Why this project exists此项目为何存在
What M31's 0.6–0.8 keV emission isM31 的 0.6–0.8 keV 发射是什么
M31's diffuse X-ray emission is dominated by a cool (\(\sim\)0.2 keV) vapec component (Zhang+2019: kT=0.20–0.30 keV across subregions). But when the vapec kT is left free, the fit converges to a fundamentally different temperature: kT \(\approx\) 0.74 keV with O \(\sim\)1.9 and Fe \(\sim\)0.9 (angr). This is the hot ISM — a distinct temperature regime that may trace the galactic fountain/disk-halo interface, CGM enrichment, or a degeneracy with the Local Hot Bubble / Milky Way halo foreground.
M31 的弥散 X 射线发射由一个凉（\(\sim\)0.2 keV）vapec 成分主导（Zhang+2019：各子区域 kT=0.20–0.30 keV）。但当 vapec kT 被自由设定时，拟合收敛到一个根本不同的温度：kT \(\approx\) 0.74 keV，带 O \(\sim\)1.9 和 Fe \(\sim\)0.9（angr）。这是热星际介质——一个不同的温度体系，可能追踪 galactic fountain/disk-halo 接口、CGM 富集，或与 Local Hot Bubble / 银河晕前景的退化。
Why the origin matters起源为何重要
If the 0.7 keV emission traces old stars (stellar mass \(M_*\)), it is an unresolved-stellar floor (active binaries, cataclysmic variables, LMXB tail) and tells us little about hot gas. If it traces star formation (\(\Sigma_\mathrm{SFR}\)), it is feedback-heated ISM (superbubbles, SN-heated gas). If it traces projected radius \(R\), it is a diffuse hot halo / CGM component. The key question: is the 0.7 keV component real and spatially resolved, or a fitting artifact from parameter degeneracy (especially O abundance vs vapec_norm)?
如果 0.7 keV 发射追踪旧恒星（恒星质量 \(M_*\)），它是未解析恒星底板（活跃双星、猫变星、LMXB 尾部），对热气说明不多。如果它追踪恒星形成（\(\Sigma_\mathrm{SFR}\)），它是反馈加热的 ISM（超级气泡、SN 加热气体）。如果它追踪投影半径 \(R\)，它是弥散热晕 / CGM 成分。关键问题：0.7 keV 成分是真实且空间可解的，还是参数退化（尤其是 O 丰度 vs vapec_norm）带来的拟合伪象？
The fourth option, now on the table第四个选项，现在上了桌
The original framing had three candidate origins: old stars, star formation, and a diffuse hot halo. Since 2026-11-02 a fourth has joined them and is currently the leading one: the Milky Way's own 0.7 keV foreground. The records do not claim it is settled — the label is Provisional for the foreground reading, and Questioned for the claim that one common level sits behind the halo fields and the disk floor, because the level is estimator-dependent. Three independent numbers point the same way, and they are the reason this page is written the way it is.
最初的框架有三个候选起源：旧恒星、恒星形成，以及弥散热晕。自 2026-11-02 起，第四个加入其中，并且 目前是领先者：银河系自身的 0.7 keV 前景。记录并未宣称它已定案——对前景读法标签是临时性， 而对“晕场与圆盘底板背后存在一个共同水平”这一主张标签是受质疑，因为该水平依赖于估计器。 三个独立的数字指向同一方向，这也是本页这样写的原因。
| Number数字 | What it is它是什么 | Value数值 | Source来源 |
|---|---|---|---|
| Halo-field level晕场水平 | 20 XMM fields 20–100′ from M31, where no M31 gas should be距 M31 20–100′ 的 20 个 XMM 视场，那里不应有 M31 气体 | detected, but the level is estimator-dependent: \(9.66 \pm 1.16\times10^{-8}\) in one registered fit and \(5.0 [3.56, 7.43]\times10^{-8}\) in another, 2.3–2.7\(\sigma\) apart (the older single reading was \(0.97 \pm 0.12\times10^{-7}\) at \(8\sigma\))已检出，但水平依赖于估计器：在一个已注册拟合中为 \(9.66 \pm 1.16\times10^{-8}\)，在另一个中为 \(5.0 [3.56, 7.43]\times10^{-8}\)，相差 2.3–2.7\(\sigma\)（早先的单一读数为 \(0.97 \pm 0.12\times10^{-7}\)，\(8\sigma\)） | R027, R071, R093, R110, R112R027、R071、R093、R110、R112 |
| Disk soft floor圆盘软底板 | the part of M31's 0.5–2 keV emission that does not follow stellar massM31 0.5–2 keV 发射中不随恒星质量变化的部分 | \(1.13 \pm 0.08\times10^{-7}\) arcmin\(^{-2}\) (same convention)\(1.13 \pm 0.08\times10^{-7}\) arcmin\(^{-2}\)（同一体例） | R024, R027R024，R027 |
| Literature prediction文献预测 | unresolved Milky Way coronal stars left after the point-source masks点源掩护后残留的银河系未解析日冕恒星 | \(0.72\)–\(1.05\times10^{-7}\) arcmin\(^{-2}\) bright-removed\(0.72\)–\(1.05\times10^{-7}\) arcmin\(^{-2}\)（亮源移除） | R014, R025R014，R025 |
If the Milky Way's foreground is what the data are seeing, then the outer-disk rise in the observed-to-predicted ratio (\(0.38 \to 1.64\)) is not evidence for a hot phase in M31 at all — it is evidence that the foreground was left out of the model. That is a much less exciting result, but a much more likely one, and it is why the project now spends its effort on the foreground rather than on new detections. The state page tells the story in full.
如果数据看到的是银河系的前景，那么观测/预测比的外盘上升（\(0.38 \to 1.64\)）根本不是 M31 存在热气相的证据 ——它是前景被排除在模型之外的证据。这个结果没那么激动人心，但可能性大得多，这也是项目现在把精力放在前景而非 新检出上的原因。状态页完整讲述这个故事。
Framing from AGENTS.md §1 and 02来自 AGENTS.md §1 和 02 的框架
Project goal (02): decide the physical origin of M31's 0.6–0.8 keV disk emission — old stars (\(\Sigma_*\)), star formation (\(\Sigma_\mathrm{SFR}\)), or a diffuse hot halo / Galactic foreground — and whether a residual beyond the stellar floor exists. The main question as the records now word it: does the 0.6–0.8 keV emission trace stellar mass, star-formation rate, or projected radius, and is there a diffuse hot-gas residual beyond the expected unresolved-stellar floor? Success criteria: (1) profile of the 0.7 keV and 0.2 keV components versus radius with profile-likelihood errors and a foreground nH matched to the halo baseline; (2) a template decomposition (old, young, constant) whose coefficients are identifiable, or a documented proof they are not; (3) the halo-field 0.7 keV question settled with a valid interval; (4) azimuthal symmetry tested along both axes.
项目目标（02）：决定 M31 0.6–0.8 keV 圆盘发射的物理起源——旧恒星（\(\Sigma_*\)）、恒星形成（\(\Sigma_\mathrm{SFR}\)），还是弥散热晕 / 银河前景——以及是否存在恒星底板之外的残余。记录现在的措辞是：0.6–0.8 keV 发射追踪恒星质量、恒星形成率还是投影半径，以及在预期的未解析恒星底板之外是否存在弥散热气残余？成功标准：（1）0.7 keV 和 0.2 keV 成分随半径的剖面，带 profile-likelihood 误差和与晕基准匹配的前景 nH；（2）模板分解（old, young, constant），其系数可辨识，或有文档证明不可辨识；（3）晕场 0.7 keV 问题用有效区间解决；（4）沿两轴测试方位对称性。
Newest source read: cognition-os/08_RUNNING.md revision 49, updated 2026-11-05 03:56 EST; 07_REVISION_LOG.md R054–R131 and 04_DECISION_LOG.md D26–D30 read in full.
最新读取的来源：cognition-os/08_RUNNING.md 修订版 49，更新于 2026-11-05 03:56 EST；07_REVISION_LOG.md R054–R131 与 04_DECISION_LOG.md D26–D30 已全文读取。