ABSTRACT
We present radio and optical afterglow observations of the TeV-bright long gamma-ray burst 190114C at a redshift of z = 0.425, which was detected by the Major Atmospheric Gamma Imaging ...Cherenkov telescope. Our observations with Atacama Large Millimeter/submillitmeter Array, Australia Telescope Compact Array, and upgraded Giant Metre-wave Radio Telescope were obtained by our low frequency observing campaign and range from ∼1 to ∼140 d after the burst and the optical observations were done with three optical telescopes spanning up to ∼25 d after the burst. Long-term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission.
Abstract
Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after discovery to over a year after the outburst are presented here. The spectral evolution is found to be similar to ...that in previous outbursts. The early-phase spectra are dominated by hydrogen and helium (i and ii) lines. Coronal and nebular lines appear in the later phases. Emission line widths are found to narrow with time, which is interpreted as a shock expanding into the red giant wind. Using the photoionization code cloudy, spectra at nine epochs spanning 14 months after the outburst peak, thus covering a broad range of ionization and excitation levels in the ejecta, are modelled. The best-fitting model parameters indicate the presence of a hot white dwarf source with a roughly constant luminosity of 1.26 × 1037 erg s−1. During the first three months, the abundances (by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found to be above solar abundances; the abundances of these elements decreased in the later phase. Also presented are spectra obtained during quiescence. A photoionization model of the quiescent spectrum indicates the presence of a low-luminosity accretion disc. The helium abundance is found to be subsolar at quiescence.
We present optical photometry and spectroscopy of the Type IIP supernova SN 2004et that occurred in the nearby galaxy NGC 6946. The observations span a time range of 8–541 d after explosion. The late ...time bolometric luminosity and the Hα luminosity in the nebular phase indicate that 0.06 ± 0.02 M⊙ of 56Ni was synthesized during the explosion. The plateau luminosity, its duration and the expansion velocity of the supernova at the middle of the plateau indicate an explosion energy of Eexp= 1.20+0.38−0.30× 1051 erg. The late time light curve and the evolution of the O i and Hα emission-line profiles indicate the possibility of an early dust formation in the supernova ejecta. The luminosity of O i 6300, 6364 Å doublet, before the dust formation phase, is found to be comparable to that of SN 1987A at similar epochs, implying an oxygen mass in the range 1.5–2 M⊙, and a main-sequence mass of 20 M⊙ for the progenitor.
Abstract
Very-high-energy (VHE; 100 GeV <
E
≤ 100 TeV) and high-energy (HE; 100 MeV <
E
≤ 100 GeV) gamma rays were observed from the symbiotic recurrent nova RS Ophiuchi (RS Oph) during its outburst ...in 2021 August by various observatories, such as the High Energy Stereoscopic System (HESS), Major Atmospheric Gamma Imaging Cherenkov (MAGIC), and Fermi-Large Area Telescope (LAT). The models that have been explored so far tend to favor a hadronic scenario of particle acceleration over an alternative leptonic scenario. This paper explores a time-dependent lepto-hadronic scenario to explain the emission from the RS Oph source region. We have used simultaneous low-frequency radio data observed by various observatories along with the data provided by HESS, MAGIC, and Fermi-LAT to explain the multiwavelength spectral energy distributions corresponding to 4 days after the outburst. Our results show that a lepto-hadronic interpretation of the source not only explains the observed HE-VHE gamma-ray data but the corresponding model synchrotron component is also consistent with the first 4 days of low-radio-frequency data, indicating the presence of nonthermal radio emission at the initial stage of the nova outburst. We have also calculated the expected neutrino flux from the source region and discuss the possibility of detecting neutrinos.
ABSTRACT
The optical spectroscopic observations of ASASSN-18fv observed from 2018 March 24 to 2019 January 26 are presented. The optical spectra are obtained from Mirranook, Vainu Bappu, and South ...African Astronomical observatories. The spectra are dominated by the hydrogen Balmer, Fe ii, and O i lines with P-Cygni profiles in the early phase, typical of an Fe ii class nova. The spectra show He i lines along with H i and O i emission lines in the decline phase placing the nova in the hybrid class of novae. The spectra show rapid development in high-ionization lines in this phase. Analysis of the light curve indicates t2 and t3 values of about 50 and 70 d, respectively, placing the nova in the category of moderately fast nova. The ejectum geometry, inclination, and position angle are estimated using morpho-kinematic analysis. The geometry of the ejecta is found to be an asymmetric bipolar structure with an inclination angle of about 53○. The ejected mass using photoionization analysis is found to be 6.07 × 10−4 M⊙.
Optical UBVRI photometry and low-resolution spectroscopy of the Type IIb supernova SN 2011dh in M51 are presented, covering the first year after the explosion. The light curve and spectral evolution ...are discussed. The early phase light-curve evolution of SN 2011dh is very similar to SN 1993J and SN 2008ax. In the late phase, however, SN 2011dh declines faster than SN 1993J. The late phase decline in the B band is steeper than in the R and I bands, indicating the possibility of dust formation. With a peak V-band absolute magnitude of M
V
= −17.123 ± 0.18 mag, SN 2011dh is a marginally faint type IIb event. The reddening corrected colour curves of SN 2011dh are found to be redder than other well-studied Type IIb supernovae. The bolometric light curve indicates ∼0.09 M of 56Ni is synthesized during the explosion. The He i
lines were detected in the spectra during the rise to maximum. The nebular spectra of SN 2011dh show a box-shaped emission in the red wing of the O i 6300−6363 Å feature, that is attributed to Hα emission from a shock-excited circumstellar material. The analysis of nebular spectra indicates that ∼0.2 M of oxygen was ejected during the explosion. Further, the Ca ii/O i line ratio in the nebular phase is ∼0.7, indicating a progenitor with a main-sequence mass of 10-15 M.
Abstract We report the optical, UV, and soft X-ray observations of the 2017–2022 eruptions of the recurrent nova M31N 2008-12a. We find a cusp feature in the r ′ - and i ′ -band light curves close to ...the peak, which could be related to jets. The geometry of the nova ejecta based on morpho-kinematic modeling of the H α emission line indicates an extended jet-like bipolar structure. Spectral modeling indicates an ejecta mass of 10 −7 –10 −8 M ⊙ during each eruption and an enhanced helium abundance. The supersoft source phase shows significant variability, which is anticorrelated to the UV emission, indicating a common origin. The variability could be due to the reformation of the accretion disk. We infer a steady decrease in the accretion rate over the years based on the intereruption recurrence period. A comparison of the accretion rate with different models on the M WD – M ̇ plane yields the mass of a CO white dwarf, powering the H-shell flashes every ∼1 yr, to be >1.36 M ⊙ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of the Type Ia supernovae progenitor.
Optical and NIR observations of the Type Ia supernova SN 2014J in M82 are presented. The observed light curves are found to be similar to normal Type Ia supernovae (SNe Ia), with a decline rate ...parameter Δm
15(B) = 1.08 ± 0.03. The supernova reached B-band maximum on JD 2456690.14, at an apparent magnitude m
B
(max) = 11.94. The optical spectra show a red continuum with deep interstellar Na i absorption, but otherwise resemble those of normal SNe Ia. The Si ii λ6355 feature indicates a velocity of ∼12 000 km s−1 at B-band maximum, which places SN 2014J at the border of the normal velocity and high velocity group of SNe Ia. The velocity evolution of SN 2014J places it in the Low Velocity Gradient subclass, whereas the equivalent widths of Si ii features near B-band maximum place it at the border of the core normal and Broad Line subclasses of SNe Ia. An analytic model fit to the bolometric light curve indicates that a total of ∼1.3 M⊙ was ejected in the explosion, and the ejected 56Ni mass M
Ni ∼ 0.6 M⊙. The low Fe iii λ4701 to Fe ii λ5200 ratio in the nebular spectra of SN 2014J hints towards clumpiness in the ejecta. Optical broad-band, linear polarimetric observations of SN 2014J obtained on four epochs indicate an almost constant polarization (P
R ∼2.7 per cent; θ ∼ 37°), which suggests that the polarization signal is of interstellar origin.
ABSTRACT
We investigate the observational properties of a hydrogen-deficient superluminous supernova (SLSN) SN 2020ank (at z = 0.2485), with the help of early phase observations carried out between ...–21 and +52 d since g-band maximum. Photometrically, SN 2020ank is one of the brightest SLSN ($M_{\mathrm{ g,peak}}\, \sim$ –21.84 ± 0.10 mag), having fast pre-peak rising and post-peak decaying rates. The bolometric light curve of SN 2020ank exhibits a higher peak luminosity (Lmax) of ∼ (3.9 ± 0.7) × 1044 erg s−1 and appears to be symmetric around the peak with $L^{\mathrm{ rise}}_{\mathrm{ max}}$/e ${\approx}L^{\mathrm{ fall}}_{\mathrm{ max}}$/e ≈ 15 d. The semi-analytical light-curve modelling using the minim code suggests a spin-down millisecond magnetar with $P_i\, \sim$ 2.2 ± 0.5 ms and $B\, \sim$ (2.9 ± 0.1) $\times \, 10^{14}$ G as a possible powering source for SN 2020ank. The possible magnetar origin and excess ultraviolet flux at early epochs indicate a central-engine based powering source for SN 2020ank. Near-peak spectra of SN 2020ank are enriched with the W-shaped O ii features but with the weaker signatures of C ii and Fe iii. Using the estimated rise time of ∼ 27.9 d and the photospheric velocity of ∼ 12 050 km s−1, we constrain the ejecta mass to ∼ 7.2 M⊙ and the kinetic energy of ∼6.3 × 1051 erg. The near-peak spectrum of SN 2020ank exhibits a close spectral resemblance with that of fast-evolving SN 2010gx. The absorption features of SN 2020ank are blueshifted compared to Gaia16apd, suggesting a higher expansion velocity. The spectral similarity with SN 2010gx and comparatively faster spectral evolution than PTF12dam (a slow-evolving SLSN) indicate the fast-evolving behaviour of SN 2020ank.
Abstract
We present an extensive, panchromatic photometric (UV, optical, and near-IR) 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 days, placing it among the very few well-sampled short plateau supernovae (SNe). With
V
-band peak absolute magnitude
M
V
≤ −17.0 ± 0.1 mag, it falls in the middle of the luminosity distribution of the Type II SNe. The color evolution is typical to other Type II SNe except for an early elbow-like feature in the evolution of
V
−
R
color 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 blueshift in emission lines until the late nebular phase, not ordinarily observed in Type II SNe. The amount of radioactive nickel (
56
Ni) yield in the explosion was estimated to be 0.026 ± 0.007
M
⊙
. We infer from semianalytical modeling, nebular spectrum, and 1D hydrodynamical modeling that the probable progenitor was a red supergiant with a zero-age-main-sequence mass ≤13
M
⊙
. 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.
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