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Constraints on Late-Time Flaring from Luminous Fast Blue Optical Transients using the Transiting Exoplanet Survey Satellite and the Zwicky Transient Facility

Using TESS and ZTF data, this study constrains late-time flaring in Luminous Fast Blue Optical Transients by identifying seven detected flare-like signals as solar system objects rather than central engine activity, thereby ruling out similar high-luminosity flares for specific LFBOTs and suggesting their engines shut off or declined within hundreds of days.

Original authors: Rahul Jayaraman, Anna Y. Q. Ho, Michael M. Fausnaugh, Eran Ofek, Daniel A. Perley, Ruslan Konno, Martti Kristiansen, Tracy X. Chen, Michael W. Coughlin, Steven L. Groom, George Helou, K. -Ryan Hinds

Published 2026-06-17

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CC BY 4.0

Original authors: Rahul Jayaraman, Anna Y. Q. Ho, Michael M. Fausnaugh, Eran Ofek, Daniel A. Perley, Ruslan Konno, Martti Kristiansen, Tracy X. Chen, Michael W. Coughlin, Steven L. Groom, George Helou, K. -Ryan Hinds, Mansi M. Kasliwal, Zoë McGrath, Josiah N. Purdum, Argyro Sasli, Jesper Sollerman

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: Hunting for Cosmic "Burps"

Imagine the universe is a dark ocean, and astronomers are looking for rare, glowing fish called Luminous Fast Blue Optical Transients (LFBOTs). These aren't normal fish; they are massive stellar explosions that flash brightly and fade away in just a few days.

For a long time, scientists thought these explosions were just a one-time event, like a firework that goes off and then is done. However, one specific explosion (named AT2022tsd) surprised everyone. Weeks and months after the initial flash, it started "burping" out sudden, intense bursts of light that lasted only minutes.

The big question was: Is this a unique quirk of that one explosion, or do all these cosmic fish do this?

The Detective Work: Two Sets of Eyes

To answer this, the researchers acted like cosmic detectives using two different tools:

TESS (The Transiting Exoplanet Survey Satellite): Think of this as a high-speed camera in space. It takes pictures of the same patch of sky every 200 seconds (about 3 minutes). It's great at catching fast, fleeting events, but it has a wide field of view, meaning it sees a lot of "noise."
ZTF (The Zwicky Transient Facility): This is a powerful ground-based telescope that checks the sky every few days. It's like a security guard who checks the perimeter regularly but might miss something that happens in the 10 seconds between checks.

The team looked at 12 out of the 14 known LFBOTs to see if they could catch any of these late-time "burps" (flares) using these cameras.

The False Alarms: Cosmic "Mosquitoes"

The researchers found seven bright flashes that looked exactly like the "burps" they were hunting for. However, after a closer look, they realized these weren't from the explosions at all.

The Analogy: Imagine you are trying to watch a specific lighthouse in the distance. Suddenly, a bright airplane flies right in front of your window, creating a flash of light. You might think the lighthouse just flashed, but it was actually the plane.

In this case, the "planes" were Solar System Objects (SSOs)—mostly asteroids or space rocks passing right in front of the telescope's view. Because TESS has a wide lens, these space rocks often drift through the frame, creating a fake signal that looks like a stellar flare. The team used special software to track these rocks and confirmed that all seven "flares" were just cosmic mosquitoes buzzing in front of the lens.

The Real Findings: Silence is the Answer

After filtering out the false alarms, the team looked at the real data. Here is what they found:

No New Burps: None of the other 11 LFBOTs showed any signs of these late-time flares.
The Engine is Turning Off: For the one LFBOT that did flare (AT2022tsd), the team watched it for a long time. They found that after about a year, the flaring stopped. It's as if the "engine" inside the explosion (likely a black hole or a magnetar) ran out of fuel or shut down after a few hundred days.
The "Beaming" Theory: Since only one LFBOT showed these flares, the team suspects two possibilities:
1. The engine simply turns off quickly for most of them.
2. The flares are like a laser pointer. If you are standing directly in the beam, you see a blinding light. If you are standing to the side, you see nothing. Maybe the other 13 LFBOTs are flaring, but we are looking at them from the "side," so we can't see the beam.

What This Means for the Future

The paper concludes that while TESS is a great tool, it's hard to catch these specific flares because they are rare and short.

The "Goldilocks" Zone: To catch these flares, we need telescopes that are fast enough to see the minutes-long bursts but sensitive enough to see them from far away.
Future Hunters: The paper suggests that upcoming telescopes like LAST (a giant array of small telescopes) and ULTRASAT (a satellite looking at ultraviolet light) will be the best "nets" for catching these rare events in the future. They are like upgrading from a fishing rod to a massive, high-speed trawler.

Summary

In short, the researchers used space and ground telescopes to hunt for late-time flares in stellar explosions. They found that the few flashes they saw were actually just asteroids passing by. The real explosions they studied didn't flare again, suggesting that the powerful engines driving these events either run out of gas or point their light in a direction we can't see. This helps scientists understand that these cosmic events are likely short-lived and perhaps very directional.

Technical Summary: Constraints on Late-Time Flaring from Luminous Fast Blue Optical Transients using TESS and ZTF

Problem Statement
Luminous Fast Blue Optical Transients (LFBOTs) are a rare class of transients characterized by rapid rise times, blue colors, and high luminosities, distinct from typical core-collapse supernovae. While the prototypical LFBOT, AT2018cow, showed evidence of a central engine, the unambiguous detection of minutes-timescale, luminous optical flares in the LFBOT AT2022tsd provided the strongest evidence to date for a central engine (likely an accreting black hole or magnetar) in this class. However, it remains unknown whether this flaring behavior is universal among LFBOTs or if it is a rare occurrence. Targeted searches for such flares are challenging due to the need for high temporal resolution (minutes) and the low duty cycle of existing telescopes. Furthermore, previous non-detections in other LFBOTs (e.g., AT2024wpp) could be attributed to beaming effects or the cessation of engine activity. This paper addresses the question of whether late-time flaring is a common property of LFBOTs by constraining the occurrence, timescale, and luminosity of such flares across the known population.

Methodology
The authors utilized data from the Transiting Exoplanet Survey Satellite (TESS) and the Zwicky Transient Facility (ZTF) to analyze 12 of the 14 currently known LFBOTs.

TESS Analysis: The team extracted light curves at the locations of known LFBOTs from TESS Full Frame Images (FFIs). They employed a difference imaging approach using the ISIS software to subtract reference images and perform forced PSF-fitting photometry. The analysis covered timescales ranging from tens of days to thousands of days post-discovery.
Data Processing: To mitigate systematic errors, particularly scattered light from the Earth and Moon, the authors visually inspected light curves to mask periods of high background. They corrected for Galactic extinction using standard maps.
Flare Identification: The team searched for flux excesses resembling flares. To distinguish genuine astrophysical flares from false positives, they cross-referenced detections with the Sky Body Tracker (SkyBoT) and analyzed TESS cutouts and Root-Mean-Square (RMS) maps to identify moving Solar System Objects (SSOs).
ZTF and ATLAS: Forced photometry was performed on ZTF and ATLAS difference images to search for late-time flux excesses and precursor emission, filtering for detections hundreds of days after the initial transient.
Statistical Limits: The authors calculated upper limits on flare luminosity and duty cycle using Poisson statistics (3-σ confidence), assuming that any detected "flare-like" signals were SSOs rather than intrinsic to the LFBOTs.

Key Results

Flare Detections: The analysis identified seven flare-like signals at the locations of four unique LFBOTs. However, detailed vetting confirmed that all seven signals were caused by Solar System Objects (SSOs) moving through the TESS aperture, not intrinsic flares.
Constraints on AT2024qfm: For the LFBOT AT2024qfm, observed during the same post-transient timescale (40–65 days) as the flaring in AT2022tsd, the authors found no evidence of flaring. They ruled out flares with a luminosity comparable to AT2022tsd ( $\nu L_\nu \sim 10^{43}$ erg s $^{-1}$ ) at this epoch.
Constraints on AT2022tsd: For AT2022tsd itself, TESS observations taken 380–430 days after the initial event (roughly 260 days after the last observed flares) showed no flaring activity as luminous as the earlier flares. This suggests the central engine's power declined or shut off on a timescale of hundreds of days.
Constraints on AT2018cow: No late-time activity was detected in TESS thousands of days after the prototype LFBOT, AT2018cow. The luminosity of any potential late-time flaring is constrained to be hundreds of times fainter than the initial transient.
Duty Cycle: The authors constrained the duty cycle of such flaring to be $< 0.007$ (at 3-σ) for the observed periods, assuming an average flare duration of 40 minutes.
Precursors: No precursor emission comparable to the peak luminosity of the transients was found in TESS data for the five LFBOTs with contiguous pre-discovery coverage.

Key Contributions

Systematic Survey: This work provides the first systematic constraints on late-time flaring for the majority of the known LFBOT population (12 of 14 events) using high-cadence space-based data.
False Positive Characterization: The study rigorously characterized SSOs as the primary source of false positives in TESS light curves for LFBOT searches, particularly for objects near the ecliptic plane, and established a vetting protocol using cutouts and RMS maps.
Engine Evolution Constraints: By ruling out flaring in AT2022tsd at late times (hundreds of days), the paper provides evidence that the central engine powering these events may decline or cease activity on timescales of $\sim 100$ –$400$ days.
Beaming vs. Shutdown: The non-detection of flares in other LFBOTs is discussed in the context of two hypotheses: either the engine shuts off, or the emission is beamed (requiring an on-axis observer), with the latter suggesting a beaming angle of $5^\circ$ – $30^\circ$ .

Significance and Claims
The paper claims that while AT2022tsd is the only LFBOT to date with confirmed late-time flaring, the lack of similar detections in other events suggests that such flaring is not a universal, persistent feature of all LFBOTs. The results imply that if a central engine exists, its activity may be transient, shutting down within a few hundred days, or that the emission is highly beamed, making it observable only in rare, fortuitous orientations.

The authors modestly conclude that while TESS has successfully constrained the duty cycle and luminosity of late-time flaring, the next generation of high-cadence, wide-field surveys—specifically the Large Array Survey Telescope (LAST), ULTRASAT, and the Argus Array—will be required to robustly detect these rare events. They estimate that these future facilities could detect between 0.5 and 80 flares per year, depending on the survey's cadence and field of view, potentially resolving the debate over the universality and geometry of LFBOT central engines. The paper does not claim to have discovered a new class of transients but rather to have placed strict observational limits on the behavior of a known, rare class.