A welcome to "LOFAR and the Transient Radio Sky".

This talk will describe the current progress in building LOFAR and the plan for the coming year.

An overview of the plan to use LOFAR in the search for transients.

X-ray binary systems produce relativistic, synchrotron-emitting jets which have been well-studied at GHz frequencies over the past few decades. They spend the majority of their lives in a quiescent, low-luminosity state, but occasionally brighten by several orders of magnitude as they undergo giant flares. These spectacular outbursts will be prime targets for study with LOFAR, which, in its radio sky monitor mode, will alert the wider community to new outbursts and allow us to study them in the radio band in unprecedented detail. I will give an overview of X-ray binary research, and summarize what we have learned from previous low-frequency radio observations by existing facilities, presenting observations made with the WSRT and VLA in order to help characterise the emission from these sources in the relatively unexplored low-frequency regime. I will review the theoretical predictions for what we can expect to see with LOFAR, and suggest how its unprecedented sensitivity and resolution at these frequencies can be used to answer some of the pressing questions in the field.

Recent developments in the diagnostic diagrams for X-ray binaries allow for the easier connection between stellar and supermassive black holes. With the future demise of purpose-built X-ray timing instruments suited to long term monitoring of X-ray binaries, LOFAR will be on the front line for detecting and monitoring transient X-ray binary outbursts. X-ray binaries will also be the brightest transient sources in Galactic Plane and hence understanding the processes occuring during an outburst are vital. I will present the method and reasoning behind this new diagnostic diagram and how LOFAR observations will further enhance its usefulness in studying the behaviour of X-ray binaries.

The magnetic field of a compact object can present a barrier to the the accretion flow towards it in an interacting binary. In extreme cases the magnetic field can prevent the formation of an accretion disc altogether and rather eject the material from the system as happens around the rapidly rotating white dwarf in AE Aqr, which frequently flares at radio wavelengths. I will present recent observations of AE Aqr at submillimeter wavelengths using the LABOCA bolometer on Apex.

In those cases when an accretion disc does form the magnetic field diffuses into the disc and couples the disc to the compact object. They can then exchange angular momentum, which can be studied through the variations in the spin periods of disc-accreting X-ray pulsars. The standard model of this interaction neglects the role of an intrinsic magnetic field in the disc, but in view of the magnetohydrodynamic nature of the turbulence in an accretion disc one should take into account the effect of a disc dynamo on the exchange of angular momentum between the accretion disc and the compact object.

The accretion/ejection process is one of the most intriguing phenomena in astrophysics. It operates in objects with central masses from far less than a solar mass - young brown dwarfs - to order of 10$^9$ solar masses - the supermassive black holes in the centres of active galactic nuclei. Magnetic fields seem to be crucial for this phenomenon to work.

Especially in young stars, the most nearby accretion/ejection sources, this process can be studied in great detail. I will review the current knowledge on accretion and the highly collimated jets in young stars, and report on recent observations that support the importance of magnetic fields for the jet formation and collimation. I will highlight the transient character of the phenomena in the jets and their sources.

LOFAR is an excellent instrument for discovering new pulsars. I will present our plans and prospects for a survey of the entire Northern Hemisphere as well as targetted searches of globular clusters and nearby galaxies. I will also consider survey strategies for finding classes of pulsars which have more transient radio emission, such as intermittent pulsars and magnetars. The prospects for finding new millisecond pulsars will also be discussed. Recent results of test observations with CS1 will be presented.

We will first report on the current commissioning observations for pulsars@LOFAR; next outline the simulations that help us determine survey strategies for different science drivers; and finally report on the expected results and yields for the LOFAR all-sky pulsar survey.

I will discuss search techniques for dispersed, sub-second bursts in timeseries data. I will focus specifically on advanced methods for extracting astronomical signals from a potentially high interference background and will provide some instructive examples. In particular, I will discuss such searches in the context of an all-sky, "pulsar-like" survey with LOFAR, where the sheer volume of data will require a sophisticated, automated signal-detection algorithm, possibly including machine learning techniques.

Rotating Radio Transients (RRATs) are neutron stars detected only through their sporadic radio bursts. Over 20 of these objects have been discovered thus far in searches with various telescopes. Due to the selection effects inherent in their detection, there may be more RRATs than normal radio pulsars. Therefore, understanding their emission processes and their relationships to other classes of neutron stars is an important goal. In this talk, I will describe our recent progress in searching for new RRATs, obtaining phase-connected timing solutions for RRATs, and observing RRATs at other wavelengths. I will discuss the implications of the new results for the RRATs place in the zoo of Galactic neutron stars, and for the numbers of such sources detectable in ongoing and future surveys.

I willl summarize the theoretical groungs for searching magnetospheric emissions from extrasolar planets, especially hot Jupiters and planets around magnetic stars. Then I will review the past observations and discuss their results. Finally, I will details the strategy defined for LOFAR, consisting both of targeted observations and of piggybacking on surveys.

Lightning-generated radio emission from Saturn has been observed by satellite missions (1980, 1981, and since 2004) and from the ground (since 2006). The highest frequency covered by these instruments is 40 MHz, so that the high frequency spectrum of Saturn lightning remains unknown. Also, in the past, only the average spectrum could be determined. Using a new broadband receiver at UTR-2 (Ukraine), SED were detected over the whole spectral range of the instrument (10-30 MHz) in December 2007. For the first time, this allows to study the instantaneous spectrum of the discharge. However, this study is limited to frequencies below 30 MHz. LOFAR will allow to greatly extend this frequency range, giving information on the slope of the SED spectrum and the energy of the discharge. LOFAR will also allow to directly observe the temporal fine structure of the emission, solving the standing problem of the stroke duration.

Recent studies of cyclotron maser emission mechanism have shown that energetic electron beams are capable of producing intense coherent radio emission from magnetized objects. Studies of strongly magnetized brown dwarfs, flare stars and MCP stars (for example CU Virginis generate strong coherent maser emission that is also characteristic of radio bursts from planets. The radio signature from CU Virginis is particularly interesting since it is of a pulsed nature reminiscent of pulsar radiation. The pulse period is equal to the rotations period of the oblique rotator CU Virginis just as in pulsars. LOFAR will be able to resolve the emitting region and shed light on emission mechanisms. One mechanism that is distinct from the usual loss - cone process is the direct radiation from an energetic electron beam moving into a converging magnetic field. It is conceivable that this mechanism can operate in pulsar magnetospheres. We present the theory, laboratory experimental results and astrophysical obervations demonstrating the applicability of the model.

I will review the expected and observed behavior of stars at low frequencies, using the detailed and numerous observations of solar phenomenology as a starting block, and provide reasons to be optimistic about the impact that the next generation of low frequency arrays will have in the arena of stellar emissions. The expectation of detectable stellar cm-wave and X-ray emission was initially pessimistic based on scaling the Sun’s observed range of flux densities; happily the fields of stellar X-ray emission and cm-wavelength radio emission have matured in the roughly three decades since sensitive detectors capable of good-quality spatial discrimination were deployed. I will discuss lessons learned from experience with Swift triggering on large stellar flares as a different philosophical approach to observing stellar transient emissions. In order to be fair and balanced, I will also play devils’s advocate and present some arguments for why there may not be as many stellar transient low frequency signals as expected by extrapolating from the behavior of a few well-studied systems.

A reanalysis of the discovery dataset of GCRT J1745-3009 revealed several new aspects. In particular, we extracted a more accurate and more complete lightcurve from this dataset. We were able to rule out some of the suggested models for this peculiar radio transient. Also, we derived mild constraints for its maximum distance and maximum size.

We review recent activity in searching for highly dispersed radio bursts with durations of order milliseconds or less. New limits will be placed on the event rate of extragalactic sources and the implications will be discussed. We also look ahead to the next five years and review the potential of upcoming facilities.

Even during commissioning, LOFAR's capabilities can probe new domains in the transients universe. I will show early efforts of using LOFAR in the search for variable and transient radio sources. I will also describe the Transients Key Project software pipeline and future efforts in automated transient detection. One of the greatest opportunities provided by LOFAR is also one of its greatest challenges: massive amounts of data. This flow of data constrains how we search for transients and should be considered in future transient searches.

The LOFAR Transients Key Project is developing a pipeline system for identiftying, monitoring, classifying and responding to transients in LOFAR data, automatically and in real time.

The large quantities of data which must be processed by such as system, combined with the need for accurate and timely response, present significant technical challenges. This talk will outline the architecture adopted, and will emphasise the potential for wider application of our code outside the relatively narrow focus of this particular pipeline.

Testing of the LOFAR transient pipeline is currently being conducted with archival data taken from a variety of radio observatories. The first objective of these tests is to produce a vast number of images, via an automated imaging pipeline of commonly observed fields. These images will then be used to test the efficiency, accuracy and reproducibility of transient searches with LOFAR. The second objective is to discover, classify and interpret previously undetected transient events in these archival observations. A sample of images is currently being produced from the ATCA and VLA archives and will consist of commonly observed astronomical and calibration fields. The total number of images hopefully reaching many thousands. The author will present in his talk an overview of the pipeline imaging techniques used to interrogate these archives. A summary will be given of how transient identification can be performed using source extraction and databasing techniques. Finally a discussion of any new transient events discovered within the tests will be presented.

Exploration of transient sources represents one of the last frontiers in modern astrophysics. The development of a comprehensive understanding of a new event requires real-time observation with multiple instruments. VOEventNet (Caltech, NOAO Tucson and Exeter UK) provides access to a wide range of astronomical events, the X and gamma-ray satellites in space, two microlensing projects, asteroids, several synoptic surveys in optical wavelengths, and others. There is no human in the loop: astronomical alerts and reports are uploaded to a publisher node in a special format, then automatically added to the web pages and also forwarded to other brokers in the network. VOEventNet (voeventnet.org) supplies Google Sky with part of the "Current Sky Events" layer. We are now building a customized subscription service for these events. The idea is that both people and robotic systems can get the alerts quickly enough to respond with follow-up observations. Events have persistent identifiers based on the notion of event Stream: meaning a scientifically uniform set of observations that have not yet happened -- a "catalog of future observation". I will briefly cover authoring and publishing, discovery of event nodes, the Google layer, and subscription to event streams. I hope that LOFAR transients can be included in VOEventNet.

The Allen Telescope Array (ATA), dedicated on October 11, 2007 at Hat Creek, California, is currently undertaking transient surveys of the radio sky at 1.4 GHz. We will discuss ATATS (the ATA Twenty-cm Survey), an 800 square degree field which we have mapped repeatedly (19 times, as of September 2008) in a search for transient sources. As well as searching for changes from epoch to epoch, we are also able to build up a deep, multi-epoch image and associated catalog of the sky, which we can compare to previous surveys such as NVSS.

We present the ATA survey strategy, and the data reduction and transient detection pipelines. We hope that our strategy for studying transients with ATA can inform the LOFAR strategy, and vice versa.

Investigating transient and variable phenomena is a key science project of the Murchison Widefield Array (MWA). I will outline the approach to transient source detection and monitoring that the MWA transient group is taking, including algorithms, data management and event handling.

The Large Area Telescope (LAT) on the Fermi Gamma ray Space Telescope is sensitive to gamma rays with energies between 20 MeV and > 300 GeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, ...

Compared to previous telescopes, Fermi and Lofar will give a two-order magnitude improvement in term of daily sensitivity. They will provide a continuous all sky monitor (only Northern Hemisphere for LOFAR) in the two extreme parts of the electromagnetic spectrum. In this talk, I will focus on the Fermi/LOFAR capabilities in order to probe the nature of the non thermal transient Universe.

LOFAR will trigger an avalanche of transient objects. Followup of many sources at other wavelengths will add significant value to LOFAR data, and may even be necessary for some type of objects.

The capability of the Liverpool Telescope to automatically respond to external triggers makes it perfectly suited to observe LOFAR transients in near-real time. We will describe our general strategy to observe LOFAR transients with the LT and its actual implementation.

I will review the capabilities of the optical cameras ULTRACAM and ULTRASPEC and how they can be used to support the LOFAR Transient Key Science Project. ULTRACAM provides three-colour imaging at frame rates of up to 500 Hz on 4-m and 8-m class telescopes. ULTRASPEC provides intermediate resolution spectroscopy at up to 20 Hz with zero readout noise on 4-m (and hopefully in the future 8-m) telescopes. Such facilities will be crucial to perform follow up optical observations of the very faintest, most rapidly varying signals discovered by LOFAR.

We present the first results from a monitoring project of 30 Low-Mass X-ray Binaries (LMXBs) using the 2-metre robotic Faulkes Telescopes. Since early 2006, we have performed multi-waveband optical photometry of LMXBs using the Faulkes Telescope North on Haleakala, Maui, and have added the Faulkes Telescope South at Siding Spring, Australia since summer 2007. We have detected outburst activity in six sources and variability in quiescence in many others.

Aside from our weekly monitoring of these sources, we are able to react to any outbursts or increased activity, either noted by us, or in Astronomers Telegrams. In these instances, we are able to increase the frequency of our observations or perform studies to detect orbital modulations.

MAGIC is a single Cherenkov telescope sensitive to Very High Energy (VHE) gamma rays above 25 GeV. Since it started operations in 2004 it has detected several galactic and extragalactic radio sources, some of them variable and/or transient. Among the galactic sources we can emphasize the detection and discovery of periodic TeV emission from the peculiar X-ray binary LS I +61 303, as well as experimental evidence of a TeV flare from the accreting stellar-mass black hole Cygnus X-1. Among the extragalactic sources we detected the radio galaxy M87 and several AGNs, including High-frequency-peaked BL Lac objects and the first detections of two Low-frequency-peaked BL Lacs and a Flat Spectrum Radio Quasar. Some of these AGNs were detected/discovered after triggering from our parallel optical monitoring program. We have also observed several Gamma Ray Bursts with typical slewing times of 50s after receiving external triggers, with no detection up to now. In 2009 we will start operating a second telescope, MAGIC-II. Together with the MAGIC-I telescope, stereoscopic observations will become possible, thus improving the background rejection, the sensitivity and the energy and angular resolution of the system. The new MAGIC-stereo system of telescopes will allow us to conduct detailed follow-up studies of transient sources between 25-100 GeV, not achievable with other Cherenkov telescopes, after receiving alerts from other facilities such as LOFAR.

The observation of an electromagnetic counterpart to a putative gravitational wave transient would be one of the more convincing smoking guns for the first direct detection of gravitational waves, and would open up a new observational method for the study of compact objects and strong gravitational fields. The LIGO scientific collaboration and the VIRGO collaboration operate a total of five broadband ground-based gravitational wave interferometers in North America and Europe. Gravitational wave transients received by a network of such instruments should allow the reconstruction of the point of origin of the signal on the sky, permitting follow-up electromagnetic observations. Low frequency radio transients detected by LOFAR are also interesting sources for follow-up analysis of gravitational wave data. After outlining the principles of gravitational wave interferometry and the status and planned schedule for the instruments, we discuss astrophysical sources that make promising candidates for collaborative searches and give a tentative indication of requirements for a LOFAR transient survey to maximize the probability of successful joint observations.