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Abstract:

Tidal disruption events (TDEs) that are spatially offset from the nuclei of their host galaxies offer a new probe of massive black hole (MBH) wanderers, binaries, triples, and recoiling MBHs. Here we present AT2024tvd, the first off-nuclear TDE identified through optical sky surveys. High-resolution imaging with the Hubble Space Telescope shows that AT2024tvd is 0 .″ 914 ± 0 .″ 010 offset from the apparent center of its host galaxy, corresponding to a projected distance of 0.808 ± 0.009 kpc at z = 0.045. Chandra and Very Large Array observations support the same conclusion for the TDE’s X-ray and radio emission. AT2024tvd exhibits typical properties of nuclear TDEs, including a persistent hot UV/optical component that peaks at Lbb ∼ 6 × 1043 erg s−1, broad hydrogen lines in its optical spectra, and delayed brightening of luminous (LX,peak ∼ 3 × 1043 erg s−1), highly variable soft X-ray emission. The MBH mass of AT2024tvd is 106±1 M⊙, at least 10 times lower than its host galaxy’s central black hole mass (≳108 M⊙). The MBH in AT2024tvd has two possible origins: a wandering MBH from the lower-mass galaxy in a minor merger during the dynamical friction phase or a recoiling MBH ejected by triple interactions. Combining AT2024tvd with two previously known off-nuclear TDEs discovered in X-rays (3XMM J2150 and EP240222a), which likely involve intermediate-mass black holes in satellite galaxies, we find that the parent galaxies of all three events are very massive (∼1010.9 M⊙). This result aligns with expectations from cosmological simulations that the number of offset MBHs scales linearly with the host halo mass.

Abstract:

We present observations of the Type IIP supernova (SN) SN 2024jlf, including spectroscopy beginning just 0.7 days (∼17 hr) after first light. Rapid follow-up was enabled by the new BTSbot-nearby program, which involves autonomously triggering target-of-opportunity requests for new transients in Zwicky Transient Facility data that are coincident with nearby (D < 60 Mpc) galaxies and identified by the BTSbot machine learning model. Early photometry and nondetections shortly prior to first light show that SN 2024jlf initially brightened by >4 mag day−1, quicker than ∼90% of Type II SNe. Early spectra reveal weak flash ionization features: narrow, short-lived (1.3 < τ[days] < 1.8) emission lines of Hα, He ii, and C iv. Assuming a wind velocity of vw = 50 km s−1, these properties indicate that the red supergiant progenitor exhibited enhanced mass loss in the last year before explosion. We constrain the mass-loss rate to 10−4

Abstract:

The Imaging X-ray Polarimetry Explorer (IXPE) observations of accreting X-ray pulsars (XRPs) continue to provide novel insights into the physics and geometry of these sources. We present the first X-ray polarimetric study of the persistent wind-fed XRP 4U 1538−52, based on five IXPE observations totaling 360 ks, conducted in March and October 2024. We detect marginally significant polarization in the combined data set in the full 2–8 keV energy band, with a polarization degree (PD) of 3.0 ± 1.1% and polarization angle (PA) of −18° ±11°. The energy-resolved analysis shows a clear energy dependence of the polarization properties, with a remarkable ∼70° switch in PA between low and high energies. Similarly, the pulse phase-resolved spectro-polarimetric analysis reveals different signatures at low and high energies. At low energies (2–3 keV), the PD spans from ∼2% up to ∼18%, accompanied by large-amplitude swings in the PA. At higher energies (4–8 keV), the PD varies between ∼3% and ∼12%, and the PA not only is similarly highly variable but also exhibits a markedly different phase dependence. Fitting the rotating vector model to the pulse phase dependence of the PA at the lower energies, we constrain the geometric configuration of the pulsar. The analysis favors a high spin-axis inclination of > 50°, which agrees with both previous pulse-phase-dependent spectral fitting of the cyclotron line region and the known high orbital inclination of the binary system. The magnetic obliquity is estimated to be 30° and the spin position angle to be 19°. A sharp switch in PA around 3 keV presents a particular theoretical challenge, as it is not consistent with the right-angle switch that was only seen in one other pulsar, Vela X-1.

Abstract:

PSR J0901−4046, a likely radio-loud neutron star with a period of 75.88 s, challenges conventional models of neutron star radio emission. Here, we showcase results from 46 h of follow-up observations of PSR J0901−4046 using the MeerKAT, Murriyang, Giant Metrewave Radio Telescope, and Murchison Widefield Array radio telescopes. We demonstrate the intriguing stability of the source’s timing solution over more than 3 yr, leading to an RMS arrival-time uncertainty of just of the rotation period. Furthermore, non-detection below 500 MHz may indicate a low-frequency turnover in the source’s spectrum, while no secular decline in the flux density of the source over time, as was apparent from previous observations, has been observed. Using high time-resolution MeerKAT data, we demonstrate two distinct quasi-periodic oscillation modes present in single pulses, with characteristic time-scales of 73 and 21 ms. We also observe a statistically significant change in the relative prevalence of distinct pulse morphologies compared to previous observations, possibly indicating a shift in the magnetospheric composition over time. Finally, we show that the W pulse width is nearly constant from 544 to 4032 MHz, consistent with zero radius-to-frequency mapping. The very short duty cycle () is more similar to radio pulsars with periods >5 s than to radio-loud magnetars. This, along with the lack of magnetar-like outbursts or timing glitches, complicates the identification of the source with ultralong period magnetar models.