First Results from the LSST Shadow Survey: The Restless Luminous Blue Variable AT2017des in the Virgo-Cluster Galaxy, NGC4532

arXiv:2606.23784 · astro-ph.HE, astro-ph.GA, astro-ph.SR · Submitted 2026-06-22 · Read on arXiv

Conor L. Ransome, Bhagya M. Subrayan, David J. Sand, Brian Hsu, Xander J. Hall, Jeniveve Pearson, K. Azalee Bostroem, Jennifer E. Andrews, Joszef Vinko, J. Craig Wheeler, Phillip Noel, Lei Hu, Tomas Cabrera, Stefano Valenti, Wynn V. Jacobson-Galan, Nathan Smith, Alexei V. Filippenko, Mojgan Aghakhanloo, Igor Andreoni, Moira Andrews, Iair Arcavi, Raphael Baer-Way, Emma R. Beasor, Edo Berger, Federica B. Bianco, Peter Blanchard, Thomas G. Brink, Siddarth Chaini, Adrian Crawford, Yize Dong, Joseph Farah, Noah Franz, Sebastian Gomez, Melissa L. Graham, Daichi Hiramatsu, Agoston Horti-David, Griffin Hosseinzadeh, D. Andrew Howell, Philip A. James, Saurabh W. Jha, Charles D. Kilpatrick, Lindsey A. Kwok, Gavin P. Lamb, Amanda R. Lopes, Michael Lundquist, Clara E. Martinez-Vasquez, Thomas Matheson, Curtis McCully, Maryam Modjaz, Gregory S. H. Paek, Antonella Palmese, Avi Patel, Joanne L. Pledger, Aravind P. Ravi, Jeonghee Rho, Krisztian Sarneczky, Manisha Shrestha, Richard Smith, Analia V. Smith Castelli, Monika Soraisam, Jay Strader, Francisco Valdes, Sergiy Vasylyev, V. Ashley Villar, A. Katherina Vivas, Lifan Wang, Samuel D. Wyatt, Kathryn Wynn, WeiKang Zheng

astro-ph.HE, astro-ph.GA, astro-ph.SR

Submitted: 2026-06-22

Comments: 23 pages, 9 figures, submitted to ApJL

Code: https://github.com/CIERA-Transients/POTPyRI

License: http://creativecommons.org/licenses/by/4.0/

The gist: The Legacy Survey of Space and Time (LSST) will start in late-summer 2026, revolutionizing transient astronomy.

Terminology

Abstract

The Legacy Survey of Space and Time (LSST) will start in late-summer 2026, revolutionizing transient astronomy. Here, we present the Dark Energy Camera (DECam) Shadow Survey, which is designed to maximize the science potential of LSST by shadowing LSST observations of local galaxy-cluster fields, producing a nightly cadence of these fields. The Shadow Survey will discover extremely young supernovae (SNe), SN precursors, as well as other explosive transients and exotic phenomena, helping to characterize such transients at unprecedented cadence and depth when combined with LSST. We describe our workflow, pipeline, public data releases, and candidate vetting. As an early result of Shadow, we present the fitful luminous blue variable (LBV) eruptions of AT2017des in the Virgo-Cluster galaxy NGC4532. AT2017des has short-timescale variability (of order 10 days), peaking at around M r=-12.5 mag, brighter than normal LBVs, and similar to the more extreme flaring of hot LBVs/SN impostors such as SN2000ch, AT2016blu, and the precursor activity of SN2009ip. Our spectral time-series reveals features typical of these hot LBVs and SN impostors/precursors. Combining our data with long-baseline photometry from additional observatories, we find that the peaks of the outbursts of AT2017des are getting brighter over time, with 2026 peak fluxes being up to 5 times greater than in 2023 and an average brightening of about0.05 mag yr-1. The peaks of AT2017des are more luminous than those of most other LBVs, only being fainter than bright precursors such as SN2009ip, and extreme SN impostors such as AT2016blu. AT2017des may therefore be ``ramping up'' to a terminal explosion.

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