A Multi-wavelength Characterization of the 2023 Outburst of MAXI J1807+132: Manifestations of Disk Instability and Jet Emission

The Astrophysical Journal American Astronomical Society 988:2 (2025) 153

Authors:

Sandeep K Rout, M Cristina Baglio, Andrew K Hughes, David M Russell, DM Bramich, Payaswini Saikia, Kevin Alabarta, Montserrat Armas Padilla, Sergio Campana, Stefano Covino, Paolo D’Avanzo, Rob Fender, Paolo Goldoni, Jeroen Homan, Fraser Lewis, Nicola Masetti, Sara Motta, Teo Muñoz-Darias, Alessandro Papitto, Thomas D Russell, Gregory Sivakoff, Jakob van den Eijnden

Abstract:

Several phenomenological aspects of low-luminosity neutron star transients, such as atolls, remain poorly understood. One such source, MAXI J1807+132, entered its latest outburst in 2023 July. To thoroughly characterize this outburst, we conducted an extensive observational campaign spanning radio to X-ray wavelengths. Here we present the results of this campaign, which covered the period from before the outburst to the return to quiescence. We detected a delay between the X-ray and optical rise times, which is consistent with the predictions of the disk instability model with a truncated disk. The color evolution and optical/X-ray correlations, along with infrared and radio detections, support the presence of jet synchrotron emission during the gradual decay phase following the peak. We also report for the first time in an X-ray binary a near-orthogonal rotation of the optical polarization just before a small flare, after which the jet is thought to be quenched. The main outburst is followed by several high-amplitude, rapid reflares in the optical, ultraviolet, and X-ray bands, the origin of which remains difficult to constrain.

MIGHTEE: A first look at MIGHTEE quasars

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2025) staf1187

Authors:

Sarah V White, Ivan Delvecchio, Nathan Adams, Ian Heywood, Imogen H Whittam, Catherine L Hale, Neo Namane, Rebecca AA Bowler, Jordan D Collier

Abstract:

Abstract In this work we study a robust, Ks-band complete, spectroscopically-confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM-LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at 0.60 < zspec < 3.41. The quasars are selected via gJKs colour-space and, with 1.3-GHz flux-densities reaching rms ≈ 3.0 μ Jy beam−1, we find a radio-loudness fraction of 5percnt. Thanks to the deep, multiwavelength datasets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically-robust way, with the emphasis of this work being on the active-galactic-nuclei (AGN)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more-easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as ‘starbursts’. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.

Optical spectroscopy of blazars for the Cherenkov Telescope Array Observatory- IV

(2025)

Authors:

B Rajput, P Goldoni, W Max-Moerbeck, E Kasai, DA Williams, C Boisson, S Pita, M Backes, U Barres de Almeida, J Becerra González, G Cotter, F D'Ammando, V Fallah Ramazani, B Hnatyk, O Hervet, E Lindfors, D Mukhi-Nilo, M Nikołajuk, M Splettstoesser, B Van Soelen

Comprehensive Radio Monitoring of the Black Hole X-Ray Binary Swift J1727.8−1613 during Its 2023–2024 Outburst

The Astrophysical Journal American Astronomical Society 988:1 (2025) 109

Authors:

Andrew K Hughes, Francesco Carotenuto, Thomas D Russell, Alexandra J Tetarenko, James CA Miller-Jones, Arash Bahramian, Joe S Bright, Fraser J Cowie, Rob Fender, Mark A Gurwell, Jasvinderjit K Khaulsay, Anastasia Kirby, Serena Jones, Elodie Lescure, Michael McCollough, Richard M Plotkin, Ramprasad Rao, Saeqa D Vrtilek, David RA Williams-Baldwin, Callan M Wood, Gregory R Sivakoff, Diego Altamirano, Piergiorgio Casella, Stéphane Corbel, James H Matthews, Andrew Siemion

Abstract:

This work presents comprehensive multifrequency radio monitoring of the black hole low-mass X-ray binary (LMXB) Swift J1727.8−1613, which underwent its first recorded outburst after its discovery in 2023 August. Through a considerable community effort, we have coalesced the data from multiple, distinct observing programs; the light curves include ∼10 months and 197 epochs of monitoring from seven radio facilities with observing frequencies ranging from (approximately) 0.3–230 GHz. The primary purpose of this work is to provide the broader astronomical community with these light curves to assist with the interpretation of other observing campaigns, particularly nonradio observing frequencies. We discuss the phenomenological evolution of the source, which included (i) multiple radio flares consistent with the launching of discrete jet ejections, the brightest of which reached ∼1 Jy; (ii) temporally evolving radio spectral indices (α), reaching values steeper than expected for optically thin synchrotron emission (α < −1) and emission with significant radiative cooling (α < −1.5). We have published a digital copy of the data and intend for this work to set a precedent for the community to continue releasing comprehensive radio light curves of future LMXB outbursts.

The Kangaroo’s First Hop: The Early Fast Cooling Phase of EP250108a/SN 2025kg

The Astrophysical Journal Letters American Astronomical Society 988:1 (2025) L14

Authors:

Rob AJ Eyles-Ferris, Peter G Jonker, Andrew J Levan, Daniele Bjørn Malesani, Nikhil Sarin, Christopher L Fryer, Jillian C Rastinejad, Eric Burns, Nial R Tanvir, Paul T O’Brien, Wen-fai Fong, Ilya Mandel, Benjamin P Gompertz, Charles D Kilpatrick, Steven Bloemen, Joe S Bright, Francesco Carotenuto, Gregory Corcoran, Laura Cotter, Paul J Groot, Luca Izzo, Tanmoy Laskar, Antonio Martin-Carrillo, Jesse Palmerio

Abstract:

Fast X-ray transients are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its Wide-field X-ray Telescope has led to a rapid expansionof the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart, SN 2025kg, or “the kangaroo.” Together with a companion Letter we present our observing campaign and analysis of this event. In this letter, we focus on the early evolution of the optical counterpart over the first 6 days, including our measurement of the redshift of z = 0.17641. We compare to other supernovae and fast transients showing similar features, finding significant similarities with SN 2006aj and SN 2020bvc, and show that the source is well modelled by a rapidly expanding cooling blackbody. We show the observed X-ray and radio properties are consistent with a collapsar-powered jet that is low energy (≲1051 erg) and/or fails to break out of the dense material surrounding it. While we examine the possibility that the optical emission emerges from the shock produced as the supernova ejecta expand into a dense shell of circumstellar material, due to our X-ray and radio inferences, we favour a model where it arises from a shocked cocoon resulting from a trapped jet. This makes SN 2025 one of the few examples of this currently observationally rare event.