Search

The number of binaries containing black holes (BH) or neutron stars (NS) depends critically on the fraction of binaries that survive supernova (SN) explosions. We searched for surviving star plus remnant binaries in a sample of 49 supernova remnants (SNR) containing 23 previously identified compact remnants and three high-mass X-ray binaries (HMXB), finding no new interacting or non-interacting binaries. The upper limits on any main-sequence stellar companion are typically |$\lesssim 0.2\, \mathrm{M}_\odot$| and are at worst |$\lesssim 3\, \mathrm{M}_\odot$|⁠. This implies that f < 0.1 of core-collapse SNRs contain a non-interacting binary, and f  = 0.083 (0.032 < f < 0.17) contain an interacting binary at 90 per cent confidence. We also find that the transverse velocities of HMXBs are low, with a median of only 12 km s−1 for field HMXBs, so surviving binaries will generally be found very close to the explosion centre. We compare the results to a 'standard' StarTrack binary population synthesis (BPS) model, finding reasonable agreement with the observations. In particular, the BPS models predict that 6 per cent of initial binaries leave a star plus remnant binary, or 5 per cent of SNRs assuming an 84 per cent binary fraction. [ABSTRACT FROM AUTHOR]

Fomalhaut b is a directly imaged object in the debris disc of the star Fomalhaut. It has been hypothesized to be a planet; however, there are issues with the observed colours of the object that do not fit planetary models. An alternative hypothesis is that the object is a neutron star in the near fore- or background of Fomalhaut's disc. We test if Fomalhaut b could be a neutron star using X-ray observations with Chandra's HRC-I instrument in the energy range of 0.08–10 keV. We do not detect X-ray emission from either Fomalhaut b or the star Fomalhaut itself. Our non-detection corresponds to an upper limit on the X-ray flux of Fomalhaut b of FX < 1.3 × 10-14 erg cm-2 s-1 in the energy range 0.08–10 keV. For the A-type central star Fomalhaut, we derive an X-ray upper limit of LX < 2.0 × 1025 erg s-1 in the energy range 0.08–10 keV. Fomalhaut b's X-ray non-detection constrains the parameter space for a possible neutron star significantly, implying surface temperatures lower than 91 000 K and distances closer than 13.3 pc to the Solar system. In addition, we find that reflected starlight from the central star fits the available optical detections of Fomalhaut b; a smaller planet with a large ring system might explain such a scenario. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of the photometric and spectroscopic evolution of SN 2021foa, unique among the class of transitional supernovae for repeatedly changing its spectroscopic appearance from hydrogen-to-helium-to-hydrogen dominated (IIn-to-Ibn-to-IIn) within 50 days past peak brightness. The spectra exhibit multiple narrow (≈300–600 km s−1) absorption lines of hydrogen, helium, calcium, and iron together with broad helium emission lines with a full width at half-maximum (FWHM) of ∼6000 km s−1. For a steady, wind mass-loss regime, light-curve modeling results in an ejecta mass of ∼8 M ⊙ and circumstellar material (CSM) mass below 1 M ⊙, and an ejecta velocity consistent with the FWHM of the broad helium lines. We obtain a mass-loss rate of ≈2 M ⊙ yr−1. This mass-loss rate is 3 orders of magnitude larger than derived for normal Type II supernovae. We estimate that the bulk of the CSM of SN 2021foa must have been expelled within half a year, about 12 yr ago. Our analysis suggests that SN 2021foa had a helium-rich ejecta that swept up a dense shell of hydrogen-rich CSM shortly after explosion. At about 60 days past peak brightness, the photosphere recedes through the dense ejecta-CSM region, occulting much of the redshifted emission of the hydrogen and helium lines, which results in an observed blueshift (∼−3000 km s−1). Strong mass-loss activity prior to explosion, such as those seen in SN 2009ip-like objects and SN 2021foa as precursor emission, are the likely origin of a complex, multiple-shell CSM close to the progenitor star. [ABSTRACT FROM AUTHOR]

We present Lightcurve Anomaly Identification and Similarity Search (LAISS), an automated pipeline to detect anomalous astrophysical transients in real-time data streams. We deploy our anomaly detection model on the nightly Zwicky Transient Facility (ZTF) Alert Stream via the ANTARES broker, identifying a manageable ∼1–5 candidates per night for expert vetting and coordinating follow-up observations. Our method leverages statistical light-curve and contextual host galaxy features within a random forest classifier, tagging transients of rare classes (spectroscopic anomalies), of uncommon host galaxy environments (contextual anomalies), and of peculiar or interaction-powered phenomena (behavioral anomalies). Moreover, we demonstrate the power of a low-latency (∼ms) approximate similarity search method to find transient analogs with similar light-curve evolution and host galaxy environments. We use analogs for data-driven discovery, characterization, (re)classification, and imputation in retrospective and real-time searches. To date, we have identified ∼50 previously known and previously missed rare transients from real-time and retrospective searches, including but not limited to superluminous supernovae (SLSNe), tidal disruption events, SNe IIn, SNe IIb, SNe I-CSM, SNe Ia-91bg-like, SNe Ib, SNe Ic, SNe Ic-BL, and M31 novae. Lastly, we report the discovery of 325 total transients, all observed between 2018 and 2021 and absent from public catalogs (∼1% of all ZTF Astronomical Transient reports to the Transient Name Server through 2021). These methods enable a systematic approach to finding the "needle in the haystack" in large-volume data streams. Because of its integration with the ANTARES broker, LAISS is built to detect exciting transients in Rubin data. [ABSTRACT FROM AUTHOR]

We report the All-Sky Automated Survey for SuperNovae discovery of the tidal disruption event (TDE) ASASSN-23bd (AT 2023clx) in NGC 3799, a LINER galaxy with no evidence of strong active galactic nucleus (AGN) activity over the past decade. With a redshift of z  = 0.01107 and a peak ultraviolet (UV)/optical luminosity of (5.4 ± 0.4) × 1042 erg s−1, ASASSN-23bd is the lowest-redshift and least-luminous TDE discovered to date. Spectroscopically, ASASSN-23bd shows H α and He  i emission throughout its spectral time series, there are no coronal lines in its near-infrared spectrum, and the UV spectrum shows nitrogen lines without the strong carbon and magnesium lines typically seen for AGN. Fits to the rising ASAS-SN light curve show that ASASSN-23bd started to brighten on MJD 59988 |$^{+1}_{-1}$|⁠ , ∼9 d before discovery, with a nearly linear rise in flux, peaking in the g band on MJD |$60 \, 000^{+3}_{-3}$|⁠. Scaling relations and TDE light curve modelling find a black hole mass of ∼106 M⊙, which is on the lower end of supermassive black hole masses. ASASSN-23bd is a dim X-ray source, with an upper limit of |$L_{0.3-10\, \mathrm{keV}} \lt 1.0\times 10^{40}$| erg s−1 from stacking all Swift observations prior to MJD 60061, but with soft (∼0.1 keV) thermal emission with a luminosity of |$L_{0.3-2 \, \mathrm{keV}}\sim 4\times 10^{39}$| erg s−1 in XMM-Newton observations on MJD 60095. The rapid (t < 15 d) light curve rise, low UV/optical luminosity, and a luminosity decline over 40 d of Δ L 40 ≈ −0.7 dex make ASASSN-23bd one of the dimmest TDEs to date and a member of the growing 'Low Luminosity and Fast' class of TDEs. [ABSTRACT FROM AUTHOR]

Observational astronomy of tidal disruption events (TDEs) began with the detection of X-ray flares from quiescent galaxies during the ROSAT all-sky survey of 1990–1991. The flares complied with theoretical expectations, having high peak luminosities ( L x up to ≥ 4 × 10 44 erg/s), a thermal spectrum with k T ∼ few × 10 5 K, and a decline on timescales of months to years, consistent with a diminishing return of stellar debris to a black hole of mass 10 6 – 8 M ⊙ . These measurements gave solid proof that the nuclei of quiescent galaxies are habitually populated by a super-massive black hole. Beginning in 2000, XMM-Newton, Chandra and Swift have discovered further TDEs which have been monitored closely at multiple wavelengths. A general picture has emerged of, initially near-Eddington accretion, powering outflows of highly-ionised material, giving way to a calmer sub-Eddington phase, where the flux decays monotonically, and finally a low accretion rate phase with a harder X-ray spectrum indicative of the formation of a disk corona. There are exceptions to this rule though which at the moment are not well understood. A few bright X-ray TDEs have been discovered in optical surveys but in general X-ray TDEs show little excess emission in the optical band, at least at times coincident with the X-ray flare. X-ray TDEs are powerful new probes of accretion physics down to the last stable orbit, revealing the conditions necessary for launching jets and winds. Finally we see that evidence is mounting for nuclear and non-nuclear intermediate mass black holes based on TDE flares which are relatively hot and/or fast. [ABSTRACT FROM AUTHOR]

We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE) discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 98 Mpc. We observed ASASSN-19dj from −21 to 392 d relative to peak ultraviolet (UV)/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From the ASAS-SN g -band data, we determine that the TDE began to brighten on 2019 February 6.8 and for the first 16 d the rise was consistent with a flux ∝ t 2 power law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD = 58548.5) at a bolometric luminosity of L = (6.2 ± 0.2) × 1044 erg s−1. Initially remaining roughly constant in X-rays and slowly fading in the UV/optical, the X-ray flux increased by over an order of magnitude ∼225 d after peak, resulting from the expansion of the X-ray emitting region. The late-time X-ray emission is well fitted by a blackbody with an effective radius of ∼1 × 1012 cm and a temperature of ∼6 × 105 K. The X-ray hardness ratio becomes softer after brightening and then returns to a harder state as the X-rays fade. Analysis of Catalina Real-Time Transient Survey images reveals a nuclear outburst roughly 14.5 yr earlier with a smooth decline and a luminosity of LV ≥ 1.4 × 1043 erg s−1, although the nature of the flare is unknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet to host a TDE, with Lick Hδ A = 7.67 ± 0.17 Å. [ABSTRACT FROM AUTHOR]

Observational astronomy of tidal disruption events (TDEs) began with the detection of X-ray flares from quiescent galaxies during the ROSAT all-sky survey of 1990–1991. The flares complied with theoretical expectations, having high peak luminosities ( L x up to ≥ 4 × 10 44 erg/s ), a thermal spectrum with k T ∼ few × 10 5 K , and a decline on timescales of months to years, consistent with a diminishing return of stellar debris to a black hole of mass 10 6 – 8 M ⊙ . These measurements gave solid proof that the nuclei of quiescent galaxies are habitually populated by a super-massive black hole. Beginning in 2000, XMM-Newton, Chandra and Swift have discovered further TDEs which have been monitored closely at multiple wavelengths. A general picture has emerged of, initially near-Eddington accretion, powering outflows of highly-ionised material, giving way to a calmer sub-Eddington phase, where the flux decays monotonically, and finally a low accretion rate phase with a harder X-ray spectrum indicative of the formation of a disk corona. There are exceptions to this rule though which at the moment are not well understood. A few bright X-ray TDEs have been discovered in optical surveys but in general X-ray TDEs show little excess emission in the optical band, at least at times coincident with the X-ray flare. X-ray TDEs are powerful new probes of accretion physics down to the last stable orbit, revealing the conditions necessary for launching jets and winds. Finally we see that evidence is mounting for nuclear and non-nuclear intermediate mass black holes based on TDE flares which are relatively hot and/or fast. [ABSTRACT FROM AUTHOR]

We present late-time optical spectroscopy and X-ray, UV, and optical photometry of the nearby (d = 214 Mpc, |$z$| = 0.0479) tidal disruption event (TDE) ASASSN-15oi. The optical spectra span 450 days after discovery and show little remaining transient emission or evolution after roughly three months. In contrast, the Swift and XMM–Newton observations indicate the presence of evolving X-ray emission and lingering thermal UV emission that is still present 600 days after discovery. The thermal component of the X-ray emission shows a unique, slow brightening by roughly an order of magnitude to become the dominant source of emission from the TDE at later times, while the hard component of the X-ray emission remains weak and relatively constant throughout the flare. The TDE radiated (1.32 ± 0.06) × 1051 erg across all wavelengths, and the UV and optical emission, is consistent with a power-law decline and potentially indicative of a late-time shift in the power-law index that could be caused by a transition in the dominant emission mechanism. [ABSTRACT FROM AUTHOR]

NGC 5273 is a known optical and X-ray variable AGN. We analyse new and archival IR, optical, UV, and X-ray data in order to characterize its long-term variability from 2000–2022. At least one optical changing-look event occurred between 2011 and 2014 when the AGN changed from a Type 1.8/1.9 Seyfert to a Type 1. It then faded considerably at all wavelengths, followed by a dramatic but slow increase in UV/optical brightness between 2021 and 2022. Near-IR (NIR) spectra in 2022 show prominent broad Paschen lines that are absent in an archival spectrum from 2010, making NGC 5273 one of the few AGNs to be observed changing-look in the NIR. We propose that NGC 5273 underwent multiple changing-look events between 2000 and 2022 – starting as a Type 1.8/1.9, NGC 5273 changes-look to a Type 1 temporarily in 2002 and again in 2014, reverting back to a Type 1.8/1.9 by 2005 and 2017, respectively. In 2022, it is again a Type 1 Seyfert. We characterize the changing-look events and their connection to the dynamic accretion and radiative processes in NGC 5273 and propose that the variable luminosity (and thus, Eddington ratio) of the source is changing how the broad-line region (BLR) reprocesses the continuum emission. [ABSTRACT FROM AUTHOR]

AT2019pev is a nuclear transient in a narrow-line Seyfert 1 galaxy at z  = 0.096. The archival ultraviolet, optical, and infrared data showed features of both tidal disruption events and active galactic nuclei (AGNs), and its nature is not fully understood. We present detailed X-ray observations of AT2019pev taken with Swift, Chandra , and NICER over 173 d of its evolution since the first Swift XRT epoch. The X-ray luminosity increases by a factor of 5 in 5 d from the first Swift XRT epoch to the light-curve peak. The light curve decays by a factor of 10 over ∼75 d and then flattens with a weak re-brightening trend at late times. The X-ray spectra show a 'harder-when-brighter' trend before peak and a 'harder-when-fainter' trend after peak, which may indicate a transition of accretion states. The archival ground-based optical observations show similar time evolution as the X-ray light curves. Beyond the seasonal limit of the ground-based observations, the Gaia light curve is rising towards an equally bright or brighter peak 223 d after the optical discovery. Combining our X-ray analysis and archival multiwavelength data, AT2019pev more closely resembles an AGN transient. [ABSTRACT FROM AUTHOR]

We present multiwavelength follow-up observations of the ATLAS discovered faint Iax supernova SN 2020kyg that peaked at an absolute magnitude of Mg ≈ −14.9 ± 0.2, making it another member of the faint Iax supernova population. The bolometric light curve requires only ≈7 × 10−3 M⊙ of radioactive 56Ni, with an ejected mass of M ej ∼ 0.4 M⊙ and a low kinetic energy of E ≈ 0.05 ± 0.02 × 1051 erg. We construct a homogeneous volume-limited sample of 902 transients observed by ATLAS within 100 Mpc during a 3.5 yr span. Using this sample, we constrain the rates of faint Iax (Mr ≳ −16) events within 60 Mpc at |$12^{+14}_{-8}{{\ \rm per\ cent}}$| of the SN Ia rate. The overall Iax rate, at |$15^{+17}_{-9}{{\ \rm per\ cent}}$| of the Ia rate, is dominated by the low-luminosity events, with luminous SNe Iax (Mr ≲ −17.5) like 2002cx and 2005hk, accounting for only |$0.9^{+1.1}_{-0.5}{{\ \rm per\ cent}}$| of the Ia rate (a 2σ upper limit of approximately 3 per cent). We favour the hybrid CONe WD + He star progenitor channel involving a failed deflagration of a near Chandrasekhar mass white dwarf, expected to leave a bound remnant and a surviving secondary companion, as a candidate explanation for faint Iax explosions. This scenario requires short delay times, consistent with the observed environments of SNe Iax. Furthermore, binary population synthesis calculations have suggested rates of |$1\!-\!18{{\ \rm per\ cent}}$| of the SN Ia rate for this channel, consistent with our rate estimates. [ABSTRACT FROM AUTHOR]

We present multiwavelength observations of the Type II SN 2020pni. Classified at ∼1.3 days after explosion, the object showed narrow (FWHM intensity <250 km sâˆ'1) recombination lines of ionized helium, nitrogen, and carbon, as typically seen in flash-spectroscopy events. Using the non-LTE radiative transfer code CMFGEN to model our first high-resolution spectrum, we infer a progenitor mass-loss rate of M ̇ = (3.5 â€" 5.3) Ă— 10 âˆ' 3 M ⊙ yrâˆ'1 (assuming a wind velocity of v w = 200 km sâˆ'1), estimated at a radius of R in = 2.5 Ă— 1014 cm. In addition, we find that the progenitor of SN 2020pni was enriched in helium and nitrogen (relative abundances in mass fractions of 0.30â€"0.40 and 8.2 Ă— 10âˆ'3, respectively). Radio upper limits are also consistent with dense circumstellar material (CSM) and a mass-loss rate of M ̇ > 5 Ă— 10 âˆ' 4 M ☉ yr âˆ' 1 . During the initial 4 days after first light, we also observe an increase in velocity of the hydrogen lines (from ∼250 to ∼1000 km sâˆ'1), suggesting complex CSM. The presence of dense and confined CSM, as well as its inhomogeneous structure, indicates a phase of enhanced mass loss of the progenitor of SN 2020pni during the last year before explosion. Finally, we compare SN 2020pni to a sample of other shock-photoionization events. We find no evidence of correlations among the physical parameters of the explosions and the characteristics of the CSM surrounding the progenitors of these events. This favors the idea that the mass loss experienced by massive stars during their final years could be governed by stochastic phenomena and that, at the same time, the physical mechanisms responsible for this mass loss must be common to a variety of different progenitors. [ABSTRACT FROM AUTHOR]

We characterize the extreme heartbeat star system MACHO 80.7443.1718 in the Large Magellanic Cloud using Transiting Exoplanet Survey Satellite (TESS) photometry and spectroscopic observations from the Magellan Inamori Kyocera Echelle (MIKE) and SOAR Goodman spectographs. MACHO 80.7443.1718 was first identified as a heartbeat star system in the All-Sky Automated Survey for SuperNovae (ASAS-SN) with |$P_{\rm orb}=32.836\pm 0.008\, {\rm d}$|⁠. MACHO 80.7443.1718 is a young (∼6 Myr), massive binary, composed of a B0 Iae supergiant with |$M_1 \simeq 35\, {\rm M}_\odot$| and an O9.5V secondary with |$M_2 \simeq 16\, {\rm M}_\odot$| on an eccentric (e = 0.51 ± 0.03) orbit. In addition to having the largest variability amplitude amongst all known heartbeats stars, MACHO 80.7443.1718 is also one of the most massive heartbeat stars yet discovered. The B[e] supergiant has Balmer emission lines and permitted/forbidden metallic emission lines associated with a circumstellar disc. The disc rapidly dissipates at periastron that could indicate mass transfer to the secondary, but re-emerges immediately following periastron passage. MACHO 80.7443.1718 also shows tidally excited oscillations at the N = 25 and N = 41 orbital harmonics and has a rotational period of 4.4 d. [ABSTRACT FROM AUTHOR]

We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (⁠|$d\sim 460\, \rm pc$|⁠), bright (V ≃ 8.3 mag), evolved (T eff, giant ≃ 4440 K, and L giant ≃ 173 L⊙) red giant in a high mass function, f (M) = 1.72 ± 0.01 M⊙, nearly circular binary (P  = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of |$87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$|⁠ , a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of M comp = 3.04 ± 0.06 M⊙, a stellar radius of R giant = 24.9 ± 0.7 R⊙, and a giant mass of M giant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of |${\sim }63{{\ \rm per\ cent}}$| and |${\sim }24{{\ \rm per\ cent}}$|⁠ , respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion discs. The X-ray luminosity of the system is |$L_{\rm X}\simeq 7.6\times 10^{29}~\rm ergs~s^{-1}$|⁠ , corresponding to L / L edd ∼ 10−9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the 'mass gap'. [ABSTRACT FROM AUTHOR]

Time-domain science has undergone a revolution over the past decade, with tens of thousands of new supernovae (SNe) discovered each year. However, several observational domains, including SNe within days or hours of explosion and faint, red transients, are just beginning to be explored. Here we present the Young Supernova Experiment (YSE), a novel optical time-domain survey on the Pan-STARRS telescopes. Our survey is designed to obtain well-sampled griz light curves for thousands of transient events up to z ≈ 0.2. This large sample of transients with four-band light curves will lay the foundation for the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, providing a critical training set in similar filters and a well-calibrated low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy science. As the name suggests, YSE complements and extends other ongoing time-domain surveys by discovering fast-rising SNe within a few hours to days of explosion. YSE is the only current four-band time-domain survey and is able to discover transients as faint as ∼21.5 mag in gri and ∼20.5 mag in z, depths that allow us to probe the earliest epochs of stellar explosions. YSE is currently observing approximately 750 deg2 of sky every 3 days, and we plan to increase the area to 1500 deg2 in the near future. When operating at full capacity, survey simulations show that YSE will find ∼5000 new SNe per year and at least two SNe within 3 days of explosion per month. To date, YSE has discovered or observed 8.3% of the transient candidates reported to the International Astronomical Union in 2020. We present an overview of YSE, including science goals, survey characteristics, and a summary of our transient discoveries to date. [ABSTRACT FROM AUTHOR]

We present and analyse a new tidal disruption event (TDE), AT2017eqx at redshift z  = 0.1089, discovered by Pan-STARRS and ATLAS. The position of the transient is consistent with the nucleus of its host galaxy; the spectrum shows a persistent blackbody temperature T ≳ 20 000 K with broad H  i and He  ii emission; and it peaks at a blackbody luminosity of L ≈ 1044 erg s−1. The lines are initially centred at zero velocity, but by 100 d, the H  i lines disappear while the He  ii develops a blueshift of ≳ 5000 km s−1. Both the early- and late-time morphologies have been seen in other TDEs, but the complete transition between them is unprecedented. The evolution can be explained by combining an extended atmosphere, undergoing slow contraction, with a wind in the polar direction becoming visible at late times. Our observations confirm that a lack of hydrogen a TDE spectrum does not indicate a stripped star, while the proposed model implies that much of the diversity in TDEs may be due to the observer viewing angle. Modelling the light curve suggests AT2017eqx resulted from the complete disruption of a solar-mass star by a black hole of ∼106.3 M⊙. The host is another Balmer-strong absorption galaxy, though fainter and less centrally concentrated than most TDE hosts. Radio limits rule out a relativistic jet, while X-ray limits at 500 d are among the deepest for a TDE at this phase. [ABSTRACT FROM AUTHOR]

We present the ultraviolet (UV) spectroscopic evolution of a tidal disruption event (TDE) for the first time. After the discovery of the nearby TDE iPTF16fnl, we obtained a series of observations with the Space Telescope Imaging Spectrograph (STIS) onboard the HubbleSpaceTelescope (HST). The dominant emission features closely resemble those seen in the UV spectra of the TDE ASASSN-14li and are also similar to those of N-rich quasars. There is evolution in the shape and central wavelength of the dominant emission features over the course of our observations, such that at early times the lines tend to be broad and redshifted, while at later times they are narrower and peak near the wavelengths of their atomic transitions. Like ASASSN-14li, but unlike N-rich quasars, iPTF16fnl shows neither Mg II 2798 Å nor C III] 1909 Å emission features. We also present optical photometry and spectroscopy, which suggest that the complex He II profiles observed in the optical spectra of many TDEs are in part due to the presence of N III and C III Wolf-Rayet features, which can potentially serve as probes of the far-UV when space-based observations are not possible. Finally, we use Swift X-ray Telescope and Ultraviolet/Optical Telescope (UVOT) observations to place strong limits on the X-ray emission and determine the characteristic temperature, radius and luminosity of the emitting material. We find that iPTF16fnl is subluminous and evolves more rapidly than other optically discovered TDEs. [ABSTRACT FROM AUTHOR]