---
title: 'AT 2024wpp: Record Luminous FBOT'
url: https://www.emergentmind.com/topics/at-2024wpp
type: topic
---

# AT 2024wpp: Record Luminous FBOT

AT 2024wpp is an exceptionally luminous, rapidly evolving extragalactic transient belonging to the fast blue optical transient (FBOT) class, most precisely the “Cow-like” or AT 2018cow-like subclass. Discovered in 2024, AT 2024wpp set new records for peak optical and ultraviolet luminosity in the FBOT population, with compelling multiwavelength evidence for central-engine activity and a likely progenitor scenario involving the merger of a Wolf–Rayet star with a stellar-mass black hole. Its photometric, spectroscopic, polarimetric, X-ray, and radio characteristics place it at the boundary between engine-driven supernovae and tidal disruption events (TDEs), highlighting both the diversity and the unifying physics of extreme stellar explosions.

## 1. Discovery, Photometric and Spectroscopic Properties

AT 2024wpp was identified by the Zwicky Transient Facility (ZTF) on 2024 September 26 at $z = 0.0868$ in the outskirts of a dwarf galaxy. The transient rose to a peak absolute $r$-band magnitude $M_r\approx -21.5$ within 3–4 days and achieved a bolometric luminosity across bands of $L_{\rm pk} \approx (2-4)\times 10^{45}$ erg s$^{-1}$, radiating $>10^{51}$ erg in its first ~45 days—an order of magnitude more than AT 2018cow, the prototypical FBOT [2509.00951, 2602.20523].

Multi-band UV/optical/infrared photometry is accurately described at all times by a single and persistently blue blackbody continuum, with color temperatures $T_{\rm bb} \gtrsim 2\times 10^4$–$3\times 10^4\,$K and blackbody radii expanding at $0.2c$–$0.3c$ up to $R_{\rm BB}\sim 10^{15}\,$cm. The high luminosity and blue colors were maintained for weeks, with negligible cooling and a receding photosphere [2509.00951, 2411.03272].

Spectroscopy from +4 to +35 days revealed a featureless, blue continuum, lacking narrow host- or hydrogen/helium-like lines in the early phase. At late times ($\gtrsim35$ days), faint, broad H/He lines with both rest and blueshifted ($-6400$ km s$^{-1}$) components appeared, indicating deviations from spherical symmetry and the presence of both polar and equatorial outflows [2509.00951, 2411.03272]. The spectra remained dominated by thermal emission, with any bound-bound features highly Doppler broadened and washed out by ionization and electron scattering.

Polarimetric observations between +6 and +14 days showed continuum polarization $P < 0.5\%$ across all optical bands, implying a high degree of spherical symmetry for the outflow. In combination with similar profiles for AT 2018cow, this disfavors strongly aspherical outflows during the optically thick photospheric phase [2411.03272].

## 2. Multiwavelength Behavior: X-ray and Radio Evolution

AT 2024wpp displayed luminous and variable X-ray emission ($L_{\rm X}\sim 1.5\times 10^{43}$ erg s$^{-1}$, 0.3–10 keV) and robust radio through millimeter (0.25–203 GHz) counterparts [2509.00952, 2602.20523]. The X-ray spectrum evolved from an initially soft power-law ($F_\nu\propto\nu^{-0.6}$) to extreme hardness ($F_\nu\propto\nu^{+1.26}$) around 50 days, coincident with an X-ray rebrightening and the emergence of a transient Compton “hump.” These features are interpreted as the evolving transmission of an embedded, variable high-energy source (e.g., an accreting compact object) through expanding, asymmetric, and initially Compton-thick ejecta. The X-ray light curve shows an early plateau, steep decay, and a delayed rebrightening interpreted as engine-driven fallback accretion [2509.00952, 2602.20523].

In the radio, the earliest fluxes in the millimeter/centimeter bands showed a rapid, order-of-magnitude rise during $t\approx$17–32 days, followed by a spectral peak at 9 GHz ($L_{9\,{\rm GHz}}\approx 1.7\times 10^{29}$ erg s$^{-1}$ Hz$^{-1}$ at 73 days) and a subsequent decay [2509.00952]. The radio/millimeter spectral energy distributions fit standard synchrotron self-absorption formalisms with optically thin (α ∼ -1.5) and thick (α ∼ 1–1.5) slopes. Equipartition modeling yields rapidly expanding emission regions ($v \rightarrow 0.07c$ to $0.42c$) and internal energies growing from $10^{47}$ erg to $3\times10^{49}$ erg [2509.00952, 2602.20523].

The collective X-ray and radio evolution provides direct evidence for a shock propagating through a dense circumstellar medium (CSM), including a confined shell ($R\sim10^{16}$ cm, $n\sim 10^8$ cm$^{-3}$) and a radial density profile $\rho(r)\propto r^{-3.1}$ at large scales, characteristic of extreme pre-explosion mass loss [2509.00952].

## 3. Physical Interpretation: Central Engine and Progenitor Models

AT 2024wpp’s extreme energetics and multi-component outflows require a central engine capable of sustained energy injection far exceeding that of standard core-collapse supernovae. The chronology and energetics are well explained by the delayed merger explosion of a $34\,M_\odot$ Wolf–Rayet (WR) star and a $15\,M_\odot$ black hole. In this scenario, during a common-envelope inspiral, extensive H-poor CSM is deposited. The final coalescence triggers:

- Hyper-accretion onto the BH, powering early X-ray and optical emission through a Blandford–Znajek (BZ) jet process, with $L_{BZ}(t)\propto t^{-k}$ ($k\approx1.77$), producing the initial X-ray plateau and high-velocity ejecta (best fit $M_{\rm ej}\approx0.27\,M_\odot$, $v_{\rm ej}\approx0.25c$).
- A magnetically arrested disk (MAD) transition at $t\sim16\,$days induces precipitous jet power drop and an X-ray decline.
- Fallback of equatorially ejected debris ignites renewed accretion at $t_{\rm fb}\sim30\,$days, with a fallback rate $\dot M_{\rm fb}\sim t^{-5/3}$, fueling a second phase of X-ray and optical rebrightening and producing slower equatorial outflows ($M_w\approx0.052\,M_\odot$, $v_w\approx0.032c$) [2602.20523].

The observed late-time bolometric luminosity decay precisely follows the $t^{-5/3}$ power law expected for fallback-dominated TDEs, providing quantitative support for this model [2602.20523]. The high-velocity, highly ionized, bipolar/polar outflows and delayed emergence of broad H/He lines are hallmark signatures of this engine-driven configuration, though the polarimetry at early times points to outflow sphericalization by the time the ejecta become photospheric [2411.03272, 2509.00951, 2509.00952].

## 4. AT 2024wpp in the Context of FBOTs and TDEs

AT 2024wpp stands at the luminous, energetic, and kinematic extreme of the FBOT family. Its key properties can be compared as follows:

| Event         | $L_{\rm pk}$ [erg/s] | $T_{\rm bb,peak}$ [K] | $v_{\rm ph,max}$ [c] | $E_{\rm rad}$ [erg] | Distinctive Features                             |
|---------------|---------------------|--------------------|---------------------|---------------------|-------------------------------------------------|
| AT 2024wpp    | $(2-4)\times10^{45}$| $>3\times10^{4}$   | $0.2-0.3$           | $>10^{51}$          | X-ray rebrightening, late $t^{-5/3}$ falloff     |
| AT 2018cow    | $2-4\times10^{44}$  | $>2\times10^{4}$   | $0.1-0.2$           | $\sim10^{50}$       | Early X-ray/optical flares, polarization drop    |
| AT 2022tsd    | $>10^{44}$          | $\gtrsim2\times10^{4}$| $0.1$            | $\sim10^{50}$       | Numerous minute-scale optical flares             |

Whereas AT 2018cow and AT 2022tsd display rapidly evolving blue continua and high-velocity outflows, only AT 2024wpp shows clear late-time X-ray rebrightening, an extended $t^{-5/3}$ luminosity tail, and aspherical but predominantly spherical outflows at photospheric radii [2509.00951, 2411.03272, 2509.00952, 2602.20523].

A defining distinction is that, despite deep searches in the window $t=28$–$74$ days, AT 2024wpp shows no evidence for the minute-scale optical flares previously observed in AT 2022tsd, with an upper limit to the flare duty cycle $\delta<0.02$ (2$\sigma$) and flare rate $R<0.11$ hr$^{-1}$ for $L_{\rm flare}>3\times10^{42}$ erg s$^{-1}$ [2508.18359]. This heterogeneity suggests diversity in engine properties, viewing-angle effects, or differences in envelope optical depth between AT 2018cow-like events.

## 5. Circumstellar Environment and Outflow Geometry

Radio modeling and late-time spectroscopy reveal that AT 2024wpp’s blastwave encountered a dense shell ($n\sim10^8$ cm$^{-3}$, $R\sim10^{16}$ cm), likely created by pre-explosion or binary-driven mass loss, followed by a medium with $\rho_{\rm CSM}(r)\propto r^{-3.1}$ out to at least $10^{17}$ cm. Such steep CSM gradients are consistently seen in other luminous radio-bright FBOTs and are interpreted as signatures of super-Eddington disk winds from compact-object progenitors or circumbinary outflows [2509.00952].

The presence of two kinematic components in late-time H/He lines, the emergence of a near-infrared excess ($F_{\nu,{\rm NIR}}\propto\nu^{-0.3}$) between 20–30 days, and polarization data together require both fast, polar and slower, equatorial outflows. The aspherical geometry is consistent with axisymmetric disk-wind models but becomes highly spherical in regions of highest optical depth [2509.00951, 2411.03272].

## 6. Outstanding Questions and Future Prospects

The case of AT 2024wpp demonstrates that FBOTs can result from engine-driven explosions that manifest classical TDE-like fallback and multi-phase accretion-driven luminosity, yet reside in massive stellar progenitors rather than galactic nuclei. The observed diversity—particularly the presence or absence of minute-scale flaring, the role of outflow geometry, and the detailed structure of the CSM—remains to be explained. Systematic multiwavelength and time-domain monitoring, as well as polarization and high-resolution spectroscopy of future events, are essential to disentangle geometrical, progenitor, and viewing-angle effects [2508.18359, 2411.03272, 2509.00952, 2602.20523]. Broader samples and modeling will further clarify the relationship between FBOTs, engine-driven SNe, and stellar TDEs.

Source: https://www.emergentmind.com/topics/at-2024wpp