Speaker: Anupam Ray (Tata Institute Of Fundamental Research)
Unravelling the Mystery of Dark Matter with Black Holes
Primordial black holes (PBHs), possibly formed via gravitational collapse of large density perturbations in the very early universe, are one of the earliest proposed and viable dark matter (DM) candidates. PBHs can make up a large or even entirety of DM over a wide range of masses. Ultralight PBHs in the mass range of 10^{15} - 10^{17} g, emit particles via Hawking radiation, act as a decaying DM, and can be probed via observations of those emitted particles in various space as well as ground based detectors. In this talk, I will discuss how diffuse supernova neutrino background searches at the Super-Kamiokande neutrino observatory, measurement of the 511 keV gamma-ray line by INTEGRAL telescope, observations of low energy Galactic Center photons by the imminent soft gamma-ray telescope AMEGO, and EDGES measurement of the global 21-cm signal can set robust, world-leading exclusions on the fraction of DM composed of ultralight PBHs. Finally, I will also discuss a novel formation mechanism of low mass transmuted black holes which can be a viable non-primordial solution to sub-Chandrasekhar mass, pointing out several avenues to test the transmuted origin of low mass black holes.
Speaker: Yuanhong Qu (University of Nevada, Las Vegas)
Neutrino emission from FRB-emitting magnetars
The detection of FRB 200428 in association with a hard X-ray burst from the Galactic magnetar SGR 1935+2154 suggests that magnetars can make FRBs. We study possible neutrino emission from FRB-emitting magnetars by developing a general theoretical framework. We consider three different sites for proton acceleration and neutrino emission, i.e. within the magnetosphere, in the current sheet region beyond the light cylinder, and in relativistic shocks far away from the magnetosphere. All three scenarios can allow protons to be accelerated to high enough energies to interact with 10 − 200 keV X-ray photons to produce neutrinos. Different cooling processes for protons and pions are considered to calculate the neutrino emission suppression factor within each scenario. We find that the flux of the neutrino emission decreases with increasing radius from the magnetar due to the decrease of the target photon number density. We calculate the neutrino flux from FRB200428 and its associated X-ray burst. The flux of the most optimistic case invoking magnetospheric proton acceleration is still ∼ 4 orders of magnitude below the IceCube sensitivity. We also estimate the diffuse neutrino background from all FRB-emitting magnetars in the universe. The total neutrino flux of magnetars during their FRB emission phases is a negligible fraction of observed diffuse emission even under the most optimistic magnetospheric scenario for neutrino emission. However, if one assumes that many more X-ray bursts without FRB associations can also produce neutrinos with similar mechanisms, magnetars can contribute up to 10^(−8) GeV s^(−1) sr^(−1) cm^(−2) diffuse neutrino background flux in the GeV to multi-TeV range. Future detection or non-detection of neutrinos from bright Galactic magnetar-associated FRBs may provide a diagnosis on the particle acceleration site in FRB-emitting magnetars.
