Blazing Breakthrough: The December 2024 Flare of Blazar 1ES 1959+650

An international team of astronomers analyzed the powerful flare of the blazar 1ES 1959+650, recorded in December 2024 by the space observatories SVOM and Swift. The observations allowed detailed tracking of changes in the properties of the relativistic jet as its brightness surged and provided clarity on the particle acceleration mechanisms near the supermassive black hole.

Insights into Blazar Mechanics

In the hearts of blazars lie supermassive black holes ejecting narrow jets of plasma that travel nearly at the speed of light. If such a jet is directed toward Earth, its radiation is amplified due to the relativistic Doppler effect, making the object intensely bright across all wavelengths-from radio to gamma rays.

Blazar 1ES 1959+650, located approximately 700 million light-years away, has long been known for its high variability. On December 6, 2024, the Sino-French SVOM mission recorded an abrupt X-ray flare from this object using the ECLAIRs telescope. The flux in the 4–20 keV band reached around 2 mCrab, while the MXT X-ray telescope data showed about 5.5 mCrab in the 0.5–10 keV range, significantly exceeding usual levels.

Simultaneously, an increase in brightness was also registered in the optical range, marking the first blazar flare detection of the SVOM mission. Upon automatic triggering, urgent observations were conducted under the Target of Opportunity program. From December 6 to 26, the source was continuously monitored by SVOM instruments, with the Swift observatory joining the campaign on December 12, continuing the surveillance until March 2025. This coordination provided a comprehensive timeline of the flare’s evolution over nearly three months.

Utilizing Advanced Spectrum Analysis

For spectral analysis, scientists used a logarithmic parabola model, effectively describing the synchrotron radiation of relativistic electrons in the jet’s magnetic field. This model’s parameters allowed the calculation of peak emission energy and spectrum flux, key indicators of the plasma’s physical state.

Observations divided the whole period into two stages: In December 2024, the blazar was in a high-activity phase with maximum average flux, a harder spectrum, and low curvature. From January to March 2025, brightness decreased, the spectrum softened, and curvature increased.

A characteristic dependence was identified: as brightness grows, the spectrum becomes harder and the synchrotron emission peak shifts to higher energies.

Investigating Particle Acceleration

Particular focus was given to particle acceleration techniques within the jet. Two scenarios were considered: acceleration at shock waves and stochastic acceleration in turbulent plasma. However, neither correlation analysis nor theoretical model comparison revealed a clear dominance of any process. No distinguishing features indicated a dominant mode of electron acceleration or cooling.

The authors concluded the flare most likely formed within a mixed scenario. Initially, particles accelerate at shock wave fronts and then are further sped up in the jet’s turbulent environment. A similar pattern was noticed for the same object in 2015-2016, indicating consistent physical processes within the system.

The study also demonstrated the high efficiency of the SVOM mission in detecting and following extragalactic transients. Thanks to the ECLAIRs telescope’s low energy threshold, scientists gathered data up to 150 keV, precisely constraining radiation parameters. Joint efforts by SVOM and Swift exhibited coordinated observations remaining crucial for studying extreme processes near supermassive black holes.

mCrab (milli-Crab) is a standard unit of flux measurement in X-ray astronomy, representing one thousandth of the Crab Nebula flux. The Crab Nebula serves as a “standard candle” due to its intense and stable X-ray emission.