arXiv:1303.0863v2 [astro-ph.SR] 8 Apr 2013 June 20, 2018 6:24 WSPC - Proceedings Trim Size: 9.75in x 6.5in main 1 DO SGRs/AXPs AND RADIO AXPs HAVE THE SAME NATURE? GOULART COELHO, JAZIEL * ; MALHEIRO, MANUEL Departamento de F´ ısica, Instituto Tecnol´ ogico de Aeron´ autica, S˜ ao Jos´ e dos Campos, SP 12.228-900, Brazil * E-mail: jaziel@ita.br www.ita.br SGRs/AXPs are assumed to be a class of neutron stars (NS) powered by magnetic energy and not by rotation, as normal radio pulsars. However, the recent discovery of radio-pulsed emission in four of this class of sources, where the spin-down rotational energy lost ˙ Erot is larger than the X-ray luminosity L X during the quiescent state - as in normal pulsars - opens the question of the nature of these radio AXPs in comparison to the others of this class. In this work, we show that the radio AXPs obey a linear log-log relation between L X and ˙ Erot , very similar to the one of normal X-ray pulsars, a correlation not seen for the others SGRs/AXPs. This result suggests a different nature between the radio AXPs comparing to the others SGRs/AXPs. Keywords : SGRs/AXPs; radio magnetars; white dwarf pulsars. 1. Introduction Over the last decade, observational evidence has mounted that SGRs/AXPs be- long to a particular class of pulsars. 1 They are understood in the framework of strongly magnetized neutron star, 2,3 but there are alternative scenarios, in partic- ular the white dwarf (WD) pulsar model. 4–6 Recently, four over a total of about 20 SGRs/AXPs presented radio-pulsed emission. These radio AXPs showed several properties that make them different from the others SGRs/AXPs: loud radio (tran- sient radio emission different of the radio pulsar emission), low quiescent X-ray luminosity L X (decreasing with time) that can be explained from the spin-down rotational energy lost ˙ E rot of a neutron star, as normal rotation-powered pulsar. As pointed out in Malheiro et al., 4 the X-ray efficiency η X = L X / ˙ E rot for these radio AXPs, seems to be to small comparing to the others SGRs/AXPs when in- terpreted as magnetized white dwarfs. However, as neutron star pulsars these radio AXPs have η X ∼ (0.2 − 0.1), a little bit larger than the values of normal pulsars (where η X ∼ (0.3 − 0.4)). This can be understood due to their large magnetic dipole momentum m ∼ 10 32 emu, giving support for their neutron star interpretation. In this contribution, we suggest that the radio SGRs/AXPs are rotation-powered neu- tron star pulsars L X ≃ k ˙ E n rot (L X < ˙ E NS rot ), in contrast to the others that are rotation-powered magnetized white dwarfs. In our understanding the large steady X-ray luminosity seen for almost all the no-radio SGRs/AXPs, can be explained as coming from a large spin-down energy lost of a massive white dwarf with a much large magnetic dipole moment of 10 34 ≤ m ≤ 10 36 emu consistent with the range observed for isolated and very magnetic WDs (see Coelho & Malheiro 2012 7 for dis- cussions), indicating a different nature between these sources and the radio AXPs. These radio AXPs have large magnetic field and seem to be very similar to the high-B pulsars recently founded, 8 as already pointed out in Ref. 9 (see Fig. 1 - right