On the energy budget of starquake-induced repeating fast radio bursts

With a growing sample of fast radio bursts (FRBs), we investigate the energy budget of different power sources within the framework of magnetar starquake triggering mechanism. During a starquake, the energy can be released in any form through magnetic, strain, rotational, and gravitational energies. Following findings are revealed: 1. The crust can store a free magnetic energy of the amount of at least 6.3×10^46 erg via toroidal fields, with frequent starquakes happening due to the instability of the crust. 2. The strain energy develops as a rigid object spins down, which can be released during a global starquake accompanied by a glitch. However, it takes a long time to accumulate enough strain energy via spin-down. 3. The rotational energy of a magnetar with P≲0.1 s can match the energy and luminosity budget of FRBs. 4. The budget of the total gravitational energy is high, but the mechanism and efficiency of converting this energy to radiation deserve further exploration.