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Arcminute Microkelvin Imager observations at 15.5 GHz of the tidal disruption event Swift J164449.3+573451 from 2011 Mar to 2014 Mar

This paper reports on 308 Arcminute Microkelvin Imager observations at 15.5 GHz of the tidal disruption event Swift J164449.3+573451 between March 2011 and March 2014, revealing a flux density that rose from approximately 3 mJy to a peak of nearly 30 mJy around 140 days after the initial gamma-ray detection before steadily declining.

Original authors: David A. Green

Published 2026-08-26

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CC BY 4.0

Original authors: David A. Green

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

Deep in the cosmos, where the gravity of a black hole is strong enough to tear a passing star apart, a violent and rare event can unfold. This phenomenon, known as a tidal disruption event, occurs when a star wanders too close to a supermassive black hole at the center of a galaxy. The black hole's immense gravitational pull stretches the star into a long stream of gas, eventually swallowing it in a spectacular flare of energy. While these events are often detected by their sudden burst of high-energy light, such as X-rays or gamma rays, astronomers are also keen to watch how the aftermath plays out over time. By tracking the radio waves emitted by the debris as it spirals inward, scientists can piece together the story of how the black hole consumes its meal and how the surrounding environment reacts to the violence. Understanding these long-term changes helps researchers refine their models of black hole behavior and the physics of extreme gravity.

In March 2011, a specific tidal disruption event caught the attention of astronomers when a satellite detected a sudden flash of gamma rays from a distant galaxy. This object, designated Swift J164449.3+573451, was initially mistaken for a standard gamma-ray burst, a common type of explosion in the universe. However, its behavior quickly revealed it to be something different; it continued to flicker and brighten in ways that suggested a star was being devoured by a black hole rather than a single, instantaneous explosion. To understand the full lifecycle of this event, a researcher turned their attention to the radio waves coming from the same spot in the sky. Using a specialized radio telescope array in Cambridge, United Kingdom, they monitored the object with observations starting daily and later spaced two or more days apart, covering the period from March 2011 to March 2014. Their goal was to capture a detailed record of how the radio brightness changed day by day, filling in gaps left by earlier, shorter observations.

The researcher used a powerful instrument called the Arcminute Microkelvin Imager, which consists of eight large radio dishes working together to create a sharp image of the sky. They focused their observations on a specific range of radio frequencies, taking measurements of the target object daily or every few days. To ensure their data was accurate, they frequently checked their instruments against a known, steady source of radio waves nearby. Over the course of three years, they completed 308 separate observations, carefully filtering out data collected during bad weather or technical glitches. This massive dataset allowed them to construct a precise timeline of the event's radio emission, showing exactly how the light from the dying star evolved over time.

The results of this long-term monitoring tell a clear story of rise and fall. Shortly after the initial detection of the gamma-ray flash, the radio signal from the object was faint, measuring about 3 units of brightness. Over the next few months, this signal grew steadily stronger. It reached its peak intensity roughly 140 days after the first gamma-ray detection, shining nearly ten times brighter than it had at the start. After this peak, the radio light began a slow, steady decline, fading gradually over the remaining two years of the study. This pattern of a sharp rise followed by a long, smooth fade confirms that the black hole was actively consuming the stellar debris, with the radio waves serving as a beacon of the material heating up and then cooling down as it was swallowed. The study provides a complete, three-year portrait of this cosmic event, offering a rare and detailed look at the long-term aftermath of a star being torn apart by a black hole.

Technical Summary: Arcminute Microkelvin Imager Observations of Swift J164449.3+573451

Problem and Context
Swift J164449.3+573451 is a tidal disruption event (TDE) resulting from a star being disrupted by the nuclear black hole of a galaxy at a redshift of $z \approx 0.35$ . Initially detected in $\gamma$ -rays on 2011 March 28 and misidentified as a long gamma-ray burst (GRB 110328A), the source was subsequently characterized as a TDE. While previous studies (e.g., Berger et al. 2012; Zauderer et al. 2013) established that the source brightened in radio wavelengths for approximately the first 100 days before declining, a comprehensive, reprocessed dataset covering the first three years of the outburst was required to refine the light curve and flux density measurements.

Methodology
This study reports on 308 radio monitoring observations of Swift J164449.3+573451 conducted between 2011 March and 2014 March using the Arcminute Microkelvin Imager (AMI) 'Large Array' at the Mullard Radio Astronomy Observatory. The AMI consists of eight 13.5-m diameter antennas operating as a radio interferometer.

Observation Parameters: The observations targeted a single linear polarization (Stokes parameter $I+Q$ ) across a frequency range of 13 to 18 GHz. The analog correlator split the band into eight channels; however, the end channels were excluded from analysis due to lower sensitivity and susceptibility to interference, leaving six broad channels covering 13.6 to 17.4 GHz.
Procedure: Observations typically involved multiple 10-minute scans of the target interleaved with 100-second scans of the compact calibrator J1638+5720. While initial observations were daily, the cadence later increased to intervals of two or more days. Observations were excluded if weather conditions (high winds, heavy rain) or technical issues compromised calibration.
Data Reduction: Data were processed using the reduce package. The flux density scale was established using standard calibrators (3C286 or 3C48) and "rain gauge" measurements to account for atmospheric variations. Data were flagged both automatically (to remove technical artifacts) and manually (to remove residual interference and rain-affected periods).
Calibration: Phase calibration for each antenna was derived from the interleaved observations of J1638+5720. The flux density scale was adjusted observation-to-observation based on a spline fit to the apparent flux density of J1638+5720, which varied slowly between 0.8 and 2.0 Jy.
Analysis: Flux densities were derived for each observation across the six valid frequency channels. A power-law fit was subsequently applied to these channels to determine a single flux density value at the central frequency of 15.5 GHz.

Key Contributions and Results
The primary contribution of this work is the presentation of a reprocessed and extended dataset covering the first three years of the Swift J164449.3+573451 outburst. This dataset supersedes earlier presentations of the 2011–2012 data by providing smaller statistical errors and a continuous timeline through 2014 March.

The resulting 15.5 GHz light curve reveals a distinct evolutionary pattern:

Rise Phase: A steady increase in flux density was observed, rising from approximately 3 mJy (three days after the initial $\gamma$ -ray detection) to a peak of nearly 30 mJy.
Peak Timing: The peak flux density occurred approximately 140 days after the initial detection.
Decline Phase: Following the peak, the source exhibited a steady decline in flux density through the end of the observation period in 2014 March.

Significance
The paper claims significance primarily through the refinement of the radio light curve for this specific TDE. By reprocessing earlier data and incorporating new observations, the author provides a more precise characterization of the source's temporal evolution. The results confirm the initial brightening and subsequent steady decline previously noted in the literature but with improved statistical precision. The work serves as a definitive observational record of the radio continuum emission of Swift J164449.3+573451 over its first three years, acknowledging that the original observations were conducted by the late Guy Pooley. The study does not propose new physical models or future applications but strictly reports the observational data and its immediate derived properties.

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