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Hadronic processes after Fermi
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241 www.elsevier.com/locate/npbps
Hadronic processes after Fermi F. Giordano and M. Caragiulo †
Dipartimento Interateneo dell’Universit`a e del Politecnico di Bari and INFN Sez. Bari
Abstract After more than 4 years of data taking, the Fermi-LAT has collected many evidences of hadronic accelerations in some galactic sites. Among the most promising sources are the remnants of Supernovae explosions. A first tentative of cataloging the gamma GeV-TeV emission from Supernovae Remnants (SNRs) is in progress, in terms of efficiency of the process, maximum energy available and spectral features, in dependence of the age of the remnant and its environment. Using Kamae et al 2006 [1] parametrization we have interpreted the observed gamma-ray emission as originated in hadronic scenario, estimating the neutrino flux from the most promising SNRs is estimated. Keywords: SuperNova Remnants, hadronic processes, gamma rays, neutrinos
1. SNRs as galactic CRs sources Among the latest results of the Fermi-LAT collaboration is the publication of the 2FGL catalog that includes the list of detected sources in two years of data taking. In the paper we listed about 2000 sources, half of which identified as AGNs and only few % identified as SNR/PWN. Moreover, we have also counted about 78 GeV sources spatially associated with known SNRs, but we claimed that only 45% of these might have been associated to a SNR by chance. For all these reasons, it was decided within the collaboration to go further and start the SNR Catalog project. The purpose of the project is manyfold: • Characterize GeV emission in regions containing known SNRs • Evaluate systematics, including diffuse models and variability • Examine multiwavelength correlation, including spectrum and morphology for radio, X-ray, and TeV and CO, maser, IR, • Determine statistically significant SNR classification(s) and perform spectral modeling 0920-5632/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.nuclphysbps.2013.04.097
We started collecting data from Green 2009 [3] who collected 274 detected SNR in one catalog. For all these SNRs we have extracted the centroid of the emission, the extension, radio index, flux and some of them also the distance. The modeling of SNRs spectra would be of great interest in the search for clear signatures of cosmic ray acceleration. Eventual neutrinos detection from such astrophysical sites would be the definitive proof of hadronic processes and proton acceleration. In the following paragraphs we describe the parametrization applied and results obtained in fitting the GeV-TeV data of a few SNRs detected by Fermi so far and estimate the expected neutrinos flux from these acceleration sites. 1.1. Gamma ray emission modeling A fit of the GeV-TeV data has been performed using the parametrization of the cross sections and the gamma ray yield from Kamae et al. 2006. The flux of gamma rays at earth has been evaluated starting from the yield per unit volume: Fγ,S NR =
dn VS NR , dt 4πd2
(1)
where VS NR is the volume of the SNR, in the hypothesis of uniform distribution of particles and magnetic
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F. Giordano, M. Caragiulo / Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241
fields, and d being the distance of the source from the solar system. The particle distribution in momentum (or equivalently in energy), is described by a smoothed broken power law: −(γ1 −γ2 )/γ3 −γ3 −γ1 E dN E , (2) 1+ =A dE E0 Ebr where the free parameters are the normalization, closely related to the energetics of the process, the index γ1 and the maximum achieved energy Ebr . It is also important to note that the gamma ray flux strongly depends on the density of the environment the SNR is interacting with. It is worth to underline that in the proposed modeling there are two major simplifications: the particle population is described by a simple broken power law and the GeV-TeV gamma ray emission for various SNRs are interpreted as produced by hadronic processes only. Therefore the efficiency and the energy budget associated to protons accelerated in SNRs have to be considered upper limits. According to Fermi results of SNRs, two major classes of SNRs seem to be emerging: the first class includes those SNRs interacting with molecular clouds which exhibit very high gamma ray flux, with breaks at few GeV; the second class contains young SNRs, expanding in lighter environment, like CasA and Tycho, which show breaks in the TeV range, being more suitable as far as neutrino physics is concerned. What could make a source more interesting than others is the flux above a certain threshold, i.e. few TeV, that might lead to a clear signal from the source over the atmospheric neutrinos background. In this perspectives, young SNRs, that show higher break in the particle energy distribution, might be more suitable sources for neutrino telescope targets. In Fig.1 and 2 the SEDs for Tycho and CasA SNRs are shown: the data points come from Fermi [4] [5] for Tycho and CasA papers respectively and Veritas[6],[7] analysis and the black line represents the two fits extracted by our model. The results of the fit in terms of proton energy distribution for the CasA case is shown in Fig.3 and summarized in Table1. Parameters Ap Ebr,p γ1,p γ2,p Wp
Figure 1: Tycho GeV-TeV π0 peak fit according to Kamae et al 2006
Figure 2: CasA GeV-TeV π0 peak fit according to Kamae et al 2006
Values (7.74±0.69)·10−8 eV−1 cm−2 s−1 sr−1 (3.27±0.45)TeV (2.19±0.05) (5.91±0.72) (2.94±0.48)·1049 erg Figure 3: Proton energy spectrum for CasA SNR
Table 1: PowerLaw for proton in CasA SNR
F. Giordano, M. Caragiulo / Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241
1.2. Neutrino flux estimations Kamae et al 2006 has also parameterized the neutrino yield produced in p-p interactions. While gamma ray data in almost all SNR cases can be fitted both assuming hadronic scenarios or leptonic models, the eventual detection of neutrinos from this kind of astrophysics sources would be a clear and un-ambiguous signature of p-p interactions taking place. Moreover, as already pointed out, the harder the source, the better its detectability for the next generation neutrino telescopes. Figure4 and 5 show the observed gamma ray flux compared with the neutrinos estimations. 102 γ νe νμ νe νμ
E2 dN (eV cm-2 s-1) dE
10
total neutrino contribute
1
5
6
10
10
8
107
10
9
10
10
10 1011 E (eV)
1012
13
1014
10
15
10
16
10
Figure 4: Neutrinos flux estimation for Tycho SNR
103 γ νe νμ νe
2
νμ
E2 dN (eV cm-2 s-1) dE
10
total neutrino contribute
10
1
10-1
sites would be the definitive proof of hadronic processes and proton acceleration and injection into the Milky Way. According to gamma ray data, young SNRs (like Tycho and CasA) might be among the most promising galactic neutrino sources. 3. Acknowledgment The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged. References
10-1
10-2
241
6
10
107
8
10
9
10
10
10 E (eV)
1011
1012
13
10
1014
15
10
Figure 5: Neutrinos flux estimation for CasA SNR
2. Conclusions The Fermi Collaboration is collecting data for cataloging SNRs in term of GeV emission and processes interpretation. Almost all SNRs detected so far have been modeled both in hadronic and leptonic scenarios, still not having a clear signature on cosmic rays acceleration in act; eventual neutrinos detection from astrophysical
[1] Kamae, T., et al. 2006, ApJ, 647, 692 [2] Atwood et al., ApJ 697, 2009 [3] Green, D.A., 2009, Bulletin of the Astronomical Society of India, 37, 45 [4] Giordano, F., et al. 2012, 744, L2 [5] A. A. Abdo et al. 2010 ApJ 710 L92 [6] Acciari et al, ApJL 730 (2011) L20 [7] Acciari et al, ApJ, 714 (2010), 201
Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241 www.elsevier.com/locate/npbps
Hadronic processes after Fermi F. Giordano and M. Caragiulo †
Dipartimento Interateneo dell’Universit`a e del Politecnico di Bari and INFN Sez. Bari
Abstract After more than 4 years of data taking, the Fermi-LAT has collected many evidences of hadronic accelerations in some galactic sites. Among the most promising sources are the remnants of Supernovae explosions. A first tentative of cataloging the gamma GeV-TeV emission from Supernovae Remnants (SNRs) is in progress, in terms of efficiency of the process, maximum energy available and spectral features, in dependence of the age of the remnant and its environment. Using Kamae et al 2006 [1] parametrization we have interpreted the observed gamma-ray emission as originated in hadronic scenario, estimating the neutrino flux from the most promising SNRs is estimated. Keywords: SuperNova Remnants, hadronic processes, gamma rays, neutrinos
1. SNRs as galactic CRs sources Among the latest results of the Fermi-LAT collaboration is the publication of the 2FGL catalog that includes the list of detected sources in two years of data taking. In the paper we listed about 2000 sources, half of which identified as AGNs and only few % identified as SNR/PWN. Moreover, we have also counted about 78 GeV sources spatially associated with known SNRs, but we claimed that only 45% of these might have been associated to a SNR by chance. For all these reasons, it was decided within the collaboration to go further and start the SNR Catalog project. The purpose of the project is manyfold: • Characterize GeV emission in regions containing known SNRs • Evaluate systematics, including diffuse models and variability • Examine multiwavelength correlation, including spectrum and morphology for radio, X-ray, and TeV and CO, maser, IR, • Determine statistically significant SNR classification(s) and perform spectral modeling 0920-5632/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.nuclphysbps.2013.04.097
We started collecting data from Green 2009 [3] who collected 274 detected SNR in one catalog. For all these SNRs we have extracted the centroid of the emission, the extension, radio index, flux and some of them also the distance. The modeling of SNRs spectra would be of great interest in the search for clear signatures of cosmic ray acceleration. Eventual neutrinos detection from such astrophysical sites would be the definitive proof of hadronic processes and proton acceleration. In the following paragraphs we describe the parametrization applied and results obtained in fitting the GeV-TeV data of a few SNRs detected by Fermi so far and estimate the expected neutrinos flux from these acceleration sites. 1.1. Gamma ray emission modeling A fit of the GeV-TeV data has been performed using the parametrization of the cross sections and the gamma ray yield from Kamae et al. 2006. The flux of gamma rays at earth has been evaluated starting from the yield per unit volume: Fγ,S NR =
dn VS NR , dt 4πd2
(1)
where VS NR is the volume of the SNR, in the hypothesis of uniform distribution of particles and magnetic
240
F. Giordano, M. Caragiulo / Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241
fields, and d being the distance of the source from the solar system. The particle distribution in momentum (or equivalently in energy), is described by a smoothed broken power law: −(γ1 −γ2 )/γ3 −γ3 −γ1 E dN E , (2) 1+ =A dE E0 Ebr where the free parameters are the normalization, closely related to the energetics of the process, the index γ1 and the maximum achieved energy Ebr . It is also important to note that the gamma ray flux strongly depends on the density of the environment the SNR is interacting with. It is worth to underline that in the proposed modeling there are two major simplifications: the particle population is described by a simple broken power law and the GeV-TeV gamma ray emission for various SNRs are interpreted as produced by hadronic processes only. Therefore the efficiency and the energy budget associated to protons accelerated in SNRs have to be considered upper limits. According to Fermi results of SNRs, two major classes of SNRs seem to be emerging: the first class includes those SNRs interacting with molecular clouds which exhibit very high gamma ray flux, with breaks at few GeV; the second class contains young SNRs, expanding in lighter environment, like CasA and Tycho, which show breaks in the TeV range, being more suitable as far as neutrino physics is concerned. What could make a source more interesting than others is the flux above a certain threshold, i.e. few TeV, that might lead to a clear signal from the source over the atmospheric neutrinos background. In this perspectives, young SNRs, that show higher break in the particle energy distribution, might be more suitable sources for neutrino telescope targets. In Fig.1 and 2 the SEDs for Tycho and CasA SNRs are shown: the data points come from Fermi [4] [5] for Tycho and CasA papers respectively and Veritas[6],[7] analysis and the black line represents the two fits extracted by our model. The results of the fit in terms of proton energy distribution for the CasA case is shown in Fig.3 and summarized in Table1. Parameters Ap Ebr,p γ1,p γ2,p Wp
Figure 1: Tycho GeV-TeV π0 peak fit according to Kamae et al 2006
Figure 2: CasA GeV-TeV π0 peak fit according to Kamae et al 2006
Values (7.74±0.69)·10−8 eV−1 cm−2 s−1 sr−1 (3.27±0.45)TeV (2.19±0.05) (5.91±0.72) (2.94±0.48)·1049 erg Figure 3: Proton energy spectrum for CasA SNR
Table 1: PowerLaw for proton in CasA SNR
F. Giordano, M. Caragiulo / Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 239–241
1.2. Neutrino flux estimations Kamae et al 2006 has also parameterized the neutrino yield produced in p-p interactions. While gamma ray data in almost all SNR cases can be fitted both assuming hadronic scenarios or leptonic models, the eventual detection of neutrinos from this kind of astrophysics sources would be a clear and un-ambiguous signature of p-p interactions taking place. Moreover, as already pointed out, the harder the source, the better its detectability for the next generation neutrino telescopes. Figure4 and 5 show the observed gamma ray flux compared with the neutrinos estimations. 102 γ νe νμ νe νμ
E2 dN (eV cm-2 s-1) dE
10
total neutrino contribute
1
5
6
10
10
8
107
10
9
10
10
10 1011 E (eV)
1012
13
1014
10
15
10
16
10
Figure 4: Neutrinos flux estimation for Tycho SNR
103 γ νe νμ νe
2
νμ
E2 dN (eV cm-2 s-1) dE
10
total neutrino contribute
10
1
10-1
sites would be the definitive proof of hadronic processes and proton acceleration and injection into the Milky Way. According to gamma ray data, young SNRs (like Tycho and CasA) might be among the most promising galactic neutrino sources. 3. Acknowledgment The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged. References
10-1
10-2
241
6
10
107
8
10
9
10
10
10 E (eV)
1011
1012
13
10
1014
15
10
Figure 5: Neutrinos flux estimation for CasA SNR
2. Conclusions The Fermi Collaboration is collecting data for cataloging SNRs in term of GeV emission and processes interpretation. Almost all SNRs detected so far have been modeled both in hadronic and leptonic scenarios, still not having a clear signature on cosmic rays acceleration in act; eventual neutrinos detection from astrophysical
[1] Kamae, T., et al. 2006, ApJ, 647, 692 [2] Atwood et al., ApJ 697, 2009 [3] Green, D.A., 2009, Bulletin of the Astronomical Society of India, 37, 45 [4] Giordano, F., et al. 2012, 744, L2 [5] A. A. Abdo et al. 2010 ApJ 710 L92 [6] Acciari et al, ApJL 730 (2011) L20 [7] Acciari et al, ApJ, 714 (2010), 201