- Rapid-response monitoring of a "nearby monster"
- Bumps, Burps and Bangs hit this year's National Astronomy Meeting in Portsmouth
- LT used to follow the brightest supernovae
- LT used to monitor a remarkable recurrent nova in M31
- Black Hole discovered orbiting a Spinning Star
- LT's GAIA tracking featured on the BBC's Northwest Tonight news show
- RINGO2 Used to Probe Early Evolution of Gamma Ray Bursts
- Comet chasing with the BBC
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).
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.
|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|
|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)|
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.
In late 2013 another outburst of a rather unusual "recurrent nova (RN)" in the Andromeda galaxy, M31, was announced by the intermediate Palomar Transient Factory (iPTF). Novae are thought to be associated with binary systems which undergo a sudden brightening as material from an evolved secondary star falls (or "accretes") onto a compact primary star, usually a white dwarf. The accreting material ignites via nuclear fusion producing a sudden burst of radiation. Recurrent novae are - as the name suggests - objects which undergo multiple outbursts.
Like other RN, the object in M31, dubbed M31N 2008-12a, has been observed in outburst a number of times in the past. What makes this particular object interesting is its very short "recurrence timescale", i.e. the time between outbursts. M31N 2008-12a outbursts have been recorded almost annually since late 2008, when the object was first identified as a nova. Previously the most frequent RN was the Galactic system U Scorpii, which has a ~10 year inter-outburst time, making M31N 2008-12a all the more remarkable!
M31N 2008-12a is classed as a "very-fast" nova because it takes just four days for the brightness of the object to decline by two magnitudes. As such, our knowledge of its "lightcurve" (a graph showing how the object's brightness changes with time) is limited, even after five outbursts have been witnessed. Follow-up observations of the RN - something the LT does extremely well - were clearly needed.
Following the 2013 outburst, Dr Matt Darnley of the Astrophysics Research Institute here at Liverpool John Moores University formed a collaboration with Dr Martin Henze of the European Space Astronomy Centre in Spain. Their goal was to investigate ground-based optical plus space-based Swift X-ray and UV observations of the outburst, as well as Hubble Space Telescope (HST) infra-red, optical and UV observations of the "progenitor" system, i.e. the system before an outburst occurred. The collaboration also included LJMU's Steven Williams and Prof. Mike Bode.
A Liverpool Telescope IO:O image of the 2013 outburst, shown on the right, was used to precisely determine the position of the nova so that a search for a progenitor could be made. Archival HST observations - taken when the system was not in outburst - indicated the presence of a system coincident with the outburst position. This progenitor is consistent with a binary system known to contain an evolved secondary star (a sub-giant or red giant) and a luminous accretion disk. Such a bright disk indicates a high accretion rate, which is required for a system with such a short recurrence timescale.
An X-ray plus UV monitoring campaign undertaken with the Swift satellite soon after the 2013 outburst clearly detected a bright X-ray source only six days after the optical discovery. Such X-ray emission can only be detected when the nuclear burning on the surface of the white dwarf is viewed directly. The X-ray source persisted for two weeks before "turning-off", indicating the end of the nuclear burning phase. From these and other supporting observations Darnley et al. were able to identify the primary as a very high mass white dwarf.
Such a system - containing an evolved secondary star, a high mass white dwarf star, and a luminous accretion disk - coupled with a short recurrence time, is a prime candidate for a system that may one day become a "Type Ia supernova". SN Ia can be used to accurately measure the distances to very distant galaxies, and thereby map the expansion (and indeed the acceleration!) of the universe. As such our understanding of Type Ia supernova is of considerable importance. With its one-year outburst timescale, the team will be eagerly monitoring M31N 2008-12a with the LT and with other facilities over the next 12 months to see what happens next with this remarkable object.
A group of Spanish astronomers using the Liverpool and Mercator Telescopes at the Observatorio del Roque de los Muchachos have recently reported the discovery of a binary star system comprising a Be-type star and, remarkably, a black hole.
Jorge Casares of the Instituto de Astrofisica de Canarias (IAC) and La Laguna University (ULL) is lead author on a paper1, recently published in the science journal Nature, in which he and his colleagues present their exciting results.
Be-type stars are known to be fast rotators, and many find themselves to be one-half of an interacting binary system. However, their companions are usually neutron stars. This is the first time that the object orbiting the Be star has been identified as a black hole.
The newly-discovered system is located in the constellation Lacerta (the Lizard), at a distance of about 8,500 light years from the Earth. Known as MWC 656, the Be star rotates with an angular velocity of more than 1 million kilometres per hour. At this speed the star is close to being ripped apart by centrifugal forces, and is ejecting matter through an equatorial disk towards its mysterious companion. Casares' new spectroscopic observations indicate that this companion is a black hole.
A detailed analysis of the spectrum of MWC 656 suggests that its companion has a mass somewhere between 3.8 and 6.9 times that of the sun. Such an object is too massive to be a neutron star, and can only be a black hole. Matter is transferred from the Be star, though its equatorial disk, down onto the black hole via a second disk (an "accretion disk"). By analysing the emission from this second disk Casares and his team were able to measure the mass of the black hole.
In all likelihood, binary systems comprising Be-type stars and black holes are far more common than previously thought. Even so, it is notable that such a discovery was made using two relatively modest-sized telescopes, the 2.0 meter LT and the 1.2 meter Mercator telescope.
|Spectroscopic observations obtained with FRODOspec on the Liverpool Telescope showing the orbital evolution of emission lines from ionised Iron (Fe) and ionised Helium (He) atoms: (a) a sequence of spectra showing the change in line profile shape through one orbital phase; the vertical dashed line indicates the rest wavelength of each transition. (b) trailed intensity images of the same two emission lines plotted across two orbital cycles. See paper [ Nature | Astro-ph ] for further details.|
As part of the BBC's Stargazing Live 2014 series of events, the Liverpool Telescope featured recently on the Northwest Tonight news programme. LT staff and scientists from the Astrophysics Research Institute at Liverpool John Moores University explained how the telescope is being used to track the recently-launched GAIA satellite.
GAIA is a major ESA space telescope which aims at obtaining a 3-dimensional map of large chunks of the Milky Way. To do this, the position of the satellite must be known precisely. Telescopes like the LT are thus conducting nightly observations of the satellite, which will observe from a gravitationally stable point in space called 'L2'. At a distance of 1.5 million km from Earth, L2 lies on the axis that links the Earth to the Sun, and is in fact in the shadow of the Earth. GAIA will therefore orbit this point so that sunlight can be used to provide power to the satellite.
GAIA will measure the positions and velocities of about one billion stars - that's about 1% of all stars in the Milky Way. With these data astronomers should be able to probe the composition, formation and evolution of our Galaxy. GAIA should also reveal thousands of variable and transient phenomena, since it will re-observe large sections of sky every few days.
GAIA will observe the Milky Way for at least five years. Monitoring the position of GAIA is just one of many nightly duties conducted robotically by the LT. It is, however, arguably one of its most important.
A team led by Professors Carole Mundell and Iain Steele of Liverpool John Moores University (LJMU) is making great strides in understanding the enigmatic jets produced by massive stars in distant galaxies. These jets slam into gas and dust surrounding the system, producing a sudden burst of energy which, when directed towards the earth, is identified as a surge in gamma-ray emission. This surge is usually spotted first by NASA's SWIFT satellite, which immediately alerts astronomers on the ground who can then pursue rapid follow-up observations with other telescopes.
Gamma-Ray Bursts, as they have become known, are intrinsically the brightest sources of electromagnetic radiation in the night sky. Yet these burst are extremely short-lived, lasting in some cases less than minutes or even much less than a second. The initial burst is followed by a longer-lived though quickly fading afterglow. Rapid response to these events is therefore a necessity - and that's where the LT comes in.
Together with her team, Prof. Mundell has made use of a custom designed instrument, RINGO2, to measure and, importantly, monitor the polarisation of the optical emission from these events. RINGO2 was built by Prof. Steele and his small yet highly talented group of instrument builders at LJMU (indeed, RINGO2 has already been replaced by an upgraded "three beam" polarimeter, RINGO3, which is on the telescope and is currently being characterized).
As reported recently in the science journal Nature, the detection of highly polarized light from a Gamma Ray Burst detected in March 2012 (GRB 120308A), and the evolution of its afterglow with time, showed that GRBs contain large-scale, uniform magnetic fields that can survive long after the initial explosion.
Previous observations of optical afterglows from GRBs have detected polarizations of about 10 percent. However, these studies provided no information about how this value changed with time. As a result, they could not be used to test competing GRB jet models.
Remarkably, the LT managed to slew to and observe GRB 120308A within just four minutes of its discovery. Professor Mundell and her colleagues were able to report the initial detection of visible light with 28% polarization; within ten minutes the degree of polarization had decreased to 16%, although the polarization angle remained remarkably stable. Theoretical models predict the presence of strong and stable polarized emission if the jet possesses a structured magnetic field. Mundell's findings infer the existence of such a globally ordered magnetic field, and therefore support these models. Moreover, the observations suggest that these fantastic cosmic explosions are powered magnetically, like a solar flare, and not by radiation, like the big bang.
As well as providing new insight into the physical mechanisms of the most powerful and distant explosions in the Universe, the discovery of highly polarised light from this GRB afterglow may pave the way for future space missions. Conducting measurements similar to those described above - but in X-rays - could be of great value. This could, for examople, be accomplished by fitting a burst monitor and X-ray polarimeter to the recently approved ESA mission ATHENA+. Such a device could be the prime GRB facility for the coming decades.
Keen astronomers will no doubt have noticed that the Liverpool Telescope recently featured in an episode of the BBC's Sky at Night programme. The TV crew spent a few days at both the LT and the Isaac Newton Telescope, where images and spectroscopy of Comet C/2012 S1 ISON, the so-called "Comet of the Century", were obtained. Prof. Mike Bode and Dr Jon Marchant welcomed the TV crew and a group of amateurs and professional astronomers to the LT. Mike and Jon spent a long though fruitful night observing (a rarity for the LT, which of course is fully robotic and therefore usually operates without human intervention). The BBC team, meanwhile, went about their business, and managed to get some great footage of the observatory, including some wonderful time-lapse photography of the telescope in action.
The skies remained clear through most of the night. The telescope and instruments behaved flawlessly, and a considerable amount of data were obtained, on Comet ISON, but also on a couple of other comets which also featured in the show.
Streaming video of the episode itself can be found here: Sky at Night episodes
For older news items, see the News Archive