32 research outputs found
TESS Shines Light on the Origin of the Ambiguous Nuclear Transient ASASSN-18el
We analyze high-cadence data from the Transiting Exoplanet Survey Satellite
(TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical
changing-look phenomenon in ASASSN-18el has been argued to be due to either a
drastic change in the accretion rate of the existing active galactic nucleus
(AGN) or the result of a tidal disruption event (TDE). Throughout the TESS
observations, short-timescale stochastic variability is seen, consistent with
an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW)
model and recover a rest-frame variability amplitude of mJy and a rest-frame timescale of days.
We find that the estimated for ASASSN-18el is broadly consistent
with an apparent relationship between the DRW timescale and central
supermassive black hole mass. The large-amplitude stochastic variability of
ASASSN-18el, particularly during late stages of the flare, suggests that the
origin of this ANT is likely due to extreme AGN activity rather than a TDE.Comment: 13 pages, 8 figures. Will be submitted to AAS journals. Comments
welcom
ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003
We present the discovery that ASASSN-14ko is a periodically flaring AGN at
the center of the galaxy ESO 253-G003. At the time of its discovery by the
All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a
supernova close to the nucleus. The subsequent six years of V- and g-band
ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at
regular intervals. The seventeen observed outbursts show evidence of a
decreasing period over time, with a mean period of days
and a period derivative of . The most recent
outburst in May 2020, which took place as predicted, exhibited spectroscopic
changes during the rise and a had a UV bright, blackbody spectral energy
distribution similar to tidal disruption events (TDEs). The X-ray flux
decreased by a factor of 4 at the beginning of the outburst and then returned
to its quiescent flux after ~8 days. TESS observed an outburst during Sectors
4-6, revealing a rise time of days in the optical and a decline
that is best fit with an exponential model. We discuss several possible
scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a
repeated partial TDE. The next outbursts should peak in the optical on UT
2020-09-7.41.1 and UT 2020-12-26.51.4.Comment: 26 pages, 15 figures, 7 tables. Will be submitted to ApJ. The latest
flare is currently ongoing, as we predicte
SN 2022crv: IIb, Or Not IIb: That is the Question
We present optical and near-infrared observations of SN~2022crv, a stripped
envelope supernova in NGC~3054, discovered within 12 hrs of explosion by the
Distance Less Than 40 Mpc Survey. We suggest SN~2022crv is a transitional
object on the continuum between SNe Ib and SNe IIb. A high-velocity hydrogen
feature (20,000 -- 16,000 ) was conspicuous in
SN~2022crv at early phases, and then quickly disappeared around maximum light.
By comparing with hydrodynamic modeling, we find that a hydrogen envelope of
\msun{} can reproduce the behaviour of the hydrogen feature
observed in SN~2022crv. The early light curve of SN~2022crv did not show
envelope cooling emission, implying that SN~2022crv had a compact progenitor
with extremely low amount of hydrogen. The analysis of the nebular spectra
shows that SN~2022crv is consistent with the explosion of a He star with a
final mass of 4.5 -- 5.6 \msun{} that has evolved from a 16 -- 22
\msun{} zero-age main sequence star in a binary system with about 1.0 -- 1.7
\msun{} of oxygen finally synthesized in the core. The high metallicity at the
supernova site indicates that the progenitor experienced a strong stellar wind
mass loss. In order to retain a small amount of residual hydrogen at such a
high metallicity, the initial orbital separation of the binary system is likely
larger than 1000~. The near-infrared spectra of SN~2022crv
show a unique absorption feature on the blue side of He I line at
1.005~m. This is the first time that such a feature has been
observed in a Type Ib/IIb, and could be due to \ion{Sr}{2}. Further detailed
modelling on SN~2022crv can shed light on the progenitor and the origin of the
mysterious absorption feature in the near infrared.Comment: 33 pages, 23 figures, 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
Modeling Fluorescence Observables, Particularly for FRET Experiments, using Markov Chain Analysis of Molecular Dynamics and Quantum Mechanics Simulations
We present a new method for simulating fluorescence observables, particularly those related to bulk and single-molecule fluorescence-detected resonance energy transfer (FRET) experiments. In this method, a molecular dynamics (MD) simulation is used to sample configuration space and quantum mechanics (QM) calculations are used to estimate the electronic coupling between the donor and acceptor probes for snapshots along the MD trajectory. A Markov chain method is used to sample the resulting electronic coupling trajectory allowing accurate simulation of any desired fluorescence observables, such as FRET efficiency histograms or time-resolved donor fluorescence decays. The Markov chain results will be compared with the results of simple histogram and averaging schemes showing that the Markov chain is the only one that yields realistic results in well known examples such as the rapid diffusion limit. This combination of computational methods also avoids some pitfalls of traditional FRET analysis such as the kappa-squared and the ideal dipole approximations. Because the simulation results can be compared directly with experimental observables, this method may allow more detail to be derived from experiment than is traditionally possible.
3037-PosB80
Modeling Fluorescence Observables, Particularly for FRET Experiments, using Markov Chain Analysis of Molecular Dynamics and Quantum Mechanics Simulations
SCAT Uncovers ATLAS's First Tidal Disruption Event ATLAS18mlw: A Faint and Fast TDE in a Quiescent Balmer Strong Galaxy
We present the discovery that ATLAS18mlw was a tidal disruption event (TDE)
in the galaxy WISEA J073544.83+663717.3, at a distance of 334 Mpc. Initially
discovered by the Asteroid Terrestrial Impact Last Alert System (ATLAS) on 2018
March 17.3, the TDE nature of the transient was uncovered only recently with
the re-reduction of a SuperNova Integral Field Spectrograph (SNIFS) spectrum.
This spectrum, taken by the Spectral Classification of Astronomical Transients
(SCAT) survey, shows a strong blue continuum and a broad H emission
line. Here we present roughly six years of optical survey photometry beginning
before the TDE to constrain AGN activity, optical spectroscopy of the
transient, and a detailed study of the host galaxy properties through analysis
of archival photometry and a host spectrum. ATLAS18mlw was detected in
ground-based light curves for roughly two months. From a blackbody fit to the
transient spectrum and bolometric correction of the optical light curve, we
conclude that ATLAS18mlw is likely a low-luminosity TDE with a peak luminosity
of log(L [erg s]) = . The TDE classification is further
supported by the quiescent Balmer strong nature of the host galaxy. We also
calculated the TDE decline rate from the bolometric light curve and find
dex, making ATLAS18mlw a member of the growing
class of "faint and fast" TDEs with low peak luminosities and fast decline
rates.Comment: 14 pages, 6 figures, 1 table. Will be submitted to AAS journals.
Comments welcom
The Rise and Fall of ASASSN-18pg:Following a TDE from Early to Late Times
We present nearly 500 days of observations of the tidal disruption event
ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak
light. Our dataset includes X-ray, UV, and optical photometry, optical
spectroscopy, radio observations, and the first published spectropolarimetric
observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the
All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of
Mpc, and with a peak UV magnitude of it is both one of the nearest
and brightest TDEs discovered to-date. The photometric data allow us to track
both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg
peaked at a luminosity of erg s, and its
late-time evolution is shallower than a flux power-law
model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited
Balmer lines and spectroscopic features consistent with Bowen fluorescence
prior to peak which remained detectable for roughly 225 days after peak.
Analysis of the two-component H profile indicates that, if they are the
result of reprocessing of emission from the accretion disk, the different
spectroscopic lines may be coming from regions between and
light-days from the black hole. No X-ray emission is detected from the TDE and
there is no evidence of a jet or strong outflow detected in the radio. Our
spectropolarimetric observations give no strong evidence for significant
asphericity in the emission region, with the emission region having an axis
ratio of at least .Comment: 22 pages, 11 figures, 5 tables. Submitted to ApJ. A machine-readable
table containing the host-subtracted photometry presented in this manuscript
is included as an ancillary fil
SN 2022crv: IIb, Or Not IIb: That is the Question
International audienceWe present optical and near-infrared observations of SN~2022crv, a stripped envelope supernova in NGC~3054, discovered within 12 hrs of explosion by the Distance Less Than 40 Mpc Survey. We suggest SN~2022crv is a transitional object on the continuum between SNe Ib and SNe IIb. A high-velocity hydrogen feature (20,000 --16,000 ) was conspicuous in SN~2022crv at early phases, and then quickly disappeared around maximum light. By comparing with hydrodynamic modeling, we find that a hydrogen envelope of \msun can reproduce the behaviour of the hydrogen feature observed in SN~2022crv. The early light curve of SN~2022crv did not show envelope cooling emission, implying that SN~2022crv had a compact progenitor with extremely low amount of hydrogen. The analysis of the nebular spectra shows that SN~2022crv is consistent with the explosion of a He star with a final mass of 4.5 -- 5.6 \msun that has evolved from a 16 -- 22 \msun zero-age main sequence star in a binary system with about 1.0 -- 1.7 \msun of oxygen finally synthesized in the core. The high metallicity at the supernova site indicates that the progenitor experienced a strong stellar wind mass loss. In order to retain a small amount of residual hydrogen at such a high metallicity, the initial orbital separation of the binary system is likely larger than 1000~. The near-infrared spectra of SN~2022crv show a unique absorption feature on the blue side of He I line at 1.005~m. This is the first time that such a feature has been observed in a Type Ib/IIb, and could be due to \ion{Sr}2. Further detailed modelling on SN~2022crv can shed light on the progenitor and the origin of the mysterious absorption feature in the near infrared