- RECENT HEADLINES
- LT adds spectroscopy to its automatic rapid-response capabilities
- Liverpool Telescope Involved in Gravitational Wave Followup Campaign
- Memorandum Of Understanding signed for development of new 4-metre class telescope
- Gravitational wave science used to search for catastrophic explosion
- LT's polarimetry helps disentangle the cause of double-peaked optical outbursts
Simplified flowchart of user RTML submission to LT.
© 2016 LT Group
The low-resolution spectrograph SPRAT recently joined IO:O and IO:I as an instrument that can also be accessed by an alternative method — that in some cases can be faster, more convenient, and allow for immediate response to transient events (TAC permitting of course). This method is RTML.
RTML and the LT
Regular users of the Liverpool Telescope (LT) will be familiar with the standard method of setting up their observations, namely the Java-based Phase 2 User Interface or "Phase2UI".
This user interface, accessible only to registered users of the LT, enables them to manually define their observation details: the coordinates of their targets; the timing of their observations; the instruments and filters to be used; and the number and length of the exposures. The interface transmits this information directly to the telescope's Phase 2 database, which is polled by the robotic scheduler repeatedly through the night between observations to decide what to observe next — i.e. to match the best observation to current conditions.
If using the Phase2UI at night, the new or updated observation group will be considered by the scheduler as soon as it makes its next poll. So it could potentially be chosen and observed mere seconds after the "Submit" button is pressed.
What may not be so widely known is the alternative way of entering observation details, which in some cases is faster and more convenient. It uses the "Remote Telescope Markup Language" (RTML) protocol*, which was invented in 1989 at the University of California at Berkely, USA. It's a special dialect of XML (Extensible Markup Language), and is used to remote-control telescopes, or to communicate with autonomous robotic telescopes.
We provide two different ways to use RTML to send your observation details to the LT. Like the Phase2UI, both of them insert the information straight into the phase 2 database. The advantage however is that they allow you to automate the Phase 2 process, particularly useful if you have a lot of targets or observation groups to enter. The two RTML interfaces are:
- command-line tools:
- one tool to generate the RTML, and another to send the RTML directly to the LT
- can be incorporated into customised scripts and programs
- example use: generating and entering many targets quickly
- LT-specific RTML Application Programming Interface (API):
- allows users to build their own customised GUI tools at their institutions
- GUI makes use of API to generate RTML and send directly to LT
We have in the past provided a third interface: bespoke webpages created by us for users who do not want to program with the command-line tools or API. These restricted-access pages contained HTML forms tailored to a user's specific observing programme. They generated observation details in RTML and transmitted directly to the LT. These pages are now being phased out.
Both RTML interfaces can also talk directly to the Target of Opportunity Control Agent (TOCA), the system that triggers the LT's rapid-response capability to interrupt the current observation and immediately observe your target instead. The LT already does this for Gamma-Ray Burst alerts via a different protocol, but it's also possible via RTML.
As you can imagine, overrides can be very disruptive. Therefore permission to have TOCA capability has to be requested at the Phase 1 stage and approved by the TAC.
RTML capability is being phased in across the LT's suite of instruments. IO:O and IO:I have been available for RTML response for some time, and now SPRAT has been added to the list. FRODOSpec and RISE are next, and we hope to have them available soon.
Applying for RTML capability
The RTML facility is available to all users who have TAC-awarded time allocations. Please contact us if this sounds interesting, and we will provide full user instructions.
Artist's impression of the two binary black hole systems discovered by aLIGO. Credit: LIGO/A.Simmonet
The Liverpool Telescope (LT) is part of a followup collaboration of telescopes set up to find the electromagnetic (EM) component of gravitational wave events detected by the Advanced Laser Interferometer for Gravitational-wave Observations (aLIGO). The flare of light is not expected to last long, so the "traditional" telescopes that detect only EM radiation must respond rapidly to characterise the source objects.
The LT helped in the search for the EM component for the very first gravitational wave (GW) detection event on 14th September 2015. It did so again for the second event, which although announced by aLIGO last week (see https://www.ligo.caltech.edu/news/ligo20160615), actually occurred on 26th December 2015.
aLIGO alerts of GW events are passed to observatories for followup as little as 30 minutes after detection. They give a search area within which the GW event could have occurred. This search area however is huge, and only facilities with very wide fields of view can efficiently make the initial sweep to look for new transient objects. Once flagged, the LT and other EM facilities can characterise each candidate in the list.
In both events no EM facility found an EM component, but the strategy for instant followup of such alerts is now in place, and has been tested successfully several times.
In a paper entitled "Liverpool Telescope follow-up of candidate electromagnetic counterparts during the first run of Advanced LIGO" Chris Copperwheat et al discusses the LT contribution to the follow-up campaign, and describes in detail the LT's followup strategy and its observations of the candidates GW objects. The paper is currently available from here: https://arxiv.org/abs/1606.04574.
LJMU Vice-Chancellor, Prof Nigel Weatherill and the Director of the Instituto de Astrofisica de Canarias (IAC) Prof Rafael Rebolo López have signed a Memorandum of Understanding to explore the design, construction and operation of the new 4.0 metre telescope which will be on a bigger scale than the current Liverpool Telescope (LT) which has been studying the cosmos and making discoveries for over a decade.
The new telescope will be built on the Spanish Canary Island of La Palma and will be 4 times more sensitive and 10 times faster to respond to unexpected celestial events than the current world-record-holding 2-metre LT, also based on La Palma.
The new optical telescope will have the capability to see deeper into the cosmos, observe exploding stars (supernovae, gamma ray bursts, exoplanets and binary stars) and search for new planets, enabling a different type of science. This kind of study (time-domain astrophysics) will greatly increase in the coming decades, therefore the development of the new 4-metre class facility is vital in being able to explore the Universe in greater detail than ever before.
As well as being scientifically world-leading, the design and construction of the new telescope will exploit new technologies in advanced materials, optics and control systems. Researchers are keen for businesses in the region to provide that technology.
The project is also very exciting for the National Schools’ Observatory, which currently gives school children free access to the LT, and will expand to make use of the new telescope, creating an unrivalled opportunity to enthuse a generation of children about science, technology, engineering and mathematics.
Professor Iain Steele from LJMU's Astrophysics Research Institute (ARI) said: "The timing of this agreement is perfect. With new international discovery facilities like the LIGO and Virgo gravitational wave detectors and the Large Synoptic Survey Telescope coming on line over the next decade, a new high sensitivity spectroscopic capability is desperately needed. The new telescope will fill that niche perfectly”.
Professor Chris Collins, Head of the ARI, added: “This is a major opportunity to greatly expand the excellent science currently carried out by the Liverpool Telescope to cosmological distances. Investigating the exotic physics which govern many distant ultra-energetic sources using data from a large and fast reacting new 4m robotic telescope will keep us busy for many years to come.”
Dr Johan Knapen, IAC, commented: "The project builds on the hugely successful collaboration between LJMU and the IAC in building and operating the LT, which has been making discoveries for a decade. We look forward to working closely with LJMU in this project, which is of the highest calibre both technologically and scientifically."
Professor Rafael Rebolo López, IAC, said: "The new telescope will identify hundreds of exceptional astronomical sources each year, from binary black holes and supernovas, to counterparts of gravitational waves sources. By linking the new telescopes observations with those we can make with the Gran Telescopio Canarias we will be able to characterize these new sources in great detail. Both telescopes complement each other very well.”
Prof Ahmed Al-Shamma'a, Dean of the LJMU Faculty of Engineering and Technology said: "The combination of expertise of LJMU's Faculty of Engineering and Technology and the IAC's leading role as a technology development centre for astronomy puts in a unique position to deliver the technology needed for the project. The new telescope is now in the initial design phase and will be of interest to research centres, universities and companies that want to stand out in a technology sector that will have a major development in the coming decades.”
Researchers at Liverpool John Moores University's (LJMU) Astrophysics Research Institute (ARI) using the Liverpool Telescope (LT) were actually among the first to use new gravitational wave science, before the recent announcement by the USA's Caltech and MIT-run Laser Interferometer Gravitational Wave Observatory (LIGO) that they had made the first direct detection of gravitational waves.
Recognised as world leaders in this field, the ARI was asked to participate in a global study using gravitational wave astronomy months before the LIGO revealed gravitational waves had been detected. LIGO made the detection in September and a global collaboration of astronomers was asked to search for the merger of two neutron stars - a catastrophic and explosive event which should be detectable by the world's major telescopes. The LIGO detector gives only an approximate position, so astronomers were required to search a huge area of sky to find the light from the explosion.
The team from LJMU's Astrophysics Research Institute was led by Professor Iain Steele and Dr Chris Copperwheat and one of the many telescopes deployed in the search was the Liverpool Telescope, which used the SPRAT spectrograph, built by LJMU PhD Student Andrzej Piascik, to characterise candidate detections. A paper was published in the Astrophysical Journal giving a complete overview of these observations.
Dr Chris Copperwheat commented: “The search for the explosion was unsuccessful, which was not surprising given that the LIGO was also able to reveal that the event was not from a merging pair of neutron stars but from a merging pair of black holes, which are not expected to have a detectable signature.
“Nevertheless, the exercise was an important test of the capabilities of the astronomical community to coordinate and perform the challenging observations required to follow an event such as this one. We believe there are many more neutron star binaries in the universe than black hole binaries, so given that LIGO has proved its capabilities, the detection of a neutron star merger is now only a matter of time.
“The detection of such an explosive event and the observation of the associated light is the next milestone in this new and transformative field of gravitational wave astronomy.”
Over the next few years the LIGO detectors will be complemented by additional detectors currently under construction around the world, and the combined array should reach full sensitivity by around 2022, at which point astronomers are likely to be able to detect hundreds of gravitational wave events every year.
LJMU is currently developing a new, larger robotic telescope, codenamed Liverpool Telescope 2, which is also expected to come into operation in 2022. One of the core science topics for Liverpool Telescope 2 is gravitational wave astronomy, and the new facility will enable LJMU's Astrophysics Research Institute to play a major role in exploring this new frontier.
Professor Chris Collins, Head of the ARI, added: “It is hugely exciting that we have started doing gravity wave science with the Liverpool Telescope. The recent LIGO results open the way for astronomers to study those energetically violent events in the Universe that give rise to gravity wave ripples."
This story was adapted slightly from that which appeared on the LJMU News site on 11 March 2016.
Credit: Valtonen et al, 2016.
The Liverpool Telescope (LT) recently took part in a ground-breaking campaign to accurately measure the rotational rate of one of the most massive black holes in the universe: the powerhouse behind blazar OJ287. Details behind the discovery are given in a paper in the Astrophysical Journal Letters entitled "Primary Black Hole Spin in OJ287 as Determined by the General Relativity Centenary Flare" by M. J. Valtonen et al (2016).Quasars, Blazars and Black Holes
Quasi-stellar radio sources, or "quasars" for short, are the very bright centres of distant galaxies which emit huge amounts of light, via relativistic jets due to the accretion of large amounts of matter onto their massive black holes. When the jet is pointed toward the observer, the source is called a "blazar". From observations dating back to 1891, the particular blazar "OJ287" has been seen to outburst optically roughly every 12 years. More recent studies have shown that these outbursts actually have double peaks.
Prof. Mauri Valtonen of University of Turku, Finland and his collaborators developed a model to explain the outbursts: two black holes orbiting each other with a period of 12 years, interacting every orbit. The model states that one black hole (the "primary") is ~200 times the mass of the other (the "secondary"), and has an accretion disc. The secondary is in a large very elliptical orbit about the primary, and the plane of its orbit is inclined to that of the accretion disc, so it makes two crossings of the disc every orbit. Each time the secondary punches through the disc, the material it encounters is heated up to very high temperatures. This heated material flows out from both sides of the primary accretion disk and thermally radiates strongly for a few weeks.
Meanwhile, the interaction of the secondary black hole with the primary's accretion disk also results in accretion onto the secondary black hole. It is postulated that the second peak in the outburst is caused by jet emission rather than emission from the accretion disc. Evidence for jet emission is the presence of strong polarisation during the second, but not the first, flare. An accretion disc cannot create a strong polarisation signal; in this case it is likely that the magnetic fields within the jet cause the polarisation signal.
The thermal outbursts can be used as good markers to pinpoint the times when the secondary crosses the plane of the primary's accretion disc. This is useful because Einstein's General Theory of Relativity says the secondary's orbit should precess, at a rate that depends mainly on the two black hole masses and the rotation rate of the primary.The Liverpool Telescope Gets Involved
In 2010, Valtonen and collaborators were able to use the exact timing of eight outbursts to accurately put the secondary's orbital precession rate at an incredible 39 degrees per 12-year orbit, some 27,000 times faster than the relativistic contribution to Mercury's orbital precession rate.
The model also predicted that the next twin-peaked outburst would occur around 25 November 2015, ironically the 100th anniversary of Einstein's General Theory of Relativity. An international observing campaign campaign was set up, calling on observatories from around the world - including the Liverpool Telescope.Countdown to the Next Event
Credit: Valtonen et al, 2016.
OJ287 has actually been observed by the LT since 2011, and was more closely monitored from September 2015 as part of the leadup to the predicted outburst. When the increase in flux began in late November 2015, PhD student Helen Jermak, the Principal Investigator of proposal JL16A08 using the RINGO3 polarimeter on the LT, was prompted to increase the cadence of the OJ287 monitoring observations from every 3 days to hourly, to closely follow the "flare" of this outburst.
The LT automatically tracked the source many times per night, taking photometric and polarimetric data with RINGO3. The polarimetry taken during the second peak allowed the authors to study the effect of the interaction between the secondary black hole and primary accretion disc on the primary's jet.Another Black Hole Binary and More Gravitational Waves
Thanks to the valuable contribution of this data plus that of other observatories, Valtonen and his co-workers were able to directly measure the rotation rate of the more massive black hole to be one third of the maximum spin rate allowed in General Relativity.
The collected data from this latest outburst also allowed the team to confirm the loss of orbital energy to gravitational waves within two per cent of General Relativity's prediction. This provides the first indirect evidence for the existence of a massive spinning black hole binary emitting gravitational waves.
This is encouraging news for the Pulsar Timing Array efforts that will directly detect gravitational waves from such systems in the near future. Therefore, the present optical outburst of OJ287 makes a fitting contribution to the centenary celebrations of General Relativity and adds to the excitement of the first direct observation of a transient gravitational wave signal by LIGO.