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 data stream that are &gt;10″ 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 ∼10 8 M ⊙ galaxy at z = 0.356 with a low–moderate star formation rate (0.01 ± 0.003 M ⊙ yr −1 ). It produced luminous 10 44.79±0.04 erg s −1 optical/UV emission that evolved on a ∼20 day timescale, as well as 10 44.12±0.03 erg s −1 X-ray emission with a photon-index <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1.7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . 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 circumtransient medium. If the shock is dominant at early times, the circumtransient medium has a mass ∼0.1–1 M ⊙ , a radius 10 15 cm, and a density profile shallower than ∼ r −1 . A near-infrared excess appears at late-times and is suggestive of reprocessing within a wind or other circumtransient 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 ⊙ black hole, 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 and tidal disruption events, 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.