Long-term evolution, X-ray outburst and optical/infrared emission of SGR 0501+4516

Abstract

We have analyzed the long-term evolution and the X-ray outburst light curve of SGR 0501+4516 in the frame of the fallback disc model. We have shown that the X-ray luminosity, period and period derivative of this typical soft gamma repeater can be achieved by a neutron star with a large range of initial disc masses provided that the source has a magnetic dipole field of ∼ 1.4 × 10 12 G on the pole of the star. At present, the star is accreting matter from the disc, which has an age ∼ 3 × 10 4 yr, and will remain in the accretion phase until t ∼ 2-5 × 10 5 yr depending on the initial disc mass. With its current rotational rate, this source is not expected to give pulsed radio emission even if the accretion on to the star is hindered by some mechanism. The X-ray enhancement light curve of SGR 0501+4516 can be accounted for by the same model applied earlier to the X-ray enhancement light curves of other anomalous X-ray pulsars/soft gamma repeaters with the same basic disc parameters. We have further shown that the optical/IR data of SGR 0501+4516 is in good agreement with the emission from an irradiated fallback disc with the properties consistent with our long-term evolution model.

Magnetar Broadband X-Ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE

“…The employed distances and periods refer to Appendix B and the McGill catalog (Olausen & Kaspi 2013). the release occurs in the stellar interior (Pons & Rea 2012b;Li & Beloborodov 2015) or in the magnetosphere (Beloborodov & Thompson 2007;Kojima & Kato 2014;Benli et al 2015), or both.…”

“…Incidentally, the fall-back disk model tries to explain the outbursts in terms of sudden mass accretion (Alpar 2001a;Benli et al 2013Benli et al , 2015. However, in such cases, the luminosity would hit a ceiling at the Eddington limit (∼ 10 38 erg s −1 ) rather than at ∼ 10 36 erg s −1 ; the outburst would decay exponentially (Tanaka & Shibazaki 1996), or sometimes falls abruptly via the propeller effect (Asai et al 2013) rather than in power-law form; and the spectrum around the outburst peak would exhibit clear fluorescence Fe-K line (e.g., EW>100 eV), if the fast initial rise of X-ray outbursts indicates a mass reservoir close to the neutron star.…”

On the long-term evolution of rotating radio transients

“…In the same model, it is found that a large fraction of HBRPs and persistent AXP/SGRs have 𝐵 0 in the (10 12 -10 13 ) G range (Benli et al 2015;Benli & Ertan 2016, 2017, 2018a, greater than the 𝐵 0 values estimated for CCOs, RRATs, and XDINs (Ertan et al 2014;Benli & Ertan 2018b). Most of these HBRPs with relatively strong fields evolve from the SP phase to the ASD phase achieving the AXP/SGR properties.…”

“…Illustrative model curves showing the effects of the initial conditions on the evolutionary curves are plotted in the earlier works (Ertan et al 2009(Ertan et al , 2014Benli et al 2015). We can summarize the effects of the initial conditions (𝑃 0 , 𝐵 0 , and 𝑀 d ) as follows: For the sources that enter the evolution in the ASD phase, the long-term evolution is not sensitive to 𝑃 0 .…”

Clues from 4U 0142+61 on supernova fallback disc formation and precession

“…where and 1 are the area of the disc illuminated by the pulsar and the area of the disc emitting as a blackbody, respectively. Several uncertainties limit the precision of this estimate: a) the actual radius of pulsars/magnetars ranging between 10 and 14 km for a typical 1.4 solar mass star (Steiner et al 2018), b) the exact pulsar/magnetar blackbody radiation at the equatorial region (where the disc plausibly forms) being about 30% smaller than that of the hot spots and polar cap (Aguilera et al 2008) and c) the actual thickness and energy absorbed by the disc (Benli et al 2015;Shakura & Sunyaev 1973;Lu & Cheng 2002). Finally, the NS blackbody photon gravitational redshift would be of the order of 10%.…”