Minutes-duration optical flares with supernova luminosities.
Nature 623:7989 (2023) 927-931
Abstract:
In recent years, certain luminous extragalactic optical transients have been observed to last only a few days1. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks2. Some short-duration transients, most notably AT2018cow (ref. 3), show blue optical colours and bright radio and X-ray emission4. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source5, such as X-ray variability6,7, prolonged ultraviolet emission8, a tentative X-ray quasiperiodic oscillation9,10 and large energies coupled to fast (but subrelativistic) radio-emitting ejecta11,12. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the 'Tasmanian Devil'). The flares occur over a period of months, are highly energetic and are probably nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that, in some AT2018cow-like transients, the embedded energy source is a compact object, either a magnetar or an accreting black hole.Detection of large-scale synchrotron radiation from the molecular envelope of the Sgr B cloud complex at the Galactic centre
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 527:1 (2023) 1275-1282
Tracing the colliding winds of η Carinae in He i
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 526:4 (2023) 6155-6167
Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5-1
ArXiv 2310.06788 (2023)
Probing magnetic fields in the circumgalactic medium using polarization data from MIGHTEE
Astronomy and Astrophysics EDP Sciences 678 (2023) A56
Abstract:
Context. The properties and evolution of magnetic fields surrounding galaxies are observationally largely unconstrained. The detection and study of these magnetic fields is important to understand galaxy evolution since magnetic fields are tracers for dynamical processes in the circumgalactic medium (CGM) and can have a significant impact on the evolution of the CGM.Aims. The Faraday rotation measure (RM) of the polarized light of background radio sources passing through the magnetized CGM of intervening galaxies can be used as a tracer for the strength and extent of magnetic fields around galaxies.
Methods. We used rotation measures observed by the MIGHTEE-POL (MeerKAT International GHz Tiered Extragalactic Exploration polarization) survey by MeerKAT in the XMM-LSS and COSMOS fields to investigate the RM around foreground star-forming galaxies. We used spectroscopic catalogs of star-forming and blue cloud galaxies to measure the RM of MIGHTEE-POL sources as a function of the impact parameter from the intervening galaxy. In addition, we examined the dependence of the RM on redshift. We then repeated this procedure using a deeper galaxy catalog with photometric redshifts.
Results. For the spectroscopic star-forming sample, we find a redshift-corrected |RM| excess of 5.6 ± 2.3 rad m−2 which corresponds to a 2.5σ significance around galaxies with a median redshift of z = 0.46 for impact parameters below 130 kpc only selecting the intervenor with the smallest impact parameter. Making use of a photometric galaxy catalog and taking into account all intervenors with Mg < −13.6 mag, the signal disappears. We find no indication for a correlation between redshift and RM, nor do we find a connection between the total number of intervenors to the total |RM|.
Conclusions. We have presented tentative evidence that the CGM of star-forming galaxies is permeated by coherent magnetic fields within the virial radius. We conclude that mostly bright, star-forming galaxies with impact parameters less than 130 kpc significantly contribute to the RM of the background radio source.