12-20 July 2017
BEXCO
Asia/Seoul timezone
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Contribution

BEXCO - Room A(101/102)

[CRD102] Positron AMS-02 Anomaly: Single SNR Explanation without DM or Pulsar Contributions

Speakers

  • Mikhail MALKOV

Primary authors

Co-authors

Description

Precise measurements of positron/electron ratio in the 1-500 GeV range have challenged the “standard” model of CR production in SNRs. After a brief decline between 2-8 GeV, the ratio rises steadily with a trend towards saturation around 200-400GeV. These observations appear to be in conflict with the diffusive shock acceleration (DSA) mechanism, operating in a single SNR shock. We argue that e+/e- ratio is largely explicable by the DSA if e+ are derived from a subset of SNR shocks which: (i) propagate in clumpy gas media, and (ii) are modified by accelerated CR protons. The protons penetrate into the dense gas clumps upstream to produce positrons and, charge the clumps positively. The induced electric field expels positrons from the clump but traps electrons and secondary antiprotons. The positrons are then accelerated by the modified shock, thus developing a harder spectrum than that of the CR electrons accelerated in other SNR. Mixing the accelerated e+ and e- populations explains the increase in the e+/e- ratio at E>8 GeV. Its decrease at E<8 GeV is due to a subshock weakening that results from the shock modification. The subshock weakness also explains why the neutral gas clumps survive its ionizing radiation. Contrary to the positively charged secondary e+ that are expelled from the dense gas clumps, negatively charged ar{p}, as well as e- and heavier positive secondaries, such as boron, are mostly locked there. The weakened subshock engulfs the clumps, so the locked particles evade acceleration. Scenarios for the 100-300 GeV AMS-02 fraction possibly exceeding the model prediction, including possible dark matter and pulsar contributions, will also be discussed.