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arxiv: 2606.27725 · v1 · pith:Q2HDTSBVnew · submitted 2026-06-26 · 🌌 astro-ph.EP · astro-ph.SR

KMT-2025-BLG-2093: Free-Floating Planet Candidate Near the Shore of the Einstein Desert

Yoon-Hyun Ryu , Andrew Gould , Kyu-Ha Hwang , Qiyue Qian , Michael D. Albrow , Sun-Ju Chung , Cheongho Han , Youn Kil Jung
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Zhixing Li Shude Mao In-Gu Shin Yossi Shvartzvald Hongjing Yang Jennifer C. Yee Weicheng Zang Dong-Jin Kim Chung-Uk Lee Byeong-Gon Park Richard W. Pogge
This is my paper

Pith reviewed 2026-06-29 02:45 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.SR
keywords free-floating planetsmicrolensingEinstein radiusEinstein Desertisolated microlensexoplanet detectionKMTNet
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The pith

KMT-2025-BLG-2093 is the second isolated microlens with Einstein radius inside the 9-25 microarcsecond Einstein Desert.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper analyzes the microlensing event KMT-2025-BLG-2093 and reports an angular Einstein radius of 13.1 plus or minus 2.8 microarcseconds. This value positions the event inside the Einstein Desert, the interval between 9 and 25 microarcseconds that lies between free-floating planets and brown dwarfs or stars. Adding this second isolated case to the one already known, the analysis points to how such events can supply practical guidance for detecting free-floating planets with upcoming space missions that emphasize them.

Core claim

The microlensing event KMT-2025-BLG-2093 is isolated and has measured angular Einstein radius θ_E = 13.1 ± 2.8 μas, placing it as the second such object inside the Einstein Desert (9 μas < θ_E < 25 μas) that separates free-floating planets from brown dwarfs and stars.

What carries the argument

The angular Einstein radius θ_E, which fixes the angular scale of the microlensing light curve and assigns the lens to the defined mass-separation interval called the Einstein Desert.

If this is right

  • Isolated events inside the desert can mark the transition between planetary-mass and substellar lenses in microlensing samples.
  • The light-curve properties of this event supply a reference for identifying comparable candidates in future surveys.
  • Missions such as Earth 2.0 and Roman can use the desert interval to prioritize searches for additional free-floating planets.
  • Repeated detections near the desert boundaries can help trace the mass distribution of isolated low-mass objects.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If more desert events accumulate, the gap may reflect a real feature in the mass function rather than an observational selection effect.
  • Space-based astrometry could test whether any of these lenses possess wide, undetected companions that would alter their classification.
  • Ground-based networks that already reach microarcsecond precision can be applied systematically to other events to populate the desert region further.

Load-bearing premise

The event is truly isolated with no detectable host star and the light-curve fit yields an Einstein radius that correctly locates the lens inside the stated 9-25 microarcsecond interval.

What would settle it

High-resolution imaging that reveals a host star or new photometry that revises θ_E outside the 9-25 μas window would remove the event from the Einstein Desert.

Figures

Figures reproduced from arXiv: 2606.27725 by Andrew Gould, Byeong-Gon Park, Cheongho Han, Chung-Uk Lee, Dong-Jin Kim, Hongjing Yang, In-Gu Shin, Jennifer C. Yee, Kyu-Ha Hwang, Michael D. Albrow, Qiyue Qian, Richard W. Pogge, Shude Mao, Sun-Ju Chung, Weicheng Zang, Yoon-Hyun Ryu, Yossi Shvartzvald, Youn Kil Jung, Zhixing Li.

Figure 1
Figure 1. Figure 1: The parameters of this fit (t0, u0, tE, ρ, Is) are given in [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 1
Figure 1. Figure 1: — Light curve of KMT-2025-BLG-2093, which is well-fit by the FS [PITH_FULL_IMAGE:figures/full_fig_p013_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: — Color-magnitude diagram (CMD) of field stars in a 100 [PITH_FULL_IMAGE:figures/full_fig_p014_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: — ∆χ 2 = χ 2 (1L1S) − χ 2 (2L1S) test of the putative host of FFP candidate KMT￾2025-BLG-2093. The upper panel shows the difference in predicted flux between the two solutions ∆F. Because of severe extinction, this peaks at ∆F = 0.0034, corresponding to I = 18 − 2.5 log ∆F = 24.2, well below the noise level of the data, so we do not display these. The lower panel shows the contributions of the individual d… view at source ↗
Figure 4
Figure 4. Figure 4: — KMT-2025-BLG-2093 (red) is compared to 12 published FSPL [PITH_FULL_IMAGE:figures/full_fig_p016_4.png] view at source ↗
read the original abstract

We analyze KMT-2025-BLG-2093, with angular Einstein radius $\theta_{\rm E}=13.1\pm 2.8\,\mu{\rm as}$, which makes it the second isolated microlens that lies in the ``Einstein Desert'' ($9\,\mu{\rm as}<\theta_{\rm E}<25\,\mu{\rm as}$) between free-floating planets (FFPs) on one side and brown dwarfs and stars on the other. We discuss how its characteristics may give clues to future exploration of FFPs, especially in the era of satellite missions that have a major FFP focus, including Earth 2.0 and Roman.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper reports the microlensing analysis of KMT-2025-BLG-2093 and derives an angular Einstein radius θ_E = 13.1 ± 2.8 μas. This value places the event as the second isolated microlens inside the Einstein Desert (9 μas < θ_E < 25 μas), separating free-floating planets from brown dwarfs and stars. The authors discuss implications for future FFP searches with satellite missions such as Earth 2.0 and Roman.

Significance. If the θ_E measurement and isolation claim hold after accounting for systematics, the result adds a key data point to the small sample of isolated microlenses in the desert region. This can help constrain the low-mass end of the lens mass function and guide observing strategies for upcoming space-based surveys with a strong FFP focus.

major comments (2)
  1. [light-curve modeling and θ_E derivation] The 1σ lower bound on θ_E is 10.3 μas, only 1.3 μas above the 9 μas desert edge. The paper must demonstrate (via explicit tests or additional error terms) that systematics in the finite-source parameter ρ from the light-curve fit and in θ_* from the source color/spectral-type determination cannot shift the lower limit below 9 μas.
  2. [isolation and blending analysis] The central claim requires the event to be isolated (no detectable host star). The manuscript should quantify any possible host flux absorbed into the blend or source parameters and show that it does not bias ρ (and therefore θ_E) enough to move the event out of the desert.
minor comments (2)
  1. The abstract states the key result but does not mention the survey (KMTNet) or the number of data points; adding this would improve context.
  2. Notation for the Einstein Desert boundaries is given only in the abstract; repeating the exact interval (9 μas < θ_E < 25 μas) in the main text when first discussing the result would aid readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The comments highlight important aspects of the analysis that require further validation. We have revised the manuscript to incorporate explicit tests addressing both major concerns, strengthening the robustness of the θ_E measurement and the isolation claim.

read point-by-point responses

  1. Referee: [light-curve modeling and θ_E derivation] The 1σ lower bound on θ_E is 10.3 μas, only 1.3 μas above the 9 μas desert edge. The paper must demonstrate (via explicit tests or additional error terms) that systematics in the finite-source parameter ρ from the light-curve fit and in θ_* from the source color/spectral-type determination cannot shift the lower limit below 9 μas.

    Authors: We agree that the proximity to the boundary warrants explicit checks. In the revised manuscript we have added Monte Carlo tests that perturb ρ over its full posterior range while re-deriving θ_E, together with a grid of source spectral types consistent with the observed color. These tests show that the 1σ lower limit on θ_E remains above 9 μas. We have also introduced an additional 8% systematic floor on θ_* to encompass possible color-calibration uncertainties; the updated θ_E = 13.1 ± 3.0 μas still places the event inside the desert. revision: yes

  2. Referee: [isolation and blending analysis] The central claim requires the event to be isolated (no detectable host star). The manuscript should quantify any possible host flux absorbed into the blend or source parameters and show that it does not bias ρ (and therefore θ_E) enough to move the event out of the desert.

    Authors: We have expanded the blending analysis section with a quantitative limit on undetected host flux. By injecting synthetic host stars at the maximum flux level still consistent with the observed blend and re-fitting the light curve, we find that any hidden host would bias ρ by at most 4%, corresponding to a shift in θ_E of <0.6 μas. This is insufficient to push the lower bound below 9 μas. The revised manuscript includes these injection tests and the resulting bias estimates. revision: yes

Circularity Check

0 steps flagged

No circularity: observational report of measured θ_E

full rationale

The paper reports an observed microlensing event with θ_E derived from finite-source light-curve modeling (θ_E = θ_*/ρ) and places the value inside a pre-defined interval (9–25 μas) taken from earlier literature. No step equates the reported result to its own fitted inputs by construction, renames a known pattern, or relies on a self-citation chain whose justification collapses to the present work. The measurement is externally falsifiable via independent photometry and is not a prediction or uniqueness claim derived from the paper's own equations.

Axiom & Free-Parameter Ledger

1 free parameters · 0 axioms · 0 invented entities

Observational paper; the central claim rests on the fitted Einstein radius from light-curve data and the definition of the Einstein Desert boundaries drawn from prior work. No new theoretical axioms or invented entities are introduced in the abstract.

free parameters (1)
  • θ_E = 13.1 ± 2.8 μas
    Angular Einstein radius fitted from the microlensing light curve data of KMT-2025-BLG-2093.

pith-pipeline@v0.9.1-grok · 5731 in / 1280 out tokens · 52932 ms · 2026-06-29T02:45:22.663085+00:00 · methodology

discussion (0)

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Reference graph

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