🔭 astrophysics

SDSSJ110546.07+145202.4: The first long-duration radio changing-look NLS1 galaxy

This paper presents multi-wavelength observations of SDSSJ110546.07+145202.4, identifying it as the first long-duration radio changing-look Narrow-line Seyfert 1 galaxy and concluding that its dramatic, persistent brightening is best explained by an accretion rate change that ignited a powerful radio jet.

Original authors: S. Komossa, D. Grupe, A. Kraus, P. G. Edwards, E. F. Kerrison, K. Rose, R. Soria, T. An, M. J. Hardcastle, K. E. Gabanyi, S. Panda, D. W. Xu, J. Wang, S. Frey, A. Mezosi

Published 2026-04-22

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: S. Komossa, D. Grupe, A. Kraus, P. G. Edwards, E. F. Kerrison, K. Rose, R. Soria, T. An, M. J. Hardcastle, K. E. Gabanyi, S. Panda, D. W. Xu, J. Wang, S. Frey, A. Mezosi

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

Imagine the universe as a vast, dark ocean. Most of the "islands" in this ocean are galaxies, and at the center of almost every island sits a supermassive black hole—a cosmic vacuum cleaner so heavy it bends space and time. Usually, these black holes are either sleeping quietly or eating steadily, creating a predictable hum of energy.

But every once in a while, something strange happens. A black hole suddenly wakes up, eats a massive meal, and blasts out a jet of energy so powerful it lights up the entire island.

This paper is about SDSS J110546.07+145202.4 (let's call it "SDSS J1105" for short), a galaxy that just did something no one has ever seen before in this specific way.

The Story of the "Radio Changing-Look" Galaxy

1. The Quiet Neighbor
SDSS J1105 is a "Narrow-line Seyfert 1" galaxy. Think of this as a specific type of neighborhood where the black holes are smaller than usual (like a "mini" black hole) and they are very hungry, eating close to their maximum capacity. For decades, astronomers watched this galaxy. It was there, but it was radio-quiet. It was like a house that was always dark and silent on the radio frequency dial.

2. The Sudden Awakening
Then, around 2017, something changed. The galaxy suddenly turned on its radio lights. It didn't just flicker; it blazed. It became 23 times brighter in radio waves than it was before. It went from being a "radio-quiet" house to a "radio-loud" lighthouse.

3. The Mystery of the Long Night
Usually, when a black hole has a burst of energy (like a solar flare), it flares up for a few days or weeks and then fades away. But SDSS J1105 is different. It has stayed bright for over 8 years and counting. It's like a lightbulb that you flicked on in 2017, and it's still burning just as brightly today, with no sign of turning off.

What the Astronomers Found

The team of scientists (led by Dr. Komossa) pointed every telescope they could at this galaxy to figure out what was happening. Here is what they discovered, translated into everyday terms:

The X-Ray "Softness": When they looked at the galaxy in X-rays (high-energy light), the spectrum was "soft." Imagine a rock hitting a wall (hard X-rays) versus a pillow hitting a wall (soft X-rays). This galaxy was hitting the wall with a pillow. This confirmed it's a "hungry" but smaller black hole, not a giant, violent monster.
No Hiding Spots: They checked if the galaxy was just hiding behind a cloud of dust that suddenly moved away. They found no dust clouds blocking the view. The galaxy really did get brighter; it wasn't just a trick of the light.
The Radio "Peak": They mapped the radio waves across different frequencies. They found the energy peaked at a low frequency (around 2 GHz). Imagine a radio station that is strongest on the AM dial but gets weaker as you turn the knob to FM. This suggests the jet of energy is relatively young or is interacting with thick gas right near the black hole.
The Size: The black hole is about 4 million times the mass of our Sun. That sounds huge, but in the universe, it's actually quite small (our Milky Way's black hole is 4 million times heavier, but some are billions of times heavier).

Why Did It Happen? (The Theories)

The scientists played detective and ruled out several suspects:

Not a Lens: It wasn't a trick of gravity (like a magnifying glass) making it look brighter.
Not a Star Being Eaten: Usually, when a black hole eats a star (a Tidal Disruption Event), it flares up and then dies quickly. This galaxy has been bright for 8 years. That's too long for a single star snack.
Not a Merger: They didn't see signs of two galaxies crashing into each other, which sometimes flips a black hole's spin and turns it on.
Not a New Galaxy: The galaxy was already active before; it just got much louder.

The Most Likely Culprit: The Accretion Rate Change
The team believes the black hole simply changed its eating habits.

Imagine a river flowing into a dam. For years, the water flowed at a steady, moderate pace. Suddenly, a massive rainstorm upstream caused the river to swell. The dam had to release a massive, powerful jet of water to handle the pressure.

In this galaxy, the "river" is the gas falling into the black hole (the accretion disk). The "dam" is the magnetic field near the black hole. The scientists think the flow of gas changed, which allowed the magnetic fields to reorganize. This reorganization acted like a switch, suddenly launching a powerful jet of particles that we see as radio waves.

Why Does This Matter?

This is a big deal for two reasons:

It's a Prototype: This is the first time we've seen a "radio changing-look" event that lasts this long. It's like finding a new species of animal. Now we know this type of behavior exists, and we can look for more.
A Window to the Past: Because this black hole is relatively small and close to us, it acts like a time machine. In the early universe, black holes were growing fast and were smaller. SDSS J1105 is a local example of how those ancient black holes might have behaved when they were "turning on" their jets for the first time.

The Bottom Line

SDSS J1105 is a cosmic surprise. It's a galaxy that was quiet for decades, suddenly turned on a massive, 8-year-long radio beacon, and is teaching us that black holes can change their "moods" and "eating habits" in ways we didn't fully understand before. It's a reminder that even in the quietest corners of the universe, dramatic changes are happening right now.

1. Problem and Scientific Context

Active Galactic Nuclei (AGN) typically exhibit stable radio emission or short-term variability. "Changing-look" AGN, which undergo dramatic spectral state changes (e.g., between Type 1 and Type 2 or radio-quiet and radio-loud), are rare. While optical and X-ray changing-look events are increasingly documented, radio changing-look events—specifically those involving a transition from radio-quiet to radio-loud with high amplitude and long duration—are virtually unobserved, particularly in Narrow-line Seyfert 1 (NLS1) galaxies.

NLS1s are a subclass of AGN characterized by low-mass supermassive black holes (SMBHs, $<10^7 M_\odot$ ), high Eddington ratios, and narrow broad emission lines. They are generally radio-quiet, with only $\sim7\%$ showing radio-loud properties. The paper addresses the mystery of SDSS J110546.07+145202.4 (SDSS J1105+1452), a nearby NLS1 galaxy that has brightened by a factor of $>23$ at 1.4 GHz since 2017 and has remained in this "high-state" for over 8 years, defying typical transient models like Tidal Disruption Events (TDEs) or standard blazar flares.

2. Methodology

The authors conducted a comprehensive multi-wavelength (MWL) campaign to characterize the outburst and constrain its physical origin:

X-ray Observations: Eight new observations using the Swift X-ray Telescope (XRT) between October and December 2025, plus archival data from 2023 and the 1990s ROSAT survey. Spectral analysis was performed using XSPEC, fitting power-law models with Galactic absorption.
UV-Optical Observations: Simultaneous Swift UVOT observations in six bands (V, B, U, UVW1, UVM2, UVW2) to construct UV-optical Spectral Energy Distributions (SEDs) and search for variability.
Radio Observations:
- New Data: High-frequency observations (4.85–16.75 GHz) using the Effelsberg 100m telescope and the Australia Telescope Compact Array (ATCA) in late 2025/early 2026 to measure the first high-frequency radio SED.
- Archival Data: Analysis of LOFAR (144 MHz), ASKAP (RACS, FLASH), VLASS, FIRST, NVSS, and GB6 surveys to reconstruct the light curve from the 1980s to present.
Optical/IR Photometry: Review of archival data from ASAS-SN, ZTF, Catalina Sky Survey, SDSS, WISE/NEOWISE, and POSS-I/II to constrain the onset time of the outburst and check for optical/IR counterparts.
SMBH Mass Estimation: Calculated using single-epoch scaling relations based on H $\beta$ luminosity and width, H $\alpha$ relations, and the host galaxy stellar velocity dispersion ( $\sigma_*$ ).

3. Key Contributions

This paper presents the first high-frequency radio observations, the first simultaneous radio SEDs, the first optical-UV-X-ray SEDs, and the first X-ray monitoring/spectroscopy of this specific event. It introduces the term "radio changing-look" to describe high-amplitude radio variability leading to a state change between radio-quiet and radio-loud.

4. Key Results

A. Source Properties and Classification

SMBH Mass: Estimated between $2.8 \times 10^6 M_\odot$ (via $\sigma_*$ ) and $4.4 \times 10^6 M_\odot$ (via H $\beta$ scaling).
Eddington Ratio: High, $\lambda_{Edd} \approx 0.2 - 0.3$ .
Classification: Confirmed as a classic NLS1 galaxy (FWHM(H $\beta$ ) = 1498 km/s, strong Fe II emission, [O III]/H $\beta$ < 3).
X-ray Spectrum: Soft and steep with a photon index $\Gamma_X = 2.5 \pm 0.16$ . No significant intrinsic absorption ( $N_H \leq 3.1 \times 10^{20}$ cm $^{-2}$ ) or extinction ( $E(B-V) \leq 0.1$ ) was detected.

B. Radio Outburst Characteristics

Amplitude: The source brightened by a factor of $>23$ at 1.4 GHz (from $\sim1.4$ mJy to $\sim32-40$ mJy).
Duration: The high-state has persisted for $>8$ years (since late 2017) with roughly constant flux density ( $\sim10\%$ variability).
Spectral Shape: The radio SED is peaked at low frequencies ( $\nu_{peak} \approx 2.1$ $ν_{p e ak} \approx 2.1$ GHz).
- Low-frequency slope (0.14–0.9 GHz): $\alpha_{thick} = 1.6 \pm 0.1$ (optically thick).
- High-frequency slope (>4 GHz): Steep decline ( $\alpha_{thin} \approx -1.3$ ).
- This resembles Gigahertz-Peaked Spectrum (GPS) sources but with a much lower turnover frequency and longer duration than typical GPS sources.
Luminosity: Monochromatic luminosity at 4.85 GHz is $L_{4.85} \approx 7 \times 10^{40}$ erg s $^{-1}$ . The radio-loudness parameter $\log R_X = -1.6$ .

C. Timing and Trigger

Onset: The transition occurred between the FIRST survey (1999.96, low state) and VLASS (2017.96, high state).
Optical/IR Correlation: No systematic high-amplitude variability was found in optical (ASAS-SN, ZTF, SDSS) or IR (WISE) bands since 2003. This suggests the trigger occurred before 2003, or the radio outburst is decoupled from immediate optical/IR continuum changes.
Star Formation: Ruled out as the primary driver; the IR-optical SED and emission line ratios indicate the emission is dominated by the AGN, not a starburst.

5. Discussion of Scenarios

The authors evaluated several physical mechanisms:

Excluded/Unlikely:
- Gravitational Lensing: No lensing galaxy or secondary redshift system found.
- Absorption Variability: No evidence of H I or Free-Free absorption changes sufficient to explain the flux difference.
- TDEs: Typical TDE radio light curves peak and decline within 1–3 years; this source has remained constant for $>8$ years.
- Binary SMBH Merger/Spin Flip: No morphological evidence of a recent merger in the host galaxy.
- Blazar Variability: The timescale (years) and constant flux are inconsistent with Doppler-boosted blazar flares.
Most Likely Scenario: Change in Accretion Rate.
The authors propose that a change in the accretion rate (potentially a "changing-look" event in the disk) triggered a dramatic increase in jet power.
- Mechanism: A modest increase in accretion rate could lead to a non-linear increase in jet power if the black hole approaches the Magnetically Arrested Disk (MAD) limit. In this regime, the accumulation of poloidal magnetic flux ( $\Phi_{BH}$ ) allows jet efficiency to scale as $P_{jet} \propto \Phi_{BH}^2$ .
- Implication: A modest change in magnetic flux (factor of 2–3) could produce the observed order-of-magnitude jump in radio luminosity without requiring a massive change in the accretion rate itself.

6. Significance

New Class of Transients: SDSS J1105+1452 is identified as the prototype of a new class of long-duration radio changing-look AGN.
Jet Physics: It provides a unique laboratory to study the "ignition" of radio jets in low-mass SMBHs, a process relevant to the early Universe where SMBHs were growing rapidly.
MAD Physics: The event offers observational support for the non-linear coupling between accretion disk magnetic flux and jet power, specifically the transition to a MAD state.
Future Surveys: The authors predict that upcoming surveys like the Square Kilometre Array (SKA) and ongoing VLA surveys will detect many more such long-lived radio transients, allowing for statistical studies of jet formation and AGN feedback in gas-rich environments.

In conclusion, the paper establishes that SDSS J1105+1452 is a unique, long-lived radio outburst driven by a change in accretion physics (likely magnetic flux accumulation) rather than a transient stellar event or external absorption, offering critical insights into the mechanisms of radio jet launching in NLS1 galaxies.