77 research outputs found
High resolution spectroscopy of SN~2023ixf's first week: Engulfing the Asymmetric Circumstellar Material
We present a series of high-resolution echelle spectra of SN~2023ixf in M101,
obtained nightly during the first week or so after discovery using PEPSI on the
LBT. NaID absorption in these spectra indicates a host reddening of
=0.031~mag and a systemic velocity of 7~km~s relative to the
average redshift of M101. Dramatic changes are seen in in the strength and
shape of strong emission lines emitted by CSM, including HeII4686,
CIV5801,5811, H, and NIV7109,7123. In general, these narrow lines
broaden to become intermediate-width lines before disappearing from the
spectrum within a few days, indicating a limited extent to the dense CSM of
around 20-30 AU (or \la10 cm). H persists in the spectrum
for about a week as an intermediate-width emission line with P~Cyg absorption
at 700-1300 km s arising in the post-shock shell of swept-up CSM. Early
narrow emission lines are blueshifted and indicate an expansion speed in the
pre-shock CSM of about 115 km s, but with even broader emission in
higher ionization lines. This is faster than the normal winds of red
supergiants, suggesting some mode of eruptive mass loss from the progenitor or
radiative acceleration of the CSM. A lack of narrow blueshifted absorption
suggests that most of the CSM is not along our line of sight. This and several
other clues indicate that the CSM of SN~2023ixf is significantly aspherical. We
find that CSM lines disappear after a few days because the asymmetric CSM is
engulfed by the SN photosphere.Comment: Accepted verion, 8/1
The slow demise of the long-lived SN 2005ip
The Type IIn supernova (SN IIn) 2005ip is one of the most well-studied and long-lasting examples of an SN interacting with its circumstellar environment. The optical light curve plateaued at a nearly constant level for more than five years, suggesting ongoing shock interaction with an extended and clumpy circumstellar medium (CSM). Here, we present continued observations of the SN from similar to 1000 to 5000 d post-explosion at all wavelengths, including X-ray, ultraviolet, near-infrared (NIR), and mid-infrared. The UV spectra probe the pre-explosion mass loss and show evidence for CNO processing. From the bolometric light curve, we find that the total radiated energy is in excess of 10(50) erg, the progenitor star's pre-explosion mass-loss rate was greater than or similar to 1 x 10(-2)M(circle dot) yr(-1), and the total mass lost shortly before explosion was greater than or similar to 1M(circle dot), though the mass lost could have been considerably larger depending on the efficiency for the conversion of kinetic energy to radiation. The ultraviolet through NIR spectrum is characterized by two high-density components, one with narrow high-ionization lines, and one with broader low-ionization HI, HeI, [OI], MgII, and Fe II lines. The rich Fe II spectrum is strongly affected by Ly alpha fluorescence, consistent with spectral modelling. Both the Balmer and He I lines indicate a decreasing CSM density during the late interaction period. We find similarities to SN 1988Z, which shows a comparable change in spectrum at around the same time during its very slow decline. These results suggest that, at long last, the shock interaction in SN 2005ip may finally be on the decline
The Properties of Fast Yellow Pulsating Supergiants: FYPS Point the Way to Missing Red Supergiants
Fast yellow pulsating supergiants (FYPS) are a recently-discovered class of
evolved massive pulsator. As candidate post-red supergiant objects, and one of
the few classes of pulsating evolved massive stars, these objects have
incredible potential to change our understanding of the structure and evolution
of massive stars. Here we examine the lightcurves of a sample of 126 cool
supergiants in the Magellanic Clouds observed by the Transiting Exoplanet
Survey Satellite (\tess~) in order to identify pulsating stars. After making
quality cuts and filtering out contaminant objects, we examine the distribution
of pulsating stars in the Hertzprung-Russel (HR) diagram, and find that FYPS
occupy a region above . This luminosity boundary
corresponds to stars with initial masses of 18-20 , consistent
with the most massive red supergiant progenitors of supernovae (SNe) II-P, as
well as the observed properties of SNe IIb progenitors. This threshold is in
agreement with the picture that FYPS are post-RSG stars. Finally, we
characterize the behavior of FYPS pulsations as a function of their location in
the HR diagram. We find low frequency pulsations at higher effective
temperatures, higher frequency pulsations at lower temperatures, with a
transition between the two behaviors at intermediate temperatures. The observed
properties of FYPS make them fascinating objects for future theoretical study.Comment: Consistent with published version which contains significantly
improved detection and rejection of contaminant objects. Comments welcom
Ultraviolet Detection of the Binary Companion to the Type IIb SN 2001ig
We present HST/WFC3 ultraviolet imaging in the F275W and F336W bands of the
Type IIb SN 2001ig at an age of more than 14 years. A clear point source is
detected at the site of the explosion having and
mag. Despite weak constraints on both the
distance to the host galaxy NGC 7424 and the line-of-sight reddening to the
supernova, this source matches the characteristics of an early B-type main
sequence star having K and . A BPASS v2.1 binary evolution model, with
primary and secondary masses of 13 M and 9 M respectively,
is found to resemble simultaneously in the Hertzsprung-Russell diagram both the
observed location of this surviving companion, and the primary star
evolutionary endpoints for other Type IIb supernovae. This same model exhibits
highly variable late-stage mass loss, as expected from the behavior of the
radio light curves. A Gemini/GMOS optical spectrum at an age of 6 years reveals
a narrow He II emission line, indicative of continuing interaction with a dense
circumstellar medium at large radii from the progenitor. We review our findings
on SN 2001ig in the context of binary evolution channels for stripped-envelope
supernovae. Owing to the uncrowded nature of its environment in the
ultraviolet, this study of SN 2001ig represents one of the cleanest detections
to date of a surviving binary companion to a Type IIb supernova.Comment: 8 pages, 3 figures. Resubmitted to ApJ after minor changes requested
by refere
Uncovering the Putative B-star Binary Companion of the SN 1993J Progenitor
The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 M_☉ and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences
JWST Imaging of the Cartwheel Galaxy Reveals Dust Associated with SN 2021afdx
We present near- and mid-infrared (0.9-18 m) photometry of supernova
(SN) 2021afdx, which was imaged serendipitously with the James Webb Space
Telescope (JWST) as part of its Early Release Observations of the Cartwheel
Galaxy. Our ground-based optical observations show it is likely to be a Type
IIb SN, the explosion of a yellow supergiant, and its infrared spectral energy
distribution (SED) 200 days after explosion shows two distinct
components, which we attribute to hot ejecta and warm dust. By fitting models
of dust emission to the SED, we derive a dust mass of , which is the highest yet observed in a Type IIb SN
but consistent with other Type II SNe observed by the Spitzer Space Telescope.
We also find that the radius of the dust is significantly larger than the
radius of the ejecta, as derived from spectroscopic velocities during the
photospheric phase, which implies that we are seeing an infrared echo off of
preexisting dust in the progenitor environment, rather than dust newly formed
by the SN. Our results show the power of JWST to address questions of dust
formation in SNe, and therefore the presence of dust in the early universe,
with much larger samples than have been previously possible.Comment: updated to match accepted versio
AT 2021loi: A Bowen Fluorescence Flare with a Rebrightening Episode, Occurring in a Previously-Known AGN
AT 2021loi is an optical-ultraviolet transient located at the center of its
host galaxy. Its spectral features identify it as a member of the ``Bowen
Fluorescence Flare'' (BFF) class. The first member of this class was considered
to be related to a tidal disruption event, but enhanced accretion onto an
already active supermassive black hole was suggested as an alternative
explanation. AT 2021loi, having occurred in a previously-known unobscured AGN,
strengthens the latter interpretation. Its light curve is similar to those of
previous BFFs, showing a rebrightening approximately one year after the main
peak (which was not explicitly identified, but might be the case, in all
previous BFFs). An emission feature around 4680 A, seen in the pre-flare
spectrum, strengthens by a factor of 2 around the optical peak of the
flare, and is clearly seen as a double peaked feature then, suggesting a blend
of NIII with HeII as its origin. The appearance of
OIII 3133 and possible NIII (blended with
H) during the flare further support a Bowen Fluorescence
classification. Here, we present ZTF, ATLAS, Keck, Las Cumbres Observatory,
NEOWISE-R, , AMI and VLA observations of AT 2021loi, making it one of
the best observed BFFs to date. AT 2021loi thus provides some clarity on the
nature of BFFs but also further demonstrates the diversity of nuclear
transients.Comment: Submitted to ApJ. This version addresses comments from the refere
What Powers the 3000-Day Light Curve of SN 2006gy?
SN 2006gy was the most luminous supernova (SN) ever observed at the time of its discovery and the first of the newly defined class of superluminous supernovae (SLSNe). The extraordinary energetics of SN 2006gy and all SLSNe (>10^(51) erg) require either atypically large explosion energies (e.g. pair-instability explosion) or the efficient conversion of kinetic into radiative energy (e.g. shock interaction). The mass-loss characteristics can therefore offer important clues regarding the progenitor system. For the case of SN 2006gy, both a scattered and thermal light echo from circumstellar material (CSM) have been reported at later epochs (day ∼800), ruling out the likelihood of a pair-instability event and leading to constraints on the characteristics of the CSM. Owing to the proximity of the SN to the bright host-galaxy nucleus, continued monitoring of the light echo has not been trivial, requiring the high resolution offered by the Hubble Space Telescope (HST) or ground-based adaptive optics (AO). Here, we report detections of SN 2006gy using HST and Keck AO at ∼3000 d post-explosion and consider the emission mechanism for the very late-time light curve. While the optical light curve and optical spectral energy distribution are consistent with a continued scattered-light echo, a thermal echo is insufficient to power the K′-band emission by day 3000. Instead, we present evidence for late-time infrared emission from dust that is radiatively heated by CSM interaction within an extremely dense dust shell, and we consider the implications on the CSM characteristics and progenitor system
A Multi-Wavelength View on the Rapidly-Evolving Supernova 2018ivc: An Analog of SN IIb 1993J but Powered Primarily by Circumstellar Interaction
SN 2018ivc is an unusual type II supernova (SN II). It is a variant of SNe
IIL, which might represent a transitional case between SNe IIP with a massive
H-rich envelope, and IIb with only a small amount of the H-rich envelope.
However, SN 2018ivc shows an optical light curve evolution more complicated
than canonical SNe IIL. In this paper, we present the results of prompt
follow-up observations of SN 2018ivc with the Atacama Large
Millimeter/submillimeter Array (ALMA). Its synchrotron emission is similar to
that of SN IIb 1993J, suggesting that it is intrinsically an SN IIb-like
explosion of a He star with a modest (~0.5 - 1 Msun) extended H-rich envelope.
Its radio, optical, and X-ray light curves are explained primarily by the
interaction between the SN ejecta and the circumstellar material (CSM); we thus
suggest that it is a rare example (and the first involving the `canonical' SN
IIb ejecta) for which the multi-wavelength emission is powered mainly by the
SN-CSM interaction. The inner CSM density, reflecting the progenitor activity
in the final decade, is comparable to that of SN IIb 2013cu that showed a flash
spectral feature. The outer CSM density, and therefore the mass-loss rate in
the final ~200 years, is larger than that of SN 1993J by a factor of ~5. We
suggest that SN 2018ivc represents a missing link between SNe IIP and IIb/Ib/Ic
in the binary evolution scenario.Comment: 31 pages, 14 figures, 3 tables. Accepted for publication in Ap
SAGUARO: Time-domain Infrastructure for the Fourth Gravitational-wave Observing Run and Beyond
We present upgraded infrastructure for Searches after Gravitational Waves
Using ARizona Observatories (SAGUARO) during LIGO, Virgo, and KAGRA's fourth
gravitational-wave (GW) observing run (O4). These upgrades implement many of
the lessons we learned after a comprehensive analysis of potential
electromagnetic counterparts to the GWs discovered during the previous
observing run. We have developed a new web-based target and observation manager
(TOM) that allows us to coordinate sky surveys, vet potential counterparts, and
trigger follow-up observations from one centralized portal. The TOM includes
software that aggregates all publicly available information on the light curves
and possible host galaxies of targets, allowing us to rule out potential
contaminants like active galactic nuclei, variable stars, solar-system objects,
and preexisting supernovae, as well as to assess the viability of any plausible
counterparts. We have also upgraded our image-subtraction pipeline by
assembling deeper reference images and training a new neural network-based
real-bogus classifier. These infrastructure upgrades will aid coordination by
enabling the prompt reporting of observations, discoveries, and analysis to the
GW follow-up community, and put SAGUARO in an advantageous position to discover
kilonovae in the remainder of O4 and beyond. Many elements of our open-source
software stack have broad utility beyond multimessenger astronomy, and will be
particularly relevant in the "big data" era of transient discoveries by the
Vera C. Rubin Observatory.Comment: submitted to AAS Journal
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