Constraining the Braking Index and Energy Partition of Magnetar spin-down with {em Swift}/XRT data. (arXiv:1812.03465v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lu_H/0/1/0/all/0/1">Hou-Jun Lü</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lan_L/0/1/0/all/0/1">Lin Lan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liang_E/0/1/0/all/0/1">En-Wei Liang</a>
Observationally, the long-lasting X-ray plateau emission in long GRBs show
evidence for ongoing energy injection which may be from magnetar spin-down due
to energy released via magnetic dipole (MD) or gravitational wave (GW)
radiation. In this paper, by systematically analyzing the {em Swift}/XRT light
curves detected before 2018 July, we find 45 light curves that monotonously
decay as smooth broken power-law with redshift measured. By assuming that the
central engines of these GRBs are a newly-born magnetar, we measure the braking
index $n$ of putative millisecond magnetars via MD and GW radiations. The
inferred braking indices are neither closed to 3 nor to 5, but range between
them with a normal distribution ($n_{rm c}=4.02pm 0.11$). We define one
dimensionless parameter $Re$ which is the ratio between MD and GW components,
and find that the energy released of magnetar spin-down in most GRBs of our
sample are dominated by GW radiation for given $P_0=3$ ms and $epsilon=0.005$,
0.01. On the other hand, we find that $Re$ and braking index $n$ seem to be
following an anti-correlation within a large systematic error at $t=0$, but
depended on the parameters of $P_0$ and $epsilon$ values. Those results
suggest that the contribution of GW radiation can not be ignored and the larger
braking index are leading to GW dominated the energy released of magnetar
spin-down if indeed magnetars are operating in some long GRBs.
Observationally, the long-lasting X-ray plateau emission in long GRBs show
evidence for ongoing energy injection which may be from magnetar spin-down due
to energy released via magnetic dipole (MD) or gravitational wave (GW)
radiation. In this paper, by systematically analyzing the {em Swift}/XRT light
curves detected before 2018 July, we find 45 light curves that monotonously
decay as smooth broken power-law with redshift measured. By assuming that the
central engines of these GRBs are a newly-born magnetar, we measure the braking
index $n$ of putative millisecond magnetars via MD and GW radiations. The
inferred braking indices are neither closed to 3 nor to 5, but range between
them with a normal distribution ($n_{rm c}=4.02pm 0.11$). We define one
dimensionless parameter $Re$ which is the ratio between MD and GW components,
and find that the energy released of magnetar spin-down in most GRBs of our
sample are dominated by GW radiation for given $P_0=3$ ms and $epsilon=0.005$,
0.01. On the other hand, we find that $Re$ and braking index $n$ seem to be
following an anti-correlation within a large systematic error at $t=0$, but
depended on the parameters of $P_0$ and $epsilon$ values. Those results
suggest that the contribution of GW radiation can not be ignored and the larger
braking index are leading to GW dominated the energy released of magnetar
spin-down if indeed magnetars are operating in some long GRBs.
http://arxiv.org/icons/sfx.gif
