39 research outputs found
Observations of SN 2017ein Reveal Shock Breakout Emission and A Massive Progenitor Star for a Type Ic Supernova
We present optical and ultraviolet observations of nearby type Ic supernova
SN 2017ein as well as detailed analysis of its progenitor properties from both
the early-time observations and the prediscovery Hubble Space Telescope (HST)
images. The optical light curves started from within one day to 275 days
after explosion, and optical spectra range from 2 days to 90 days
after explosion. Compared to other normal SNe Ic like SN 2007gr and SN 2013ge,
\mbox{SN 2017ein} seems to have more prominent C{\footnotesize II} absorption
and higher expansion velocities in early phases, suggestive of relatively lower
ejecta mass. The earliest photometry obtained for \mbox{SN 2017ein} show
indications of shock cooling. The best-fit obtained by including a shock
cooling component gives an estimate of the envelope mass as 0.02
M and stellar radius as 84 R. Examining the
pre-explosion images taken with the HST WFPC2, we find that the SN position
coincides with a luminous and blue point-like source, with an
extinction-corrected absolute magnitude of M8.2 mag and
M7.7 mag.Comparisons of the observations to the theoretical models
indicate that the counterpart source was either a single WR star or a binary
with whose members had high initial masses, or a young compact star cluster. To
further distinguish between different scenarios requires revisiting the site of
the progenitor with HST after the SN fades away.Comment: 28 pages, 19 figures; accepted for publication in The Astrophysical
Journa
A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone Can Explain Early Excess Blue Flux in Some Type Ia Supernovae
We present early-time photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2021aefx. The early-time u-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca ii H&K feature passing from the u to the B bands on the timescale of a few days. This effect could be dominant for all SNe Ia that have broad absorption features and early-time velocities over 25,000 km s. It is likely to be one of the main causes of early excess u-band flux in SNe Ia that have early-time high velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the u band. For objects that explode at lower velocities, and have a more structured shape in the early excess emission, there must also be an additional parameter producing the early-time diversity. More early-time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia.C.A. and B.J.S. are supported by NSF grants AST-1907570, AST-1908952, AST-1920392, and AST-1911074. M.D.S. is funded in part by an Experiment grant (No. 28021) from the Villum FONDEN, and by a project 1 grant (No. 8021-00170B) from the Independent Research Fund Denmark (IRFD). P.H. acknowledges support by National Science Foundation (NSF) grant AST- 1715133. E.B. and J.D. are supported in part by NASA grant 80NSSC20K0538. This work has been generously supported by the National Science Foundation under grants AST-1008343, AST-1613426, AST-1613455, and AST1613472. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at the Las Campanas Observatory, Chile. We would like to thank the technical staff for constant support for observations on the Swope telescope. The early-time spectrum that was critical for this analysis came from SALT through Rutgers University time via program 2021-1-MLT-007 (PI: Jha). L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) "Investing in your future" under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016, and the program Unidad de Excelencia María de Maeztu CEX2020-001058-M
SN 2021fxy: Mid-Ultraviolet Flux Suppression is a Common Feature of Type Ia Supernovae
We present ultraviolet (UV) to near-infrared (NIR) observations and analysis
of the nearby Type Ia supernova SN 2021fxy. Our observations include UV
photometry from Swift/UVOT, UV spectroscopy from HST/STIS, and high-cadence
optical photometry with the Swope 1-m telescope capturing intra-night rises
during the early light curve. Early colours show SN 2021fxy is the first
"shallow-silicon" (SS) SN Ia to follow a red-to-blue evolution, compared to
other SS objects which show blue colours from the earliest observations.
Comparisons to other spectroscopically normal SNe Ia with HST UV spectra reveal
SN 2021fxy is one of several SNe Ia with flux suppression in the mid-UV. These
SNe also show blue-shifted mid-UV spectral features and strong high-velocity Ca
II features. One possible origin of this mid-UV suppression is the increased
effective opacity in the UV due to increased line blanketing from high velocity
material, but differences in the explosion mechanism cannot be ruled out. Among
SNe Ia with mid-UV suppression, SNe 2021fxy and 2017erp show substantial
similarities in their optical properties despite belonging to different Branch
subgroups, and UV flux differences of the same order as those found between SNe
2011fe and 2011by. Differential comparisons to multiple sets of synthetic SN Ia
UV spectra reveal this UV flux difference likely originates from a luminosity
difference between SNe 2021fxy and 2017erp, and not differing progenitor
metallicities as suggested for SNe 2011by and 2011fe. These comparisons
illustrate the complicated nature of UV spectral formation, and the need for
more UV spectra to determine the physical source of SNe Ia UV diversity.Comment: 26 pages, 19 figures, 9 tables; submitted to MNRAS, posted after
receiving referee comment
SN 2021gno: a Calcium-rich transient with double-peaked light curves
We present extensive ultraviolet (UV) and optical photometric and optical
spectroscopic follow-up of supernova (SN)~2021gno by the "Precision
Observations of Infant Supernova Explosions" (POISE) project, starting less
than two days after the explosion. Given its intermediate luminosity, fast
photometric evolution, and quick transition to the nebular phase with spectra
dominated by [Ca~II] lines, SN~2021gno belongs to the small family of
Calcium-rich transients. Moreover, it shows double-peaked light curves, a
phenomenon shared with only four other Calcium-rich events. The projected
distance from the center of the host galaxy is not as large as other objects in
this family. The initial optical light-curve peaks coincide with a very quick
decline of the UV flux, indicating a fast initial cooling phase. Through
hydrodynamical modelling of the bolometric light curve and line velocity
evolution, we found that the observations are compatible with the explosion of
a highly-stripped massive star with an ejecta mass of and a
Ni mass of . The initial cooling phase (first light
curve peak) is explained by the presence of an extended circumstellar material
comprising with an extension of .
We discuss if hydrogen features are present in both maximum-light and nebular
spectra, and its implications in terms of the proposed progenitor scenarios for
Calcium-rich transients.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Discovery and Rapid Follow-up Observations of the Unusual Type II SN 2018ivc in NGC 1068
We present the discovery and high-cadence follow-up observations of SN 2018ivc, an unusual SNe II that
exploded in NGC 1068 (D = 10.1 Mpc). The light curve of SN 2018ivc declines piecewise-linearly, changing
slope frequently, with four clear slope changes in the first 30 days of evolution. This rapidly changing light
curve indicates that interaction between the circumstellar material and ejecta plays a significant role in the
evolution. Circumstellar interaction is further supported by a strong X-ray detection. The spectra are rapidly
evolving and dominated by hydrogen, helium, and calcium emission lines. We identify a rare high-velocity
emission-line feature blueshifted at ∼7800 - km s 1 (in Hα, Hβ, Pβ, Pγ, He I, and Ca II), which is visible from
day 18 until at least day 78 and could be evidence of an asymmetric progenitor or explosion. From the overall
similarity between SN 2018ivc and SN 1996al, the Hα equivalent width of its parent H II region, and
constraints from pre-explosion archival Hubble Space Telescope images, we find that the progenitor of
SN 2018ivc could be as massive as 52 M but is more likely <12 M. SN 2018ivc demonstrates the importance
of the early discovery and rapid follow-up observations of nearby supernovae to study the physics and
progenitors of these cosmic explosions
Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu
We present photometric and spectroscopic observations and analysis of
SN~2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova
(SN). SN~2021bxu is unique, showing a large initial decline in brightness
followed by a short plateau phase. With
during the plateau, it is at the lower end of the luminosity distribution of
stripped-envelope supernovae (SE-SNe) and shows a distinct 10 day plateau
not caused by H- or He-recombination. SN~2021bxu shows line velocities which
are at least slower than typical SE-SNe. It is
photometrically and spectroscopically similar to Type IIb SNe during the
photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find
that the bolometric light curve is best described by a composite model of shock
interaction between the ejecta and an envelope of extended material, combined
with a typical SN~IIb powered by the radioactive decay of Ni. The
best-fit parameters for SN~2021bxu include a Ni mass of , an ejecta mass of
, and an ejecta
kinetic energy of . From the fits to the properties of the extended material of
Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing
envelope mass. SN~2021bxu has on the low end compared to
SE-SNe and Ca-rich SNe in the literature, demonstrating that SN~2021bxu-like
events are rare explosions in extreme areas of parameter space. The progenitor
of SN~2021bxu is likely a low mass He star with an extended envelope.Comment: 18 pages, 15 figures, submitted to MNRA
A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone Can Explain Early Excess Blue Flux in Some Type Ia Supernovae
We present early-time photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2021aefx. The early-time u-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca ii H&K feature passing from the u to the B bands on the timescale of a few days. This effect could be dominant for all SNe Ia that have broad absorption features and early-time velocities over 25,000 km s−1. It is likely to be one of the main causes of early excess u-band flux in SNe Ia that have early-time high velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the u band. For objects that explode at lower velocities, and have a more structured shape in the early excess emission, there must also be an additional parameter producing the early-time diversity. More early-time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia
SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features
We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d ≈ 16.2 Mpc) starting 10 hr after explosion and continuing for ~300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT–discovered X-ray emission (L_x ≈ 10⁴¹ erg s⁻¹ at 3 days; L_x ∝ t⁻³), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≈ 500 km s⁻¹) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r (0.1–1) × 10¹⁷ cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of t_r = 13.4 ± 0.210 days and a peak B-band magnitude of M_B = −15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10⁻² M_⊙ of ⁵⁶Ni and ejected M_(ej) = (0.72 ± 0.040) M⊙ total with a kinetic energy E_k = (1.8 ± 0.10) × 10⁵⁰ erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (~10 M_⊙) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries