Ultraviolet light and optical curves of ASASSN-23bd from Swift (diamonds), Swope (circles), ZTF (plus), ATLAS (squares), and ASAS-SN (pentagons). Credit: arXiv (2024). DOI: 10.48550/arxiv.2401.05490
An international team of astronomers reports the detection of a new tidal disturbance event (TDE) as part of the All-Sky Automated Survey for SuperNovae (ASAS-SN). The new TDE, designated ASASSN-23bd, turns out to be the faintest and lowest redshift TDE known to date. The discovery is reported in a paper published January 10 on the preprint server. arXiv.
TDEs occur when a star passes close enough to a supermassive black hole and is separated by tidal forces from the black hole, causing the disruption process. This tidally disrupted stellar debris begins to rain down on the black hole and radiation emerges from the innermost region of the accreting debris, which is an indicator of the presence of a TDE.
Observations by a group of astronomers led by Willem Hoogendam of the University of Hawaii discovered a new TDE in NGC 3799, an active barred spiral galaxy located about 300 million light-years away. ASASSN-23bd (AT 2023clx) was detected in February 2023 with a redshift of 0.011.
“ASAS-SN discovered ASASSN-23bd (aka AT 2023clx2) on MJD 59997.2 at (????, ????) = (11:40:09.397 +15:19:38.54) in NGC 3799 using the Cassius unit in Chile,” the researchers write in the journal.
ASASSN-23bd peaked on February 25, 2023, with a maximum ultraviolet/optical luminosity of approximately 5.4 tredecillion erg/s and a near-peak X-ray upper limit of 17.5 duodecillion erg/s. The TDE showed alpha hydrogen emissions throughout its decline and helium emissions near the peak and shortly after the peak.
Observations indicate that the black hole ASASSN-23bd has a mass of about one million solar masses. The TDE’s host, NGC 3799, appears to be still star forming and hosts low active galactic nucleus (AGN) activity.
Based on the results, astronomers concluded that ASASSN-23bd is the lowest redshift and faintest TDE detected to date. Additionally, ASASSN-23bd showed a rapid increase in light curve, less than 15 days. This makes it one of the low-luminosity, fast tidal disturbance (LLaF) events.
The researchers added that due to its low brightness, ASASSN-23bd might not have been detected if it had not been so close to Earth.
“In this sense, ASASSN-23bd is an interesting but fortunate addition to the TDE LLaF collection,” the study authors wrote.
Hoogendam’s team hopes that more LLaF TDEs like ASASSN-23bd can be discovered through deeper sky surveys, which can be conducted by facilities such as the Large Synoptic Survey Telescope (LSST). Astronomers predict that LSST is capable of identifying about 1,000 TDEs per year.
More information:
WB Hoogendam et al, Discovery and tracking of ASASSN-23bd (AT 2023clx): the lowest and faintest tidal disturbance event to date, arXiv (2024). DOI: 10.48550/arxiv.2401.05490
Journal information:
arXiv
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