ABSTRACT
We consider the largest observed sample including all intermediate-frequency peaked (IBL) and high-frequency peaked (HBL) flaring blazars above 100 GeV up to redshift z = 0.6. We show that ...the best-fitting regression line of the emitted spectral indices Γem(z) is a concave parabola decreasing as z increases, thereby implying a statistical correlation between the {Γem(z)} distribution and z. This result contradicts our expectation that such a distribution should be zindependent. We argue that the above correlation does not arise from any selection bias. We show that our expectation naturally emerges provided that axion-like particles (ALPs) are put into the game. Moreover, ALPs can also explain why flat spectrum radio quasars emit up to 400 GeV, in sharp contradiction with conventional physics (CP). So, the combination of the two very different but consistent results – taken at face value – leads to a hint at an ALP with mass $m = {\cal O} (10^{-10} \, {\rm eV})$ and two-photon coupling in the range $2.94 \times 10^{- 12} \, {\rm GeV}^{- 1} \lt g_{a \gamma \gamma } \lt 0.66 \times 10^{- 10} \, {\rm GeV}^{- 1}$. As a bonus, the Universe would become considerably more transparent above energies $E \gtrsim 1 \, {\rm TeV}$ than dictated by CP. Our prediction can be checked not only by the new generation of observatories like CTA, HAWC, GAMMA-400, LHAASO, TAIGA-HiSCORE, and HERD, but also thanks to the planned laboratory experiments ALPS II (upgraded), STAX, IAXO and with other techniques now being developed by Avignone and collaborators.
Dedication: We wish to dedicate the present work to the memory of our dear friend Nanni Bignami.
Transparency of the Universe to gamma-rays De Angelis, A; Galanti, G; Roncadelli, M
Monthly Notices of the Royal Astronomical Society,
07/2013, Volume:
432, Issue:
4
Journal Article
Peer reviewed
Open access
Using the most recent observational data concerning the extragalactic background light and the radio background for a source at an arbitrary redshift in the range z
s ≤ 3, we compute the energy E
0 ...of an observed γ-ray photon in the range 10 ≤ E
0 ≤ 1013 GeV such that the resulting optical depth τγ(E
0, z
s) takes the values 1, 2, 3 and 4.6 corresponding to an observed flux dimming of e
−1 0.37, e
−2 0.14, e
−3 0.05 and e
−4.6 0.01, respectively. Below a distance D 8 kpc, we find that τγ(E
0, DH
0/c) < 1 for any value of E
0. In the limiting case of a local Universe (z
s 0), we compare our result with the one derived in 1997 by Coppi and Aharonian. The present achievement is of paramount relevance for the planned ground-based detectors like Cherenkov Telescope Array, High Altitude Water Cherenkov Experiment and Hundred Square-km Cosmic ORigin Explorer.
No axions from the Sun Roncadelli, M; Tavecchio, F
Monthly Notices of the Royal Astronomical Society Letters,
06/2015, Volume:
450, Issue:
1
Journal Article
Peer reviewed
Open access
Preliminary evidence of solar axions in XMM–Newton observations has quite recently been claimed by Fraser et al. as an interpretation of their detection of a seasonally-modulated excess of the X-ray ...background. Within such an interpretation, these authors also estimate the axion mass to be m
a ≃ 2.3 × 10−6 eV. Since an axion with this mass behaves as a cold dark matter particle, according to the proposed interpretation the considered detection directly concerns cold dark matter as well. So, the suggested interpretation would lead to a revolutionary discovery if confirmed. Unfortunately, we have identified three distinct problems in this interpretation of the observed result of Fraser et al. which ultimately imply that the detected signal – while extremely interesting in itself – cannot have any relation with hypothetical axions produced by the Sun. Thus, a physically consistent interpretation of the observed seasonally-modulated X-ray excess still remains an exciting challenge.
Recent findings by γ-ray Cherenkov telescopes suggest a higher transparency of the Universe to very high energy (VHE) photons than expected from current models of the extragalactic background light. ...It has been shown that such transparency can be naturally explained by the DARMA scenario, in which the photon mixes with a new, very light, axion-like particle predicted by many extensions of the Standard Model of elementary particles. We discuss the implications of DARMA for observations of blazar VHE γ-ray spectra, and show that it successfully accounts for the observed correlation between spectral slope and redshift when the same intrinsic emission spectrum is adopted for faraway sources and for nearby ones. DARMA also predicts the observed blazar spectral index to become asymptotically independent of redshift for faraway sources. Our prediction can be tested with the satellite-borne Fermi/LAT (Large Area Telescope) detector as well as with the ground-based Cherenkov telescopes HESS, MAGIC, CANGAROO III, VERITAS and the Extensive Air Shower arrays ARGO-YBJ and Milagro.
Fundamental and exotic physics with Cherenkov telescopes De Angelis, A.; De Lotto, B.; Roncadelli, M.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2011, Volume:
630, Issue:
1
Journal Article
Peer reviewed
The detection of high-energy
γ
rays from astrophysical sources, using the Fermi/LAT detector and in the very-high-energy limit the Cherenkov telescopes MAGIC, H.E.S.S. and VERITAS, can provide tests ...of fundamental physics with unprecedented sensitivity, and possibly allows to probe new and exotic scenarios.
The e-ASTROGAM mission De Angelis, A.; Tatischeff, V.; Tavani, M. ...
Experimental astronomy,
10/2017, Volume:
44, Issue:
1
Journal Article
Peer reviewed
Open access
e-ASTROGAM (‘enhanced ASTROGAM’) is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of ...the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV – the lower energy limit can be pushed to energies as low as 150 keV, albeit with rapidly degrading angular resolution, for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of eLISA.
The WARP programme is a graded programme intended to search for cold dark matter in the form of weakly interacting massive particles. These particles may produce via weak interactions nuclear recoils ...in the energy range 10–100 keV. A cryogenic noble liquid like argon, already used in the realization of very large detector, permits the simultaneous detection of both ionization and scintillation induced by an interaction, suggesting the possibility of discriminating between nuclear recoils and electrons mediated events. A 2.3
l two-phase argon detector prototype has been used to perform several tests on the proposed technique. Next step is the construction of a 100
l sensitive volume device with potential sensitivity a factor 100 better than presently existing experiments.
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