This week's significant event is from Maya Nunez, a rising sophomore at California State University, Long Beach, who is doing a Summer Undergraduate Research Fellowship (SURF) with the NuSTAR group at Caltech. Maya is working with Murray Brightman, a NuSTAR Staff Scientist, on transient X-ray sources—that is, X-ray sources that rapidly change in brightness, such as new X-ray sources that suddenly appear in the sky. X-ray transients can be caused by a wide variety of astrophysical processes, including Tidal Disruption Events (TDEs), which occur when a star passes too close to a supermassive black hole and is torn apart. Maya identified a bright X-ray flare from a galaxy hosting an actively accreting supermassive black hole, i.e., an active galaxy. Back in 2019, this galaxy had hosted the bright optical and infrared transient AT2019fdr, whose origin has been under much debate. AT2019fdr is hypothesized to be either a superluminous supernova, a flare from a supermassive black hole, or a TDE. Maya led an approved NuSTAR Director's Discretionary Time proposal to observe this source, and the observations, obtained last week, detected the source in the 3–8 keV NuSTAR energy band. The NuSTAR data provide a late-time X-ray detection from AT2019fdr which, in combination with recent literature, solidifies AT2019fdr’s categorization as a TDE as opposed to a superluminous supernova, since late-time X-ray emission is not common for such supernovae. A flare from a supermassive black hole is also less probable, but not completely ruled out. These new data and findings will expand our understanding of TDEs, particularly TDEs in galaxies with actively accreting supermassive black holes, which have not been as well-studied as TDEs in inactive or quiescent galaxies.
