Euclid System Matches Rubin Alerts to Find Supernovae

The dawn of "Big Data" astronomy is arriving with the imminent activation of the Vera C. Rubin Observatory, which is expected to generate a staggering 10 million transient alerts every single night. To manage this torrent of information, researchers including Y. Wang, A. A. Nucita, and J. -C. Cuillandre have developed a prototype automated system designed to cross-match these ground-based alerts with high-resolution observations from the Euclid Space Telescope. This integration allows for the identification of a supernova and other transient phenomena days before ground-based facilities can detect the initial flash, significantly narrowing the window for understanding early-stage stellar explosions.

What is Euclid the automated system for matching Rubin transient alerts?

The Euclid automated system is a sophisticated software pipeline designed to synchronize real-time transient alerts from the Vera C. Rubin Observatory with space-based survey data from the Euclid mission. By matching these data streams, the system provides researchers with combined light-curves and high-resolution image cutouts that span from visible to near-infrared wavelengths. This dual-perspective approach enables the early identification of cosmic events, such as a supernova, by leveraging Euclid’s superior sensitivity in the near-infrared spectrum.

Automating the cross-matching process is a logistical necessity for modern time-domain astronomy. The Rubin Observatory’s Legacy Survey of Space and Time (LSST) will utilize ugrizy filters to scan the southern sky, identifying millions of moving or changing objects. Without an automated bridge to space-based assets like Euclid, much of the contextual data—such as the precise environment of the host galaxy or the precursor infrared signatures—would be lost in the sheer volume of nightly alerts. The prototype system ensures that whenever a transient appears in a field Euclid has observed, the data is unified immediately.

How does Euclid's wide field survey complement Rubin's ugrizy filters?

Euclid’s wide-field survey complements Rubin’s optical filters by providing high-resolution near-infrared (NIR) and VIS band imaging that ground-based telescopes cannot achieve due to atmospheric interference. While Rubin tracks changes in visible light across six filters, Euclid adds deep infrared photometry and 0.1-arcsecond resolution images. This synergy is critical for correcting differential chromatic refraction and improving the accuracy of photometric redshift estimates for transient host galaxies.

The combination of these two powerhouses creates a multi-wavelength "fingerprint" for every detected event. While Rubin provides the high-cadence temporal data required to track the rising brightness of a supernova, Euclid provides the structural detail of the surrounding cosmic neighborhood. Specifically, the researchers noted that Euclid’s Visible (VIS) instrument and Near-Infrared Spectrometer and Photometer (NISP) offer a baseline of "quiet" states or early-onset detections that ground-based optics, hindered by the Earth's atmosphere, simply cannot resolve during the earliest hours of an explosion.

• Increased Sensitivity: Euclid detects faint infrared signals that are often the first indicators of stellar cataclysms.
• Atmospheric Correction: Space-based data provides a "clean" reference point to calibrate ground-based observations affected by weather and air mass.
• Host Galaxy Context: Euclid’s high resolution allows for better separation of a transient from its host galaxy's core, improving measurement precision.

Why use Zwicky Transient Facility alerts as a proxy for Rubin?

Researchers utilized the Zwicky Transient Facility (ZTF) as a proxy because it currently provides a high-volume stream of real-world transient data that mimics the logic of the upcoming Rubin alerts. Since the Rubin Observatory is not yet in full operation, ZTF serves as the ideal testbed to validate the automated matching pipeline. This allows the team to refine algorithms for photometric matching and image subtraction using existing live data streams from the Palomar Observatory.

Testing the system with ZTF data has already yielded significant scientific results, proving that the pipeline can handle the high velocity of data required for modern surveys. By processing ZTF alerts through the Euclid matching system, the team demonstrated the ability to produce joint light-curves that combine ground-based visible light with space-based data. This validation phase is essential for ensuring that when Rubin begins its 10-year survey, the infrastructure to process its 10 million nightly alerts is already battle-tested and efficient.

Early Detection: The Case of SN 2024pvw

One of the most compelling successes of this prototype system was the detection of SN 2024pvw, a supernova that Euclid captured roughly three days before it was flagged by ground-based facilities. This early-phase data is incredibly rare and scientifically valuable, as it captures the physics of the initial "shock breakout" or early cooling phase of the explosion. Constraining the exact moment of a star's death allows astrophysicists to model the progenitor star's size and composition with unprecedented accuracy.

The identification of SN 2024pvw highlights the "early warning" potential of the Euclid-Rubin partnership. In this instance, the automated system retrospectively identified the transient in Euclid’s deep-field observations, providing a pre-discovery data point that ground-based telescopes missed due to their shallower sensitivity limits. By filling in the gaps of the first 72 hours of the explosion, the system provides the "missing link" in the life cycle of stellar deaths, transforming how we categorize different classes of supernovae.

Non-Detections and Host Morphology Measurements

The value of the Euclid system extends even to cases where the telescope does not detect a transient flagged by Rubin. A non-detection in Euclid’s sensitive infrared bands provides a critical upper limit on the object's brightness, which helps theorists rule out certain physical models. For example, if a ground-based telescope sees a bright flash but Euclid sees nothing in the infrared, it suggests the event may be a specific type of high-energy burst rather than a dust-shrouded stellar collapse.

Furthermore, Euclid’s high-resolution imaging is used to improve host morphology measurements. By observing the galaxy where a supernova occurs in extreme detail, astronomers can determine if the star was located in a dense star-forming region or a quiet galactic suburb. This environmental context is a primary factor in understanding the diversity of transient events across the universe. The prototype system automatically extracts these host galaxy characteristics, providing a ready-made dataset for researchers to analyze the relationship between stars and their environments.

The Future of Time-Domain Astronomy

As we move toward the mid-2020s, the synergy between ground and space observatories will become the backbone of time-domain astronomy. The automated matching system developed by Wang and colleagues represents a shift from manual, targeted observations to large-scale, systematic data fusion. This approach is expected to lead to the discovery of rare cosmic events, such as kilonovae (the merger of neutron stars) or tidal disruption events, where a black hole shreds a passing star.

The next steps for the research team involve scaling the system to handle the full 10-million-alert-per-night capacity of the LSST. By strengthening the collaboration between the European Space Agency’s Euclid mission and the National Science Foundation’s Rubin Observatory, the astronomical community is building a global—and orbital—net to catch the most fleeting and energetic events in the cosmos. This infrastructure ensures that no flash in the night sky, no matter how brief or distant, goes unrecorded or unanalyzed.