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Rapid SPRAT confirmation of a Gaia transient: it's a dwarf nova! 1200 GMT 16 Oct 2014

SPRAT spectrum
A SPRAT spectral image of Gaia14aat with wavelength on the horizontal axis increasing to the right (coverage approx. 400-790 nm) and offset along the spectrograph slit on the y-axis. The vertical lines are emission from the atmosphere (the two brightest sky lines are labelled). The horizontal line is the black-body continuum emission from the binary system; superimposed onto this continuum are emission lines at very specific wavelengths. The hydrogen Balmer recombination line, H-alpha, is labelled, though other lines are also evident in the fully-reduced data.

One of the secondary goals of the Gaia Space Telescope is to survey the whole sky for variables and transients, objects that suddenly increase in brightness. The Gaia Photometric Science Alerts programme hosted by Cambridge University in the U.K. has recently gone public, and one of the first alerts released has been robotically observed by the Liverpool Telescope. As part of a campaign of rapid follow-up observations with the newly-commissioned SPRAT spectrograph, a group of LJMU astronomers have just released the first Astronomer's Telegram based on a Gaia transient alert.

The transient Gaia14aat was detected by the Gaia Photometric Science Alerts programme with a magnitude of 15.7 on 10th October. The team, all part of the Liverpool Telescope group at LJMU, measured the object's position precisely. They then identified the progenitor of the outburst in archival Sloan Digital Sky Survey (SDSS) images as an object with an r-band (red) magnitude of 18.9. The target had thus suddenly brightened by over three magnitudes; that's an increase in luminosity of more than 15 times.

The question then was: what is Gaia14aat?

Using the SPRAT spectrograph installed on the Liverpool Telescope, the group obtained a 10 minute spectrum of the object on October 15th. The spectrum covers the wavelength range of 400 to 790 nanometres and exhibits emission lines from hot atomic hydrogen: a bright H-alpha line at 656 nm and fainter H-beta and H-gamma lines at 486 and 434 nm.

Observing with SPRAT involves first taking an image (so that the target can be identified and moved onto the spectrograph slit). This "white light" acquisition image can also be used for science, however, and was in this case used to estimate the r-band magnitude of the target, which by the date of the LT observations had faded to about 18.5, close to the SDSS value. The object had already returned to its quiescence state in the 5 days since the Gaia detection. Clearly, time is of the essence when observing Gaia transients!

Based on the duration and brightness of the transient and the emission features in the SPRAT spectrum, the team believe that Gaia14aat is a dwarf nova outburst in a hydrogen-rich cataclysmic variable. Dwarf novae are binary systems in which a white dwarf star accretes matter from a companion; cataclysmic variables are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state.

Gaia14aat will undoubtedly be the first of many transients discovered by the Gaia Space Telescope and subsequently observed by the LT. These early observations illustrate the power of SPRAT for categorising faint transients, and the importance of rapid response and robotic operations. Exciting times lie ahead.

The LJMU team of Andrzej Piascik, Iain Steele, Chris Copperwheat and Chris Davis would like to acknowledge the ESA Gaia mission and particularly the DPAC Photometric Science Alerts Team.

LT discovers the sixth eruption of a remarkable Recurrent Nova in M31 1700 GMT 14 Oct 2014

M31 RN A quasi-true colour LT image of the region of M31 around M31N 2008-12a. The yellow backdrop is the unresolved stellar population of the disk of M31, where the dark patches are regions of high extinction. The majority of the point sources seen in the image are in the foreground and belong to our own Galaxy. The image has been enhanced by the use of a 'H-alpha' image to highlight regions of excited Hydrogen gas. The nova can be seen in eruption in the centre of the image (marked by the white arrow).

The LT has in recent weeks been doing what it does best: making exciting discoveries in time domain astronomy! A team led by Dr Matt Darnley of the Astrophysics Research Institute at LJMU has detected the latest eruption of a remarkable Recurrent Nova (RN) in the nearby galaxy M31. This object is particularly noteworthy because of the frequency of its eruptions. Most RNe undergo an outburst once every 10-100 years; the RN in M31 seems to erupt annually.

Darnley and his team were the first to spot the latest eruption of the nova and, thanks to the LT's robotic capabilities, have been able to monitor the event with images and spectra obtained every few hours/days over a period of a few weeks. They have certainly not let the grass grow under their feet, having made full use of the recently-commissioned optical spectrograph, SPRAT.

Novae are associated with nuclear explosions on the surface of a white dwarf, which results in a sudden brightening of the star. Recurrent nova outbursts are caused by the accretion of material from a companion star, usually a red giant, onto the white dwarf through an accretion disc.

As reported in an LT news item earlier this year, the true recurrent nature of the nova system in M31, designated M31N 2008-12a, was characterised following its fifth detected optical eruption in 2013. An international study co-led by Darnley and Dr Martin Henze of the European Space Astronomy Centre in Spain, along with independent work by the Intermediate Palomar Transient Factory (iPTF), uncovered the progenitor system of M31N 2008-12a and inferred the presence of an extremely high mass white dwarf as well as a high mass accretion rate. These are the tell-tale signs that M31N 2008-12a may one day evolve into a Type Ia Supernova explosion.

Such a high mass white dwarf leads to a very rapid evolution of the 'optical lightcurve' of each eruption. The nova fades very rapidly post-eruption. Consequently, despite five optical eruptions and three separate X-ray detections of the event in recent years, very little was known about the behaviour of the system during its eruptions - until now.

In anticipation of a sixth eruption towards the end of 2014, Darnley has been leading a campaign on the Liverpool Telescope (LT) to monitor M31N 2008-12a to detect any changes in its behaviour. This LT campaign was also designed to react rapidly following a newly detected eruption, to obtain as much data on the system as possible.

Nightly monitoring of M31N 2008-12a by the LT began towards the end of July 2014, and just before 10pm (GMT) on 2nd October a sixth eruption was detected. As planned, intensive photometric monitoring of the eruption using the IO:O optical imaging CCD camera on the LT was immediately implemented. In addition, and for the first time, the team deployed the newly commissioned SPRAT (SPectrograph for the Rapid Acquisition of Transients) instrument on the LT, a low-resolution though high throughput spectrograph designed specifically for the classification of transients like novae.

Remarkably, SPRAT has been mounted on the LT for less than a month before Darnley et al. used it to obtain the first spectra of an extragalactic nova ever taken with the LT. These data have led to spectroscopic confirmation of the nature of the eruption and have allowed the team to determine the expansion velocity of its ejecta.

Sprat spectrum

A SPRAT spectrum of M31N 2008-12a taken on the night of 3rd October 2014. The spectrum shows the tell-tale Hydrogen, Helium, and Nitrogen emission lines expected of a 'He/N' nova in eruption.

As well as Matt Darnley and Martin Henze, the international collaboration also includes; Mike Bode (LJMU), Steve Williams (LJMU), Allen Shafter (San Diego State University, USA), Jan-Uwe Ness (ESAC), and former LJMU PhD student Rebekah Hounsell (Space Telescope Science Institute, USA). Iain Steele, Rob Smith, and Andrzej Piascik, all from the LT Group at LJMU, were instrumental in obtaining and analysing the SPRAT spectroscopic observations.

LJMU scientists announce the arrival of SPRAT, an exciting new instrument on the Liverpool Telescope 1600 GMT 5 September 2014
SPRAT photo SPRAT mounted on the Liverpool Telescope on La Palma.

Astronomers from the Astrophysics Research Institute (ARI) of Liverpool John Moores University recently announced the successful commissioning of an exciting new instrument on the Liverpool Telescope to colleagues and collaborators at an international conference in Poland. The conference, which was held in Warsaw in early September, brought together researchers from across Europe who are interested in observing variables and "transients" - objects that vary in brightness suddenly and dramatically. The meeting focused on objects that will be discovered with the GAIA space telescope, an ESA mission that was launched late last year. The LT will undoubtedly be a key player in this area of astronomical research.

Affectionately known as SPRAT, the SPectrometer for the Rapid Acquisition of Transients will provide astronomers from LJMU, the rest of the UK, and overseas with the opportunity to rapidly observe and analyse the light from all manner of variable objects. SPRAT will be particularly useful for studying novae and type Ia supernovae - stars in binary systems that undergo sudden outbursts - and core-collapse supernovae, massive stars that at the end of their lives collapse under their own weight causing a massive explosion of light and energy. Both areas of research are of particular interest to astronomers at the ARI.

SPRAT drawing A technical drawing showing the internal layout of SPRAT.
SPRAT spectrum Two first-light spectra of supernova ASASSN 14gh obtained with SPRAT during commissioning on Thursday, 4 September, 2014 (target courtesy D. Bersier/LJMU). The red and blue spectra show how the instrument may be optimised for observations at long or short optical wavelengths, respectively. The target itself was recently discovered by ASAS-SN, the All-Sky Automated Survey for Supernovae.

SPRAT was designed and built entirely by LJMU scientists and engineers subsidised mainly by internal LJMU funding. The instrument, the brainchild of Prof. Iain Steele, the Director of the Liverpool Telescope, was taken to La Palma in the Canary Islands on 30th August by a team from LJMU comprising Stuart Bates, Robert Smith and Andrzej Piascik. Joined by fourth team member Dirk Raback they spent the first week in September mounting the instrument on the telescope and carefully characterising it, in preparation for robotic use later in the month.

Andrzej, a PhD student at LJMU, has spent the last twelve months fine-tuning the performance of SPRAT in an optical lab in Liverpool Science Park (where the LT group is based). He joined the team on site and will present the instrument to the community at the Warsaw Conference. Meanwhile, testing will continue from Liverpool: software engineers Neil Clay, Chris Mottram and Steve Fraser will ensure that the instrument can be controlled remotely and robotically, that is, by the complex control system used to operate the telescope. Mike Tomlinson will provide IT support, while astronomers Jon Marchant, Rob Barnsley and Chris Davis will ensure that the data obtained are suitable for scientific use.

The commissioning of SPRAT brings the instrument suite on the LT to a grand total of six; a seventh instrument, the IO:I near-infrared imager, is currently being developed and will hopefully be commissioned later this year. In the meantime, SPRAT will undoubtedly prove to be an invaluable tool to a wide range of researchers in transient and time-domain astronomy.

SPRAT PN spectrum A false-colour SPRAT "spectral image" of a planetary nebula (PN), taken shortly after commissioning of the instrument by LT astronomer Robert Smith. The nebula is seen in emission from different atoms; the core of the dying star is seen as a horizontal strip of continuum emission.
RAS specialist discussion meeting on time domain astronomy with LT and LT2 1600 GMT 15 August 2014

Researchers in transient and time domain astronomy are invited to attend a Royal Astronomical Society (RAS) Specialist Discussion Meeting in London on Friday, 14 November. The discussion will focus on astronomy and astrophysics with the Liverpool Telescope and Liverpool Telescope 2. The aims of the meeting are to showcase the many varied programmes that are active on the Liverpool Telescope, to stimulate new collaborations and ideas, and to engage with the community regarding our plans for the future.

lsst An artists impression of what the Large Synoptic Survey Telescope (LSST) will look like on Cerro Pachon in Chile. Image courtesy NOAO.

The robotic 2m Liverpool Telescope, based on the Canary Island of La Palma, is owned and operated by Liverpool John Moores University, with operational support from STFC. It has a strong track record of service to the time domain community in the UK and beyond. The next decade will see time domain science becoming an increasingly prominent part of the astronomical agenda, and the LT will continue to be at the forefront, with large programmes exploiting new transient sources discovered with facilities such as iPTF, Gaia and LOFAR.

Looking further into the future, the next generation of surveys such as LSST will revolutionise the study of the time variable sky, and facilities such as CTA will probe transient phenomena at previously unexplored wavelengths. New exoplanet finders, starting with NGTS and followed by the next generation of space missions, will improve on the Kepler Space Telescope's efforts by discovering more planets orbiting bright host stars in order to maximise the potential of ground based follow-up. In addition, the anticipated discoveries of electromagnetic counterparts to astrophysical gravitational wave and neutrino sources will open new windows on the transient universe.

There will be a pressing need for follow-up facilities for scientific exploitation, in particular spectroscopic follow-up. With that in mind, plans are underway for Liverpool Telescope 2, a new 4-metre robotic telescope to be built on La Palma, with a world-leading response time for follow-up of the most rapidly varying objects.

cta The Cherenkov Telescope Array (CTA) will be a new facility for ground-based gamma-ray astronomy in the energy regime from 10 GeV to a few hundred TeV. Image courtesy University of Heidelberg.

An overview of the current status of the Liverpool Telescope 2 project is provided in a recent SPIE article (Copperwheat et al. 2014). A detailed science white paper will also shortly be made available on the astrophysics archive and on the LT2 website. In the meeting we will discuss the scientific role for LT2, focusing largely (though not exclusively) on the objectives outlined in these documents. We will also discuss the instrumental requirements for LT2, as well as potential enhancements to LT to enable it to remain relevant in the 2020 time domain landscape.

Time and location of the meeting

The meeting will be held at the Royal Astronomical Society, Burlington House, London, on 14 November, 2014. A more detailed agenda of talks will be circulated in due course.

Registration and abstracts

Attendance at this meeting is free for members of the RAS. For non-members there will be an attendance fee of £15 (£5 for students) to be paid at the door. The deadline for the submission of abstracts is 7 October 2014. Abstracts should be sent to Chris Copperwheat (c.m.copperwheat "at" ljmu.ac.uk) or Chris Davis (c.j.davis "at" ljmu.ac.uk).

Science Organising Committee:
Mike Bode, Chris Copperwheat, Chris Davis & Iain Steele

For further information on the Liverpool Telescope 2 project, please visit the LT2 web-site.

Research Council confirms future Liverpool Telescope Operations funding 1600 GMT 6 Aug 2014
LT staff An all-sky view, taken by skycam-A earlier this year, showing the La Palma summit horizon, the Liverpool Telescope, a glorious night sky, a fireball, and the William Herschel Telescope laser! Hundreds of images like these are obtained every night by our three wide-field imagers, SkyCameras A, T and Z. These images are posted on the LT Live Status webpage, with the constellations and other astronomical objects conveniently labelled, within minutes of being observed. Movies constructed from these images showing the motion of the heavens above the summit are posted on our Night reports web page the following morning.

The Liverpool Telescope is delighted to announce confirmation of receipt of a grant for £250,000 per year from the U.K. Science and Technology Facilities Council (STFC). This grant will support the operation of the LT over the next two years initially (staring 1 October 2014) as part of a five year Business Plan recently endorsed by the STFC's LT Oversight Committee. The funding ensures continuing access to the telescope for a wide range of astronomers and astrophysicists from Universities and Institutes across the UK and internationally.

The LT is currently experiencing a period of rapid growth; in terms of instrument development, but also interest from its user base. Demand for telescope time from British astronomers has doubled in recent years, and continues to be similarly high from our Spanish colleagues and, indeed, from internal Liverpool John Moores University users.

LJMU's Astrophysics Research Institute and other users of the telescope are about to embark on an ambitious and exciting few years of research at the forefront of time domain astronomy, facilitated by the commissioning of two new instruments - the infrared arm of the optical-infrared imager IO, and a high-throughput SPectrometer for the Rapid Acquisition of Transients, SPRAT. IO:I will enable near-simultaneous monitoring of all manner of transients and variables in the optical and near-infrared bands. SPRAT, on the other hand, will allow for spectral classification of much fainter targets than was previously possible (down to approximately 20th magnitude) in just a few minutes. SPRAT should, for example, be a boon for researchers trying to understand the physics and chemistry of exploding stars such as novae and supernovae before these objects fade from view.

Our expectation is that both instruments will be commissioned over the next few months, ready for use by observers towards the end of this year. In all, six instruments will be available on any given night, providing imaging, spectroscopic, and polarimetric capabilities. With the recently approved funding, these instruments are now sure to be available for exploitation by astronomers in the UK and internationally for a number of years to come.

For details on how and when to apply for telescope time on the Liverpool Telescope, please consult the LT Phase 1 webpage. If you have any questions are comments about access to the LT, please don't hesitate to contact us. Our contact details are available here.

Rapid-response monitoring of a "nearby monster" 1500 GMT 17 June 2014
Light curve Above: X-ray, Ultraviolet (w2, m2, w1 filters) and visible (B,V,u,b,v,g',r',i') light curves showing the declining brightness of GRB 130427A over a period of a few weeks. In this plot LT and Faulkes-North r' and i'-band data points are coloured red and yellow. The discovery was triggered in the X-ray (black data points). [Full size image]

On April 27, 2013 many of the world's astronomers observed the brightest Gamma-Ray Burst (GRB) ever detected by the Swift satellite. Named GRB 130427A, it was one of the most energetic nearby events ever encountered. At a redshift of z = 0.3399, which corresponds to a distance of only 3.6 billion light years, GRB 130427A was a truly unique and extraordinary "nearby monster".

GRBs trace the most energetic explosions in the Universe. Some are believed to occur after the merger of two compact objects - a pair of neutron stars or a neutron star and a black hole. Others may be caused by the collapse of a rapidly-rotating massive star. The former are classified as short-GRBs, due to the very limited durations of their gamma-ray emission (less than a few seconds). The latter are classified as long-GRBs, since the mean duration of their "prompt emission" phase lasts longer than a few tens of seconds.

GRB 130427A belongs to the second class of object (its duration lasted longer than 160 sec) and was probably the result of the collapse of a star 30-40 times the mass of the Sun with an intrinsic luminosity of 3 x 1053 erg/sec (for comparison the luminosity of the Sun is a mere 3.8 x 1033 erg/sec, one hundred billion billion times less!).

Ground-based facilities such as the Liverpool Telescope and Faulkes-North (a sister telescope to the LT) were used to monitor the optical behaviour of GRB 130427A, from very soon after the explosion up to relatively late times (see the attached light curves). These monitoring observations tracked the evolution of the burst emission with a high cadence, from the initial "prompt" phase to the "afterglow" phase (Maselli et al. 2014).

Careful analysis of these multi-wavelength data (which include GeV, Gamma-ray, X-ray, ultra-violet and optical bands) showed that the relatively nearby GRB 130427A had similar properties to the most luminous and much more distant high-redshift GRBs. This result suggests that a common central engine may be responsible for producing GRBs in both the contemporary, nearby universe and in the much more distant, early universe, as well as over the full range of GRB isotropic energies. Moreover, "monsters" like GRB 130427A seem to be strictly connected with Supernovae explosions (GRB 130427A was subsequently found to be associated with SN 2013cq) which, prior to these observations, was observed to be the case for only the weaker long-GRBs (Melandri et al. 2014).

Clearly, with their rapid response capabilities, robotic telescopes like the Liverpool Telescope are crucial to our understanding of the rapid evolution of these remarkable transient objects, both at early times during the prompt/afterglow phase and at later times as the GRB afterglow fades and the SN phase emerges.

Maselli A., Melandri A., Nava L., Mundell C. G., Kawai N. et al. 2014, Science, 343, 48 (link to paper).
Melandri A., Pian E., D'Elia V., D'Avanzo P., Della Valle M. et al. 2014, A&A in press, (arXiv:1404.6654).

Bumps, Burps and Bangs hit this year's National Astronomy Meeting in Portsmouth 1100 GMT 9 May 2014
LT staff Click above for the official NAM website.

The Liverpool Telescope team will once again be leading a session on Time Domain Astronomy at this year's U.K. National Astronomy Meeting. Entitled Bumps, Burps and Bangs - Transient and Time Domain Astronomy in the U.K., the two-block session has attracted the attention of researchers in the field from across the U.K.

In all, 23 abstracts were submitted from which 11 have been selected to give 15 minute talks. These talks will be spread across two sessions on the afternoon of Wednesday, 25th June, starting at 13:30. The presenters are listed below. In addition, poster are expected from 12 groups spanning topics in galactic, extra-galactic and solar system astrophysics.

This year NAM will be held in the historic south-coast town of Portsmouth. The Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth will host the meeting, which runs from 23-26 June. The meeting is targeted at professional astronomers but also includes a programme of public talks and other events aimed at engaging keen amateurs, members of the public, and the press. Registration is, however, required for all: the registration deadline is 30th May 2014.

Oral Presentations
Phil Lucas Univ. Hertfordshire Eruptive Variable YSOs from VVV and UKIDSS GPS
Darryl Sergison Univ. Exeter Untangling the signals: Simultaneous photometry and spectroscopy of YSOs in Orion
Danny Steeghs Univ. Warwick Galactic transients from accreting white dwarfs
Steven Williams   Liverpool John Moores Univ.   A Significant Proportion of M31 Novae Appear to Contain Red- giant Secondaries  
Matt Darnley Liverpool John Moores Univ. A remarkable recurrent nova in M31
Colin Hill Queens Univ. Belfast Roche tomography of cataclysmic variables - Differential rotation of AE Aqr
Kate Maguire ESO Exploring the diversity of low-redshift Type Ia supernovae using the Palomar Transient Factory  
Sam Connolly Univ. Southampton Long-term wind-driven X-ray spectral variability of Seyfert AGN  
Francisco Virgili   Liverpool John Moores Univ. Gamma-ray bursts with the Liverpool Telescope
Gemma Anderson   Oxford Univ. Rapid radio follow-up of GRBs with the Arcminute Microkelvin Imager
Chris Davis Liverpool John Moores Univ. The future of time-domain astronomy with Liverpool Telescope 2  

Poster Presentations
Chris Davis Liverpool John Moores Univ. Time Domain Astronomy with the Liverpool Telescope
Christopher Frohmaier Univ. Southampton Volumetric Type Ia supernova rate in the local Universe from PTF
David Starkey Univ. St Andrews Echo Mapping of AGN accretion Disks
Marie Van de Sande   Univ. Southampton Probing flickering variability in cataclysmic variable stars
Georgios Dimitriadis   Univ. Southampton Late time data of PTF Supernovae Type Ia
Marcus Lohr Open Univ. Serendipitous Time-Domain Astronomy: Exploring eclipsing binaries with SuperWASP
Gregory Brown Univ. Warwick Swift J1112.2-8238: A candidate relativistic tidal disruption flare
Adam Stewart Oxford Univ. Discovery of a Short Duration, Low Frequency Radio Transient Candidate at the North Celestial Pole with LOFAR
Helen Jermak Liverpool John Moores Univ.   The RINGO2 Blazar Catalogue
Aidan Glennie Oxford Univ. Fast X-ray transients in Chandra data archive
Ben Gompertz   Univ. Leicester The role of magnetars in short gamma-ray bursts with extended emission
Matt Darnley Liverpool John Moores Univ. Liverpool Telescope Spectroscopic and Photometric Observations of Nova Delphini 2013 (V339 Del)  

LT used to follow the brightest supernovae 0900 GMT 8 May 2014

LT staff Top: An LT image of the super-luminous supernova, PTF12dam. Bottom: A plot showing how the luminosity of PTF12dam varies over time (open circles), compared with models of pair-instability supernovae (PISN) and a magnetar-powered supernova.

Astronomers lead by a team from Queen's University Belfast have recently published new observations which help to constrain the power sources driving the brightest explosions in the Universe, known as "super-luminous" supernovae. Their findings have recently been published in a paper lead by Matt Nicholl in the journal Nature*.

Super-luminous supernovae are 10-100 times brighter than normal supernovae, but are extremely rare. Scientists have proposed several theories as to why these unusual events emit so much light. One long-standing idea is that these supernovae result from an instability (called a "pair-instability") occurring in the most massive stars, objects over 100 times the mass of our Sun. The instabillity generates huge amounts of radioactive material.

Another popular idea is that the additional energy needed to power these supernovae comes from a rapidly rotating, highly magnetic core (a "magnetar"). The more massive the star, the longer it takes for light to escape from the ejected stellar material, resulting in a slower rise to maximum brightness.

One particular super-luminous supernovae, PTF12dam, was seen to evolve very slowly. It was therefore a good candidate for a pair-instability supernova. Nicholl and his team monitored this object for over a year, using the Liverpool Telescope and others around the world. By comparing their data with pair-instability and magnetar models, they found that despite a very slow fade after peak luminosity, PTF12dam brightened too quickly in the early stages to have come from an extremely massive star. However, their analysis showed that a magnetar-powered model could reproduce the observations.

The graph shown to the left shows a comparison between the changing luminosity of the target and four models. The three pair-instability models - the three coloured lines - do not fit the data at all well. They clearly take too long to reach peak brightness, presumably because of a large diffusion mass. The magnetar model, however, indicated by the black curve, fits the data well. In this model the magnetar spins with a period of 2.6 milliseconds, possesses a very strong magnetic field (1014 Gauss), and has ejected 10 solar masses of material.

The Liverpool Telescope is ideally suited for imaging these rare transients, as frequent observations over many days are needed to show how the luminosity varies with time. These and similar observations will continue to provide major clues to unravelling the mysteries of these fascinating supernovae.

* Nicholl M., Smartt S.J., et al. 2014, Slowly fading super-luminous supernovae that are not pair-instability explosions, Nature, 502, 346.