Unresolved Gamma-Ray Sky through its Angular Power Spectrum

Ackermann, M.; Ajello, M.; Baldini, Luca; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, Pascal; Buehler, R.; Burns, E.; Buson, S.; Cameron, R. A.; Caputo, R.; Caraveo, P. A.; Cavazzuti, E.; Chen, Sina; Chiaro, G.; Ciprini, S.; Costantin, D.; Cuoco, A.; Cutini, S.; D’Ammando, F.; Luque, Pedro De la Torre; Palma, F. de; Desai, Abhishek; Digel, S. W.; Lalla, N. Di; Mauro, Mattia Di; Venere, L. Di; Dirirsa, F.; Favuzzi, C.; Franckowiak, A.; Fukazawa, Yasushi; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Grenier, I. A.; Guillemot, L.; Guiriec, S.; Horan, D.; Jóhannesson, G.; Kuss, M.; Larsson, Stefan; Latronico, L.; Li, J.; Liodakis, Ioannis; Longo, F.; Loparco, Francesco; Lubrano, P.; Magill, J. D.; Maldera, S.; Malyshev, D.; Manfreda, Alberto; Mazziotta, M. N.; Mereu, I.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Москаленко, И. В.; Negro, Michela; Nuss, E.; Orienti, M.; Orlando, E.; Palatiello, M.; Paliya, Vaidehi S.; Paneque, D.; Peršić, M.; Pesce-Rollins, Melissa; Petrosian, V.; Piron, F.; Porter, T. A.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Serini, D.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Takahashi, Mitsunari; Thayer, J. B.; Tibaldo, L.; Torres, D. F.; Troja, E.; Venters, Tonia M.; Vianello, G.; Wood, K. S.; Yassine, M.; Zaharijaš, Gabrijela; Ammazzalorso, Simone; Fornengo, N.; Regis, Marco

doi:10.1103/physrevlett.121.241101

Cited by 31 publications

(114 citation statements)

References 39 publications

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“…A spectral index lower than ∼ 2 is indicative of a hardening of the spectrum for the unresolved population of blazars, a result compatible with the findings of Ref. (Ackermann et al 2018). The AGN normalisation, instead, turns out to be much larger than expected, even though with a sizeable uncertainty.…”

Section: Resultssupporting

confidence: 90%

“…When compared with a theoretical model which contains an explicit term referring to a large-scale γ-ray emission, MCXCsub exhibits a clear preference for this type of emission as compared to the a model containing only "shot-noise" emission from unresolved point sources, like sub-threshold AGNs. The energy spectrum of this latter component is found to be slightly harder that the mean spectral behaviour of resolved blazars, possibly indicating differences between the resolved and unresolved components of the AGN population, as observed also in (Ackermann et al 2018). Further investigation of the extended emission could not disentangle between the two options offered by a large-scale 1-halo term, possibly linked to an intra-cluster medium emission, and a large-scale 2-halo contribution, like it would occur if the correlation is due to the large-scale distribution of point-like AGNs.…”

Section: Discussionmentioning

confidence: 56%

“…The resulting energy-dependent masks aim at properly covering resolved sources and avoiding artefacts due to source flux leakage outside the mask, but at the same time maintaining a good sky coverage. For further details and impact of the mask, see also Ackermann et al (2018).…”

Section: Fermi-lat γ-Rays Mapsmentioning

confidence: 99%

“…with the obtained parameters and then subtract the foreground maps from the corresponding intensity maps: this procedure is performed after having re-binned them in the macro energy-bins then used in the cross-correlation analysis. For additional information about the foreground removal, see Ackermann et al (2018) and Ammazzalorso et al (2018), where the same procedure is adopted. In figure 1, we show as an example the γ-ray masked map in the (2.3 − 4.8) GeV energy bin before (left panel) and after (right panel) the galactic foreground removal.…”

Section: Fermi-lat γ-Rays Mapsmentioning

confidence: 99%

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Searching for gamma-ray emission from galaxy clusters at low redshift

Colavincenzo

Tan

Ammazzalorso

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We report the identification of a positive cross-correlation signal between the unresolved γ-ray emission, measured by the Fermi Large Area Telescope, and four different galaxy cluster catalogues. The selected catalogues peak at low-redshift and span different frequency bands, including infrared, optical and X-rays. The signal-to-noise ratio of the detected cross-correlation amounts to 3.5 in the most significant case. We investigate and comment about its possible origin, in terms of compact γ-ray emission from AGNs inside clusters or diffuse emission from the intracluster medium. The analysis has been performed by introducing an accurate estimation of the cross-correlation power-spectrum covariance matrix, built with mock realisations of the gamma and galaxy cluster maps. Different methods to produce the mock realizations starting from the data maps have been investigated and compared, identifying suitable techniques which can be generalized to other cross-correlation studies.

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Section: Resultssupporting

confidence: 90%

Section: Discussionmentioning

confidence: 56%

Section: Fermi-lat γ-Rays Mapsmentioning

confidence: 99%

Section: Fermi-lat γ-Rays Mapsmentioning

confidence: 99%

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Searching for gamma-ray emission from galaxy clusters at low redshift

Colavincenzo

Tan

Ammazzalorso

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Fermi / LAT collaboration has recently released new photon selection P8R3_SOURCEVETO_V2 (Bruel et al 2018) which provides the suppression of the charged cosmic ray backgorund comparable to that of the ULTRACLEANVETO class, but has larger event statistics, comparable to P8R2_CLEAN_V6 (Bruel et al 2018;Ackermann et al 2018). Motivated by this improvement, we have performed a more advanced analysis of the hard TeV diffuse emission, which we report below.…”

Section: Introductionmentioning

confidence: 99%

Galactic diffuse gamma-ray emission at TeV energy

Neronov

Semikoz

2020

A&A

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Context. Measurement of diffuse Galactic gamma-ray flux in the TeV range is difficult for ground-based gamma-ray telescopes because of uncertainties of estimates of background in the telescope field of view. Its detection is also challenging for the space-based telescopes because of low signal statistics. Aims. We characterise the diffuse TeV flux from the Galaxy using decade-long exposure of Fermi Large Area Telescope. Methods. Considering that the level of diffuse Galactic emission in the TeV band approaches the level of residual cosmic ray background, we estimate the residual cosmic ray background in the SOURCEVETO event selection and verify that the TeV diffuse Galactic emission flux is well above the residual cosmic ray background up to high Galactic latitude. Results. We study spectral and imaging properties of the diffuse TeV signal from the Galactic Plane. We find much stronger emission from the inner Galactic Plane, compared to previous HESS telescope measurement. We also find significant discrepancies in the measurement of Galactic longitude and latitude profiles of the signal measured by Fermi and HESS. These discrepancies are presumably explained by the fact that regions of background estimate in HESS have non-negligible gamma-ray flux. Comparing Fermi measurements with that of ARGO-YBJ we find better agreement, with a notable exception of Cygnus region, where we find much higher flux (by a factor 1.5). We also measure the TeV diffuse emission spectrum up to high Galactic latitude and show that the spectrum of different regions of the sky have spectral slopes consistent with Γ = 2.34 ± 0.04, which is harder than the slope of locally observed spectrum of cosmic rays with energies 10-100 TeV, which produce TeV diffuse emission on their way through the interstellar medium. We discuss possible origin of the hard slope of TeV diffuse emission.

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