🔭 astrophysics

The $\gamma$ -ray-emitting blazar B3 1239+376 at $z$ = 3.82 identified in a multi-wavelength context

This paper reports the identification of B3 1239+376 as the third most distant $\gamma$ -ray-emitting blazar at redshift $z=3.82$ through multi-wavelength analysis of Fermi-LAT, WISE, and SPHEREx data, confirming its association via correlated light curves and modeling its jet properties with a one-zone leptonic radiation model.

Original authors: Wei Zhang, Neng-Hui Liao, Hao-Yi Huang, Hai Lei, Xiong Jiang, Ning Jiang, Zhen-Feng Sheng, Lu-Lu Fan, Ting-Gui Wang

Published 2026-04-16

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CC BY 4.0

Original authors: Wei Zhang, Neng-Hui Liao, Hao-Yi Huang, Hai Lei, Xiong Jiang, Ning Jiang, Zhen-Feng Sheng, Lu-Lu Fan, Ting-Gui Wang

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 Cosmic Lighthouse: Finding a Distant Giant

Imagine the universe as a vast, dark ocean. Scattered throughout this ocean are lighthouses called Active Galactic Nuclei (AGNs). These aren't normal lighthouses; they are powered by supermassive black holes at the centers of galaxies, devouring matter and shooting out massive beams of energy (jets) like laser pointers.

Most of these beams point in random directions. But occasionally, one points straight at Earth. When that happens, we call it a Blazar. It's like looking directly into the headlight of a speeding train; it's incredibly bright and blinding.

The Big Discovery:
Astronomers have found a new, incredibly distant blazar named B3 1239+376. It is so far away that its light has been traveling for over 12 billion years to reach us. It is currently the third most distant gamma-ray blazar ever found in the universe.

The Mystery of the "Ghost" Signal

For a long time, this object was a bit of a mystery. We knew it was a radio source (like a radio station broadcasting from deep space), but we couldn't see it in gamma rays (the highest energy form of light).

Think of the Fermi-LAT telescope (the tool used to see these gamma rays) as a pair of night-vision goggles. For 14 years, the goggles looked at this spot, but the signal was too faint to see clearly. It was like trying to spot a single firefly in a stadium full of bright floodlights.

The Breakthrough:
In 2025, something changed. The "firefly" suddenly flared up.

The Flash: The astronomers noticed a massive spike in gamma-ray energy coming from that exact spot.
The Proof: They didn't just see it once; they saw it peak at the same time the object got brighter in infrared light (heat radiation).
The Connection: It's like seeing a siren flash red (gamma rays) and hearing the siren wail (infrared) at the exact same moment. This confirmed that the gamma-ray source and the distant quasar are the same object.

The Detective Work: Ruling Out Imposters

Since the telescope isn't perfect (it's a bit blurry at these distances), the team had to make sure they weren't looking at a "ghost"—a bright background star that just happened to line up with the distant quasar.

They did a thorough investigation:

Spectral Check: They looked at the "fingerprint" of the light. The background stars had a different fingerprint than the target.
Probability: They ran the numbers and found a 91% chance that the gamma rays are actually coming from the distant quasar, not a background impostor.
Time Travel: They even dug up old data and found faint "ghosts" of gamma-ray activity from 2017 and 2020, suggesting this object has been active for a while, just usually too quiet to hear.

The Engine Room: How It Works

The paper also tries to explain how this thing works using a model called the "One-Zone Leptonic Model."

The Analogy: Imagine a giant, spinning water slide (the jet) made of magnetic fields. Inside this slide, particles (electrons) are being accelerated to near the speed of light.
The Flare: In 2025, the "pump" on the slide turned up. More particles were injected, and the magnetic field got stronger.
The Result: These super-fast particles bumped into light particles, boosting them into high-energy gamma rays. This is why the object suddenly got so bright in both infrared and gamma-ray views.

Why Does This Matter?

Finding this object is like finding a rare, ancient fossil, but instead of bones, it's a beam of light.

Supermassive Black Hole Growth: This black hole is huge, and it formed very early in the universe's history. Finding it helps us understand how these giants grew so fast so quickly.
The "Blazar Sequence": Most distant blazars are "Flat Spectrum Radio Quasars" (FSRQs), which are like the heavyweights of the galaxy. This discovery fits the pattern that the most distant, energetic black holes tend to be these heavyweights.
Future Hunting: Because this object is currently "waking up" (brightening), astronomers are urging others to point their radio telescopes at it immediately. They hope to catch a "blob" of material being ejected from the jet, which would give them a direct look at the engine in action.

The Bottom Line

The team has successfully identified B3 1239+376 as a cosmic giant that is firing a powerful gamma-ray beam directly at us. It is the third most distant object of its kind ever found. By watching it flare up in 2025 and matching that flare with infrared heat, they proved it's real. Now, the scientific community is on high alert, waiting to see what this ancient giant does next.

1. Problem Statement

High-redshift ( $z > 3$ ) $\gamma$ -ray-emitting blazars are extremely rare, with only a handful detected among thousands of extragalactic $\gamma$ -ray sources. These objects are critical probes for understanding:

The cosmic evolution of Active Galactic Nuclei (AGN) jets.
The initial mass growth phase of Supermassive Black Holes (SMBHs).
The Extragalactic Background Light (EBL).

Detecting $\gamma$ -rays from high- $z$ blazars is challenging due to their soft spectra and the limited angular resolution of the Fermi-Large Area Telescope (Fermi-LAT) at sub-GeV energies, which often leads to ambiguous source localization. The paper addresses the need to confirm the association between the known radio quasar B3 1239+376 ( $z=3.82$ ) and a $\gamma$ -ray source, and to characterize its multi-wavelength behavior to confirm its nature as a high- $z$ blazar.

2. Methodology

The authors employed a comprehensive multi-wavelength approach combining archival data and new observations:

$\gamma$ -ray Analysis (Fermi-LAT):
- Analyzed 17 years of Pass 8 SOURCE data (2008–2025).
- Used unbinned likelihood analysis (gtlike) with a power-law spectral model.
- Performed a temporal analysis using linear time binning (2-month and 1-year bins) to identify flares.
- Conducted a joint analysis of marginal signals from 2017–2020 to boost statistical significance.
- Applied Bayesian association methods to calculate the probability of the $\gamma$ -ray source being B3 1239+376, considering background sources and localization uncertainties.
X-ray Analysis:
- Processed Chandra data (2007 and 2022) using specextract and spectral fitting with XSPEC (C-statistic).
- Analyzed Swift XRT and UVOT data for contemporaneous coverage.
Optical/IR Analysis:
- Analyzed SDSS spectra (DR16) to refine redshift and estimate black hole mass (using Ly $\alpha$ and C IV lines).
- Extracted long-term infrared light curves from WISE/NEOWISE (W1, W2 bands) and new spectroscopy from the SPHEREx mission (launched 2025).
- Investigated radio data from RATAN-600, VLBA (K-band), and VLASS to monitor core and jet components.
Spectral Energy Distribution (SED) Modeling:
- Compiled broadband SEDs for high-flux (2025) and low-flux states.
- Modeled the jet emission using a classic one-zone leptonic radiation model (synchrotron + Inverse Compton).
- Assumed a broken power-law electron distribution and included External Compton (EC) scattering off broad-line region (BLR) photons.

3. Key Results

A. $\gamma$ -ray Detection and Association

2025 Flare: A significant $\gamma$ $γ$ -ray excess was detected in the direction of B3 1239+376 during the first half of 2025.
- Significance: Local TS = 80 ( $\sim$ 8.2 $\sigma$ ); Global significance (after trial correction) = 7.7 $\sigma$ .
- Flux: $(3.2 \pm 0.6) \times 10^{-8}$ ph cm $^{-2}$ s $^{-1}$ (5-fold increase compared to the 2.5-year prior average).
- Spectrum: Soft power law with photon index $\Gamma = 2.60 \pm 0.14$ .
Historical Activity: A joint analysis of marginal signals from 2017 and 2020 revealed a tentative detection (TS = 31, $\sim$ 4.5 $\sigma$ ) spatially coincident with the quasar.
Association: The angular separation between the $\gamma$ -ray centroid and the radio position is 0.11 $^\circ$ , well within the 95% confidence localization radius. The calculated association probability is 0.91, confirming B3 1239+376 as the counterpart.

B. Multi-wavelength Correlations

IR- $\gamma$ Correlation: The infrared (WISE/SPHEREx) and $\gamma$ -ray light curves show strong temporal coincidence. Both bands peaked simultaneously in 2025, and the 2017/2020 tentative $\gamma$ -ray signals coincided with IR flux rises.
Radio Behavior: VLBA observations showed a flux increase in the compact core (K-band) from 0.099 Jy to 0.153 Jy between 2017 and 2018, preceding the major 2025 flare.
X-ray Properties: Chandra data confirmed a hard X-ray spectrum ( $\Gamma_X \approx 1.5$ ), supporting the blazar classification.

C. SED Modeling and Jet Properties

Flux States: The source exhibits distinct low-flux (disk-dominated) and high-flux (jet-dominated) states.
Modeling: The one-zone leptonic model successfully reproduced the broadband SEDs.
- High Flux State: Requires an injection of fresh electrons with a harder spectrum and enhanced magnetic field intensity.
- Parameters: The jet is identified as a Low-Synchrotron-Peaked (LSP) source. The bulk Lorentz factor is estimated at $\Gamma \sim 15$ , and the Compton dominance (CD) is $\sim 10$ .

4. Key Contributions

Discovery of a New High- $z$ Blazar: B3 1239+376 is confirmed as the third most distant $\gamma$ -ray-emitting blazar known to date ( $z=3.82$ ), following B3 1428+422 ( $z=4.72$ ) and GB 1508+5714 ( $z=4.3$ ).
Robust Association: Provided the first definitive multi-wavelength confirmation of a $\gamma$ -ray association with this specific quasar, overcoming previous localization ambiguities through temporal correlation.
Temporal Evolution: Revealed a complex activity history, including a major 2025 flare and prior tentative activities in 2017/2020, linked by correlated IR and $\gamma$ -ray variability.
Jet Physics Constraints: Derived physical parameters (Lorentz factor, magnetic field, electron distribution) for a high- $z$ FSRQ, contributing to the understanding of jet formation and SMBH growth in the early universe.

5. Significance

Cosmic Evolution: The detection of a powerful jet at $z=3.82$ challenges and refines models of SMBH formation, suggesting that massive black holes with efficient accretion and relativistic jets existed early in the universe.
Blazar Sequence: The source fits the "blazar sequence" (luminous sources having lower synchrotron peaks and higher Compton dominance), reinforcing the universality of jet physics across cosmic time.
Future Observations: The paper highlights the necessity of prompt, multi-wavelength follow-up (especially radio interferometry) to catch jet blob ejections. The recent brightening makes B3 1239+376 a prime target for future studies of high-energy particle acceleration and EBL absorption.