---
title: 'SN2023ixf: Closest Type II Supernova in M101'
url: https://www.emergentmind.com/topics/sn2023ixf
type: topic
---

# SN2023ixf: Closest Type II Supernova in M101

SN 2023ixf is a hydrogen-rich Type II core-collapse supernova in Messier 101 (M101), discovered on 2023-05-19, with first light constrained to MJD 60082.757 ± 0.097 or MJD 60082.788$^{+0.02}_{-0.05}$ and a host distance of about 6.85–6.9 Mpc. Its proximity made it the closest core-collapse supernova of the decade and enabled observations from hours after explosion through the nebular phase and into the second and third post-explosion years across the optical, ultraviolet, infrared, radio, X-ray, spectropolarimetric, and neutrino domains. SN 2023ixf is therefore a central case for delayed shock breakout in dense circumstellar material (CSM), radiative acceleration of a slow red-supergiant wind, asymmetric CSM and ejecta geometry, and the transition from early circumstellar reprocessing to late-time dust formation and interaction-powered emission [2507.08078].

## 1. Discovery, host galaxy, and observational setting

SN 2023ixf was discovered in M101 on 2023-05-19 17:27:15 UTC at clear-band magnitude $\approx 14.9$. Several studies adopt an explosion epoch near MJD 60082.75–60082.79. The host distance is variously given as $6.85 \pm 0.15$ Mpc, $6.85 \pm 0.13$ Mpc, or $\approx 6.9$ Mpc, and the host redshift was either adopted as $z=0.0008$ or measured from narrow host Na I D and Ca II H\&K absorption as $z = 0.0008696 \pm 0.000042$ [2412.14406].

The event was followed almost immediately. Optical spectroscopy began at $\delta t \approx 1.1$ d; spectropolarimetry began at $\delta t \approx 1.4$ d; high-resolution WIYN/NEID echelle spectroscopy at $R \approx 70{,}000$ began at 1.51 d; Swift/UVOT near-UV spectroscopy was obtained at $\delta t \approx 0.7$ d; HST/STIS NUV spectroscopy at $\delta t = 3.6$ d; AstroSat/UVIT far-UV spectroscopy at $\delta t \approx 6.9$ d; NuSTAR observed at $\delta t \approx 4$ d and $\delta t \approx 11$ d; and IceCube performed targeted follow-up in 4-day and 32-day windows [2507.08078].

This cadence was unusually diagnostic because the most CSM-sensitive phases evolved on hour-to-day timescales. Multiple studies explicitly emphasize that the first 48 hours were decisive for measuring the pristine wind speed, capturing the onset of radiative acceleration, and separating flash-ionized narrow-line emission from later shocked and ejecta-dominated components [2412.14406].

## 2. Early flash spectroscopy and delayed shock breakout

The earliest spectra showed the classic flash-ionization or flash-interaction phenomenology of dense, close-in CSM. At 1.51 d, the high-resolution spectrum displayed narrow emission features with widths $\leq 200$ km s$^{-1}$ from H I, He I, He II, C III, N III, C IV, and N IV, with most peaks blueshifted by $\sim 40$ km s$^{-1}$ and with suppressed red wings. On that same epoch, He I 5876 Å was the narrowest line with ${\rm FWHM}=25 \pm 2$ km s$^{-1}$, H I/He II/N III/C III had ${\rm FWHM}\sim 60$–80 km s$^{-1}$, and the highest-ionization lines C IV/N IV had ${\rm FWHM}\sim 180$–250 km s$^{-1}$ [2412.14406].

The line forest evolved extremely rapidly. He I was visible at 1.51 d but disappeared by 2.62 d. The narrow H$\alpha$ component equivalent width dropped by a factor of $\sim 10$ between 1.51 and 2.62 d; its ${\rm FWHM}$ broadened from $\sim 70$ km s$^{-1}$ to $\sim 350$ km s$^{-1}$ over the first four days; and its centroid drifted to $\sim -200$ km s$^{-1}$. Lower-resolution early-time spectroscopy extended the same phenomenology to a broader electron-scattering context: narrow cores embedded in broad, symmetric Lorentzian wings persisted for roughly 8 days after first light before the spectra transitioned to ejecta-dominated Type II P-Cygni profiles [2306.04721].

The early continuum evolution was also extreme. One photometric analysis found that the bolometric luminosity rose from $(1.28 \pm 0.11)\times 10^{42}$ erg s$^{-1}$ at 1.1 d to $(2.5 \pm 0.3)\times 10^{43}$ erg s$^{-1}$ at $\simeq 4.5$ d, while the color temperature increased from $\simeq 14{,}000$ K to $\simeq 35{,}000$ K over $2.2 \pm 0.1$ d with the blackbody radius remaining nearly constant at $(2.0 \pm 0.2)\times 10^{14}$ cm [2405.20989]. Another spectroscopic analysis found that the continuum temperature rose from $\approx 16{,}000$ K at day 1.4 to a peak $\approx 24{,}000$ K at $\approx 2.5$ d, then declined to $\approx 13{,}000$ K by day 14 [2503.13974]. Both are consistent with delayed shock breakout in dense CSM.

The kinematic interpretation was framed explicitly in terms of radiative acceleration:
$$
g_{\rm rad} \simeq \kappa F/c,
$$
and, for single-scattering Thomson acceleration,
$$
\Delta v_{\rm CSM} \simeq 80\,E_{49}/r_{15}^{2}\ {\rm km\ s^{-1}}.
$$
Using the bolometric light curve and an adopted shock velocity $v_{\rm shock}\approx 9500 \pm 500$ km s$^{-1}$, the maximum radiative acceleration at the shock location was estimated as $\approx 45$ km s$^{-1}$ by day 1.51, $\approx 300$ km s$^{-1}$ by day 2.62, and $\approx 500$ km s$^{-1}$ by day 3.62, while the outer edge of the dense CSM had $\Delta v_{\rm CSM}\leq 5$ km s$^{-1}$ at day 1.51 [2412.14406].

A key result of this monitoring was that the narrowest He I line gave a direct upper bound on the pristine wind speed in that zone:
$$
v({\rm He\ I}) = 25^{+0}_{-5} \pm 2\ {\rm km\ s^{-1}},
$$
squarely in the expected range for red-supergiant winds. The subsequent broadening to $\geq 200$ km s$^{-1}$ over $\sim 2$–3 d and then to post-shock speeds of order $\sim 2000$ km s$^{-1}$ established that early narrow-line widths were not static wind tracers but were being modified in real time by shock-powered radiation and then by shock engulfment [2412.14406].

## 3. Circumstellar material: structure, kinematics, and mass-loss history

A consistent theme across the literature is that SN 2023ixf exploded inside dense, confined, and asymmetric CSM. In steady-wind form, the density is written as
$$
\rho(r)=\frac{\dot{M}}{4\pi r^2 v_w},
$$
and early optical/UV modeling with CMFGEN and HERACLES required a dense solar-metallicity CSM concentrated at
$$
r \simeq (0.5-1)\times 10^{15}\ {\rm cm},
$$
with a sharp reduction in density beyond $r \gtrsim 10^{15}$ cm. For an assumed red-supergiant wind speed $v_w = 50$ km s$^{-1}$, the preferred mass-loss rate was
$$
\dot{M} \approx 10^{-2}\ M_{\odot}\ {\rm yr}^{-1},
$$
sustained for $\sim 3$–6 yr before explosion, implying
$$
M_{\rm CSM}\approx 0.03-0.06\ M_{\odot}
$$
in the dense inner region [2306.04721].

The WIYN/NEID analysis found a somewhat smaller characteristic scale for the densest line-forming region,
$$
r_{\rm CSM} \approx 3.7 \times 10^{14}\,(v_{\rm shock}/9500\ {\rm km\ s^{-1}})\ {\rm cm},
$$
and inferred that the enhanced mass-loss phase began at least
$$
\gtrsim 4\,(v_{\rm shock}/9500\ {\rm km\ s^{-1}})
$$
yr before core collapse for a pre-SN outflow speed of $\sim 25$ km s$^{-1}$ [2412.14406]. This difference in radius does not erase the broader agreement that the most optically important CSM was compact and formed shortly before explosion.

A two-zone CSM was inferred in one STELLA-based hydrodynamical analysis. That work favored a confined dense CSM extending up to $5\times 10^{14}$ cm with a mass-loss rate of $10^{-2}\ M_{\odot}\ {\rm yr}^{-1}$, plus an extended CSM from $5\times 10^{14}$ cm to at least $1\times 10^{16}$ cm with a mass-loss rate of $10^{-4}\ M_{\odot}\ {\rm yr}^{-1}$, both assuming a wind velocity of 10 km s$^{-1}$ [2405.20989]. This suggests a stratified mass-loss history rather than a single steady state.

Independent hard X-ray observations supported a dense but confined line-of-sight CSM. NuSTAR spectra at $\delta t \approx 4$ d and $\delta t \approx 11$ d were fit by hot thermal bremsstrahlung with $kT>25$ keV at Epoch I and $kT = 34^{+22}_{-12}$ keV at Epoch II, absorbed by an intrinsic neutral column declining from
$$
N_{\rm H,int}=2.6^{+0.5}_{-0.7}\times 10^{23}\ {\rm cm^{-2}}
$$
to
$$
N_{\rm H,int}=(5.6 \pm 2.7)\times 10^{22}\ {\rm cm^{-2}}.
$$
The same spectra showed a prominent Fe K$\alpha$ line and an intrinsic 0.3–79 keV luminosity of order
$$
L_X \approx (2.5 \pm 0.5)\times 10^{40}\ {\rm erg\ s^{-1}},
$$
implying $n_{\rm CSM}\gtrsim 4\times 10^8\ {\rm cm^{-3}}$ at $r\lesssim 10^{15}$ cm and
$$
\dot{M}\approx (2.5-3.0)\times 10^{-4}\ M_{\odot}\ {\rm yr}^{-1}
$$
for $v_w=50$ km s$^{-1}$ [2306.04827]. Those values are lower than the flash-spectroscopy inferences, but they probe a different combination of geometry, radius, and density and are explicitly discussed in the literature as compatible with a multi-component or asymmetric CSM.

The geometry was not spherical. Predominantly blueshifted narrow-line profiles, muted red wings, the absence of narrow P-Cygni absorption at early times, and strong early polarization together indicate that the dense CSM was aspherical and likely concentrated out of the line of sight, for example as a toroidal or equatorial overdensity [2412.14406]. Polarized radiative-transfer modeling of the first week favored a pole-to-equator density contrast $\gtrsim 3$ [2505.03975].

Late-time spectroscopy showed that the mass-loss history was not limited to the final years. A nebular spectrum at 445 d displayed a boxy H$\alpha$ component with sharp edges near $\pm 8000$ km s$^{-1}$, interpreted as ejecta interaction with a CSM shell at $\approx 10^{16}$ cm. For a typical red-supergiant wind speed of $\sim 10$ km s$^{-1}$, that shell would correspond to mass loss occurring up until $\approx 500$–1000 yr before explosion [2502.10534]. Taken together, the published constraints suggest a multi-zone CSM built over timescales from years to centuries.

## 4. Progenitor star and pre-explosion environment

Pre-explosion imaging identified a dust-enshrouded, variable red-supergiant progenitor candidate at the supernova position. One HST-based study found a single red source in F814W with $m({\rm F814W}) = 24.41 \pm 0.06$ mag and no convincing detection in F435W or F555W, implying an extremely red color and a preferred progenitor mass of $\sim 8$–10 $M_{\odot}$, while explicitly noting that additional circumstellar dust could bias the mass low [2305.14447]. A later multiwavelength registration to HST, Spitzer, and ground-based near-IR data identified a single point source consistent with the SN position across optical to 4.5 $\mu$m and derived a chance-coincidence probability of $\approx 4\%$ for the favored source [2306.04722].

The pre-explosion local environment from HETDEX showed relatively low extinction and low recent star formation in the immediate vicinity. Within $r<3$ arcsec, the median values were
$$
E(B-V)=0.06\pm0.14
$$
and
$$
\Sigma_{\rm SFR}=10^{-5.44\pm0.66}\ {\rm M_{\odot}\ yr^{-1}\ arcsec^{-2}},
$$
while the metal-rich branch of $R_{23}$ gave approximately solar metallicity with $12+\log({\rm O/H})=8.65\pm0.11$ [2311.10400]. That same work found no significant change in extinction before and after explosion.

| Approach | Representative progenitor result | Reference |
|---|---|---|
| HST-only optical counterpart | Very red source; preferred initial mass $\sim 8$–10 $M_{\odot}$ | [2305.14447] |
| HST+Spitzer+NIR SED with DUSTY | $\log(L/L_{\odot})=4.74\pm0.07$; $M_{\rm ZAMS}\approx 11\pm1\ M_{\odot}$ | [2306.04722] |
| Time-dependent dusty RSG SED | $T_{\rm eff}=3343\pm27$ K, $\log L=5.10\pm0.02$, $M_{\rm init}=18.1^{+0.7}_{-1.2}\ M_{\odot}$ | [2309.10022] |
| CFHTLS progenitor plus HETDEX environment | $z=22.778\pm0.063$ mag source; progenitor $\approx 22\ M_{\odot}$ | [2311.10400] |

Despite the spread in inferred initial mass, the studies agree on several qualitative points. The progenitor was a red supergiant; it was heavily affected by circumstellar dust; and it was variable in the years before explosion. One SED analysis found a dusty shell with
$$
\tau_V = 5.8 \pm 0.2,\quad A_V = 4.6 \pm 0.2\ {\rm mag},\quad T_{\rm dust}=880\pm40\ {\rm K},
$$
and
$$
R_{\rm shell}=8600^{+900}_{-800}\ R_{\odot},
$$
with a mass-loss rate
$$
\dot{M}\approx 1.3\times 10^{-6}\ M_{\odot}\ {\rm yr}^{-1}
$$
for $v_{\rm wind}\approx 50$ km s$^{-1}$ [2306.04722]. Another, more extinction-heavy time-dependent fit instead obtained
$$
\tau(1\ \mu{\rm m})=2.83\pm0.03,\quad A_V=10.28\pm0.11\ {\rm mag},
$$
$$
R_{\star}=(1.06 \pm 0.03)\times 10^3\ R_{\odot},
$$
and
$$
\dot{M}=(3.58 \pm 0.15)\times 10^{-4}\ M_{\odot}\ {\rm yr}^{-1},
$$
with a pulsation period
$$
P = 1128.3 \pm 6.5\ {\rm d}
$$
[2309.10022].

Mid-infrared variability was pronounced. Over 29 Spitzer epochs spanning 9 yr, the source varied by $\sim 70\%$ in both 3.6 and 4.5 $\mu$m, with a quasi-sinusoidal timescale of $\approx 2.8$ yr [2306.04722]. A different time-dependent analysis interpreted the variability as a 0.11 dex luminosity modulation coupled to variable dust optical depth and/or $T_{\rm eff}$, consistent with pulsation-enhanced mass loss and dust sublimation/condensation cycles [2309.10022].

The main controversy is therefore not whether the progenitor was a dusty red supergiant, but how much of the pre-explosion luminosity was hidden or reprocessed by circumstellar dust and how strongly blending or geometry biased single-band optical estimates. That is why published progenitor masses span from the low-mass end of the SN II red-supergiant population to the high-luminosity end of the so-called red-supergiant problem.

## 5. Explosion properties and evolution from plateau to nebular phase

Photometrically, SN 2023ixf was bright and relatively fast-declining for a Type II event. A global citizen-science campaign measured a peak
$$
M_V=-18.18 \pm 0.09
$$
at 2023-05-25 21:37 UTC [2307.14347]. Another long-baseline study found
$$
M_V=-18.2 \pm 0.07,
$$
classified the event as a fast decliner in the IIL subclass, and reported a short “plateau” shorter than $\sim 70$ d with $s_2 = 1.7 \pm 0.1$ mag [2503.13974]. Other analyses placed the plateau duration closer to $\sim 80$–85 d [2310.14407, 2410.19939]. The earliest spectra were briefly IIn-like because of flash-ionized CSM, but the event did not evolve like a genuine long-lived Type IIn; within $\sim 2$–3 weeks it followed a normal Type II spectroscopic sequence [2503.13974].

One-dimensional radiation-hydrodynamical modeling of the bolometric light curve and Fe II $\lambda 5169$ velocity evolution found a preferred solution with
$$
M_{\rm ZAMS}=12\ M_{\odot},\quad E_{\rm exp}=1.2\times 10^{51}\ {\rm erg},\quad M(^{56}{\rm Ni})=0.05\ M_{\odot},
$$
a pre-SN radius of
$$
R_{\star}=720\ R_{\odot},
$$
a pre-SN mass of 10.9 $M_{\odot}$, and an ejecta mass of
$$
M_{\rm ej}\approx 9.4\ M_{\odot}.
$$
That analysis concluded that SN 2023ixf was a normal Type II event and that the modeling robustly favored
$$
M_{\rm ZAMS}<15\ M_{\odot}
$$
because 15 $M_{\odot}$ models could not simultaneously match plateau luminosity and duration [2310.14407].

A different STELLA-based interpretation proposed a lower explosion energy and a more strongly reduced hydrogen envelope:
$$
E \approx 0.7 \times 10^{51}\ {\rm erg},\quad M_{\rm ej}\approx 6\ M_{\odot},\quad R_{\star}\approx 700\ R_{\odot},
$$
with a wind-like CSM of $\sim 0.6\ M_{\odot}$ extending to $10^{15}$ cm. That work further argued that the first $\approx 5$ hr after the last non-detection could not be explained by shock–CSM interaction alone and therefore modeled a distinct precursor shell with
$$
M_{\rm prec}\approx 0.5-1.0\ M_{\odot}
$$
and
$$
E_{\rm prec}\approx (1-2)\times 10^{49}\ {\rm erg}
$$
launched a fraction of a day before the main shock breakout [2410.19939]. This remains a model-dependent alternative rather than a universally adopted interpretation.

More recent non-LTE radiative-transfer modeling from $\sim 20$ to $\sim 120$ d favored an enhanced-mass-loss 15 $M_{\odot}$ red-supergiant progenitor yielding ejecta of 7–8 $M_{\odot}$, kinetic energy
$$
E_{\rm kin}\approx 1.2\times 10^{51}\ {\rm erg},
$$
and
$$
M(^{56}{\rm Ni})\approx 0.05\ M_{\odot},
$$
with prolonged interaction mediated by a cold dense shell (CDS) at $\approx 8000$ km s$^{-1}$ and no evidence for material faster than the CDS during 20–120 d [2604.05145]. The same ejecta model, extended to $\sim 1000$ d, required persistent CSM interaction at all epochs, dominating the UV at all times and the optical after $\sim 600$ d [2605.14081].

Nebular spectroscopy has generally pulled the mass scale back toward the lower or middle part of the pre-explosion range. One 445-d analysis used the stability of [O I] and [Ca II] against interaction contamination and their flux ratio,
$$
[\mathrm{O\,I}]\,\lambda\lambda 6300,6364 / [\mathrm{Ca\,II}]\,\lambda\lambda 7291,7323 = 0.56,
$$
to favor
$$
M_{\rm ZAMS}\simeq 10-15\ M_{\odot}
$$
[2502.10534]. Another day 1–442 synthesis found that nebular spectra between 200–400 d matched best with a 15 $M_{\odot}$ progenitor model [2503.13974]. The broad implication is that, although pre-explosion SED-based masses remain model-sensitive, hydrodynamical and nebular analyses often converge on $\sim 10$–15 $M_{\odot}$.

## 6. Polarization, asymmetry, and dust formation

Polarimetry showed that asymmetry was not a secondary detail but a defining property of SN 2023ixf. At +2.33 d, the intrinsic R-band continuum polarization was
$$
p_r = 0.88 \pm 0.06\%,\quad \theta = 153.7^{\circ} \pm 1.9^{\circ},
$$
well above the Serkowski-based ISP upper limit
$$
p({\rm ISP}) < 0.35\%.
$$
During the photospheric phase the continuum polarization dropped toward the ISP level, reaching $\sim 0.05$–0.11% by +26–31 d, before rising again to
$$
p_r = 0.65 \pm 0.06\%
$$
at +73.19 d and
$$
p_r = 0.47 \pm 0.06\%
$$
at +76.19 d as the light curve left the plateau [2410.08199]. A common ambiguity in SN polarimetry is whether the signal is dominated by ISP; for SN 2023ixf, the early amplitude, the rapid time evolution, and the late return toward the ISP envelope all argue strongly for intrinsic polarization.

A denser spectropolarimetric campaign from +1.4 to +120 d found the same three-stage evolution in more detail: continuum polarization initially near $\lesssim 1\%$, falling steeply within days to $\sim 0.4\%$ as the ejecta swept up the optically thick CSM, then staying low at $\sim 0.2\%$ before rising again to $\sim 0.6\%$ near the transition to nebular conditions [2505.03975]. Two-dimensional polarized radiative-transfer modeling attributed the early phase to an aspherical CSM with pole-to-equator density contrast $\gtrsim 3$ and the late-time surge to an asymmetric distribution of $^{56}$Ni deep in the ejecta [2505.03975].

A complementary polarimetric analysis described three distinct peaks in the polarization evolution at 1.4 d, 6.4 d, and 79.2 d. It associated them, respectively, with an asymmetric dense CSM, an aspherical shock front plus clumpiness in the low-density extended CSM, and an aspherical inner ejecta or He core. The same study identified two dominant axes, one associated with the CSM and outer ejecta and the other with the inner ejecta or He core, and linked high-velocity broad Balmer absorption to an aspherical shock front [2405.20989]. The convergence of these studies is that the early and late asymmetries had distinct physical origins.

Dust formation and infrared reprocessing were likewise time-resolved. Optical/NIR photometry, spectroscopy, and JWST data from 150 to 750 d showed an early IR excess by 1.8 d, a broad secondary NIR rebrightening over about 89 to 175 d, progressive attenuation of the red wing of H$\alpha$ from about 132 d, and CO emission detected by about 217 d. The early 1.8–33.6 d excess was interpreted as a radiative “flash” IR echo from pre-existing circumstellar dust, while the 89–175 d rebrightening was more naturally explained by an extended echo from structured wind material at $\gtrsim 10^{17}$ cm [2603.14137].

The first direct signature of internal dust formation was the onset of H$\alpha$ red-wing attenuation at about 132 d. Modeling of the H$\alpha$ profile between 141 and 418 d yielded an internal silicate-equivalent dust mass rising from about
$$
1.5\times 10^{-6}\ M_{\odot}
$$
to
$$
6\times 10^{-5}\ M_{\odot}.
$$
JWST SED decomposition further required a cold silicate-bearing component that grew from
$$
2.6\times 10^{-4}\ M_{\odot}
$$
at 253 d to
$$
(2.1-2.2)\times 10^{-3}\ M_{\odot}
$$
by 601–723 d, alongside a cold graphite component of order $10^{-3}\ M_{\odot}$ that tracked lingering echo emission [2603.14137].

Late-time non-LTE UV-to-IR radiative-transfer modeling to 998 d independently required dust formation beginning at $\sim 200$ d, first in the CDS and later in the inner ejecta, with internal dust plausibly reaching
$$
\sim 10^{-4}\ M_{\odot}
$$
by $\sim 700$ d, plus an external cold dust component to match the mid-IR [2605.14081]. By 445 d, the spectrum had developed a complex H$\alpha$ profile consisting of a boxy interaction component plus a central ejecta component, indicating that ejecta–CSM interaction and dust-related asymmetry had become inseparable parts of the late-time evolution [2502.10534].

## 7. High-energy and multimessenger constraints

SN 2023ixf produced the earliest hard X-ray detection of a non-relativistic stellar explosion then known. NuSTAR detected it up to $\approx 30$ keV at $\delta t \approx 4$ d and $\delta t \approx 11$ d. The spectra were consistent with hot thermal bremsstrahlung absorbed by a thick neutral medium, with a clear neutral Fe K$\alpha$ emission line and with the intrinsic soft X-ray brightening driven mainly by declining absorption rather than by a large increase in intrinsic luminosity. The preferred interpretation was forward-shock thermal emission in dense, confined CSM at radii $r\lesssim 10^{15}$ cm [2306.04827].

These X-rays provided an independent shock diagnostic. Using
$$
kT \simeq (3/16)\,\mu m_p v_s^2,
$$
the measured temperatures implied a forward-shock velocity of at least several $10^3$ km s$^{-1}$, with the caveat that incomplete electron–ion equilibration could make the true shock speed closer to $\sim 10^4$ km s$^{-1}$ [2306.04827]. The same data gave a Thomson depth
$$
\tau_T = N_H \sigma_T
$$
of $\approx 0.17$ at Epoch I and $\approx 0.04$ at Epoch II, so the absorber was Compton-thin. Early radio/mm non-detections were then naturally attributed to very large free–free optical depth in the same dense CSM [2306.04827].

The neutrino follow-up produced a non-detection. IceCube analyzed a 4-day fast-response window and a 32-day optimized window under an $E^{-2}$ spectrum. The 4-day analysis gave
$$
p\text{-value}=0.18,
$$
and the 32-day analysis had unblinded
$$
{\rm TS}=0,
$$
both consistent with the background-only hypothesis. The reported 90% CL upper limits on time-integrated energy flux were
$$
E^2\,dN/dE = 0.44\ {\rm GeV\ cm^{-2}}
$$
for the 4-day window and
$$
E^2\,dN/dE = 0.35\ {\rm GeV\ cm^{-2}}
$$
for the 32-day window, corresponding to isotropic-equivalent source-frame energies of
$$
3.5\times 10^{48}\ {\rm erg}
$$
and
$$
2.7\times 10^{48}\ {\rm erg},
$$
respectively, under the convention used in that work [2507.07097].

These upper limits do not rule out shock acceleration in SN 2023ixf, but they do constrain very optimistic interaction-powered neutrino scenarios. In the same IceCube study, folding the Kheirandish \& Murase model flux with IceCube’s effective area yielded an expected detection probability of only $\approx 0.025$ neutrinos in 30 days, so the non-detection was itself consistent with model expectations [2507.07097]. The high-energy record of SN 2023ixf therefore complements the optical and infrared evidence: the event clearly hosted strong shock–CSM interaction, but not at a level that produced a detectable TeV neutrino burst in IceCube.

Source: https://www.emergentmind.com/topics/sn2023ixf