Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the nuclear ...transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481 and 828 rest-frame days after optical lightcurve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including Fe VII, Fe X, Fe XI and Fe XIV. The Fe lines rise and then fall, except Fe XIV which appears late and rises. We observe increasing flux of narrow H-alpha and H-beta and a decrease in broad H-alpha flux. The coronal lines have FWHMs ranging from ~150 - 300km/s, suggesting they originate from a region between the broad and narrow line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3-1 keV X-ray flux increases by a factor of ~50 while the hard X-ray flux decreases by a factor of ~6. WISE fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically-confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or AGN activity.
Time-domain astrophysics continues to grow rapidly, with the inception of new
surveys drastically increasing data volumes. Democratised, distributed
approaches to training sets for machine learning ...classifiers are crucial to
make the most of this torrent of discovery -- with citizen science approaches
proving effective at meeting these requirements. In this paper, we describe the
creation of and the initial results from the $\textit{Kilonova Seekers}$
citizen science project, built to find transient phenomena from the GOTO
telescopes in near real-time. $\textit{Kilonova Seekers}$ launched in July 2023
and received over 600,000 classifications from approximately 2,000 volunteers
over the course of the LIGO-Virgo-KAGRA O4a observing run. During this time,
the project has yielded 20 discoveries, generated a `gold-standard' training
set of 17,682 detections for augmenting deep-learned classifiers, and measured
the performance and biases of Zooniverse volunteers on real-bogus
classification. This project will continue throughout the lifetime of GOTO,
pushing candidates at ever-greater cadence, and directly facilitate the
next-generation classification algorithms currently in development.
Epidemiological, experimental, and clinical studies have established a strong correlation between plasma levels of low density lipoprotein (LDL) and risk of coronary heart disease. LDL particles are ...composed of a core of cholesterol ester surrounded by a large apolipoprotein designated apoB-100.
SN 2023emq is a fast-evolving transient initially classified as a rare Type Icn supernova (SN), interacting with a H- and He-free circumstellar medium (CSM) around maximum light. Subsequent ...spectroscopy revealed the unambiguous emergence of narrow He lines, confidently placing SN 2023emq in the more common Type Ibn class. Photometrically SN 2023emq has several uncommon properties regardless of its class, including its extreme initial decay (faster than > 90% of Ibn/Icn SNe) and sharp transition in the decline rate from 0.20 mag/d to 0.07 mag/d at +20 d. The bolometric light curve can be modelled as CSM interaction with 0.32M_Sun of ejecta and 0.12M_Sun of CSM, with 0.006M_Sun of nickel, as expected of fast interacting SNe. Furthermore, broad-band polarimetry at +8.7 days (P = 0.55 +/- 0.30%) is consistent with spherical symmetry. A discovery of a transitional Icn/Ibn SN would be unprecedented and would give valuable insights into the nature of mass loss suffered by the progenitor just before death, but we favour an interpretation that SN 2023emq is a type Ibn SN that exhibited flash-ionised features in the earliest spectrum, as the features are not an exact match with other SNe Icn to date. However, the feature at 5700Å, in the region of C III and N II emission, is significantly stronger in SN 2023emq than in the few other flash-ionised Type Ibn SNe, and if it is related to C III, it possibly implies a continuum of properties between the two classes.
SN\,2020zbf is a hydrogen-poor superluminous supernova (SLSN) at \(z = 0.1947\) that shows conspicuous \ion{C}{II} features at early times, in contrast to the majority of H-poor SLSNe. Its peak ...magnitude is \(M_{\rm g}\) = \(-21.2\)~mag and its rise time (\(\lesssim 26.4\) days from first light) places SN\,2020zbf among the fastest rising type I SLSNe. We used spectra taken from ultraviolet (UV) to near-infrared wavelengths to identify spectral features. We paid particular attention to the \ion{C}{II} lines as they present distinctive characteristics when compared to other events. We also analyzed UV and optical photometric data and modeled the light curves considering three different powering mechanisms: radioactive decay of \(^{56}\)Ni, magnetar spin-down, and circumstellar medium (CSM) interaction. The spectra of SN\,2020zbf match the model spectra of a C-rich low-mass magnetar-powered supernova model well. This is consistent with our light curve modeling, which supports a magnetar-powered event with an ejecta mass \(M_{\rm ej}\) = 1.5~\(\rm M_\odot\). However, we cannot discard the CSM-interaction model as it may also reproduce the observed features. The interaction with H-poor, carbon-oxygen CSM near peak light could explain the presence of \ion{C}{II} emission lines. A short plateau in the light curve around 35 -- 45 days after peak, in combination with the presence of an emission line at 6580~\AA,\ can also be interpreted as being due to a late interaction with an extended H-rich CSM. Both the magnetar and CSM-interaction models of SN\,2020zbf indicate that the progenitor mass at the time of explosion is between 2 and 5~\(\rm M_\odot\). Modeling the spectral energy distribution of the host galaxy reveals a host mass of 10\(^{8.7}\)~\(\rm M_\odot\), a star formation rate of 0.24\(^{+0.41}_{-0.12}\)~\(\rm M_\odot\)~yr\(^{-1}\), and a metallicity of \(\sim\) 0.4~\(\rm Z_\odot\).
We present an extensive analysis of the optical and UV properties of AT2023clx, the closest TDE to date, that occurred in the nucleus of the interacting LINER galaxy, NGC3799 (z=0.01107). From ...several standard methods, we estimate the mass of the central SMBH to be ~ 10^6 Msol. After correcting for the host reddening (E(B-V) = 0.177 mag) we measured its peak absolute g-band magnitude to be -18.25\pm0.05 mag, and its peak bolometric luminosity to be L_pk=(3.24\pm0.36)x10^43erg/s, making AT2023clx an intermediate luminosity TDE. The first distinctive feature of AT2023clx is that it rose to peak within only 10.4\pm2.5 days, making it the fastest rising TDE to date. Our SMBH mass estimate rules out the possibility of an intermediate mass BH as the reason of the fast rise. Dense spectral follow-up revealed a blue continuum that cools slowly and broad Balmer and HeII lines as well as weak HeI emission, features that are typically seen in TDEs. A flat Balmer decrement (~ 1.58) suggests that the lines are collisionally excited rather than being produced via photoionisation, as in typical active galactic nuclei. A second distinctive feature, seen for the first time in TDE spectra, is a sharp, narrow emission peak at a rest wavelength of ~6353 A. This feature is clearly visible up to 10d post-peak; we attribute it to clumpy material preceding the bulk outflow, and manifested as a high-velocity component of Ha (-9584km/s). The third distinctive feature is a break observed in the near-UV light curves that is reflected as a dip in the temperature evolution around ~18-28 days post-peak. Combining these findings, we propose a scenario for AT2023clx involving the disruption of a very low-mass star (<=0.1Msol) with an outflow launched in our line-of-sight with disruption properties that led to circularisation and prompt and efficient accretion disc formation, observed through a low-density photosphere.
The interaction of recombinant apo(a) (r-apo(a)) with low-density lipoprotein (LDL) has been examined using ultracentrifugation and affinity chromatography. R-apo(a) forms a non-covalent complex with ...human LDL. This LDL-r-apo(a) complex, reconstituted Lp(a), r-Lp(a), which can be isolated by ultracentrifugation, has protease activity. The protease activity reached maximum at an equimolar ratio of r-apo(a) and LDL. Proline and epsilon aminocaproic acid (at a concentration of 50 mM) caused dissociation of r-Lp(a) and simultaneous loss of enzyme activity. Mouse LDL that did not form a complex with r-apo(a) did not activate the protease region of r-apo(a). Unlike plasma Lp(a), r-Lp(a) was dissociated during affinity chromatography on Lysine-Sepharose. This dissociation led to loss of enzyme activity. We conclude that the formation of a non-covalent complex between r-apo(a) and LDL leads to activation of the protease region of r-apo(a). The results suggest that non-covalent binding between r-apo(a) and LDL is a pre-requisite for the enzyme activity of the protease region of r-apo(a).
We present observations from X-ray to mid-infrared wavelengths of the most energetic non-quasar transient ever observed, AT2021lwx. Our data show a single optical brightening by a factor \(>100\) to ...a luminosity of \(7\times10^{45}\) erg s\(^{-1}\), and a total radiated energy of \(1.5\times10^{53}\) erg, both greater than any known optical transient. The decline is smooth and exponential and the ultra-violet - optical spectral energy distribution resembles a black body with temperature \(1.2\times10^4\) K. Tentative X-ray detections indicate a secondary mode of emission, while a delayed mid-infrared flare points to the presence of dust surrounding the transient. The spectra are similar to recently discovered optical flares in known active galactic nuclei but lack some characteristic features. The lack of emission for the previous seven years is inconsistent with the short-term, stochastic variability observed in quasars, while the extreme luminosity and long timescale of the transient disfavour the disruption of a single solar-mass star. The luminosity could be generated by the disruption of a much more massive star, but the likelihood of such an event occurring is small. A plausible scenario is the accretion of a giant molecular cloud by a dormant black hole of \(10^8 - 10^9\) solar masses. AT2021lwx thus represents an extreme extension of the known scenarios of black hole accretion.
We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). AT2022aedm ...exhibited a rise time of \(9\pm1\) days in the ATLAS \(o\)-band, reaching a luminous peak with \(M_g\approx-22\) mag. It faded by 2 magnitudes in \(g\)-band during the next 15 days. These timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. Most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. X-ray and radio observations rule out a relativistic AT2018cow-like explosion. A spectrum in the first few days after explosion showed short-lived He II emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blue-shifted absorption lines, possibly arising in a wind with \(v\approx2700\) km s\(^{-1}\). We identify two further transients in the literature (Dougie in particular, as well as AT2020bot) that share similarities in their luminosities, timescales, colour evolution and largely featureless spectra, and propose that these may constitute a new class of transients: luminous fast-coolers (LFCs). All three events occurred in passive galaxies at offsets of \(\sim4-10\) kpc from the nucleus, posing a challenge for progenitor models involving massive stars or massive black holes. The light curves and spectra appear to be consistent with shock breakout emission, though usually this mechanism is associated with core-collapse supernovae. The encounter of a star with a stellar mass black hole may provide a promising alternative explanation.
Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive ...black holes at the centers of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines. The UV/optical light curve shows a double peak at \(\sim50\) and \(\sim100\) days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. abridged
