First Pre-peak Ultraviolet Spectrum of a Tidal Disruption Event: A Fast Outflow Revealed Prior to Maximum Light in TDE2025aarm

@misc{hammerstein2026first,
  title = {{First Pre-peak Ultraviolet Spectrum of a Tidal Disruption Event: A Fast Outflow Revealed Prior to Maximum Light in TDE2025aarm}},
  author = {Erica Hammerstein and Ryan Chornock and Jean Somalwar and Raffaella Margutti and Brenna Mockler and Olivia Aspegren and Itai Sfaradi and Natalie LeBaron and Jonathan Carney and Alexei V. Filippenko and A. J. Nayana and Igor Andreoni and Thomas Brink and Peter J. Brown and Adam J. Burgasser and S. Bradley Cenko and Suvi Gezari and Xiaoshan Huang and Mansi M. Kasliwal and Jon M. Miller and Sasha Mintz and Sam Rose and Peter Senchyna and Joshua D. Simon and Emma Softich and Robert Stein and Yuhan Yao and WeiKang Zheng and Richard Dekany and Matthew J. Graham and Russ R. Laher and Josiah Purdum and Ben Rusholme and Jesper Sollerman and Stefan van der Walt},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.28460},
  eprint = {2609.28460},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.28460},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - First Pre-peak Ultraviolet Spectrum of a Tidal Disruption Event: A Fast Outflow Revealed Prior to Maximum Light in TDE2025aarm
AU  - Erica Hammerstein
AU  - Ryan Chornock
AU  - Jean Somalwar
AU  - Raffaella Margutti
AU  - Brenna Mockler
AU  - Olivia Aspegren
AU  - Itai Sfaradi
AU  - Natalie LeBaron
AU  - Jonathan Carney
AU  - Alexei V. Filippenko
AU  - A. J. Nayana
AU  - Igor Andreoni
AU  - Thomas Brink
AU  - Peter J. Brown
AU  - Adam J. Burgasser
AU  - S. Bradley Cenko
AU  - Suvi Gezari
AU  - Xiaoshan Huang
AU  - Mansi M. Kasliwal
AU  - Jon M. Miller
AU  - Sasha Mintz
AU  - Sam Rose
AU  - Peter Senchyna
AU  - Joshua D. Simon
AU  - Emma Softich
AU  - Robert Stein
AU  - Yuhan Yao
AU  - WeiKang Zheng
AU  - Richard Dekany
AU  - Matthew J. Graham
AU  - Russ R. Laher
AU  - Josiah Purdum
AU  - Ben Rusholme
AU  - Jesper Sollerman
AU  - Stefan van der Walt
PY  - 2026
DA  - 2026/09/23
PB  - arXiv
DO  - 10.48550/arxiv.2609.28460
UR  - https://arxiv.org/abs/2609.28460
AB  - The tidal disruption and eventual accretion of a star by a massive black hole can lead to the launching of outflows and winds that encode important information about the tidal disruption and accretion processes. However, little is known about the existence and behavior of these outflows before optical light-curve peak, when processes such as stream-stream collisions and disk formation may be important. Here, we present the first pre-peak ultraviolet (UV) spectrum of a tidal disruption event (TDE), obtained ∼ 20 days before optical maximum light of the nearby (redshift z=0.0137) TDE2025aarm, along with quasi-simultaneous infrared (IR) through X-ray observations. Our HST/STIS spectrum shows strong evidence for an early-time outflow through broad near-UV (NUV) and far-UV (FUV) absorption lines blueshifted by ∼10,000 km s^−1, including two new UV broad absorption features not yet identified in a TDE. We find that the FUV--IR continuum deviates significantly from a blackbody (f_λ∝ λ^−3.08), which we interpret as a signature of reprocessing through the outflow. This deviation implies that the bolometric luminosity in optical TDEs may be underestimated by a significant factor (∼9 in this case) when inferred from single-temperature blackbody fits to NUV--optical photometry alone. This work further confirms that TDEs are capable of launching fast outflows at very early times and emphasizes the importance of prompt FUV spectroscopic observations of TDEs that can capture the full continuum emission and energetics.
ER  -