Time-domain astronomy

For more detail on transient objects, see Transient astronomical event.

Time-domain astronomy is the study of how astronomical objects change with time. Though the study may be said to begin with Galileo's Letters on Sunspots, the term now refers especially to variable objects beyond the Solar System. This may be due to movement or changes in the object itself. Common targets included are supernovae, novas, flare stars, blazars and active galactic nuclei. Visible light time domain studies include HAT-South, the Large Synoptic Survey Telescope, PanSTARRS, SkyMapper, the Wide Angle Search for Planets and the Catalina Real-time Transient Survey.

Time-domain astronomy includes the study of transient astronomical events, often shortened by astronomers to a transient: astronomical objects or phenomena whose duration may be from milliseconds to days, weeks, or even several years. This is in contrast to the timescale of the millions or billions of years during which the galaxies and their component stars in our universe have evolved. Singularly, the term is used for violent deep-sky events, such as supernovae, novae, dwarf nova outbursts, gamma-ray bursts, and tidal disruption events, as well as gravitational microlensing, transits, eclipses, and comets.

In radio astronomy the LOFAR is looking for radio transients. Radio time domain studies have long included pulsars and scintillation. Cherenkov Telescope Array, eROSITA, AGILE, Fermi, HAWC, INTEGRAL, MAXI, Swift Gamma-Ray Burst Mission and Space Variable Objects Monitor will look for transients in X-ray and gamma rays. Gamma ray bursts are a well known high energy electromagnetic transient.

Time domain astronomy uses robotic telescopes, automatic classification of transient events, and rapid notification of interested people. Blink comparators have long been used to detect differences between two photographic plates, and image subtraction became more used when digital photography eased the normalization of pairs of images. Time domain work involves storing and transferring a huge amount of data. This includes data mining techniques, classification, and the handling of heterogeneous data.

Historically time domain astronomy has come to include appearance of comets, and cepheid variable. Old astronomical plates exposed from the 1880s through the early 1990s held by the Harvard College Observatory are being digitized by the DASCH project.

Other causes of time variability are asteroids, eclipses, microlensing, planetary transits, and variable stars.

History

Before the invention of telescopes, transient events that were visible to the naked eye, from within or near the Milky Way Galaxy, were very rare, and sometimes hundreds of years apart. However, such events were recorded in antiquity, such as the supernova in 1054 observed by Chinese, Japanese and Arab astronomers, and the event in 1572 known as "Tycho's Supernova" after Tycho Brahe, who studied it until it faded after two years. Even though telescopes made it possible to see more distant events, their small fields of view – typically less than 1 square degree – meant that the chances of looking in the right place at the right time were low. Schmidt cameras and other astrographs with wide field were invented in the 20th century, but mostly used to survey the unchanging heavens.

The interest in transients has intensified because studying them helps astrophysicists to understand the mechanisms which produced our universe. As telescopes with larger fields of view come into use, such as the Palomar Transient Factory, the spacecraft Gaia and the LSST, they spot many more such occurrences. The ability of modern instruments to observe in wavelengths invisible to the human eye (radio waves, infrared, ultraviolet, X-ray) increases the amount of information that may be obtained when a transient is studied. The proposed ULTRASAT satellite will observe a field of more than 200 square degrees continuously in the ultraviolet range. This wavelength is particularly important for detecting supernovae within minutes of their occurrence.

See also

• Celestial event
• Fast blue optical transient
• List of gamma-ray bursts
• List of gravitational wave observations
• Soft X-ray transient
• X-ray burster
• X-ray pulsar
• X-ray transient

Further reading

• Vedrenne, G. & Atteia, J.-L. (2009). Gamma-Ray Bursts: The brightest explosions in the Universe. Springer. ISBN 978-3-540-39085-5.
• Gezari, S.; Martin, D. C.; Forster, K.; Neill, J. D.; Huber, M.; Heckman, T.; Bianchi, L.; Morrissey, P.; Neff, S. G.; Seibert, M.; Schiminovich, D.; Wyder, T. K.; Burgett, W. S.; Chambers, K. C.; Kaiser, N.; Magnier, E. A.; Price, P. A.; Tonry, J. L. (2013). "Thegalextime Domain Survey. I. Selection and Classification of over a Thousand Ultraviolet Variable Sources". The Astrophysical Journal. 766 (1): 60. arXiv:1302.1581. Bibcode:2013ApJ...766...60G. doi:10.1088/0004-637X/766/1/60.

External links

• "Centre for Time-Domain Informatics". Retrieved 5 May 2013.
• Bernardini, E. (2011). "Astronomy in the Time Domain". Science. 331 (6018): 686–687. Bibcode:2011Sci...331..686B. doi:10.1126/science.1201365. ISSN 0036-8075. PMID 21212319.
• SIMBAD Astronomical Database
• Sidoli, L. (2008). "Transient outburst mechanisms in Supergiant Fast X-ray Transients". arXiv:0809.3157 [astro-ph].