After almost three years of data taking in sky-survey mode, the Fermi Large Area Telescope has detected gamma-ray emission toward Tycho's supernova remnant (SNR). The Tycho SNR is among the youngest ...remnants in the Galaxy, originating from a Type Ia Supernova in AD 1572. The gamma-ray integral flux from 400 MeV up to 100 GeV has been measured to be (3.5 + or - 1.1 sub(stat) + or - 0.7 sub(syst))x 10 super(-9) cm super(-2) s super(-1) with a photon index of 2.3 + or - 0.2 sub(stat) + or - 0.1 sub(syst). A simple model consistent with TeV, X-ray, and radio data is sufficient to explain the observed emission as originating from pi super(0) decays as a result of cosmic-ray acceleration and interaction with the ambient medium.
Aims
. We are studying an unbiased sample of 42 nearby (
z
< 0.2) BL Lacertae objects with a multi-wavelength approach. The results of Very Long Baseline Interferometry observations were presented in ...the first paper of this series. In this paper, we study the
γ
-ray properties of the sample.
Methods
. We analyse data collected by the
Fermi
-Large Area Telescope (LAT) during its first 8.5 yr of operation in the energy range 0.1−300 GeV.
Results
. We reveal 23 sources with a test statistic greater than 25 (corresponding to ~4.6-
σ
) out of 42, with 3 sources not detected in the third LAT active galactic nucleus (AGN) catalogue, and fluxes between 3.5 × 10
−10
and 7.4 × 10
−8
ph cm
−2
s
−1
. The majority of the sources have hard spectra (
Γ
≤ 2), with only four having values in the range 2.1–2.4. The three newly detected sources have fluxes in the range between 0.54 × 10
−9
and 1.35 × 10
−9
ph cm
−2
s
−1
and photon index 1.7–1.9. Among the 23 LAT-detected sources, 19 are included in the third catalogue of hard
Fermi
-LAT sources, with a spectrum that connects relatively smoothly from 0.1 GeV to 2 TeV. LAT-detected BL Lacs are more luminous on parsec scales with respect to non-LAT-detected sources and have larger core dominance according to the unified models.
Conclusions
. The LAT-detected BL Lacs seem to be composed of a bulk of “classical” sources dominated by Doppler boosting and characterised by compact and bright radio emission as well as hard
γ
-ray spectra. Moreover, we have identified a possible population of low-luminosity BL Lacs not detected by LAT, lacking a VLBI core, and with a small Doppler factor. Furthermore, three LAT-detected sources show non-classical properties for
γ
-ray emitting BL Lacs (no evidence of relativistic jet, low Doppler factor in radio images, relatively low core dominance) and three other sources, while showing radio emission on parsec scales, are not detected in
γ
rays so far.
The channeling radiation is emitted by fast charged particles crossing a crystal target in a direction nearly parallel to the crystal axis or planar directions. The incident particles are trapped in ...the potential wells due to the crystal lattice, resulting in a coherence effect in the emitted radiation. Since the total energy of the emitted radiation depends on the Lorentz factor as
γ
2
, channeling radiation can be applied to discriminate between different particles with the same momentum in a collimated beam. To study this application of the channeling radiation, we have performed a beam test campaign at the CERN PS-T9 and SPS-H4 facilities using a
500
μ
m
thick
〈
1
1
0
〉
silicon crystal. A NaI calorimeter has been used to detect the channeling gamma-rays produced in the crystal. The electron (positron) pion identification performance has been studied. The preliminary results will be shown and the perspectives will be discussed.
ABSTRACT Most of the celestial γ rays detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays ...interact with interstellar nucleons and photons. Conventional point-source and extended-source studies rely on the modeling of this diffuse emission for accurate characterization. Here, we describe the development of the Galactic Interstellar Emission Model (GIEM), which is the standard adopted by the LAT Collaboration and is publicly available. This model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse-Compton emission produced in the Galaxy. In the GIEM, we also include large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20° and we observe an enhanced emission toward their base extending in the north and south Galactic directions and located within ∼4° of the Galactic Center.
We report on the search for spectral irregularities induced by oscillations between photons and axion-like particles (ALPs) in the gamma-ray spectrum of NGC 1275, the central galaxy of the Perseus ...cluster. Using 6 years of Fermi Large Area Telescope data, we find no evidence for ALPs and exclude couplings above 5 times 10 (sup -12) per gigaelectronvolt for ALP masses less than or approximately equal to 0.5 apparent magnitude (m (sub a)) less than or approximately equal to 5 nanoelectronvolts at 95 percent confidence. The limits are competitive withthe sensitivity of planned laboratory experiments, and, together with other bounds, strongly constrain thepossibility that ALPs can reduce the gamma-ray opacity of the Universe.
Abstract
An incremental version of the fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope is presented. This version (4LAC-DR3) derives from the third data ...release of the 4FGL catalog based on 12 yr of
E
> 50 MeV gamma-ray data, where the spectral parameters, spectral energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates and four radio galaxies. We describe the properties of the new sample and outline changes affecting the previously published one. We also introduce two new parameters in this release, namely the peak energy of the SED high-energy component and the corresponding flux. These parameters allow an assessment of the Compton dominance, the ratio of the inverse-Compton to the synchrotron-peak luminosities, without relying on X-ray data.
The Fermi bubbles are two large structures in the gamma-ray sky extending to 55degrees above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and ...500 GeV above 10degrees in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7sigma significance. The power law with an exponential cutoff has an index of 1.9 + or - 0.2 and a cutoff energy of 110 + or - 50 GeV. We find that the gamma-ray luminosity of the bubbles is (ProQuest: Formulae and/or non-USASCII text omitted)erg s super(-1). We confirm a significant enhancement of gamma-ray emission in the southeastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be (ProQuest: Formulae and/or non-USASCII text omitted) deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons fit the gamma-ray data well. In the IC scenario, synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 mu G.
Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that galaxies rapidly forming massive stars are more luminous at gamma-ray energies compared to their ...quiescent relatives. Building upon those results, we examine a sample of 69 dwarf, spiral, and luminous and ultraluminous infrared galaxies at photon energies 0.1-100 GeV using 3 years of data collected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi). Measured fluxes from significantly detected sources and flux upper limits for the remaining galaxies are used to explore the physics of cosmic rays in galaxies. We find further evidence for quasi-linear scaling relations between gamma-ray luminosity and both radio continuum luminosity and total infrared luminosity which apply both to quiescent galaxies of the Local Group and low-redshift starburst galaxies (conservative P-values > ~0.05 accounting for statistical and systematic uncertainties). The normalizations of these scaling relations correspond to luminosity ratios of log (L sub(0.1,100 GeV)/L sub(1.4 GHz)) = 1.7 + or - 0.1 sub((statistical)) + or - 0.2 sub((dispersion)) and log (L sub(0.1-100 GeV)/L sub(8,1000 mu m)) = -4.3 + or - 0.1 sub((statistical)) + or - 0.2 sub((dispersion)) for a galaxy with a star formation rate of 1 M sub(middot in circle) yr super(-1), assuming a Chabrier initial mass function. Using the relationship between infrared luminosity and gamma-ray luminosity, the collective intensity of unresolved star-forming galaxies at redshifts 0 > z > 2.5 above 0.1 GeV is estimated to be 0.4-2.4 x 10 super(-6) ph cm super(-2) s super(-1) sr super(-1) (4%-23% of the intensity of the isotropic diffuse component measured with the LAT). We anticipate that ~10 galaxies could be detected by their cosmic-ray-induced gamma-ray emission during a 10 year Fermi mission.
The Fermi Large Area Telescope (LAT) has opened the way for comparative studies of cosmic rays (CRs) and high-energy objects in the Milky Way (MW) and in other, external, star-forming galaxies. Using ...2 yr of observations with the Fermi LAT, Local Group galaxy M31 was detected as a marginally extended gamma-ray source, while only an upper limit has been derived for the other nearby galaxy M33. We revisited the gamma-ray emission in the direction of M31 and M33 using more than 7 yr of LAT Pass 8 data in the energy range 0.1 - 100 GeV , presenting detailed morphological and spectral analyses. M33 remains undetected, and we computed an upper limit of 2.0 × 10 − 12 erg cm − 2 s − 1 on the 0.1 - 100 GeV energy flux (95% confidence level). This revised upper limit remains consistent with the observed correlation between gamma-ray luminosity and star formation rate tracers and implies an average CR density in M33 that is at most half of that of the MW. M31 is detected with a significance of nearly 10 . Its spectrum is consistent with a power law with photon index Γ = 2.4 0.1 stat + syst and a 0.1 - 100 GeV energy flux of ( 5.6 0.6 stat + syst ) × 10 − 12 erg cm − 2 s − 1 . M31 is detected to be extended with a 4 significance. The spatial distribution of the emission is consistent with a uniform-brightness disk with a radius of 0 4 and no offset from the center of the galaxy, but nonuniform intensity distributions cannot be excluded. The flux from M31 appears confined to the inner regions of the galaxy and does not fill the disk of the galaxy or extend far from it. The gamma-ray signal is not correlated with regions rich in gas or star formation activity, which suggests that the emission is not interstellar in origin, unless the energetic particles radiating in gamma rays do not originate in recent star formation. Alternative and nonexclusive interpretations are that the emission results from a population of millisecond pulsars dispersed in the bulge and disk of M31 by disrupted globular clusters or from the decay or annihilation of dark matter particles, similar to what has been proposed to account for the so-called Galactic center excess found in Fermi-LAT observations of the MW.
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