Galactic Sources of High-Energy Neutrinos: Highlights

📝 Abstract

We overview high-energy neutrinos from galactic sources, transparent to their gamma-ray emission. We focus on young supernova remnants and in particular on RX J1713.7-3946, discussing expectations and upper bounds. We also consider the possibility to detect neutrinos from other strong galactic gamma-ray sources as Vela Junior, the Cygnus Region and the recently discovered Fermi Bubbles. We quantify the impact of the recent hint for a large value of $\theta_{13}$ on high-energy neutrino oscillations.

💡 Analysis

We overview high-energy neutrinos from galactic sources, transparent to their gamma-ray emission. We focus on young supernova remnants and in particular on RX J1713.7-3946, discussing expectations and upper bounds. We also consider the possibility to detect neutrinos from other strong galactic gamma-ray sources as Vela Junior, the Cygnus Region and the recently discovered Fermi Bubbles. We quantify the impact of the recent hint for a large value of $\theta_{13}$ on high-energy neutrino oscillations.

📄 Content

Galactic Sources of High-Energy Neutrinos: Highlights Francesco Vissani1 and Felix Aharonian2 1INFN, Gran Sasso Theory Group, Assergi (AQ) Italy 2Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland Abstract We overview high-energy neutrinos from galactic sources, transparent to their gamma-ray emission. We focus on young supernova remnants and in particular on RX J1713.7-3946, discussing expectations and upper bounds. We also consider the possibility to detect neutrinos from other strong galactic gamma-ray sources as Vela Junior, the Cygnus Region and the recently discovered Fermi Bubbles. We quantify the impact of the recent hint for a large value of θ13 on high-energy neutrino oscillations. Key words: Neutrinos and gamma rays; galactic sources of high-energy radiation; supernova remnants and cosmic rays

1. Context, motivations and assumptions The successes of low energy neutrino astronomy and the discovery of neutrino oscillations added momentum to the search for high energy neutrinos from cosmic sources, initi- ated long ago with the theoretical proposals of Zheleznykh, Markov and Greisen [1]; see Fig. 1. The first km3-class detector, IceCUBE and the smaller ANTARES (follow- ing MACRO, BAIKAL, AMANDA) have not yet revealed the first signal, yet the excitement remains high. However, nowadays it becomes clear that the search for high energy neutrino sources is difficult. In this paper, we attempt to examine certain generic and specific expectations for such a search, in the hope to contribute to the scientific plan- ning of the future experimental activities. We are inter- ested in the possibility to proceeding further, by building a new telescope of km3-class in the Northern Hemisphere–as Km3NET in the Mediterranean Sea or GVD in Lake Baikal. The fact that the first explorations of the high-energy neutrino sky, that did not reveal any signal, contradicted the over-optimistic expectations may lead one to doubt that we can reach reliable predictions. But, even if some degree of diffidence toward theory is healthy, we are convinced that the process of formulating expectations is an important step toward understanding. We would like to clarify our view by proposing some issues: Do we really need to have high expec- 1 We thank ML.Costantini, N.Sahakyan and F.Villante for collabo- ration, P.Blasi and P.Lipari for pleasant and important discussions, T.Schwetz for an explanation on θ13 and F.Halzen for an interesting public discussion on Fig. 7 at NUSKY meeting (ICTP). tations for high energy neutrinos? Perhaps not, although one should keep in mind that the surprises often happen in astronomy. As recent example in this regard are the dis- covery of the Fermi Bubbles and the variability of the Crab Nebula. Are expectations useful? Of course, yes; good pre- dictions are precious for experiments, but also reasonable expectations eventually contradicted are not useless. Do we have some relevant and succesful precedent? Yes, many: High-energy γ-ray sources have been predicted in the fifties (Morrison). For solar neutrinos, we had predictions with errorbars since the sixties (Bahcall). For supernova neutri- nos, quantitative expectations were available even before SN1987A (Nadyozhin). We adopt a rather common astrophysical attitude: the observation of high-energy neutrinos is very demanding but perhaps possible and would amount to an unambiguous sig- Fig. 1. Energy ranges of various types of neutrino telescopes, in log10(E/eV ); note that they span more than 10 decades in energy. In this paper, we are concerned with the third item, that after IceCUBE we identify with the technology ‘ice Cherenkov’. Preprint submitted to Elsevier 13 July 2021 arXiv:1112.3911v1 [astro-ph.HE] 16 Dec 2011 Fig. 2. We can exploit the strict connection of secondary muon neutrinos and γ-rays produced by collisions of cosmic rays above 10 TeV, assuming that the γ-rays are not absorbed or strongly modified. nal of cosmic ray collisions–hopefully, those in their source. We simplify our task by restricting our attention on the specific but important class of sources, those transparent to their gamma rays. We will show how to proceed towards precise expectations and eventually observations of neutri- nos, limiting the use of theory inputs and just by the help of γ-ray observations. This aspect is important enough to be emphasized, as we do with Fig. 2. In the next section, we quantify the connection between gamma and neutrinos.
2. Expected neutrino intensity and signal If we measure the very high γ-ray emission from a cos- mic source, and if we attribute it to cosmic ray colliding with other hadrons, it is straightforward to derive the muon neutrino flux. In fact, when both the neutrinos and unmod- ified, hadronic γ-rays are linear functions of the cosmic ray intensity, they are linked by a linear relation [2]: Iνµ(E) = 0.380 Iγ  E 1 −rπ 

• 0.013 Iγ  E 1 −rK  (1)

1 Z 0 dx x Kµ(x)Iγ E x  where the coefficients are determined by

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