Gravitational waves from SGRs and AXPs as fast-spinning white dwarfs

Abstract

ABSTRACT In our previous article we have explored the continuous gravitational waves (GWs) emitted from rotating magnetized white dwarfs (WDs) and their detectability by the planned GW detectors such as Laser Interferometer Space Antenna (LISA), Deci-hertz Interferometer Gravitational wave Observatory (DECIGO), and Big Bang Observer (BBO). Here, GWs’ emission due to magnetic deformation mechanism is applied for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs), described as fast-spinning and magnetized WDs. Such emission is caused by the asymmetry around the rotation axis of the star generated by its own intense magnetic field. Thus, for the first time in the literature, the GW counterparts for SGRs/AXPs are described as WD pulsars. We find that some SGRs/AXPs can be observed by the space detectors BBO and DECIGO. In particular, 1E 1547.0−5408 and SGR 1806−20 could be detected in 1 yr of observation, whereas SGR 1900+14, CXOU J171405.7−381031, Swift J1834.9−0846, SGR 1627−41, PSR J1622−4950, SGR J1745−2900, and SGR 1935+2154 could be observed with a 5-yr observation time. The sources XTE J1810−197, SGR 0501+4516, and 1E 1048.1−5937 could also be seen by BBO and DECIGO if these objects have $M_{\mathrm{ WD}} \lesssim 1.3 \, \mathrm{M}_{\odot }$ and $M_{\mathrm{ WD}} \lesssim 1.2 \, \mathrm{M}_{\odot }$, respectively. We also found that SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of BBO and DECIGO. This result indicates that a possible detection of continuous GWs originated from these objects would corroborate the WD pulsar model.