Constraining the braking indices of magnetars

Abstract

Due to the lack of long term pulsed emission in quiescence and the strong timing noise, it is impossible to directly measure the braking index n of a magnetar. Based on the estimated ages of their potentially associated supernova remnants (SNRs), we estimate the values of the mean braking indices of eight magnetars with SNRs, and find that they cluster in a range of 1 ∼42. Five magnetars have smaller mean braking indices of 1 < n < 3, and we interpret them within a combination of magneto-dipole radiation and wind aided braking, while the larger mean braking indices of n > 3 for other three magnetars are attributed to the decay of external braking torque, which might be caused by magnetic field decay. We estimate the possible wind luminosities for the magnetars with 1 < n < 3, and the dipolar magnetic field decay rates for the magnetars with n > 3 within the updated magneto-thermal evolution models. Although the constrained range of the magnetars' braking indices is tentative, due to the uncertainties in the SNR ages, which come from distance uncertainties and the unknown conditions of the expanding shells, our method provides an effective way to constrain the magnetars' braking indices if the measurements of the SNRs' ages are reliable, which can be improved by future observations.

The Dipole Magnetic Field and Spin-down Evolutions of the High Braking Index Pulsar PSR J1640–4631

“…where the SNR radius R SNR is in units of pc and the post-shock plasma temperature T is in units of keV (for details see Gao et al 2016). G338.3−0.0 is a shell-type, 8¢ diameter SNR (Shaver & Goss 1970;Whiteoak & Green 1996) and spatially relates to HESS J1640−465, which is considered to be the most luminous γ-ray source in the Galaxy.…”

“…Taking into account the QVF effect, the measured braking indices of n 3 < can be well explained (Coelho et al 2016). To account for the observed braking indices, several other interpretations have been put forward (see Gao et al 2016, for a brief summary).…”

“…The surface dipole magnetic field has a significant effect on the spin evolution of a pulsar, as well as on its braking index (e.g., Goldreich & Reisenegger 1992;Tauris & Konar 2001;Jones 2009;Marchant et al 2014). In the case of a varying dipole magnetic field at the pole B p , the braking index n can be simply expressed as follows: Kaminker et al 2014;Potekhin et al 2015), whereas n 3 < for an increasing B p (e.g., Mereghetti 2008;Gao et al 2016).…”

Magnetar crust electron capture for $$^{55}$$ 55 Co and $$^{56}$$ 56

“…Some interesting behaviors such as a wide array of X-ray activity including short bursts, large outbursts, giant flares, quasiperiodic oscillations, enhanced spin-down, glitches and antiglitches are displayed in magnetars and discussed by Kaspi and Beloborodov [23]. The electron Fermi energy, and the a e-mail: liujingjing68@126.com electron fraction in SMFs and the dipole magnetic field and spin-down evolutions were explored in detail by Gao et al [24][25][26][27][28] and Zhu et al [29].…”

Hybridization of Soft Expert Set with AHP in Decision Making

“…They combined IVFSS with IVFS and soft sets, which is the consequence of Yang et al [19] Sabir Hussain [15] worked on soft expert topological spaces, Shabir, M and Naz, M [16] on soft topological spaces, Wand Y.J and Lee [18] worked on generalized TOPSIS for fuzzy multiple criteria group decision making. Gao [5][6], Ramik [14], Dodd [3], Hwang [7] and Linkov [10] works further on decision making problems.…”