3,191 research outputs found
Is the late near-infrared bump in short-hard GRB 130603B due to the Li-Paczynski kilonova?
Short-hard gamma-ray bursts (GRBs) are widely believed to be produced by the
merger of two binary compact objects, specifically by two neutron stars or by a
neutron star orbiting a black hole. According to the Li-Paczynski kilonova
model, the merger would launch sub-relativistic ejecta and a
near-infrared/optical transient would then occur, lasting up to days, which is
powered by the radioactive decay of heavy elements synthesized in the ejecta.
The detection of a late bump using the {\em Hubble Space Telescope} ({\em HST})
in the near-infrared afterglow light curve of the short-hard GRB 130603B is
indeed consistent with such a model. However, as shown in this Letter, the
limited {\em HST} near-infrared lightcurve behavior can also be interpreted as
the synchrotron radiation of the external shock driven by a wide mildly
relativistic outflow. In such a scenario, the radio emission is expected to
peak with a flux of Jy, which is detectable for current radio
arrays. Hence, the radio afterglow data can provide complementary evidence on
the nature of the bump in GRB 130603B. It is worth noting that good
spectroscopy during the bump phase in short-hard bursts can test validity of
either model above, analogous to spectroscopy of broad-lined Type Ic supernova
in long-soft GRBs.Comment: 4 pages, 2 figures, published in ApJ Lette
The lightcurve of the macronova associated with the long-short burst GRB 060614
The {\it Swift}-detected GRB 060614 was a unique burst that straddles an
imaginary divide between long- and short-duration gamma-ray bursts (GRBs), and
its physical origin has been heavily debated over the years. Recently, a
distinct very-soft F814W-band excess at days after the burst was
identified in a joint-analysis of VLT and HST optical afterglow data of
GRB~060614, which has been interpreted as evidence for an accompanying
Li-Paczynski macronova (also called a kilonova). Under the assumption that the
afterglow data in the time interval of days after the burst are due
to external forward shock emission, when this assumption is extrapolated to
later times it is found that there is an excess of flux in several multi-band
photometric observations. This component emerges at 4 days after the
burst, and it may represent the first time that a multi-epoch/band lightcurve
of a macronova has been obtained. The macronova associated with GRB 060614
peaked at days after the burst, which is significantly earlier
than that observed for a supernova associated with a long-duration GRB. Due to
the limited data, no strong evidence for a temperature evolution is found. We
derive a conservative estimate of the macronova rate of , implying a promising prospect
for detecting the gravitational wave radiation from compact object mergers by
upcoming Advanced LIGO/VIRGO/KAGRA detectors (i.e., the rate is ).Comment: The version published in ApJL. Fig.1 has been updated, main
conclusions are unchange
A kilonova associated with GRB 070809
For on-axis typical short gamma-ray bursts (sGRBs), the forward shock
emission is usually so bright that renders the identification of kilonovae
(also known as macronovae) in the early afterglow ( d) phase rather
challenging. This is why previously no thermal-like kilonova component has been
identified at such early time except in the off-axis dim GRB 170817A associated
with GW170817. Here we report the identification of an unusual optical
radiation component in GRB 070809 at d, thanks plausibly to the
very-weak/subdominant forward shock emission. The optical emission with a very
red spectrum is well in excess of the extrapolation of the X-ray emission that
is distinguished by an unusually hard spectrum, which is at odds with the
forward shock afterglow prediction but can be naturally interpreted as a
kilonova. Our finding supports the speculation that kilonovae are ubiquitous ,
and demonstrates the possibility of revealing the neutron star merger origin
with the early afterglow data of some typical sGRBs that take place well beyond
the sensitive radius of the advanced gravitational wave detectors and hence the
opportunity of organizing dedicated follow-up observations for events of
interest.Comment: 20 pages, 5 figures, published in Nature Astronom
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