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The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision

The Astrophysical Journal American Astronomical Society 994:1 (2025) 5-5

Authors:

GE Anderson, GP Lamb, BP Gompertz, L Rhodes, A Martin-Carrillo, AJ van der Horst, A Rowlinson, ME Bell, T-W Chen, HM Fausey, M Ferro, PJ Hancock, SR Oates, S Schulze, RLC Starling, S Yang, K Ackley, JP Anderson, A Andersson, JF Agüí Fernández, R Brivio, E Burns, KC Chambers, T de Boer, V D’Elia, M De Pasquale, A de Ugarte Postigo, Dimple, R Fender, MD Fulton, H Gao, JH Gillanders, DA Green, M Gromadzki, A Gulati, DH Hartmann, ME Huber, NJ Klingler, NPM Kuin, JK Leung, AJ Levan, C-C Lin, E Magnier, DB Malesani, P Minguez, KP Mooley, T Mukherjee, M Nicholl, PT O’Brien, G Pugliese, A Rossi, SD Ryder, B Sbarufatti, B Schneider, F Schüssler, SJ Smartt, KW Smith, S Srivastav, D Steeghs, NR Tanvir, CC Thoene, SD Vergani, RJ Wainscoat, Z-N Wang, RAMJ Wijers, D Williams-Baldwin, I Worssam, T Zafar

Abstract:

Abstract We present the early radio detection and multiwavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift z = 0.257. The Australia Telescope Compact Array automatically triggered a 9 hr observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hr post-burst. Splitting this observation into 1 hr time bins, the early radio afterglow exhibited flaring, scintillating and plateau phases. The scintillation allowed us to place the earliest upper limit (<10 hr) on the size of a GRB blast wave to date, constraining it to <1 × 10 16 cm. Multiwavelength modeling of the full afterglow required a period of significant energy injection between ∼0.02 and 1 day. The energy injection was modeled as a violent collision of two shells: a reverse shock passing through the injection shell explains the early radio plateau, while an X-ray flare is consistent with a shock passing through the leading impulsive shell. Beyond 1 day, the blast wave evolves as a classic decelerating forward shock with an electron distribution index of p  = 1.66 ± 0.01. Our model also indicates a jet break at ∼2 days, and a half-opening angle of θ j = 16 . ° 6 ± 1 . ° 1 . Following the period of injection, the total energy is ζ  ∼ 18 times the initial impulsive energy, with a final collimation-corrected energy of E Kf  ∼ 5.7 × 10 49 erg. The minimum Lorentz factors this model requires are consistent with constraints from the early radio measurements of Γ > 35 to Γ > 5 between ∼0.1 and 1 day. These results demonstrate the importance of rapid and sensitive radio follow-up of GRBs for exploring their central engines and outflow behaviour.
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Radio Galaxy Zoo: Morphological classification by Fanaroff-Riley designation using self-supervised pre-training

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2025) staf1942

Authors:

Nutthawara Buatthaisong, Inigo Val Slijepcevic, Anna MM Scaife, Micah Bowles, Andrew Hopkins, Devina Mohan, Stanislav S Shabala, O Ivy Wong

Abstract:

Abstract In this study, we examine over 14,000 radio galaxies finely selected from Radio Galaxy Zoo (RGZ) project and provide classifications for approximately 5,900 FRIs and 8,100 FRIIs. We present an analysis of these predicted radio galaxy morphologies for the RGZ catalogue, classified using a pre-trained radio galaxy foundation model that has been fine-tuned to predict Fanaroff-Riley (FR) morphology. As seen in previous studies, our results show overlap between morphologically classified FRI and FRII luminosity-size distributions and we find that the model’s confidence in its predictions is lowest in this overlap region, suggesting that source morphologies are more ambiguous. We identify the presence of low-luminosity FRII sources, the proportion of which, with respect to the total number of FRIIs, is consistent with previous studies. However, a comparison of the low-luminosity FRII sources found in this work with those identified by previous studies reveals differences that may indicate their selection is influenced by the choice of classification methodology. We investigate the impacts of both pre-training and fine-tuning data selection on model performance for the downstream classification task, and show that while different pre-training data choices affect model confidence they do not appear to cause systematic generalisation biases for the range of physical and observational characteristics considered in this work; however, we note that the same is not necessarily true for fine-tuning. As automated approaches to astronomical source identification and classification become increasingly prevalent, we highlight training data choices that can affect the model outputs and propagate into downstream analyses.
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Unprecedentedly bright X-ray flaring in Cygnus X-1 observed by INTEGRAL

Astronomy & Astrophysics EDP Sciences 703 (2025) A109-A109

Authors:

P Thalhammer, T Bouchet, J Rodriguez, F Cangemi, K Pottschmidt, DA Green, L Rhodes, C Ferrigno, MA Nowak, V Grinberg, T Siegert, P Laurent, I Kreykenbohm, M Perucho, J Tomsick, C Sánchez-Fernández, J Wilms

Abstract:

We study three extraordinarily bright X-ray flares originating from Cyg X-1 seen on July 10, 2023, detected with INTEGRAL. The flares had a duration on the order of only ten minutes each, and within seconds reached a 1–100 keV peak luminosity of 1.1 − 2.6 × 10 38  erg s −1 . The associated INTEGRAL/IBIS count rate was approximately ten times higher than usual for the hard state. To our knowledge, this is the first time that such strong flaring has been seen in Cyg X-1, despite the more than 21 years of INTEGRAL monitoring – with almost ∼20 Ms of exposure – and the similarly deep monitoring with RXTE/PCA from 1997 to 2012. The flares were seen in all three X-ray and γ -ray instruments of INTEGRAL. Radio monitoring by the AMI Large Array with observations 6 h before and 40 h after the X-ray flares did not detect a corresponding increase in radio flux. The shape of the X-ray spectrum shows only marginal change during the flares, i.e., photon index and cut-off energy are largely preserved. The overall flaring behavior points toward a sudden and brief release of energy either due to the ejection of material in an unstable jet or due to the interaction of the jet with the ambient clumpy stellar wind.
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MIGHTEE-H  i : The M H  i – M ☆ relation of massive galaxies and the H  i mass function at 0.25 &lt; z &lt; 0.5

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2025) staf1857

Authors:

Hengxing Pan, Matt J Jarvis, Ian Heywood, Tariq Yasin, Natasha Maddox, Mario G Santos, Maarten Baes, Anastasia A Ponomareva, Sambatriniaina HA Rajohnson

Abstract:

Abstract The relationship between the already formed stellar mass in a galaxy and the gas reservoir of neutral atomic hydrogen, is a key element in our understanding of how gas is turned into stars in galaxy haloes. In this paper, we measure the $M_{\rm H\, \small {\rm i}}-M_{\star }$ relation based on a stellar-mass selected sample at 0.25 &lt; z &lt; 0.5 and the MIGHTEE-H i DR1 spectral data. Using a powerful Bayesian stacking technique, for the first time we are also able to measure the underlying bivariate distribution of H i mass and stellar mass of galaxies with M⋆ &gt; 109.5 M⊙, finding that an asymmetric underlying H i distribution is strongly preferred by our complete samples. We define the concepts of the average of the logarithmic H i mass, $\langle \log _{10}(M_{\rm H\, \small {\rm i}})\rangle$, and the logarithmic average of the H i mass, $\log _{10}(\langle M_{\rm H\, \small {\rm i}}\rangle )$, and find that the difference between $\langle \log _{10}(M_{\rm H\, \small {\rm i}})\rangle$ and $\log _{10}(\langle M_{\rm H\, \small {\rm i}}\rangle )$ can be as large as ∼0.5 dex for the preferred asymmetric H i distribution. We observe shallow slopes in the underlying $M_{\rm H\, \small {\rm i}}-M_{\star }$ scaling relations, suggesting the presence of an upper H i mass limit beyond which a galaxy can no longer retain further H i gas. From our bivariate distribution we also infer the H i mass function at this redshift and find tentative evidence for a decrease of 2-10 times in the co-moving space density of the most H i massive galaxies up to z ∼ 0.5.
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MIGHTEE-H  i : the direct detection of neutral hydrogen in galaxies at z &gt; 0.25

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 544:1 (2025) 193-210

Authors:

Matt J Jarvis, Madalina N Tudorache, I Heywood, Anastasia A Ponomareva, M Baes, Natasha Maddox, Kristine Spekkens, Andreea Vărăşteanu, CL Hale, Mario G Santos, RG Varadaraj, Elizabeth AK Adams, Alessandro Bianchetti, Barbara Catinella, Jacinta Delhaize, M Maksymowicz-Maciata, Pavel E Mancera Piña, Hengxing Pan, Amélie Saintonge, Gauri Sharma, O Ivy Wong

Abstract:

ABSTRACT Atomic hydrogen constitutes the gas reservoir from which molecular gas and star formation in galaxies emerges. However, the weakness of the line means it has been difficult to directly detect in all but the very local Universe. Here, we present results from the first search using the MeerKAT International Tiered Extragalactic Exploration (MIGHTEE) Survey for high-redshift ($z&gt;0.25$) H i emission from individual galaxies. By searching for 21-cm emission centred on the position and redshift of optically selected emission-line galaxies we overcome difficulties that hinder untargeted searches. We detect 11 galaxies at $z&gt;0.25$, forming the first sample of $z&gt;0.25$ detections with an interferometer, with the highest redshift detection at $z = 0.3841$. We find they have much larger H i masses than their low-redshift H i-selected counterparts for a given stellar mass. This can be explained by the much larger cosmological volume probed at these high redshifts, and does not require any evolution of the H i mass function. We make the first-ever measurement of the baryonic Tully–Fisher relation (bTFr) with H  i at $z&gt;0.25$ and find consistency with the local bTFr, but with tentative evidence of a flattening in the relation at these redshifts for higher-mass objects. This may signify evolution, in line with predictions from hydrodynamic simulations, or that the molecular gas mass in these high-mass galaxies could be significant. This study paves the way for future studies of H i beyond the local Universe, using both searches targeted at known objects and via pure H i selection.
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