The GAMMA-400 space observatory: status and perspectives

The solar disk is a bright gamma-ray source. Surprisingly, its flux is about one order of magnitude higher than predicted. As a first step toward understanding the physical origin of this discrepancy, we perform a new analysis in 1-100 GeV using 6 years of public Fermi-LAT data. Compared to the previous analysis by the Fermi Collaboration, who analyzed 1.5 years of data and detected the solar disk in 0.1-10 GeV, we find two new and significant results: 1. In the 1-10 GeV flux (detected at > 5σ), we discover a significant time variation that anticorrelates with solar activity. 2. We detect gamma rays in 10-30 GeV at > 5σ, and in 30-100 GeV at > 2σ. The time variation strongly indicates that solar-disk gamma rays are induced by cosmic rays and that solar atmospheric magnetic fields play an important role. Our results provide essential clues for understanding the underlying gamma-ray production processes, which may allow new probes of solar atmospheric magnetic fields, cosmic rays in the solar system, and possible new physics. Finally, we show that the Sun is a promising new target for ground-based TeV gamma-ray telescopes such as HAWC and LHAASO.PACS numbers: 95.85. Pw, 13.85.Qk, 96.50.Vg

Section: Prospects For Fermi and Future Space Missionsmentioning

confidence: 99%

First observation of time variation in the solar-disk gamma-ray flux with Fermi

Beacom

Peter

et al. 2016

“…Finally, we would point out that some other on-orbit or proposed space borne gamma-ray telescopes, such as DAMPE [2], Gamma-400 [39] and HERD [40], all of which have significantly better energy resolution com- 4: The 95% confidence level upper limits on the cross sections of DM annihilating into double γ-rays derived in our analysis. As a comparison, we also plot the constraints set by the Fermi-LAT observations of the Galactic central regions [15].…”

Section: Discussionmentioning

confidence: 88%

Search for line-like signals in the all-sky Fermi-LAT data

Xia²,

Liang³

et al. 2019

In order to search for the line-like signals in the Fermi-LAT data, we have analyzed totally 49152 regions of interest (ROIs) that cover the whole sky. No ROI displays a line signal with test statistic (TS) value above 25, while for 50 ROIs weak line-like excesses with TS > 16 are presented. The intrinsic significances of these potential signals are further reduced by the large trial factor introduced in such kind of analysis. For the largest TS value of 24.3 derived in our analysis, the corresponding global significance is only 0.54σ. We thus do not find any significant line-like signal and set up constraints on the cross section of dark matter annihilating to gamma-ray lines, σv γγ .PACS numbers: 95.35.+d, 95.85.Pw

“…Finally, we would like to point out that an operating space mission, the Dark Matter Particle Explorer (DAMPE) [39,40] with an energy resolutions better than 1.5% at energies >50GeV [41], and some proposing future missions including for instance the High Energy cosmic-Radiation Detection Facality [42] and the GAMMA-400 gamma-ray telescope [43], are expected to contribute significantly to the gamma-ray line search in the next decade.…”

Section: Discussionmentioning

confidence: 99%

Limits on dark matter annihilation cross sections to gamma-ray lines with subhalo distributions inN-body simulations and Fermi LAT data

Liang¹,

Xia²,

Duan³

et al. 2017

In this work, we simulate a set of realizations of local volume dark matter subhalo population based on the distributions and relations derived from Via Lactea II N-body simulation. We calculate the J-factors of these subhalos, and find that the low mass subhalos contribute a lot to the total J-factors. Combining with 91 months of the Fermi LAT observation, we constrain on the cross section of dark matter annihilating directly to two gamma rays. This is the first work combining numerical simulation results and Fermi LAT observations to constrain dark matter cross section to gamma-ray line with subhalo population. Though the constraints derived from subhalo population are weaker than those from Fermi LAT observation of the Galactic center, they are supports of and complementary to these other results.PACS numbers: 95.35.+d, 95.85.Pw