The diversity of transients from magnetar birth in core collapse supernovae

Abstract

Strongly-magnetized, rapidly-rotating neutron stars are contenders for the central engines of both long-duration gamma-ray bursts (LGRBs) and hydrogen-poor super-luminous supernovae (SLSNe-I). Models for typical (∼ minute long) LGRBs invoke magnetars with high dipole magnetic fields (B d ∼ > 10 15 G) and short spin-down times, while models for SLSNe-I invoke neutron stars with weaker fields and longer spin-down times of weeks. Here we identify a transition region in the space of B d and birth period for which a magnetar can power both a long GRB and a luminous SN. In particular, we show that a 2 ms period magnetar with a spin-down time of ∼ 10 4 s can explain the observations of both the ultra-long GRB 111209 and its associated luminous SN2011kl. For magnetars with longer spin down times, we predict even longer duration (∼ 10 6 s) GRBs and brighter supernovae, a correlation that extends to Swift J2058+05 (commonly interpreted as a tidal disruption event). We further show that previous estimates of the maximum rotational energy of a proto-magnetar were too conservative and energies up to E max ∼ 1 − 2 × 10 53 ergs are possible. The magnetar model can therefore comfortably accommodate the extreme energy requirements recently posed by the most luminous supernova ASASSN-15lh. The high ionization flux from a pulsar wind nebula powering ASASSN-15lh may lead to an ionization break-out X-ray burst over the coming months, which would be accompanied by an abrupt change in the optical spectrum. We conclude by briefly contrasting millisecond magnetar and black hole models for SLSNe and ultra-long GRBs.

Magnetars in Ultra-Long Gamma-Ray Bursts and GRB 111209A

“…This corresponds to an isotropic equivalent energy of 5.64 × 10 55 erg. However, even with this concession, this lower density limit is inconsistent with the maximum density permitted to avoid a jet-break during the course of the X-ray light curve for a tight beam with a beaming factor of 800, as we calculated for the Metzger et al (2015) model (n 0 ≤ 4.63 × 10 −6 atoms cm −3 , Section 2.1). The wind case can still be consistent with our limit of A * ≤ 3.41 × 10 −2 g cm −1 from Section 2.1 if B ≥ 0.07.…”

“…Observations of NSs with masses slightly in excess of 2 M (Demorest et al 2010;Antoniadis et al 2013) suggest at least 3 × 10 52 erg is attainable for a millisecond magnetar, and Metzger et al (2015) show that in extreme cases, up to ∼ 10 53 erg is attainable for larger NS radii and sub-ms spin periods. Both the SN and GRB benefit from the energy released during core collapse, but while the total gravitational energy released is ∼ 10 53 erg, the majority of this is carried away by neutrinos, leaving of the order of a few ×10 51 erg, depending on the mass of the stellar core and the efficiency of the energy conversion.…”

“…The suggestion that ULGRB 111209A/SN 2011kl is powered by a magnetar has sparked great interest in the community, and a number of authors have proposed magnetar physical parameters (spin periods and dipole field strengths) capable of reproducing the observations (Greiner et al 2015;Metzger et al 2015;Bersten et al 2016;Cano et al 2016). However, many of these have focused on powering the SN alone.…”

“…The narrower the jet opening angle, the earlier the break should be observed. The very narrow jet employed by Metzger et al (2015) suggests a jet break may occur fairly early in the light curve evolution.…”

Hydrogen-poor Superluminous Supernovae from the Pan-STARRS1 Medium Deep Survey

“…The lack of narrow lines seen in the spectra at any epoch is also a puzzle if CSM interaction is the power source. Alternative explanations include a central-engine model, such as the spin-down of a newborn magnetar energizing the ejecta over timescales of weeks (Kasen & Bildsten 2010;Woosley 2010;Dessart et al 2012;Metzger et al 2015;Wang et al 2015). This model has gained popularity thanks to its ability to explain a wide variety of SLSN light curves (e.g., Chomiuk et al 2011;Inserra et al 2013;Lunnan et al 2013Lunnan et al , 2016Nicholl et al 2013Nicholl et al , 2017a, though a smoking-gun signature of the magnetar engine, such as X-ray breakout (Metzger et al 2014), remains elusive ).…”