80 research outputs found
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 spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409
The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is
based on the assumption that their photometric and spectroscopic properties are
invariant with redshift. However, this fundamental assumption needs to be
tested with observations of high-z SNe Ia. To date, the majority of SNe Ia
observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the
resultant analyses are based on observations with modest signal-to-noise ratios
that impart a degree of ambiguity in their determined properties. In rare cases
however, the Universe offers a helping hand: to date a few SNe Ia have been
observed that have had their luminosities magnified by intervening galaxies and
galaxy clusters acting as gravitational lenses. In this paper we present
long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a
redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located
at z=0.216. We compared our spectra, which were obtained a couple weeks to a
couple months past peak light, with the spectroscopic properties of
well-observed, nearby SNe Ia, finding that SN 2016geu's properties are
commensurate with those of SNe Ia in the local universe. Based primarily on the
velocity and strength of the Si II 6355 absorption feature, we find that SN
2016geu can be classified as a high-velocity, high-velocity gradient and
"core-normal" SN Ia. The strength of various features (measured though their
pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined,
cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of
SN 2016geu imply that it is a normal SN Ia, and when taking previous results by
other authors into consideration, there is very little, if any, evolution in
the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome
Modeling the Light Curves of the Luminous Type Ic Supernova 2007D
SN~2007D is a nearby (redshift ), luminous Type Ic supernova
(SN) having a narrow light curve (LC) and high peak luminosity. Previous
research based on the assumption that it was powered by the Ni cascade
decay suggested that the inferred Ni mass and the ejecta mass are M and M, respectively. In this paper, we
employ some multiband LC models to model the -band LC and the color ()
evolution of SN~2007D to investigate the possible energy sources powering them.
We find that the pure Ni model is disfavored; the multiband LCs of
SN~2007D can be reproduced by a magnetar whose initial rotational period
and magnetic field strength are (or
) ms and (or
) G, respectively. By comparing the
spectrum of SN~2007D with that of some superluminous SNe (SLSNe), we find that
it might be a luminous SN like several luminous ``gap-filler" optical
transients that bridge ordinary and SLSNe, rather than a genuine SLSN.Comment: 11 pages, 5 figures, 1 table, accepted for publication in Ap
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