ABSTRACT
Type IIn supernovae (SNe IIn) are a relatively infrequently observed subclass of SNe whose photometric and spectroscopic properties are varied. A common thread among SNe IIn is the complex ...multiple-component hydrogen Balmer lines. Owing to the heterogeneity of SNe IIn, online data bases contain some outdated, erroneous, or even contradictory classifications. SN IIn classification is further complicated by SN ‘impostors’ and contamination from underlying H ii regions. We have compiled a catalogue of systematically classified nearby (redshift z < 0.02) SNe IIn using the Open Supernova Catalogue (OSC). We present spectral classifications for 115 objects previously classified as SNe IIn. Our classification is based on results obtained by fitting multiple Gaussians to the H α profiles. We compare classifications reported by the OSC and Transient Name Server (TNS) along with the best matched templates from snid
. We find that 28 objects have been misclassified as SNe IIn. TNS and OSC can be unreliable; they disagree on the classifications of 51 of the objects and contain a number of erroneous classifications. Furthermore, OSC and TNS hold misclassifications for 34 and 12 (respectively) of the transients we classify as SNe IIn. In total, we classify 87 SNe IIn. We highlight the importance of ensuring that online data bases remain up to date when new or even contemporaneous data become available. Our work shows the great range of spectral properties and features that SNe IIn exhibit, which may be linked to multiple progenitor channels and environment diversity. We set out a classification scheme for SNe IIn based on the H α profile that is not greatly affected by the inhomogeneity of SNe IIn.
ABSTRACT
The nova super-remnant (NSR) surrounding M 31N 2008-12a (12a), the annually erupting recurrent nova (RN), is the only known example of this phenomenon. As this structure has grown as a ...result of frequent eruptions from 12a, we might expect to see NSRs around other RNe; this would confirm the RN–NSR association and strengthen the connection between novae and type Ia supernovae (SN Ia) as NSRs centred on SN Ia provide a lasting, unequivocal signpost to the single degenerate progenitor type of that explosion. The only previous NSR simulation used identical eruptions from a static white dwarf (WD). In this Paper, we simulate the growth of NSRs alongside the natural growth/erosion of the central WD, within a range of environments, accretion rates, WD temperatures, and initial WD masses. The subsequent evolving eruptions create dynamic NSRs tens of parsecs in radius comprising a low-density cavity, bordered by a hot ejecta pile-up region, and surrounded by a cool high-density, thin, shell. Higher density environments restrict NSR size, as do higher accretion rates, whereas the WD temperature and initial mass have less impact. NSRs form around growing or eroding WDs, indicating that NSRs also exist around old novae with low-mass WDs. Observables such as X-ray and H α emission from the modelled NSRs are derived to aid searches for more examples; only NSRs around high accretion rate novae will currently be observable. The observed properties of the 12a NSR can be reproduced when considering both the dynamically grown NSR and photoionization by the nova system.
Context. Classical novae are eruptions on the surface of a white dwarf in a binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell of gas and dust ...around the system. The three-dimensional structure of these shells is difficult to untangle when viewed on the plane of the sky. In this work a geometrical model is developed to explain new observations of the 2015 nova V5668 Sagittarii. Aim. We aim to better understand the early evolution of classical nova shells in the context of the relationship between polarisation, photometry, and spectroscopy in the optical regime. To understand the ionisation structure in terms of the nova shell morphology and estimate the emission distribution directly following the light curve’s dust-dip. Methods. High-cadence optical polarimetry and spectroscopy observations of a nova are presented. The ejecta is modelled in terms of morpho-kinematics and photoionisation structure. Results. Initially observational results are presented, including broadband polarimetry and spectroscopy of V5668 Sgr nova during eruption. Variability over these observations provides clues towards the evolving structure of the nova shell. The position angle of the shell is derived from polarimetry, which is attributed to scattering from small dust grains. Shocks in the nova outflow are suggested in the photometry and the effect of these on the nova shell are illustrated with various physical diagnostics. Changes in density and temperature as the super soft source phase of the nova began are discussed. Gas densities are found to be of the order of 109 cm−3 for the nova in its auroral phase. The blackbody temperature of the central stellar system is estimated to be around 2.2 × 105 K at times coincident with the super soft source turn-on. It was found that the blend around 4640 Å commonly called “nitrogen flaring” is more naturally explained as flaring of the O II multiplet (V1) from 4638–4696 Å, i.e. “oxygen flaring”. Conclusions. V5668 Sgr (2015) was a remarkable nova of the DQ Her class. Changes in absolute polarimetric and spectroscopic multi-epoch observations lead to interpretations of physical characteristics of the nova’s evolving outflow. The high densities that were found early-on combined with knowledge of the system’s behaviour at other wavelengths and polarimetric measurements strongly suggest that the visual “cusps” are due to radiative shocks between fast and slow ejecta that destroy and create dust seed nuclei cyclically.
ABSTRACT
Wide-field time domain facilities detect transient events in large numbers through difference imaging. For example, Zwicky Transient Facility produces alerts for hundreds of thousands of ...transient events per night, a rate set to be dwarfed by the upcoming Vera C. Rubin Observatory. The automation provided by machine learning (ML) is therefore necessary to classify these events and select the most interesting sources for follow-up observations. Cataclysmic variables (CVs) are a transient class that are numerous, bright, and nearby, providing excellent laboratories for the study of accretion and binary evolution. Here we focus on our use of ML to identify CVs from photometric data of transient sources published by the Gaia Science Alerts (GSA) program – a large, easily accessible resource, not fully explored with ML. Use of light-curve feature extraction techniques and source metadata from the Gaia survey resulted in a random forest model capable of distinguishing CVs from supernovae, active galactic nuclei, and young stellar objects with a 92 per cent precision score and an 85 per cent hit rate. Of 13 280 sources within GSA without an assigned transient classification our model predicts the CV class for ∼2800. Spectroscopic observations are underway to classify a statistically significant sample of these targets to validate the performance of the model. This work puts us on a path towards the classification of rare CV subtypes from future wide-field surveys such as the Legacy Survey of Space and Time.
Abstract
We report on multiwavelength observations of nova Small Magellanic Cloud Nova 2016-10a. The present observational set is one of the most comprehensive for any nova in the Small Magellanic ...Cloud, including low-, medium-, and high-resolution optical spectroscopy and spectropolarimetry from Southern African Large Telescope, Folded Low-Order Yte-Pupil Double-Dispersed Spectrograph, and Southern Astrophysical Research; long-term Optical Gravitational Lensing Experiment V- and I-bands photometry dating back to 6 yr before eruption; Small and Moderate Aperture Research Telescope System optical and near-IR photometry from ∼11 d until over 280 d post-eruption; Swift satellite X-ray and ultraviolet observations from ∼6 d until 319 d post-eruption. The progenitor system contains a bright disc and a main sequence or a sub-giant secondary. The nova is very fast with t2 ≃ 4.0 ± 1.0 d and t3 ≃ 7.8 ± 2.0 d in the V band. If the nova is in the SMC, at a distance of ∼61 ± 10 kpc, we derive MV, max ≃ −10.5 ± 0.5, making it the brightest nova ever discovered in the SMC and one of the brightest on record. At day 5 post-eruption the spectral lines show a He/N spectroscopic class and an Full Width at Half Maximum of ∼3500 km s−1, indicating moderately high ejection velocities. The nova entered the nebular phase ∼20 d post-eruption, predicting the imminent super-soft source turn-on in the X-rays, which started ∼28 d post-eruption. The super-soft source properties indicate a white dwarf mass between 1.2 and 1.3 M⊙ in good agreement with the optical conclusions.
The first direct detection of gravitational waves was made in 2015 September with the Advanced LIGO detectors. By prior arrangement, a worldwide collaboration of electromagnetic follow-up observers ...were notified of candidate gravitational wave events during the first science run, and many facilities were engaged in the search for counterparts. Three alerts were issued to the electromagnetic collaboration over the course of the first science run, which lasted from 2015 September to 2016 January. Two of these alerts were associated with the gravitational wave events since named GW150914 and GW151226. In this paper we provide an overview of the Liverpool Telescope contribution to the follow-up campaign over this period. Given the hundreds of square degree uncertainty in the sky position of any gravitational wave event, efficient searching for candidate counterparts required survey telescopes with large (∼degrees) fields of view. The role of the Liverpool Telescope was to provide follow-up classification spectroscopy of any candidates. We followed candidates associated with all three alerts, observing 1, 9 and 17 candidates respectively. We classify the majority of the transients we observed as supernovae. No counterparts were identified, which is in line with expectations given that the events were classified as black hole–black hole mergers. However these searches laid the foundation for similar follow-up campaigns in future gravitational wave detector science runs, in which the detection of neutron star merger events with observable electromagnetic counterparts is much more likely.
Context.
AT 2019abn was discovered in the nearby M51 galaxy by the Zwicky Transient Facility at more than two magnitudes and around three weeks prior to its optical peak.
Aims.
We aim to conduct a ...detailed photometric and spectroscopic follow-up campaign for AT 2019abn, with early discovery allowing for significant pre-maximum observations of an intermediate luminosity red transient (ILRT) for the first time.
Methods.
This work is based on the analysis of
u
′
B
V
r
′
i
′
z
′
H
photometry and low-resolution spectroscopy using the Liverpool Telescope, medium-resolution spectroscopy with the Gran Telescopio Canarias (GTC), and near-infrared imaging with the GTC and the Nordic Optical Telescope.
Results.
We present the most detailed optical light curve of an ILRT to date, with multi-band photometry starting around three weeks before peak brightness. The transient peaked at an observed absolute magnitude of
M
r
′
= −13.1, although it is subject to significant reddening from dust in M51, implying an intrinsic
M
r
′
∼ −15.2. The initial light curve showed a linear, achromatic rise in magnitude before becoming bluer at peak. After peak brightness, the transient gradually cooled. This is reflected in our spectra, which at later times show absorption from such species as Fe
I
, Ni
I
and Li
I
. A spectrum taken around peak brightness shows narrow, low-velocity absorption lines, which we interpret as likely to originate from pre-existing circumstellar material.
Conclusions.
We conclude that while there are some peculiarities, such as the radius evolution, AT 2019abn fits in well overall with the ILRT class of objects and is the most luminous member of the class seen to date.
We report Hubble Space Telescope (HST) imaging, obtained 155 and 449 days after the 2006 outburst of the recurrent nova RS Ophiuchi, together with ground-based spectroscopic observations, obtained ...from the Observatorio Astronomico Nacional en San Pedro Martir, Baja California, Mexico and at the Observatorio Astrofisico Guillermo Haro, at Cananea, Sonora, Mexico. The observations at the first epoch were used as inputs to model the geometry and kinematic structure of the evolving RS Oph nebular remnant. We find that the modeled remnant comprises two distinct co-aligned bipolar components; a low-velocity, high-density innermost (hour glass) region and a more extended, high-velocity (dumbbell) structure. This overall structure is in agreement with that deduced from radio observations and optical interferometry at earlier epochs. We find that the asymmetry observed in the west lobe is an instrumental effect caused by the profile of the HST filter and hence demonstrate that this lobe is approaching the observer. We then conclude that the system has an inclination to the line of sight of 39+1 deg -10. This is in agreement with the inclination of the binary orbit and lends support to the proposal that this morphology is due to the interaction of the outburst ejecta with either an accretion disk around the central white dwarf and/or a pre-existing red giant wind that is significantly denser in the equatorial regions of the binary than at the poles. The second epoch HST observation was also modeled. However, as no spectra were taken at this epoch, it is more difficult to constrain any model. Nevertheless, we demonstrate that between the two HST epochs the outer dumbbell structure seems to have expanded linearly. For the central (hour glass) region, there may be evidence of deceleration, but it is harder to draw firm conclusions in this case.
Abstract
A nova in the Local Group irregular dwarf galaxy IC 1613 was discovered on 2015 September 10 and is the first nova in that galaxy to be spectroscopically confirmed. We conducted a detailed ...multiwavelength observing campaign of the eruption with the Liverpool Telescope, the LCO 2 m telescope at Siding Spring Observatory, and Swift, the results of which we present here. The nova peaked at MV = −7.93 ± 0.08 and was fast-fading, with decline times of t2(V) = 13 ± 2 and t3(V) = 26 ± 2 d. The overall light-curve decline was relatively smooth, as often seen in fast-fading novae. Swift observations spanned 40–332 d post-discovery, but no X-ray source was detected. Optical spectra show the nova to be a member of the hybrid spectroscopic class, simultaneously showing Fe ii and N ii lines of similar strength during the early decline phase. The spectra cover the eruption from the early optically thick phase, through the early decline and into the nebular phase. The Hγ absorption minimum from the optically thick spectrum indicates an expansion velocity of 1200 ± 200 km s−1. The full width at half-maximum of the Hα emission line between 10.54 and 57.51 d post-discovery shows no significant evolution and remains at ∼1750 km s−1, although the morphology of this line does show some evolution. The nova appears close to a faint stellar source in archival imaging; however, we find the most likely explanation for this is simply a chance alignment.
ABSTRACT
Type IIn supernovae (SNe IIn) are an uncommon and highly heterogeneous class of SN where the SN ejecta interact with pre-existing circumstellar media (CSM). Previous studies have found a ...mass ladder in terms of the association of the SN location with H α emission and the progenitor masses of SN classes. In this paper, we present the largest environmental study of SNe IIn. We analyse the H α environments of 77 type SNeIIn using continuum subtracted H α images. We use the pixel statistics technique, normalized cumulative ranking (NCR), to associate SN pixels with H α emission. We find that our 77 SNe IIn do not follow the H α emission. This is not consistent with the proposed progenitors of SNe IIn, luminous blue variables (LBVs) as LBVs are high-mass stars that undergo dramatic episodic mass loss. However, a subset of the NCR values follow the H α emission, suggesting a population of high-mass progenitors. This suggests there may be multiple progenitor paths with ∼60 per cent having non-zero NCR values with a distribution consistent with high-mass progenitors such as LBVs and ∼40 per cent of these SNe not being associated with H α emission. We discuss the possible progenitor routes of SNe IIn, especially for the zero NCR value population. We also investigate the radial distribution of the SNe in their hosts in terms of H α and r′-band flux.
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