Gravitational Radiation from Newborn Magnetars in the Virgo Cluster

Abstract

There is growing evidence that two classes of high-energy sources, the soft gamma repeaters and the anomalous X-ray pulsars, contain slowly spinning "magnetars," i.e., neutron stars whose emission is powered by the release of energy from their extremely strong magnetic fields (110 15 G). We show here that the enormous energy liberated in the 2004 December 27 giant flare from SGR 1806Ϫ20 (∼ ergs), together with the likely recurrence 46 5 # 10 time of such events, requires an internal field strength of տ10 16 G. Toroidal magnetic fields of this strength are within an order of magnitude of the maximum fields that can be generated in the core of differentially rotating neutron stars immediately after their formation, if their initial spin period is on the order of a few milliseconds. A substantial deformation of the neutron star is induced by these magnetic fields and, provided the deformation axis is offset from the spin axis, a newborn fast-spinning magnetar would radiate for a few weeks a strong gravitational wave signal, the frequency of which (∼0.5-2 kHz range) decreases in time. The signal from a newborn magnetar with internal field 110 16.5 G could be detected with Advanced LIGO-class detectors up to the distance of the Virgo Cluster (characteristic amplitude ). Magnetars are expected to form in Virgo at Ϫ21 h ∼ 10 c a rate of ≥1 yr Ϫ1 . If a fraction of these have sufficiently high internal magnetic fields, then newborn magnetars constitute a promising new class of gravitational wave emitters.

High-energy Neutrinos from Millisecond Magnetars Formed from the Merger of Binary Neutron Stars

“…Clark et al 2014) can produce a measurable GW signal for hundreds of milliseconds following the merger and provide information on the NS EOS, but they are unlikely to provide unambiguous evidence for an extremely long remnant lifetime (the ringdown signature of the newly-formed BH will probably not be measurable). The magnetar itself will produce a periodic gravitational wave signal; however, its strength depends on the presence of a strong toroidal magnetic field misaligned with the rotation axis (e.g., Stella et al 2005;Fan et al 2013;Lasky et al 2014;Dall'Osso et al 2015) or the growth and saturation of the f-mode instability (e.g., Doneva et al 2015).…”

The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars

“…The emission of gravitational waves is also expected during the formation of magnetars. In fact, if events as powerful as the December 2004 giant flare are not unique in a magnetar lifetime, energetic arguments 16 require that the internal magnetic field of a newly born magnetar be larger than 10 16 G. Such a high field can induce a substantial deformation in the neutron star, which can give rise to the emission of gravitational waves if the rotation and symmetry axis are not aligned [223]. Thus, there is the exciting possibility that magnetars might be among the first detected sources of gravitational waves.…”

Gamma-ray bursts afterglows with energy injection from a spinning down neutron star

“…Different possibilities for this to occur have been investigated in the literature (Palomba 2001;Cutler 2002;Stella et al 2005;Dall'Osso & Stella 2007;Dall'Osso et al 2009;Corsi & Meszaros 2009) showing that in astrophysically plausible conditions, GW emission might efficiently extract spin energy from the NS, in competition with magnetic dipole losses. The study presented here builds on the ansatz that millisecond spinning magnetars are formed in the events that give rise to long GRBs.…”