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<\/p>\nOn 14 November 2014, a bright flash flagged the All Sky Automated Survey for Supernovae, or ASAS-SN \u2014 a global network of 20 telescopes managed at Ohio State University in the U.S. The flash originated in galaxy ESO 253-3, located 570 million light-years away.<\/p>\n
The sudden burst of energy was examined by astronomers and categorized as a likely supernova and assigned the event designation ASASSN-14ko. Six years later, Anna Payne, a NASA Graduate Fellow at the University of Hawai\u2019i at M\u0101noa, discovered it was something much different.<\/p>\n<\/p>\n
While sifting through ASAS-SN data on active galactic nuclei, she discovered a previously unnoticed periodic series of bright flares emanating from galaxy ESO 253-3 \u2014 repeating in such a way that led directly back to ASASSN-14ko as the point of first detection.<\/p>\n
This was not a supernova as first thought, as a stellar explosion would not repeat at all let alone with such regularity as that observed with ASASSN-14ko.<\/p>\n
Anna and her team began to study the phenomenon in more detail, as the possibility emerged that they had found a periodic variable active galactic nuclei \u2014 a long sought for entity that could, in part, help astronomers better understand some of the processes taking place around supermassive black holes.<\/p>\n
An original event repetition calculation of 111.82 \u00b1 1.9 days was derived from the ASAS-SN light curve data. As more data was analyzed from other sources and missions, including the NASA and MIT Transiting Exoplanet Survey Satellite (TESS), the period was refined to 114.2 \u00b1 0.4 days.<\/p>\n
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Galaxy ESO 253-3, seen by the European Space Observatory\u2019s Multi Unit Spectroscopic Explorer. (Credit: Michael Tucker at the University of Hawai\u2019i and the AMUSING survey)<\/p>\n
The use of TESS data is not surprising. The platform is an exoplanet hunting satellite designed to observe large portions of the sky at a single time for month-long periods as part of its initiative to perform an near all sky survey for transiting exoplanets (those that visibly pass across the surface of their host star when observed) close to Earth.<\/p>\n
NASA mission updates (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n Due to its wide field of view, TESS is ideal for passive monitoring of large sections of the background sky that just happen to lie within its observation field.<\/p>\n This proved useful for Anna and her team as the telescope observed one of the ASASSN-14ko flare events during its observations of Sectors 4, 5, and 6 of the southern hemisphere from 18 October 2018 to 7 January 2019.<\/p>\n From that period, the team was able to extract crucial data from the TESS archive to study the November 2018 flare event from beginning to end.<\/p>\n Because TESS was designed with precision optics to be able to identify the smallest of changes in light curves from thousands of stars simultaneously across a wide field of view, the telescope\u2019s data allowed the team to observe the ASASSN-14ko outburst with unprecedented detail that revealed a very smooth rise in brightness over a 5.6 day period prior to peak.<\/p>\n Likewise, the decline from peak luminosity was extremely smooth.<\/p>\n \u201cTESS provided a very thorough picture of that particular flare,\u201d said study co-author Patrick Vallely, an ASAS-SN team member and National Science Foundation graduate research fellow at Ohio State University. \u201cASAS-SN collects less detail on individual outbursts but provides a longer baseline, which was crucial in this case. The two surveys complement one another.\u201d<\/p>\n Crucially, using the calculated repetition period, the team was able to correctly predict flare events on 17 May, 7 September, and 20 December 2020 \u2014 all of which were observed.<\/p>\n As with the November 2018 event, TESS again observed the entire December 2020 flare during its survey of Sectors 31, 32, and 33.<\/p>\n<\/p>\n