20 research outputs found
Early-time Spectropolarimetry of the Asymmetric Type II Supernova SN 2023ixf
We present six epochs of optical spectropolarimetry of the Type II supernova
(SN) 2023ixf ranging from 2 to 15 days after the explosion. Polarimetry
was obtained with the Kast double spectrograph on the Shane 3 m telescope at
Lick Observatory, representing the earliest such observations ever captured for
an SN. We observe a high continuum polarization %
on days +1.4 and +2.5 before dropping to 0.5 % on day +3.5, persisting at that
level up to day +14.5. Remarkably, this change coincides temporally with the
disappearance of highly ionized "flash" features. The decrease of the continuum
polarization is accompanied by a rotation of the polarization
position angle () as seen across the continuum. The early evolution of the
polarization may indicate different geometric configurations of the
electron-scattering atmosphere as seen before and after the disappearance of
the emission lines associated with highly-ionized species (e.g., He II, C IV, N
III), which are likely produced by elevated mass loss shortly prior to the SN
explosion. We interpret the rapid change of polarization and from days
+2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric
circumstellar material (CSM). The temporal evolution of the continuum
polarization and the is consistent with an aspherical SN explosion that
exhibits a distinct geometry compared to the CSM. The rapid follow-up
spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an
exceptionally asymmetric mass-loss process leading up to the explosion.Comment: Submitted to Ap
Scary Barbie: An Extremely Energetic, Long-Duration Tidal Disruption Event Candidate Without a Detected Host Galaxy at z = 0.995
We report multi-wavelength observations and characterization of the
ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka ``Barbie'') identified in
the alert stream of the Zwicky Transient Facility (ZTF) using a Recommender
Engine For Intelligent Transient Tracking (REFITT) filter on the ANTARES alert
broker. From a spectroscopically measured redshift of 0.995, we estimate a peak
observed pseudo-bolometric luminosity of log (L) = 45.7 from slowly fading ztf- and ztf-
light curves spanning over 1000 observer-frame days. The host galaxy is not
detected in archival Pan-STARRS observations ( mag), implying a lower
limit to the outburst amplitude of more than 5 mag relative to the quiescent
host galaxy. Optical spectra from Lick and Keck Observatories exhibit strong
emission lines with narrow cores from the H Balmer series and ultraviolet
semi-forbidden lines of Si III] 1892, C III] 1909, and C II]
2325. Typical nebular lines in AGN spectra from ions such as [O II]
and [O III] are not detected. These spectral features, along with the smooth
light curve that is unlike most AGN flaring activity, and the luminosity that
exceeds any observed or theorized supernova, lead us to conclude that AT
2021lwx is most likely an extreme tidal disruption event (TDE). Modeling of ZTF
photometry with MOSFiT suggests that the TDE was between a star and a supermassive black hole of mass
. Continued monitoring of the still-evolving light curve
along with deep imaging of the field once AT 2021lwx has faded can test this
hypothesis and potentially detect the host galaxy.Comment: 15 pages, 4 figures, 1 Table; Version as published in The
Astrophysical Journal Letters. Observations of AT 2021lwx published in the
paper can be found at https://bsubraya.github.io/research
Flight of the Bumblebee: the Early Excess Flux of Type Ia Supernova 2023bee revealed by , and Young Supernova Experiment Observations
We present high-cadence ultraviolet through near-infrared observations of the
Type Ia supernova (SN Ia) 2023bee in NGC~2708 ( Mpc), finding
excess flux in the first days after explosion relative to the expected
power-law rise from an expanding fireball. This deviation from typical behavior
for SNe Ia is particularly obvious in our 10-minute cadence light curve
and UV data. Compared to a few other normal SNe Ia with detected early
excess flux, the excess flux in SN 2023bee is redder in the UV and less
luminous. We present optical spectra of SN 2023bee, including two spectra
during the period where the flux excess is dominant. At this time, the spectra
are similar to those of other SNe Ia but with weaker Si II, C II and Ca II
absorption lines, perhaps because the excess flux creates a stronger continuum.
We compare the data to several theoretical models that have been proposed to
explain the early flux excess in SNe Ia. Interaction with either a nearby
companion star or close-in circumstellar material is expected to produce a
faster evolution than seen in the data. Radioactive material in the outer
layers of the ejecta, either from a double detonation explosion or simply an
explosion with a Ni clump near the surface, can not fully reproduce the
evolution either, likely due to the sensitivity of early UV observable to the
treatment of the outer part of ejecta in simulation. We conclude that no
current model can adequately explain the full set of observations. We find that
a relatively large fraction of nearby, bright SNe Ia with high-cadence
observations have some amount of excess flux within a few days of explosion.
Considering potential asymmetric emission, the physical cause of this excess
flux may be ubiquitous in normal SNe Ia.Comment: 21 pages, 12 figures. Accepted by the astrophysical journa
SN 2022oqm: A Multi-peaked Calcium-rich Transient from a White Dwarf Binary Progenitor System
We present the photometric and spectroscopic evolution of SN 2022oqm, a
nearby multi-peaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN
2022oqm was detected 19.9 kpc from its host galaxy, the face-on spiral galaxy
NGC 5875. Extensive spectroscopic coverage reveals a hot (T >= 40,000 K)
continuum and carbon features observed ~1 day after discovery, SN Ic-like
photospheric-phase spectra, and strong forbidden calcium emission starting 38
days after discovery. SN 2022oqm has a relatively high peak luminosity (MB =
-17 mag) for CaRTs, making it an outlier in the population. We determine that
three power sources are necessary to explain SN 2022oqm's light curve, with
each power source corresponding to a distinct peak in its light curve. The
first peak of the light curve is powered by an expanding blackbody with a power
law luminosity, consistent with shock cooling by circumstellar material.
Subsequent peaks are powered by a double radioactive decay model, consistent
with two separate sources of photons diffusing through an optically thick
ejecta. From the optical light curve, we derive an ejecta mass and 56Ni mass of
~0.89 solar masses and ~0.09 solar masses, respectively. Detailed spectroscopic
modeling reveals ejecta that is dominated by intermediate-mass elements, with
signs that Fe-peak elements have been well-mixed. We discuss several physical
origins for SN 2022oqm and favor a white dwarf progenitor model. The inferred
ejecta mass points to a surprisingly massive white dwarf, challenging models of
CaRT progenitors.Comment: 33 pages, 17 figures, 5 tables, Submitted to Ap
Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq
We present optical, infrared, ultraviolet, and radio observations of SN
2022xkq, an underluminous fast-declining type Ia supernova (SN Ia) in NGC 1784
( Mpc), from to 180 days after explosion. The
high-cadence observations of SN 2022xkq, a photometrically transitional and
spectroscopically 91bg-like SN Ia, cover the first days and weeks following
explosion which are critical to distinguishing between explosion scenarios. The
early light curve of SN 2022xkq has a red early color and exhibits a flux
excess which is more prominent in redder bands; this is the first time such a
feature has been seen in a transitional/91bg-like SN Ia. We also present 92
optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion
in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a
long-lived C I 1.0693 m feature which persists until 5 days post-maximum.
We also detect C II 6580 in the pre-maximum optical spectra. These
lines are evidence for unburnt carbon that is difficult to reconcile with the
double detonation of a sub-Chandrasekhar mass white dwarf. No existing
explosion model can fully explain the photometric and spectroscopic dataset of
SN 2022xkq, but the considerable breadth of the observations is ideal for
furthering our understanding of the processes which produce faint SNe Ia.Comment: 38 pages, 16 figures, accepted for publication in ApJ, the figure 15
input models and synthetic spectra are now available at
https://zenodo.org/record/837925
Flight of the bumblebee : the early excess flux of Type Ia supernova 2023bee revealed by TESS, Swift, and Young Supernova Experiment observations
We present high-cadence ultraviolet through near-infrared observations of the Type Ia supernova (SN Ia) 2023bee at D = 32 ± 3 Mpc, finding excess flux in the first days after explosion, particularly in our 10 minutes cadence TESS light curve and Swift UV data. Compared to a few other normal SNe Ia with early excess flux, the excess flux in SN 2023bee is redder in the UV and less luminous. We present optical spectra of SN 2023bee, including two spectra during the period where the flux excess is dominant. At this time, the spectra are similar to those of other SNe Ia but with weaker Si ii, C ii, and Ca ii absorption lines, perhaps because the excess flux creates a stronger continuum. We compare the data to several theoretical models on the origin of early excess flux in SNe Ia. Interaction with either the companion star or close-in circumstellar material is expected to produce a faster evolution than observed. Radioactive material in the outer layers of the ejecta, either from double detonation explosion or from a 56Ni clump near the surface, cannot fully reproduce the evolution either, likely due to the sensitivity of early UV observable to the treatment of the outer part of ejecta in simulation. We conclude that no current model can adequately explain the full set of observations. We find that a relatively large fraction of nearby, bright SNe Ia with high-cadence observations have some amount of excess flux within a few days of explosion. Considering potential asymmetric emission, the physical cause of this excess flux may be ubiquitous in normal SNe Ia
Disproportionate Learning Disparities Among Student of Color During the COVID-19 Pandemic
This presentation will address initial research on the disproportionate impact of the COVID-19 pandemic on students of color in K-12 education. An important question as COVID-19 has occurred is how it has impacted various diverse communities in many areas, such as health, employment, and education. There is much variability in the United States in the resources available to various communities to support education, and as the pandemic hit it is possible that communities and school districts with different resources impacted the learning experiences of students. Reports of communities of color facing higher exposure and death to the COVID-19 pandemic suggests that communities that faced health disparities prior to the COVID-19 pandemic will also face disproportioned health disparities (Hopper et al., 2020). It is also possible that students of color who faced structural inequalities prior to the pandemic will face higher rates of school disengagement due to the disparities amplified by the pandemic (Jones et al., 2021). For example, Haderlein and colleagues (2021) explain that there is a difference in access to technology, instruction, instructional supports, services, and preferences for in-person learning among various groups (race/ethnicity, income, urbanicity, partisanship, and grade level). This presentation will provide an overview of what we have learned of the effects of the pandemic and how it has impacted the school experiences and learning for low-income students of color in K-12 education.
College of the Sciences Presentation Award Winner
The COVID Slide: Learning Loss during the COVID-19 Pandemic
This presentation will address the impact of the COVID-19 pandemic on K-12 students in the United States. Previous research has found that during extended times away from school – such as summer vacations – many K-12 students lose proficiency in important academic skills such as language, reading, writing, and math. The process of learning loss over the summer has been termed the Summer Slide. With the extended school closures and difficulties with accessing online instruction during the COVID-19 pandemic, many researchers are concerned with a new COVID Slide (Kuhfeld et al., 2020). There were numerous disparities in learning models across states, communities, and school districts, which may have an impact on learning outcomes. In addition, initial research suggests that there has been a disproportional impact on BIPOC and low-income students in regards to learning loss when compared to wealthier white counterparts, with months of learning loss across all demographics (Dorn et al., 2021). Research has also indicated that in-person education varied from state-to-state, and that disparities in access to in-person, or even high-quality virtual learning has led to learning loss and worsening mental health in students (Oster et al., 2021). Washington state has experienced a dramatic increase in high school students that have earned failing or no-credit grades. Coupled with falling enrollment rates in postsecondary institutions, these implications could have long-term effects on student livelihood and satisfaction, as well as reveal that students may be feeling less prepared in continuing their education or have not met high school graduation requirements (Kwakye & Kibort-Crocker, 2021). The COVID-19 pandemic, and the consequent COVID Slide , broadly had negative outcomes for student learning and exacerbated existing inequities in the form of student achievement and opportunity
"Communicate to vaccinate" : the development of a taxonomy of communication interventions to improve routine childhood vaccination
Vaccination is a cost-effective public health measure and is central to the Millennium Development Goal of reducing child mortality. However, childhood vaccination coverage remains sub-optimal in many settings. While communication is a key feature of vaccination programmes, we are not aware of any comprehensive approach to organising the broad range of communication interventions that can be delivered to parents and communities to improve vaccination coverage. Developing a classification system (taxonomy) organised into conceptually similar categories will aid in: understanding the relationships between different types of communication interventions; facilitating conceptual mapping of these interventions; clarifying the key purposes and features of interventions to aid implementation and evaluation; and identifying areas where evidence is strong and where there are gaps. This paper reports on the development of the 'Communicate to vaccinate' taxonomy.; The taxonomy was developed in two stages. Stage 1 included: 1) forming an advisory group; 2) searching for descriptions of interventions in trials (CENTRAL database) and general health literature (Medline); 3) developing a sampling strategy; 4) screening the search results; 5) developing a data extraction form; and 6) extracting intervention data. Stage 2 included: 1) grouping the interventions according to purpose; 2) holding deliberative forums in English and French with key vaccination stakeholders to gather feedback; 3) conducting a targeted search of grey literature to supplement the taxonomy; 4) finalising the taxonomy based on the input provided.; The taxonomy includes seven main categories of communication interventions: inform or educate, remind or recall, teach skills, provide support, facilitate decision making, enable communication and enhance community ownership. These categories are broken down into 43 intervention types across three target groups: parents or soon-to-be-parents; communities, community members or volunteers; and health care providers.; Our taxonomy illuminates and organises this field and identifies the range of available communication interventions to increase routine childhood vaccination uptake. We have utilised a variety of data sources, capturing information from rigorous evaluations such as randomised trials as well as experiences and knowledge of practitioners and vaccination stakeholders. The taxonomy reflects current public health practice and can guide the future development of vaccination programmes
Keck Infrared Transient Survey Data Release 1
We present the first data release from the Keck Infrared Transient Survey (KITS), a NASA Key Strategic Mission Support program to obtain near-infrared (NIR) spectra of astrophysical transients of all types. This data release consists of 105 NIR spectra of 50 transients. As we are entering a new era of infrared astronomy with the James Webb Space Telescope (JWST) and the upcoming Nancy Grace Roman Space Telescope (Roman), KITS provides a large, publicly available sample of IR spectroscopy for a wide range of transients. These data will be essential to search JWST images for stellar explosions of the first stars and to plan an effective Roman SN Ia cosmology survey, both key science objectives for mission success. The first data release represents the first semester, which is one third of the full survey. We systematically observed three samples: a flux-limited sample that includes all transients brighter than 17~mag in a red optical band (usually ZTF r or ATLAS o bands); a volume-limited sample including all transients within redshift z < 0.01; and an SN Ia sample targeting objects at phases and light-curve parameters that had scant existing NIR data in the literature. Please see the accompanying paper where we describe our observing procedures and data reduction using an automated pipeline pypeit with minimal human interaction to ensure reproducibility. In this dataset, we provide telluric-corrected spectra of the transient in CSV format. We also provide one-dimensional extracted spectra of transients and telluric standard stars in FITS format from pypeit. Users can use these intermediate data products to redo telluric correction if desired