Transient phenomena in astrophysics are among the most interesting and enigmatic subjects of study in the entire Universe. Yet, with the notable exceptions of the wide-field satellite experiments BATSE, EGRET, and ALEXIS, and the Milagro detector under construction at Fenton Hill, present astrophysical research programs sample the world of transients only haphazardly. It can be argued that we sample the time domain much more poorly than we do the spectral or the spatial domains. It is our ultimate aim to develop a multiwavelength observational facility, at the Los Alamos site on Fenton Hill, dedicated to the study of transient phenomena.
We include here a list of examples of transient phenomena, to which we expect Fenton Hill Observatory to contribute.
The most energetic phenomena known are Active Galactic Nuclei and Quasars. These emit radiation at almost every frequency we have been able to observe, from very long wavelength radio waves to very high energy (TeV) gamma rays, and are variable on time scales from sub-seconds to years. We do not understand these objects very well, though we believe they are powered by the accretion of matter onto million-solar-mass (or bigger) black holes. The transient phenomena observed in these sources could be associated with the accretion process, or more generally with the dynamics of matter in the vicinity of the black hole. More observations of flaring and variability, preferably coordinated over many wavelengths, would give us valuable new information as to the nature and character of these fascinating objects.
Supernovae are the explosions of stars at the end of their lives, and are most often seen in distant galaxies, frequently outshining the entire galaxy. They are as yet unpredictable, and are best discovered through a regular program of monitoring a large number of candidate galaxies. Besides their intrinsic interest, they function as standard candles for the measurement of the scale, age, and evolution of the Universe.
Gamma-ray bursts were discovered by Los Alamos scientists with the Department of Energy VELA satellites in the 1960's, and their cause remains unknown. In the spring of 1997, the first three optical counterparts to gamma-ray bursts have been discovered, and there is clear evidence from one of these that it is at a cosmological distance. Discovering an optical counterpart requires accurate positions at the high energies at which they are first detected, and these are now becoming available from the Beppo/SAX experiment, and in the future from MOXE and LOBSTER. The Milagro TeV gamma-ray telescope now under construction at Fenton Hill will also provide alerts with sufficient accuracy for an optical observation.
Microlensing events are examples of the phenomenon of the bending of light by gravitational mass, predicted by Einstein's General Theory of Relativity. Since most of the mass of the Universe apparently does not shine by its own light, it must be detected indirectly, by the effect that it has on the light of distant stars. The study of microlensing events, of which about 100 have already been observed, can tell us much about the location and physical characteristics of the dark matter, and therefore about the main constituent of the Universe.
Variable stars have fascinated humans since the dawn of our species, and while we know much about how many of them work, we still do not understand all the different types of variability, and how stars become variable, or cease variability. Certain types of variable stars are also standard candles for measuring cosmological distances.
Flare stars are low-temperature stars that experience sudden brightenings, by a mechanism thought to be the same as that which produces the much more modest flares on our own sun, namely the rapid reconnection of magnetic flux lines and the consequent conversion of magnetic energy to accelerated particles, heat and light.
Comets and Asteroids, temporary visitors to our part of space, have long been subjects of human fascination, dread and fear. The thrill of discovery has motivated many thousands of amateurs to spend long hours sweeping the heavens with modest equipment. Some of these people have been rewarded with objects bearing their own names, yet the population and size distribution of these objects is still poorly known. The mounting evidence that such objects may have been responsible for some of the mass species extinctions on Earth, and the recent observation of a comet's demise in the atmosphere of Jupiter, has heightened interest in the task of thorough characterization of those Solar System objects that might someday be a threat to life on Earth.
An observational facility for the study of transient astrophysical phenomena could detect all these, and possibly reveal new objects that aren't known at all today, or completely new characteristics of previously known objects. The physics of astrophysical transients is, as indicated in the list above, extremely diverse, while the technology for detecting such phenomena does not discriminate among them. It is therefore necessary to acquire expertise across a wide range of astrophysics to adequately maintain and operate such an observatory, and make sense of the data obtained. Establishing new collaborations across a broad spectrum of the scientific community, possibly including a program of visiting scientists and postdoctoral fellows, would help us keep up to speed in all of these phenomena.