A luminous and hot infrared through X-ray transient at a 5 kpc offset from a dwarf galaxy

Abstract

We are searching for hot, constant-color, offset optical flares in the Zwicky Transient Facility (ZTF) data stream that are $>10^{\prime \prime }$ from any galaxy in public imaging data from the PanSTARRS survey. Here, we present the first discovery from this search: AT 2024puz, a luminous multiwavelength transient offset by $5$kpc from a $\sim 10^8{M}_{\odot }$ galaxy at $z=0.356$ with a low-moderate star formation rate. It produced luminous $10^{44.79\pm 0.04}{\mathrm{erg}\mathrm{s}}^{-1}$ optical/UV emission that evolved on a $\sim 20$day timescale, as well as $10^{44.12\pm 0.03}{\mathrm{erg}\mathrm{s}}^{-1}$ X-ray emission with a photon-index $\hat{I}“=1.7$. No associated radio or millimeter emission was detected. We show that the early-time optical emission is likely powered by reprocessing of high-energy, accretion-powered radiation, with a possible contribution from a shock in a dense circum-transient medium. If the shock is dominant at early-times, the circum-transient medium has a mass $\sim 0.1-1M_{\odot }$, radius $10^{15}$cm, and a density profile shallower than $\sim r^{-1}$. A near-infrared excess appears at late-times and is suggestive of reprocessing within a wind or other circum-transient medium. The X-rays are most consistent with a central engine. We suggest that AT 2024puz may be associated with an accretion event onto a $50-10^5{M}_{\odot }$ BH, where the lower masses are preferred based on the large projected offset from the host galaxy. AT2024puz exhibits properties similar to both luminous fast blue optical transients (LFBOTs) and tidal disruption events (TDEs), but is intermediate between them in its energetics and evolution timescale. This highlights the need for broader exploration of the landscape of hot optical transients to trace their origins.

42 pages, 18 figures, 13 tables, submitted to ApJ