. Using surveys over a wide range of radio frequencies and polarization measurements, we derive constraints on the low-energy interstellar cosmic-ray electron spectrum, magnetic fields and cosmic-ray propagation models. This work is of interest for studies of interstellar gamma-ray emission with Fermi-LAT, and synchrotron for the Planck mission.

astro-ph.GA↗
arXiv2013

Accounting for the Sun and the Moon in Fermi-LAT Analysis

The Sun and the Moon are quiescent gamma-ray sources that are clearly detectable in Fermi-LAT data. While moving through the sky, the Sun and the Moon can be a significant background in the analysis of Fermi-LAT data if they pass through the region of interest. Accurate modeling of their intensity is needed in this case, accounting for the correct exposure of their track along the sky. We present the Solar System Tools (SST) which calculate the templates of the Sun's and the Moon's intensity in the sky for a given observing period and a model of their steady emission. These tools are available in the standard Fermi-LAT Science Tools.

astro-ph.IM↗
arXiv2013

Cosmic rays: interstellar gamma-ray and radio emission

We discuss the relation between cosmic-ray induced interstellar gamma-ray and radio emission from our Galaxy, and emphasize the importance of their parallel study. We give an overview of results from Fermi-LAT on the interstellar gamma-ray emission, and then focus on complementary studies of the radio emission from the Galaxy.

astro-ph.HE↗
arXiv2013

A software package for stellar and solar inverse-Compton emission: Stellarics

We present our software to compute gamma-ray emission from inverse-Compton scattering by cosmic-ray leptons in the heliosphere, as well as in the photospheres of stars. It includes a formulation of modulation in the heliosphere, but it can be used for any user-defined modulation model. Profiles and spectra are output to FITS files in a variety of forms for convenient use. Also included are general-purpose inverse-Compton routines with other features like energy loss rates and emissivity for any user-defined target photon and lepton spectra. The software is publicly available and it is under continuing development.

astro-ph.SR↗
arXiv2011

GALPROP WebRun: an internet-based service for calculating galactic cosmic ray propagation and associated photon emissions

GALPROP is a numerical code for calculating the galactic propagation of relativistic charged particles and the diffuse emissions produced during their propagation. The code incorporates as much realistic astrophysical input as possible together with latest theoretical developments and has become a de facto standard in astrophysics of cosmic rays. We present GALPROP WebRun, a service to the scientific community enabling easy use of the freely available GALPROP code via web browsers. In addition, we introduce the latest GALPROP version 54, available through this service.

astro-ph.HE↗
arXiv2009

Fermi-LAT Observation of Quiet Solar Emission

The Large Area Telescope (LAT) on board Fermi has detected high-energy gamma rays from the quiet Sun produced by interactions of cosmic-ray nucleons with the solar surface and cosmic-ray electrons with solar photons in the heliosphere. Such observations provide a probe of the extreme conditions near the solar atmosphere and photosphere and permit the study of the modulation of cosmic rays over the inner heliosphere. For the first year of Fermi observations the solar modulation was at its minimum corresponding to a maximum cosmic-ray flux and, hence, maximum gamma-ray emission from the Sun. We discuss the study of the quiescent solar emission, including spectral analysis of its two components, disk and inverse Compton, using the first-year data of the mission and models using the electron spectrum measured by Fermi.

astro-ph.SR↗
arXiv2009

Fermi-LAT Observation of Quiescent Solar Emission

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope is a pair-conversion detector designed to study the gamma-ray sky in the energy range 30 MeV to 300 GeV. Fermi has detected high-energy gamma rays from the quiet Sun produced by interactions of cosmic-ray nucleons with the solar surface, and cosmic-ray electrons with solar photons in the heliosphere. While the Sun was detected by EGRET on CGRO with low statistics, Fermi provides high-quality detections on a daily basis allowing variability to be addressed. Such observations will provide a probe of the extreme conditions near the solar surface and a monitor the modulation of cosmic rays over the inner heliosphere. We discuss the study of the quiescent solar emission including spectral analysis of its two components, disk and inverse Compton.

astro-ph.SR↗
arXiv2008

Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge

A recent re-determination of the non-thermal component of the hard X-ray to soft gamma-ray emission from the Galactic ridge, using the SPI instrument on the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) Observatory, is shown to be well reproduced as inverse-Compton emission from the interstellar medium. Both cosmic-ray primary electrons and secondary electrons and positrons contribute to the emission. The prediction uses the GALPROP model and includes a new calculation of the interstellar radiation field. This may solve a long-standing mystery of the origin of this emission, and potentially opens a new window on Galactic cosmic rays.

astro-ph↗
arXiv2008

Gamma-ray emission from the solar halo and disk: a study with EGRET data

Context: The Sun has recently been predicted to be an extended source of gamma-ray emission, produced by inverse-Compton (IC) scattering of cosmic-ray (CR) electrons on the solar radiation field. The emission was predicted to be extended and a confusing foreground for the diffuse extragalactic background even at large angular distances from the Sun. The solar disk is also expected to be a steady gamma-ray source. While these emissions are expected to be readily detectable in the future by GLAST, the situation for available EGRET data is more challenging. Aims: The theory of gamma-ray emission from IC scattering on the solar radiation field by Galactic CR electrons is given in detail. This is used as the basis for detection and model verification using EGRET data. Methods: We present a detailed study of the solar emission using the EGRET database, accounting for the effect of the emission from 3C 279, the moon, and other sources, which interfere with the solar emission. The analysis was performed for 2 energy ranges, above 300 MeV and for 100-300 MeV, as well as for the combination to improve the detection statistics. The technique was tested on the moon signal, with our results consistent with previous work. Results: Analyzing the EGRET database, we find evidence of emission from the solar disk and its halo. The observations are compared with our model for the extended emission. The spectrum of the solar disk emission and the spectrum of the extended emission have been obtained. The spectrum of the moon is also given. Conclusions: The observed intensity distribution and the flux are consistent with the predicted model of IC gamma-rays from the halo around the Sun.

astro-ph↗
arXiv2007

Inverse-Compton emission from halos around stars

Inverse Compton scattering by relativistic electrons produces a major component of the diffuse emission from the Galaxy. The photon fields involved are the cosmic microwave background and the interstellar radiation field from stars and dust. Calculations of the inverse Compton distribution have usually assumed a smooth ISRF, but in fact a large part of the Galactic luminosity comes from the most luminous stars which are rare. Therefore we expect the ISRF, and hence the inverse Compton emission, to be clumpy. We also show that some of the most luminous stars may be visible to GLAST. In this paper we give an update on our previous work including examples of the intensity distribution around stars, and the predicted spectrum of Cygnus OB2.

astro-ph↗
arXiv2007

Extended solar emission - an analysis of the EGRET data

The Sun was recently predicted to be an extended source of gamma-ray emission, produced by inverse-Compton scattering of cosmic-ray electrons with the solar radiation. The emission was predicted to contribute to the diffuse extragalactic background even at large angular distances from the Sun. While this emission is expected to be readily detectable in future by GLAST, the situation for available EGRET data is more challenging. We present a detailed study of the EGRET database, using a time dependent analysis, accounting for the effect of the emission from 3C 279, the moon, and other sources, which interfere with the solar signal. The technique has been tested on the moon signal, with results consistent with previous work. We find clear evidence for emission from the Sun and its vicinity. The observations are compared with our model for the extended emission.

astro-ph↗
arXiv2006

Gamma-rays from halos around stars and the Sun

Inverse Compton scattering by relativistic electrons produces a major component of the diffuse emission from the Galaxy. The photon fields involved are the cosmic microwave background and the interstellar radiation field from stars and dust. Calculations of the inverse Compton distribution have usually assumed a smooth ISRF, but in fact a large part of the Galactic luminosity comes from the most luminous stars which are rare. Therefore we expect the ISRF, and hence the inverse Compton emission, to be clumpy at some level which could be detectable by instruments such as GLAST. Even individual nearby luminous stars could be detectable assuming just the normal cosmic-ray electron spectrum. We present the basic formalism required and give possible candidate stars to be detected, and make predictions for GLAST. Then we apply the formalism to OB associations and the Sun, showing that the IC emission produced is not negligible compared to the sensitivity of current or coming detectors. We estimate that the gamma-ray flux from the halo around the Sun contributes to the diffuse background emission at about the few percent level.

astro-ph↗