{"id":"7df243f7-e988-4307-b5cc-11baee4333f5","arxiv_id":"2602.21624","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"Featureless TDEs around ~10^8 M_sun black holes emit early hard X-rays from a compact corona, and TDE X-ray spectral evolution separates by black hole mass as expected for a soft-to-hard transition at ~3% Eddington.","lead":"Two tidal disruption events around ~100-million-solar-mass black holes shine in hard X-rays, flicker on hour timescales, and show no spectral lines. Across the known population, TDE X-ray spectral states sort by black hole mass, which the authors tie to a universal accretion-state switch at ~3% of the Eddington rate.","discovery_kind":"unification","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Mass segregation of TDE X-ray states may be a bandpass selection artifact: high-mass soft-state disks peak in the EUV and evade eROSITA, so the claimed confirmation of the ṁ=0.03 transition is not yet established.","rationale":"The reader's weakest assumption exactly identifies the most load-bearing vulnerability of the central claim: the mass segregation of X-ray spectral states across M_BH could be a consequence of soft-X-ray bandpass selection rather than an accretion-state effect. The paper itself acknowledges the bandpass issue in §4.2.1 but does not quantify its impact on the sample. My analysis confirms this is the critical point because the theoretical prediction being 'confirmed' (Mummery & Balbus 2021b) is the same effect that produces the selection bias, making the reasoning potentially circular. The concrete test I propose would settle the issue by simulating the detectability of high-mass soft-state disks. Since the reader already flagged this and requested quantification, the verdict remains CONDITIONAL; my read does not change it, but it underscores that the condition is essential. No other concern (e.g., unpublished formula, small sample) is as fundamental because even a larger sample would not resolve the ambiguity without correcting for the bandpass selection. The two TDEs themselves are well-observed and their hard X-ray nature is solid, but the population-level inference is the central claim and it is currently underdetermined by the data.","tokens_in":37325,"tokens_out":5158,"duration_ms":51598,"concrete_test":"Forward-model the eROSITA detectability of the 30-TDE comparison sample. For each TDE, assume it is in the soft (thermal) state with an accretion rate above the claimed threshold (e.g., ṁ=0.1), compute the 0.3–2 keV flux using the Mummery & Balbus (2021b) disk spectrum at the estimated M_BH, and compare to the eROSITA point-source sensitivity. Determine how many high-M_BH (>3e7 M_sun) systems would be undetectable even in the soft state. If a substantial fraction (e.g., >50%) of high-M_BH systems are undetectable when soft, then the observed hard-only population is consistent with pure selection bias, and the mass segregation cannot confirm the ṁ=0.03 transition. Additionally, examine the M_BH distribution of the 19 non-detected TDEs: if it includes high-M_BH sources, these may be soft-state high-mass disks missed by eROSITA, directly contradicting the 'hard from the outset' claim.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that TDE soft-to-hard state transitions occur at ṁ~0.03 rests on the observed mass segregation in the eROSITA-selected sample: low-M_BH TDEs stay soft, intermediate transition, high-M_BH are hard from the outset. However, the paper itself (§4.2.1) notes that at fixed Eddington ratio, higher-M_BH disks have thermal peaks in the EUV and become undetectable in the 0.3–2 keV band (Mummery & Balbus 2021b). Thus a high-M_BH TDE in the soft state would be invisible to eROSITA, while the same TDE would be detected once it becomes hard (coronal). The observed 'hard from the outset' for M_BH~1e8 may therefore simply reflect that these objects are only detectable in the hard state, not that they transitioned at ṁ=0.03. The comparison sample is selected on X-ray detection, so the mass segregation could be entirely a selection effect. The paper acknowledges this possibility but never quantifies it: it does not compute the fraction of high-mass soft-state systems that would fall below the eROSITA sensitivity, nor does it report the M_BH distribution of the 19 non-detected TDEs. Without such an accounting, the population-level conclusion is circular: the same bandpass effect that makes high-mass soft-state TDEs invisible also predicts they will appear hard when detected. Therefore the claimed confirmation of the theoretical ṁ=0.03 prediction is not yet demonstrated; it is a plausible interpretation but not a validated one.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents multi-wavelength observations of two luminous featureless TDEs, AT2024kmq and AT2024lhc, hosted by ~1e8 Msun black holes. It reports early, luminous, rapidly variable hard X-ray emission (minimum 1.3 hr and 4.8 hr variability), interprets the X-ray source as a compact corona, and uses radio nondetections to rule out J1644-like jets. The paper also compiles a 49-object comparison sample of ZTF TDEs and reports statistically significant bimodality in the peak blackbody luminosity and radius of the featureless subclass. Finally, using a 30-TDE eROSITA-selected sample, it finds that X-ray spectral evolution is mass-segregated (low-MBH soft, intermediate transitions, high-MBH hard from the outset) and interprets this as evidence that TDEs undergo a soft-to-hard state transition at mdot ~ 0.03 mdot_Edd, confirming a theoretical prediction based on the scaling t_tr ∝ M_BH^{-3/4}.","tokens_in":37758,"tokens_out":6494,"duration_ms":58419,"significance":"If the central state-transition claim holds, the paper would unify TDE accretion with X-ray binary state transitions and establish a mass-dependent framework for TDE X-ray detectability. The manuscript's strengths are the detailed, multi-instrument X-ray spectral analysis; the bootstrap test for bimodality; the construction of a well-defined eROSITA comparison sample; and the population-synthesis check with the FitTeD code. The radio limits and host-galaxy AGN constraints are also carefully presented. However, the central claim is not yet established because the observed mass segregation may be a bandpass selection effect, and the key theoretical scaling is unpublished. The paper is a useful contribution but requires additional quantitative work before it can be regarded as a confirmation.","major_comments":[{"comment":"The mass segregation of X-ray spectral states may be an artifact of eROSITA's soft-band selection. The paper itself notes (paragraph beginning 'We note that at fixed Eddington ratio...') that high-MBH soft-state disks peak in the EUV and would be undetectable, so such systems would appear only when they become hard. The analysis does not quantify this: it does not compute the eROSITA detection probability as a function of MBH and spectral state, nor does it include the 19 non-detected TDEs in the mass-segregation comparison. Without a forward model of the selection, the conclusion that the data 'confirm' the mdot=0.03 prediction is not supported; it is consistent with the null hypothesis that the sample is simply visibility-limited.","section":"§4.2.1, Fig. 14"},{"comment":"The central theoretical scaling t_tr ≈ 4000 d ... M_BH^{-3/4} is attributed to 'Mummery in prep.' This is unpublished work by a co-author, and the population-synthesis details (sampling distributions for stellar and disk parameters, the FitTeD code version) are not fully specified. Since the paper's headline claim is that the observed mass segregation 'confirms the theoretical prediction,' the derivation of Eq. (6) and the simulation setup must be available for independent scrutiny. At minimum, the derivation should be included in an appendix or the manuscript should cite a published source.","section":"§4.2.1, Eq. (6)"},{"comment":"The abstract and conclusion state that the rapid variability supports a compact corona of ≲10 rg for both events. However, the 4.8 hr variability of AT2024lhc corresponds to cΔt ≈ 35 rg for MBH≈10^8 Msun, so the ≲10 rg limit is only justified for AT2024kmq's 1.3 hr timescale. The text in §4.2 says 'The rapid X-ray variability therefore constrains the X-ray emitting region to ≲10 rg' after citing both timescales, which conflates the two. The claim should be qualified to apply only to the object with the 1.3 hr variability, or the physical argument (e.g., the emitting region is much smaller than cΔt) should be made explicit.","section":"§4.2, Table 2; Abstract; §5"},{"comment":"The theoretical comparison uses mdot_crit = 0.03 as an input parameter, not as a fitted value. The population synthesis shows that this assumed threshold yields mass-segregated transition times consistent with the data, but it does not test whether other values of mdot_crit (or the bandpass selection effect alone) can reproduce the observed segregation. A direct quantitative test would be to compare the predicted t_tr(MBH) with the observed transition times of the intermediate-mass objects (e.g., AT2020ocn, AT2021ehb) without assuming the threshold a priori. As presented, the agreement does not constitute a confirmation of the 0.03 value.","section":"§4.2.1, Figs. 15–16"}],"minor_comments":[{"comment":"The conclusion says the result 'confirms the theoretical prediction of Mummery & Balbus (2021b)', but §4.2.1 states that the mass-segregation result was 'predicted by Mummery & Balbus (2021a)'. Please correct the citation.","section":"§5 and §4.2.1"},{"comment":"The HST spectrum shows that a single blackbody underestimates the FUV flux. The paper still uses the blackbody parameters from photometry in later analyses. This is a known systematic, but it would be useful to quote the updated Tbb/Rbb from the joint fit in Section 4.1 when discussing the bimodality.","section":"§3.7"},{"comment":"The classification 'soft (Γ>4)' is unusual because power-law photon indices >4 are rarely physical. Please clarify whether these are eROSITA hardness ratios converted to an equivalent photon index, and note the large uncertainties in this regime.","section":"§4.2.1"},{"comment":"The y-axis label 'LX (erg s-1)' and the color coding by Γ are clear, but the legend for the state categories (soft/intermediate/hard) is small; consider making it more prominent.","section":"Fig. 13"},{"comment":"The variability criterion requires a flux ratio exceeding a factor of two; the choice is reasonable but should be justified, as shorter-timescale variability with smaller amplitude may be missed. A brief justification would help.","section":"§3.4.6"}],"recommendation":"major_revision","confidential_remarks":"The manuscript relies heavily on unpublished theory from a co-author (Eq. 6). This creates a circularity risk and a reproducibility issue that the editor may want to flag. The selection-bias problem is serious but fixable; the authors have the expertise to compute the eROSITA detectability. The paper is otherwise a solid observational contribution from a strong team."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The two-object results are the real meat here. AT2024kmq and AT2024lhc are carefully characterized across many facilities: early luminous hard X-rays, hour-scale variability, featureless optical spectra, high host masses, and radio non-detections. That is new and solid, and the paper deserves credit for the multi-wavelength effort and for the conservative bootstrap analysis of bimodality in featureless TDEs. The precursor interpretation via self-intersection shocks is reasonable and well tied to existing simulations.\n\nThe population-level claim is where I get off the bus, at least for now. The eROSITA mass segregation — low-mass soft, intermediate transitioning, high-mass hard — is visually striking, but the paper itself notes the selection problem: at fixed Eddington ratio, a 10^8 Msun soft-state disk peaks in the EUV and would be nearly invisible in the eROSITA band. So 'hard from the outset' for high-mass BHs may simply mean 'detected only when hard.' That is not a straw man; the paper acknowledges it in §4.2.1 but never quantifies it. Without computing the fraction of high-mass soft-state systems that fall below sensitivity, or the mass distribution of the 19 non-detected TDEs, the central confirmation of the mdot=0.03 transition is not yet demonstrated. It is a plausible interpretation, not a validated one.\n\nA few smaller concerns. The claim of an emitting region ≲10 r_g from the 4.8 hr variability is too strong: cΔt is about 35 r_g for 10^8 Msun, so the limit is more like a few tens of r_g. The key scaling, Eq. 6, is from 'Mummery in prep' — unpublished and co-authored by a paper co-author. That is not fatal, because the simulations do reproduce the trend and the data were not fitted to force agreement, but it does put a burden on the authors to make that derivation public before the population claim can be fully checked. The black hole masses also carry large systematic uncertainties, though they use reasonable scaling relations.\n\nThe paper is honest about its caveats, and the writing is clear. It is a serious piece of work that would benefit from referee scrutiny, especially on the selection-effect quantification and the unpublished theory. I would cite it for the two TDEs and the featureless bimodality, and I would bring it to a reading group to discuss the bandpass issue. Send it to review, but expect the referee to push for a quantitative treatment of the soft-state invisibility before the mdot=0.03 story hardens.","headline":"Two well-observed high-mass TDEs with early hard X-rays, plus a suggestive but not yet established population-level state-transition claim; the bandpass selection effect is the main unresolved issue.","tokens_in":38485,"tokens_out":1126,"would_cite":true,"duration_ms":14629,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Tidal disruption events around massive black holes confirm a universal accretion-state threshold at ~3% of Eddington, unifying them with X-ray binaries.","keywords":["tidal disruption events","X-ray binaries","accretion state transitions","black hole accretion","featureless spectra","coronal X-ray emission","Eddington ratio","disk theory"],"falsifier":"A direct test would be to find a TDE around a black hole of ~10^8 solar masses that shows a soft X-ray spectrum (Γ > 4) at early times (within a few months of optical peak), which would contradict the claim that high-mass TDEs are hard from the outset. Conversely, if a systematic X-ray survey with sensitivity down to the EUV/soft X-ray band reveals a population of soft-state high-mass TDEs, the visibility-bias interpretation would be favored over the universal-state-transition interpretation.","tokens_in":37186,"feed_emoji":"🌌","tokens_out":1526,"duration_ms":17940,"temperature":0.7,"pith_summary":"This paper studies two newly discovered tidal disruption events (TDEs) — stars torn apart by supermassive black holes — hosted by black holes of roughly 10^8 solar masses. Both show luminous, rapidly varying hard X-ray emission that appears within weeks, which the authors attribute to a compact corona rather than a jet. By placing these events in a sample of thirty X-ray-observed TDEs, they find a clear mass segregation: low-mass black holes (10^6 solar masses) stay in a soft X-ray state for years, intermediate masses (10^7) transition from soft to hard around one year, and high masses (10^8) are hard from the start. The authors argue this pattern is exactly what simple accretion disk theory predicts if TDE disks undergo the same soft-to-hard state transition as stellar-mass X-ray binaries, at a critical Eddington-scaled accretion rate of about 0.03. If correct, this unifies TDE accretion physics with the well-studied state transitions in X-ray binaries and confirms a theoretical prediction about when TDE disks should turn hard.","feed_headline":"TDEs confirm a universal accretion threshold at 3% Eddington","feed_subtitle":"Massive black holes turn hard fast; low-mass ones stay soft for years, unifying TDEs with X-ray binaries.","key_machinery":"The central mechanism is the time-dependent evolution of a standard thin accretion disk fed by stellar debris, whose accretion rate declines as a power law in time. The key identity is the scaling of the time to reach a given Eddington ratio: t_tr ∝ M_BH^{-3/4}, derived from viscous disk theory. This scaling implies that for a fixed critical threshold (here ṁ = 0.03), higher-mass black holes cross the threshold much sooner after disruption, which naturally produces the observed mass segregation of X-ray spectral states. The paper also uses the concept of the critical Eddington-scaled accretion rate for the soft-to-hard transition, borrowed from X-ray binary phenomenology, to set the threshol","core_discovery":"The paper's central claim is that the diverse X-ray spectral states observed in tidal disruption events can be understood as a single mass-dependent sequence driven by the decline of the Eddington-normalized accretion rate. Using two new high-mass TDEs plus a comparison sample of eROSITA-observed TDEs, the authors show that black hole mass segregates the X-ray behavior: low-mass black holes stay soft, intermediate masses transition, and high masses are hard from the outset. They interpret this as evidence that TDE disks undergo a soft-to-hard state transition at a critical accretion rate of Ṁ_acc ≈ 0.03 Ṁ_Edd, matching the value seen in X-ray binaries. The transition timescale predicted by s","pith_inferences":["The claimed mass segregation could alternatively be driven by a soft-X-ray visibility bias: at fixed Eddington ratio, a 10^8 solar mass disk's thermal peak lies in the EUV, so a soft-state high-mass TDE would be nearly invisible in the 0.3–2 keV band. The paper acknowledges this but does not quantify it; if this selection effect dominates, the inferred universal transition threshold would be weake","A testable extension: if the ṁ = 0.03 threshold is real, then X-ray-selected TDEs around intermediate-mass black holes should show a sharp spectral transition at a predictable time based on their black hole mass and inferred fallback rate. Monitoring a larger sample with uniform X-ray cadence could directly verify the t_tr ∝ M_BH^{-3/4} scaling.","The authors' interpretation implies that TDEs can serve as scaled-up analogs of X-ray binary state transitions, but the fast transition duration (days to tens of days in TDEs vs. hours in XRBs) remains unexplained — a theoretical gap that future disk simulations might address.","If the two subclasses of featureless TDEs represent distinct line-suppression mechanisms, then their luminosity and radius distributions should correlate with outflow velocity measurements from UV spectroscopy; this could be tested with JWST or HST observations of a larger sample."],"forward_implications":["If the ṁ ≈ 0.03 transition is universal, then the X-ray spectral state of a TDE at a given time encodes its black hole mass and accretion rate, enabling mass estimates from X-ray observations alone.","The mass segregation implies that soft X-ray surveys preferentially detect TDEs around low-mass black holes, while hard X-ray surveys are needed to find the high-mass population — a selection effect that must be folded into TDE rate calculations.","The rapid appearance of hard X-rays in high-mass TDEs (within weeks) means that coronal formation can be much faster than previously inferred from low-mass events, tightening constraints on coronal physics.","The radio non-detections of the two new TDEs, despite X-ray luminosities that would predict radio emission via the Fundamental Plane, suggest that TDE coronae may be more radiatively efficient or jets weaker than in X-ray binaries, requiring further monitoring to test for delayed jet launch.","The bimodality in peak blackbody luminosity/radius among featureless TDEs — if real — points to two distinct physical regimes that suppress line formation, which future UV spectroscopy can directly probe."],"fun_headline_variants":["TDEs hit same 3% Eddington switch as X-ray binaries","Black hole mass sets TDE X-ray state at 3% Eddington","TDE soft-to-hard shift tied to 3% Eddington rate","Universal 3% Eddington threshold governs TDE X-rays","Mass dictates TDE X-ray state at 3% Eddington"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The entire mass-segregation interpretation hinges on the assumption that the observed X-ray spectral states are driven by accretion-rate evolution rather than by a soft-X-ray detection bias — that a soft-state high-mass TDE would not have been detected in the eROSITA sample.","fun_headline_variants_meta":{"raw":{"variants":["TDEs hit same 3% Eddington switch as X-ray binaries","Black hole mass sets TDE X-ray state at 3% Eddington","TDE soft-to-hard shift tied to 3% Eddington rate","Universal 3% Eddington threshold governs TDE X-rays","Mass dictates TDE X-ray state at 3% Eddington"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00066,"raw_usage":{"total_tokens":2980,"prompt_tokens":993,"completion_tokens":1987,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":737,"completion_tokens_details":{"reasoning_tokens":1887}},"tokens_in":737,"tokens_out":1987,"duration_ms":13221,"temperature":1.0,"reasoning_tokens":1887,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-02T20:58:19.774775+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A direct test would be to find a TDE around a black hole of ~10^8 solar masses that shows a soft X-ray spectrum (Γ > 4) at early times (within a few months of optical peak), which would contradict the claim that high-mass TDEs are hard from the outset. Conversely, if a systematic X-ray survey with sensitivity down to the EUV/soft X-ray band reveals a population of soft-state high-mass TDEs, the visibility-bias interpretation would be favored over the universal-state-transition interpretation.","supporting_citations":[],"review_version":1}