The Rise and Fall of ASASSN-18pg: Following a TDE from Early to Late Times
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- The Observatories of the Carnegie Institution for Science, Pasadena, CA (United States)
- Univ. of Copenhagen (Denmark); University of Melbourne, Parkville (Australia); ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) (Australia); Univ. of California, Santa Cruz, CA (United States)
- Univ. of Hawaii, Honolulu, HI (United States)
- Curtin University, Perth (Australia)
- Univ. of California, Santa Cruz, CA (United States)
- South African Astronomical Observatory, Cape Town (South Africa); Southern African Large Telescope Foundation (South Africa)
- The Ohio State Univ., Columbus, OH (United States)
- Peking Univ., Beijing (China)
- Universidad Diego Portales, Santiago (Chile); Millennium Institute of Astrophysics, Santiago (Chile)
- The Observatories of the Carnegie Institution for Science, Pasadena, CA (United States); Princeton Univ., Princeton, NJ (United States)
- Pomona College, Claremont, CA (United States)
- Carnegie Observatories, La Serena (Chile)
- South African Astronomical Observatory, Cape Town (South Africa)
- Univ. of Warsaw (Poland)
- The Inter-University Centre for Astronomy and Astrophysics (India)
- New York Univ., NY (United States)
Here, we present nearly 500 days of observations of the tidal disruption event (TDE) ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our data set includes X-ray, UV, and optical photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of $$\textit{d}$$ = 78.6 Mpc; with a peak UV magnitude of $$\textit{m}$$ ≃ 14, it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of $$\textit{L}$$ ≃ 2.4 × 1044 erg s-1, and its late-time evolution is shallower than a flux ∝$$\textit{t}^{–5/3}$$ power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak, which remained detectable for roughly 225 days after peak. Analysis of the two-component Hα profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between ~10 and ~60 lt-days from the black hole. No X-ray emission is detected from the TDE, and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations indicate that the projected emission region is likely not significantly aspherical, with the projected emission region having an axis ratio of ≳0.65.
- Research Organization:
- Krell Institute, Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); Gordon and Betty Moore Foundation; National Science Foundation (NSF); Mt. Cuba Astronomical Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Fund for Scientific and Technological Development (FONDECYT); Ministry of Economy, Development, and Tourism; Research Corporation; National Aeronautics and Space Administration (NASA); National Research Foundation (NRF) of South Africa; National Science Centre of Poland (NCN); Heising-Simons Foundation; David and Lucile Packard Foundation; Australian Research Council (ARC)
- Grant/Contract Number:
- SC0019323; GBMF5490; AST-1515927; AST-1908570; AST-0908816; AST-1920392; AST-1911074; 1151445; IC120009; 24215; HSTHF2-51404.001 A; NAS 5-26555; HST-HF2-51391.001 A; NAS5-26555; 2014/14/A/ST9/00121; AST-1518052; 80NSSC19K1386
- OSTI ID:
- 1803691
- Journal Information:
- The Astrophysical Journal (Online), Vol. 898, Issue 2; ISSN 1538-4357
- Publisher:
- IOP PublishingCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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