326 research outputs found
Relativistic supernovae have shorter-lived central engines or more extended progenitors: the case of SN\,2012ap
Deep late-time X-ray observations of the relativistic, engine-driven, type Ic
SN2012ap allow us to probe the nearby environment of the explosion and reveal
the unique properties of relativistic SNe. We find that on a local scale of
~0.01 pc the environment was shaped directly by the evolution of the progenitor
star with a pre-explosion mass-loss rate <5x10^-6 Msun yr-1 in line with GRBs
and the other relativistic SN2009bb. Like sub-energetic GRBs, SN2012ap is
characterized by a bright radio emission and evidence for mildly relativistic
ejecta. However, its late time (t~20 days) X-ray emission is ~100 times fainter
than the faintest sub-energetic GRB at the same epoch, with no evidence for
late-time central engine activity. These results support theoretical proposals
that link relativistic SNe like 2009bb and 2012ap with the weakest observed
engine-driven explosions, where the jet barely fails to breakout. Furthermore,
our observations demonstrate that the difference between relativistic SNe and
sub-energetic GRBs is intrinsic and not due to line-of-sight effects. This
phenomenology can either be due to an intrinsically shorter-lived engine or to
a more extended progenitor in relativistic SNe.Comment: Version accepted to ApJ. Significantly broadened discussio
The magnetic environment in the central region of nearby galaxies
The central regions of galaxies harbor some of the most extreme physical
phenomena, including dense stellar clusters, non-circular motions of molecular
clouds and strong and pervasive magnetic field structures. In particular, radio
observations have shown that the central few hundred parsecs of our Galaxy has
a striking magnetic field configuration. It is not yet clear whether these
magnetic structures are unique to our Milky Way or a common feature of all
similar galaxies. Therefore, we report on (a) a new radio polarimetric survey
of the central 200 pc of the Galaxy to better characterize the magnetic field
structure and (b) a search for large-scale and organized magnetized structure
in the nuclear regions of nearby galaxies using data from the Very Large Array
(VLA) archive. The high angular resolution of the VLA allows us to study the
central 1 kpc of the nearest galaxies to search for magnetized nuclear features
similar to what is detected in our own Galactic center. Such magnetic features
play a important role in the nuclear regions of galaxies in terms of gas
transport and the physical conditions of the interstellar medium in this
unusual region of galaxies.Comment: 8 pages; Proceedings for "The Universe under the Microscope" (AHAR
2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal
of Physics: Conference Series by Institute of Physics Publishing, R.
Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.
Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
On 2017 August 17, the Laser Interferometer Gravitational-wave Observatory
(LIGO) and the Virgo interferometer detected gravitational waves emanating from
a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and
INTEGRAL telescopes detected a gamma-ray transient, GRB 170817A. 10.9 hours
after the gravitational wave trigger, we discovered a transient and fading
optical source, Swope Supernova Survey 2017a (SSS17a), coincident with
GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40
megaparsecs. The precise location of GW170817 provides an opportunity to probe
the nature of these cataclysmic events by combining electromagnetic and
gravitational-wave observations.Comment: 25 pages, 10 figures, 2 tables, published today in Scienc
The Old Host-Galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational Wave Source
We present an analysis of the host-galaxy environment of Swope Supernova
Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a
gravitational wave source, GW170817. SSS17a occurred 1.9 kpc (in projection;
10.2") from the nucleus of NGC 4993, an S0 galaxy at a distance of 40 Mpc. We
present a Hubble Space Telescope (HST) pre-trigger image of NGC 4993, Magellan
optical spectroscopy of the nucleus of NGC 4993 and the location of SSS17a, and
broad-band UV through IR photometry of NGC 4993. The spectrum and broad-band
spectral-energy distribution indicate that NGC 4993 has a stellar mass of log
(M/M_solar) = 10.49^{+0.08}_{-0.20} and star formation rate of 0.003
M_solar/yr, and the progenitor system of SSS17a likely had an age of >2.8 Gyr.
There is no counterpart at the position of SSS17a in the HST pre-trigger image,
indicating that the progenitor system had an absolute magnitude M_V > -5.8 mag.
We detect dust lanes extending out to almost the position of SSS17a and >100
likely globular clusters associated with NGC 4993. The offset of SSS17a is
similar to many short gamma-ray burst offsets, and its progenitor system was
likely bound to NGC 4993. The environment of SSS17a is consistent with an old
progenitor system such as a binary neutron star system.Comment: ApJL in pres
Zooming In on the Progenitors of Superluminous Supernovae With the HST
We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the
host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including
11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the
superb angular resolution of HST, we characterize the galaxies' morphological
properties, sizes and star formation rate (SFR) densities. We determine the
supernova (SN) locations within the host galaxies through precise astrometric
matching, and measure physical and host-normalized offsets, as well as the SN
positions within the cumulative distribution of UV light pixel brightness. We
find that the host galaxies of H-poor SLSNe are irregular, compact dwarf
galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR
densities are high ( ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe
form in overdense environments. Their locations trace the UV light of their
host galaxies, with a distribution intermediate between that of long-duration
gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions
of their hosts) and a uniform distribution (characteristic of normal
core-collapse SNe), though cannot be statistically distinguished from either
with the current sample size. Taken together, this strengthens the picture that
SLSN progenitors require different conditions than those of ordinary
core-collapse SNe to form, and that they explode in broadly similar galaxies as
do LGRBs. If the tendency for SLSNe to be less clustered on the brightest
regions than are LGRBs is confirmed by a larger sample, this would indicate a
different, potentially lower-mass progenitor for SLSNe than LRGBs.Comment: ApJ in press; matches published version. Minor changes following
referee's comments; conclusions unchange
The Fast and Furious Decay of the Peculiar Type Ic Supernova 2005ek
We present extensive multi-wavelength observations of the extremely rapidly
declining Type Ic supernova, SN 2005ek. Reaching a peak magnitude of M_R =
-17.3 and decaying by ~3 mag in the first 15 days post-maximum, SN 2005ek is
among the fastest Type I supernovae observed to date. The spectra of SN 2005ek
closely resemble those of normal SN Ic, but with an accelerated evolution.
There is evidence for the onset of nebular features at only nine days
post-maximum. Spectroscopic modeling reveals an ejecta mass of ~0.3 Msun that
is dominated by oxygen (~80%), while the pseudo-bolometric light curve is
consistent with an explosion powered by ~0.03 Msun of radioactive Ni-56.
Although previous rapidly evolving events (e.g., SN 1885A, SN 1939B, SN 2002bj,
SN 2010X) were hypothesized to be produced by the detonation of a helium shell
on a white dwarf, oxygen-dominated ejecta are difficult to reconcile with this
proposed mechanism. We find that the properties of SN 2005ek are consistent
with either the edge-lit double detonation of a low-mass white dwarf or the
iron-core collapse of a massive star, stripped by binary interaction. However,
if we assume that the strong spectroscopic similarity of SN 2005ek to other SN
Ic is an indication of a similar progenitor channel, then a white-dwarf
progenitor becomes very improbable. SN 2005ek may be one of the lowest mass
stripped-envelope core-collapse explosions ever observed. We find that the rate
of such rapidly declining Type I events is at least 1-3% of the normal SN Ia
rate.Comment: Accepted for publication in ApJ. Please visit
http://www.cfa.harvard.edu/~mdrout to hear a sonification of SN2005e
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-Time Emission from the Kilonova Ejecta
We present Very Large Array (VLA) and Atacama Large Millimeter/sub-millimeter
Array ALMA radio observations of GW\,170817, the first Laser Interferometer
Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from
a binary neutron star merger and the first GW event with an electromagnetic
(EM) counterpart. Our data include the first observations following the
discovery of the optical transient at both the centimeter ( hours post
merger) and millimeter ( days post merger) bands. We detect faint
emission at 6 GHz at 19.47 and 39.23 days after the merger, but not in an
earlier observation at 2.46 d. We do not detect cm/mm emission at the position
of the optical counterpart at frequencies of 10-97.5 GHz at times ranging from
0.6 to 30 days post merger, ruling out an on-axis short gamma-ray burst (SGRB)
for energies erg. For fiducial SGRB parameters, our limits
require an observer viewer angle of . The radio and X-ray
data can be jointly explained as the afterglow emission from an SGRB with a jet
energy of erg that exploded in a uniform density
environment with cm, viewed at an angle of from the jet axis. Using the results of our light curve
and spectral modeling, in conjunction with the inference of the circumbinary
density, we predict the emergence of late-time radio emission from the
deceleration of the kilonova (KN) ejecta on a timescale of years
that will remain detectable for decades with next-generation radio facilities,
making GW\,170817 a compelling target for long-term radio monitoring.Comment: 8 pages, 4 figures, 1 table. ApJL, in press. Keywords: GW170817, LV
Interaction Between The Broad-lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands
The diffuse interstellar bands (DIBs) are absorption features observed in
optical and near-infrared spectra that are thought to be associated with
carbon-rich polyatomic molecules in interstellar gas. However, because the
central wavelengths of these bands do not correspond with electronic
transitions of any known atomic or molecular species, their nature has remained
uncertain since their discovery almost a century ago. Here we report on
unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova
SN 2012ap that exhibit changes in equivalent width over short (~30 days)
timescales. The 4428 and 6283 Angstrom DIB features get weaker with time,
whereas the 5780 Angstrom feature shows a marginal increase. These nonuniform
changes suggest that the supernova is interacting with a nearby source of the
DIBs and that the DIB carriers possess high ionization potentials, such as
small cations or charged fullerenes. We conclude that moderate-resolution
spectra of supernovae with DIB absorptions obtained within weeks of outburst
could reveal unique information about the mass-loss environment of their
progenitor systems and provide new constraints on the properties of DIB
carriers.Comment: 6 pages, 3 figures, accepted for publication in ApJ
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