ABSTRACT
We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. ...Our extensive multiwavelength follow-up spans ∼900 d, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad ∼2000 km s−1 hydrogen, He i, and O i emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 × 1050 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies.
Context.
We present observations of ZTF20aatqesi (SN 2020faa). This Type II supernova (SN) displays a luminous light curve (LC) that started to rebrighten from an initial decline. We investigate this ...in relation to the famous SN iPTF14hls, which received a great deal of attention and multiple interpretations in the literature, but whose nature and source of energy still remain unknown.
Aims.
We demonstrate the great similarity between SN 2020faa and iPTF14hls during the first 6 months, and use this comparison to forecast the evolution of SN 2020faa and to reflect on the less well observed early evolution of iPTF14hls.
Methods.
We present and analyse our observational data, consisting mainly of optical LCs from the Zwicky Transient Facility in the
gri
bands and of a sequence of optical spectra. We construct colour curves and a bolometric lc, and we compare ejecta-velocity and black-body radius evolutions for the two supernovae (SNe) and for more typical Type II SNe.
Results.
The LCs show a great similarity with those of iPTF14hls over the first 6 months in luminosity, timescale, and colour. In addition, the spectral evolution of SN 2020faa is that of a Type II SN, although it probes earlier epochs than those available for iPTF14hls.
Conclusions.
The similar LC behaviour is suggestive of SN 2020faa being a new iPTF14hls. We present these observations now to advocate follow-up observations, since most of the more striking evolution of SN iPTF14hls came later, with LC undulations and a spectacular longevity. On the other hand, for SN 2020faa we have better constraints on the explosion epoch than we had for iPTF14hls, and we have been able to spectroscopically monitor it from earlier phases than was done for the more famous sibling.
ABSTRACT
We present results from extensive broadband follow-up of GRB 210204A over the period of 30 d. We detect optical flares in the afterglow at 7.6 × 105 s and 1.1 × 106 s after the burst: the ...most delayed flaring ever detected in a GRB afterglow. At the source redshift of 0.876, the rest-frame delay is 5.8 × 105 s (6.71 d). We investigate possible causes for this flaring and conclude that the most likely cause is a refreshed shock in the jet. The prompt emission of the GRB is within the range of typical long bursts: it shows three disjoint emission episodes, which all follow the typical GRB correlations. This suggests that GRB 210204A might not have any special properties that caused late-time flaring, and the lack of such detections for other afterglows might be resulting from the paucity of late-time observations. Systematic late-time follow-up of a larger sample of GRBs can shed more light on such afterglow behaviour. Further analysis of the GRB 210204A shows that the late-time bump in the light curve is highly unlikely due to underlying SNe at redshift (z) = 0.876 and is more likely due to the late-time flaring activity. The cause of this variability is not clearly quantifiable due to the lack of multiband data at late-time constraints by bad weather conditions. The flare of GRB 210204A is the latest flare detected to date.
The fraction of core-collapse supernovae (CCSNe) occurring in the central regions of galaxies is not well constrained at present. This is partly because large-scale transient surveys operate at ...optical wavelengths, making it challenging to detect transient sources that occur in regions susceptible to high extinction factors. Here we present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG) NGC 3256. The first, SN 2018ec, was discovered using the ESO HAWK-I/GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of
A
V
= 2.1
−0.1
+0.3
mag. The second, AT 2018cux, was discovered during the course of follow-up observations of SN 2018ec, and is consistent with a subluminous Type IIP classification with an
A
V
= 2.1 ± 0.4 mag of host extinction. A third CCSN, PSN J10275082−4354034 in NGC 3256, was previously reported in 2014, and we recovered the source in late-time archival
Hubble
Space Telescope imaging. Based on template light curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of
A
V
= 0.3
−0.3
+0.4
mag. We also extend our study with follow-up data of the recent Type IIb SN 2019lqo and Type Ib SN 2020fkb that occurred in the LIRG system Arp 299 with host extinctions of
A
V
= 2.1
−0.3
+0.1
and
A
V
= 0.4
−0.2
+0.1
mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, that there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb/Ib/Ic/Ibn) and 15 H-rich (Type II/IIn) CCSNe have different underlying progenitor age distributions, with the H-poor progenitors being younger at 3
σ
significance. However, we note that the currently available sample sizes of CCSNe and host LIRGs are small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages.
Context.
Type Ibn supernovae (SNe Ibn) are a rare class of stripped envelope supernovae interacting with a helium-rich circumstellar medium (CSM). The majority of the SNe Ibn reported in the ...literature display a surprising homogeneity in their fast-evolving lightcurves and are typically found in actively starforming spiral galaxies.
Aims.
We present the discovery and the study of SN 2020bqj (ZTF20aalrqbu), a SN Ibn with a long-duration peak plateau lasting 40 days and hosted by a faint low-mass galaxy. We aim to explain its peculiar properties using an extensive photometric and spectroscopic data set.
Methods.
We compare the photometric and spectral evolution of SN 2020bqj with regular SNe Ibn from the literature, as well as with other outliers in the SN Ibn subclass. We fit the bolometric and multi-band lightcurves with powering mechanism models such as radioactive decay and CSM interaction. We also model the host galaxy of SN 2020bqj.
Results.
The risetime, peak magnitude and spectral features of SN 2020bqj are consistent with those of most SNe Ibn, but the SN is a clear outlier in the subclass based on its bright, long-lasting peak plateau and the low mass of its faint host galaxy. We show through modeling that the lightcurve of SN 2020bqj can be powered predominantly by shock heating from the interaction of the SN ejecta and a dense CSM, combined with radioactive decay. The peculiar Type Ibn SN 2011hw is a close analog to SN 2020bqj in terms of lightcurve and spectral evolution, suggesting a similar progenitor and CSM scenario. In this scenario a very massive progenitor star in the transitional phase between a luminous blue variable and a compact Wolf-Rayet star undergoes core-collapse, embedded in a dense helium-rich CSM with an elevated opacity compared to normal SNe Ibn, due to the presence of residual hydrogen. This scenario is consistent with the observed properties of SN 2020bqj and the modeling results.
Conclusions.
SN 2020bqj is a compelling example of a transitional SN Ibn/IIn based on not only its spectral features, but also its lightcurve, host galaxy properties and the inferred progenitor properties. The strong similarity with SN 2011hw suggests this subclass may be the result of a progenitor in a stellar evolution phase that is distinct from those of progenitors of regular SNe Ibn.
Abstract
BACKGROUND
The demand for donor oocytes has increased dramatically over the years. Today people in need of ART with the use of donor oocytes can appeal to commercial or public donor oocyte ...banks. The introduction of oocyte banks has shed a new light on the practice of ART using donor oocytes. The establishment and maintenance of oocyte banks should be sensitive to the ethical considerations. However, it is currently unclear which ethical aspects have to be taken into account.
OBJECTIVE AND RATIONALE
The aim of this article is to identify the ethical aspects of establishing and maintaining oocyte banks for third-party ART.
SEARCH METHODS
A systematic search was performed in July 2016 and February 2017 in both PubMed and Embase using a search string that combined synonyms for oocytes, donation or banking, reproductive care and ethics. We included a wide variety of English-language articles with a reasoned description of ethical aspects or moral considerations on oocyte donation or banking for third-party ART.
OUTCOMES
The practice of oocyte banking consists of three components, namely, the intake, storage and distribution of donor oocytes, and each is associated with multiple ethical challenges. The majority of the literature discusses ethical aspects with regard to the intake of donor oocytes, taking into account both the interests of the donor and those of the potential child. Ethical aspects related to the donor are the risks and psychosocial impact of donation, motivations and compensation in donor recruitment, and requirements for informed consent. Ethical aspects related to the potential child are 2-fold: first, the welfare standard and the selection of donors, and second, anonymity and disclosure. Ethical aspects of storing donor oocytes for ART are quality standards, confidentiality, issues of ownership and control, and international transport of donor oocytes. Ethical aspects of the distribution of donor oocytes concern the selection of recipients and the acceptability of treatment of ‘non-traditional’ families in particular, prioritization of recipients in case of scarcity, cross-border reproductive care, matching of recipients and donor oocytes, informed consent and counselling for recipients.
WIDER IMPLICATIONS
Our review demonstrates that multiple ethical aspects have to be taken into account when establishing and maintaining an oocyte bank. Yet, for many of these aspects there is no consensus regarding what approach should be employed. Remarkably, the existing literature focuses mainly on ethical aspects related to the intake of donor oocytes, while aspects related to storage and distribution of donor oocytes are less often addressed. An important gap in the existing literature should therefore be acknowledged. To conclude, our findings can serve as a starting point for clinicians in the field of ART, to conceptualize what challenges arise when establishing and maintaining oocyte banks for third-party ART. The review may also stimulate policy makers to set up a trustworthy and adaptive governance structure for the intake, storage and distribution of donor oocytes.
Only three extragalactic supernovae have been detected at late times at millimeter wavelengths: SN 1987A, SN 1978K, and SN 1996cr. SN 1978K is a remarkably luminous Type IIn supernova that remains ...bright at all wavelengths 40 years after its explosion. Here, we present Atacama Large Millimeter/submillimeter Array (ALMA) observations taken in 2016 using Bands 3, 4, 6, and 7 that show a steepening in the spectrum. An absorbed single power-law model broadly fits all of the radio and millimeter observations, but would require significant chromatic variability. Alternatively, a broken power law fits the radio-millimeter spectrum; this can be explained using an ultra-relativistic spherical blast wave in a wind scaling with a cooling break, as in a gamma-ray burst afterglow. Using updated Australia Telescope Compact Array light curves, we show that the non-thermal radio continuum continues to decay as t−1.53; in the fireball model, this independently defines the power-law indices found in the radio-millimeter spectrum. Supernovae such as SN 1978K might be important contributors to the universal dust budget: only SN 1978K was detected in a search for warm dust in supernovae in the transitional phase (age 10-100 yr). Using Spitzer Space Telescope observations, we show that at least some of this dust emission has been decaying rapidly as t−2.45 over the past decade, suggesting it is being destroyed. Depending on the modeling of the synchrotron emission, the ALMA observations suggest there may be emission from a cold dust component.
Over the years, the demand for ART with donated embryos has increased. Treatment can be performed using donated 'surplus embryos' from IVF treatment or with embryos intentionally created through ...so-called 'double gamete donation'. Embryo donation is particularly sensitive because treatment results in the absence of a genetic link between the parent(s) and the child, creating complex family structures, including full genetic siblings living in another family in the case of surplus embryo donation. In this paper, we explore the ethical acceptability of embryo donation in light of the similarities and differences between surplus embryo donation and double gamete donation. We will argue that no overriding objections to either form of embryo donation exist. First of all, ART with donated embryos respects patients' reproductive autonomy by allowing them to experience gestational parenthood. It also respects IVF patients' reproductive autonomy by providing an additional option to discarding or donating surplus embryos to research. Second, an extensive body of empirical research has shown that a genetic link between parent and child is not a condition for a loving caring relationship between parent(s) and child. Third, the low moral status of a pre-implantation embryo signifies no moral duty for clinics to first use available surplus embryos or to prevent the development of (more) surplus embryos through double gamete donation. Fourth, there is no reason to assume that knowledge of having (full or half) genetically related persons living elsewhere provides an unacceptable impact on the welfare of donor-conceived offspring, existing children of the donors, and their respective families. Thus, patients and clinicians should discuss which form of ART would be suitable in their specific situation. To guarantee ethically sound ART with donated embryos certain conditions have to be met. Counselling of IVF patients should involve a discussion on the destination of potential surplus embryos. When counselling donors and recipient(s) a discussion of the significance of early disclosure of the child's mode of conception, the implications of having children raised in families with whom they share no genetic ties, expectations around information-exchange and contact between donor and recipient families or genetically related siblings is warranted. Importantly, conclusions are mainly drawn from results of empirical studies on single gamete donation families. To evaluate the welfare of families created through surplus embryo donation or double gamete donation additional empirical research on these particular families is warranted.
Various physicochemical factors influence DNA replication fidelity. Since it
is now known that Watson-Crick hydrogen bonds are not necessary for efficient
and selective replication of a base pair by ...DNA polymerase enzymes, a number of
alternative physical factors have been examined to explain the efficiency of
these enzymes. Among these factors are minor groove hydrogen bonding, base
stacking, solvation, and steric effects. We discuss the concept of active site
tightness in DNA polymerases, and consider how it might influence steric (size
and shape) effects of nucleotide selection in synthesis of a base pair. A high
level of active site tightness is expected to lead to higher fidelity relative
to proteins with looser active sites. We review the current data on what parts
and dimensions of active sites are most affected by size and shape, based on
data with modified nucleotides that have been examined as polymerase
substrates. We also discuss recent data on nucleotide analogs displaying higher
fidelity than the natural ones. The published data are discussed with a view
toward testing this sterically based hypothesis and unifying existing
observations into a narrowly defined range of effects.
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