66 research outputs found
SN 2018gj: A Short-plateau Type II Supernova with Persistent Blue-shifted H-alpha Emission
We present an extensive, panchromatic photometric (UV, Optical, and NIR) and
low-resolution optical spectroscopic coverage of a Type IIP supernova SN 2018gj
that occurred on the outskirts of the host galaxy NGC 6217. From the V-band
light curve, we estimate the plateau length to be ~ 70 +- 2 d, placing it among
the very few well-sampled short plateau supernovae (SNe). With V-band peak
absolute magnitude Mv < -17.0 +- 0.1 mag, it falls in the middle of the
luminosity distribution of the Type II SNe. The colour evolution is typical to
other Type II SNe except for an early elbow-like feature in the evolution of
V-R colour owing to its early transition from the plateau to the nebular phase.
Using the expanding photospheric method, we present an independent estimate of
the distance to SN 2018gj. We report the spectral evolution to be typical of a
Type II SNe. However, we see a persistent blue shift in emission lines until
the late nebular phase, not ordinarily observed in Type II SNe. The amount of
radioactive nickel (56Ni) yield in the explosion was estimated to be 0.026 +-
0.007 Msol. We infer from semi-analytical modelling, nebular spectrum, and 1-D
hydrodynamical modelling that the probable progenitor was a red supergiant with
a zero-age-main-sequence mass < 13 Msol. In the simulated hydrodynamical model
light curves, reproducing the early optical bolometric light curve required an
additional radiation source, which could be the interaction with the proximal
circumstellar matter (CSM).Comment: Accepted for publication in ApJ (31 pages, 23 figures and 7 tables
Gamma rays from a reverse shock with turbulent magnetic fields in GRB 180720B
Gamma-ray bursts (GRBs) are the most electromagnetically luminous cosmic
explosions. They are powered by collimated streams of plasma (jets) ejected by
a newborn stellar-mass black hole or neutron star at relativistic velocities
(near the speed of light). Their short-lived (typically tens of seconds) prompt
-ray emission from within the ejecta is followed by long-lived
multi-wavelength afterglow emission from the ultra-relativistic forward shock.
This shock is driven into the circumburst medium by the GRB ejecta that are in
turn decelerated by a mildly-relativistic reverse shock. Forward shock emission
was recently detected up to teraelectronvolt-energy -rays, and such
very-high-energy emission was also predicted from the reverse shock. Here we
report the detection of optical and gigaelectronvolt-energy -ray
emission from GRB 180720B during the first few hundred seconds, which is
explained by synchrotron and inverse-Compton emission from the reverse shock
propagating into the ejecta, implying a low-magnetization ejecta. Our optical
measurements show a clear transition from the reverse shock to the forward
shock driven into the circumburst medium, accompanied by a 90-degree change in
the mean polarization angle and fluctuations in the polarization degree and
angle. This indicates turbulence with large-scale toroidal and
radially-stretched magnetic field structures in the reverse and forward shocks,
respectively, which tightly couple to the physics of relativistic shocks and
GRB jets -- launching, composition, dissipation and particle acceleration.Comment: 5 pages, 4 figures (main) plus Methods and Supplementary Methods,
accepted for publicatio
Far-Ultraviolet to Near-Infrared Observations of SN 2023ixf: A high energy explosion engulfed in complex circumstellar material
We present early-phase panchromatic photometric and spectroscopic coverage
spanning far-ultraviolet (FUV) to the near-infrared (NIR) regime of the nearest
hydrogen-rich core-collapse supernova in the last 25 years, SN~2023ixf. We
observe early `flash' features in the optical spectra due to a confined dense
circumstellar material (CSM). We observe high-ionization absorption lines Fe
II, Mg II in the ultraviolet spectra from very early on. We also observe a
multi-peaked emission profile of H-alpha in the spectrum beginning ~16 d, which
indicates ongoing interaction of the SN ejecta with a pre-existing shell-shaped
CSM having an inner radius of ~ 75 AU and an outer radius of ~140 AU. The
shell-shaped CSM is likely a result of enhanced mass loss ~ 35 - 65 years
before the explosion assuming a standard Red-Supergiant wind. Spectral modeling
of the FUV, NUV, and the optical spectra during 9-12 d, using the radiative
transfer spectrum synthesis code TARDIS indicates that the supernova ejecta
could be well represented by a progenitor elemental composition greater than
solar abundances. Based on early light curve models of Type II SNe, we infer
that the nearby dense CSM confined to ~7+-3e14~cm(~45 AU) is a result of
enhanced mass loss ~1e-(3.0+-0.5) Msol/yr two decades before the explosion.Comment: Submitted to AAS Journals, 4 figures, 2 table
Photometry and Polarimetry of 2010 XC: Observational Confirmation of E-type Near-Earth Asteroid Pair
Asteroid systems such as binaries and pairs are indicative of physical
properties and dynamical histories of the Small Solar System Bodies. Although
numerous observational and theoretical studies have been carried out, the
formation mechanism of asteroid pairs is still unclear, especially for
near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric
and polarimetric observations of a small NEA 2010 XC in 2022 December to
investigate its surface properties. The rotation period of 2010 XC is
possibly a few to several dozen hours and color indices of 2010 XC are
derived as , , and in
the Pan-STARRS system. The linear polarization degrees of 2010 XC are a
few percent at the phase angle range of 58 to 114. We found
that 2010 XC is a rare E-type NEA on the basis of its photometric and
polarimetric properties. Taking the similarity of not only physical properties
but also dynamical integrals and the rarity of E-type NEAs into account, we
suppose that 2010 XC and 1998 WT are of common origin (i.e.,
asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair
ever confirmed, possibly formed by rotational fission. We conjecture that the
parent body of 2010 XC and 1998 WT was transported from the
main-belt through the resonance or Hungaria region.Comment: Resubmitted to AAS Journals. Any comments are welcom
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