
Astronomy & Astrophysics manuscript no. blitzar-v6.1-astroph
c
ESO 2014
January 22, 2014
Fast radio bursts: the last sign of supramassive neutron stars
Heino Falcke
1,2,3
and Luciano Rezzolla
4,5
1
Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, P.O. Box
9010, 6500 GL Nijmegen, The Netherlands
2
ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
3
Max-Planck-Institut f
¨
ur Radioastronomie, Auf dem H
¨
ugel 69, 53121 Bonn, Germany
4
Max-Planck-Institut f
¨
ur Gravitationsphysik, Albert-Einstein-Institut, Potsdam, D-14476, Germany
5
Institut f
¨
ur Theoretische Physik, Frankfurt am Main, D-60438, Germany
Submitted: May 30, 2013, accepted: Jan 20, 2014
ABSTRACT
Context. Several fast radio bursts have been discovered recently, showing a bright, highly dispersed millisecond radio pulse. The
pulses do not repeat and are not associated with a known pulsar or gamma-ray burst. The high dispersion suggests sources at cosmo-
logical distances, hence implying an extremely high radio luminosity, far larger than the power of single pulses from a pulsar.
Aims. We suggest that a fast radio burst represents the final signal of a supramassive rotating neutron star that collapses to a black
hole due to magnetic braking. The neutron star is initially above the critical mass for non-rotating models and is supported by rapid
rotation. As magnetic braking constantly reduces the spin, the neutron star will suddenly collapse to a black hole several thousand to
million years after its birth.
Methods. We discuss several formation scenarios for supramassive neutron stars and estimate the possible observational signatures
making use of the results of recent numerical general-relativistic calculations.
Results. While the collapse will hide the stellar surface behind an event horizon, the magnetic-field lines will snap violently. This
can turn an almost ordinary pulsar into a bright radio “blitzar”: Accelerated electrons from the travelling magnetic shock dissipate a
significant fraction of the magnetosphere and produce a massive radio burst that is observable out to z > 0.7. Only a few percent of
the neutron stars needs to be supramassive in order to explain the observed rate.
Conclusions. We suggest the intriguing possibility that fast radio bursts might trace the solitary and almost silent formation of stellar
mass black holes at high redshifts. These bursts could be an electromagnetic complement to gravitational-wave emission and reveal
a new formation and evolutionary channel for black holes and neutron stars that are not seen as gamma-ray bursts. If supramassive
neutron stars are formed at birth and not by accretion, radio observations of these bursts could trace the core-collapse supernova rate
throughout the universe.
Key words. radiation mechanisms: non-thermal
1. Introduction
Recently, a number of isolated fast radio bursts (FRBs) have
been discovered that last for only a millisecond and which
may come from cosmological distances (Lorimer et al. 2007;
Thornton et al. 2013). What could possibly produce such a bright
emission in such a short time? A natural explanation may be
gravitational collapse involving neutron stars (NSs) or stellar
mass black holes (BHs). Typically, the formation of NSs and
BHs are associated with some rather energetic observational sig-
natures across all wavelengths, such as a supernova (SN) or a
gamma-ray burst (GRBs). The latter are short-term flares of X-
ray and gamma-ray emission, lasting only a fraction of seconds
to tens of seconds, sometimes with an extended afterglow. The
total energy radiated in a GRB is ∼ 10
48−50
erg s
−1
and the bright
emission was explained initially in a fireball model (Cavallo &
Rees 1978; Paczynski 1986; Eichler et al. 1989), where a signif-
icant fraction of the energy is thermalized in an optically thick
outflow eventually radiated in the form of high-energy emission
(see Nakar 2007; Lee & Ramirez-Ruiz 2007, for recent reviews).
Short GRBs, of duration less than 2 s, are thought to be asso-
ciated with NS-NS mergers and not to trace well star formation
(Gehrels et al. 2005). Their average timescale is around 50 ms
(Nakar 2007) with some spread. Long GRBs, with a duration
longer than 2 s, may be associated with the SN of a massive star,
thereby well tracing cosmic star formation (Woosley & Bloom
2006). For the latter scenario, the GRB is suggested to be due to
a plasma jet that propagates through the dense outer layers of the
exploding star (Woosley 1993). Hence, baryon loading and par-
ticle acceleration in internal or external shocks play an important
role in the observational appearance of GRBs. However, do all
forms of collapse lead to such bright observational signatures?
We here discuss the collapse of an isolated and magnetized
supramassive rotating neutron star (SURON) to a BH in a rar-
efied environment. Such a collapse would be inevitable if a
rapidly spinning NS was formed above the critical mass for a
non-rotating NS. Over time, magnetic braking would clear out
the immediate environment of the star and slow it down. With
a significant delay after the creation of the neutron star in a su-
pernova implosion, the SURON will eventually collapse almost
instantly. The formation of an event horizon over the free-fall
timescale, i.e. < 1 ms, during the collapse would immediately
hide most of the matter and radiation apart from the SURON’s
magnetosphere. Instead, the magnetosphere will experience a vi-
olent disruption leading to a strong magnetic shock wave travel-
ling outwards near the speed of light and producing radio emis-
sion. Hence, the observational signatures of such a system would
1
arXiv:1307.1409v2 [astro-ph.HE] 21 Jan 2014