In this episode, we dive into the exciting future of **multi-messenger astronomy**, specifically focusing on the detection and characterization of binary neutron star (BNS) mergers.

* **The Dawn of Multi-Messenger Astrophysics:** Our understanding of cosmic events was revolutionized by the extraordinary joint detection of gravitational waves (GWs) and light from a BNS merger on August 17, 2017 (GW170817). This single event confirmed theoretical hypotheses about short gamma-ray bursts (SGRBs) originating from BNS mergers and provided insights into kilonovae (KNe) – the thermal radiation powered by radioactive decay of heavy elements.

* **Next-Generation Observatories:** The upcoming third-generation GW observatories, such as the **Einstein Telescope (ET)** and **Cosmic Explorer (CE)**, are poised to dramatically increase detection rates, potentially observing hundreds of thousands of BNS mergers annually, reaching distances beyond redshift (z) ~ 3.

* **The Wide-field Spectroscopic Telescope (WST):** This proposed 12-meter-class spectroscopic facility, expected to operate in the 2040s in the southern hemisphere, will be crucial for exploiting the unique information from joint GW and electromagnetic (EM) detections. WST will employ both **Integral Field Spectroscopy (IFS)** and **Multi-Object Spectroscopy (MOS)**, enabling simultaneous acquisition of multiple spectra over wide fields of view.

* **Detecting Faint Counterparts:**

* WST is designed to detect **Kilonovae (KNe)** up to **z ~ 0.4** and apparent magnitudes as faint as **mAB ~ 25 (with fibres) to ~25.5 (with IFS)**. The optimal time for KN detection observations is **12–24 hours after the merger**.

* **GRB afterglows** can be observed at even higher redshifts, beyond z = 1, particularly for on-axis or slightly off-axis systems (viewing angles Θview ≲ 15°). Timely follow-up, within a few hours of the GRB prompt detection, is critical due to their rapid decay.

* **Observing Strategies and Challenges:**

* The vast majority of next-generation GW events will have **large sky localization regions** and **faint EM counterparts**, making their identification challenging.

* **Galaxy-targeted searches** with WST involve identifying galaxies within the 3D error volume of the GW signal, leveraging high multiplexing capabilities. These searches benefit greatly from complete galaxy catalogues with redshift information up to z ≤ 0.5.

* **Synergy with photometric surveys**, like the Vera Rubin Observatory, allows WST to target transient candidates identified by these wide-field facilities.

* **The "Golden Events"**: BNS mergers detected by ET+CE at z < 0.3 (or ET-alone at z < 0.2) with sky localizations better than 10 deg² are ideal for WST, as it can cover all galaxies in the error volume with limited exposures (e.g., 3 one-hour exposures for 10 deg² or 1 one-hour exposure for 1 deg²).

* **Addressing Offsets and Host Galaxies:** Many EM counterparts are not expected to be at the exact center of their host galaxies. The use of **mini-IFUs or "fibre bundles"** is proposed as an extremely valuable solution to cover regions around host galaxy centers and detect counterparts with larger offsets. Spectral subtraction techniques can also be used to separate the transient's spectrum from the host galaxy's.

* **The Future is Multi-Messenger:** This research underscores the need for **new instruments** that are developed with multi-messenger science as a core design case, enabling rapid data reduction and analysis for timely alerts to the astronomical community.

**Reference:**

Bisero, S., Vergani, S. D., Loffredo, E., et al. (2025). Multi-messenger observations of binary neutron star mergers: synergies between the next generation gravitational wave interferometers and wide-field, high-multiplex spectroscopic facilities. *Astronomy & Astrophysics*.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: ESO

Dive into the fascinating world of cosmic rays with the latest research from the IceCube Neutrino Observatory! This episode explores new measurements of high-energy muons in extensive air showers, shedding light on the mysterious mass composition of cosmic rays and the challenges of simulating their interactions in Earth's atmosphere.

**What we discuss:**

* **Measuring High-Energy Muons:** Learn about the first measurement of the **mean number of muons with energies above 500 GeV** in near-vertical extensive air showers. These "TeV muons" are crucial because they originate predominantly in the early stages of shower development and their number depends strongly on the energy and mass of the primary cosmic ray.

* **The IceCube Neutrino Observatory's Unique Capabilities:** Discover how this research uses a **coincident detection method** combining IceTop, the surface detector array, with the large-volume in-ice detector located 1.5 km to 2.5 km below the surface. The thick ice absorbs lower-energy muons, allowing for a pure measurement of high-energy muons.

* **Cosmic Ray Energies and Hadronic Models:** The study focuses on cosmic rays with primary energies between **2.5 PeV and 100 PeV**. The results were analyzed using various hadronic interaction models, including **Sibyll 2.1, QGSJet-II.04, and EPOS-LHC**, which are vital for simulating air shower development.

* **The "Muon Puzzle" and Inconsistencies:** We'll explore the intriguing **"Muon Puzzle,"** a known discrepancy between measurements and simulations of muons in air showers. This new study compares high-energy (TeV) muon measurements with previous low-energy (GeV) muon measurements from IceTop alone. While Sibyll 2.1 shows excellent agreement between the two measurements, **the EPOS-LHC model reveals a significant tension**, indicating it doesn't consistently describe both low and high-energy muon data.

* **Implications for Particle Physics and Astronomy:** Understanding these hadronic interactions is crucial for inferring cosmic-ray mass composition, calculating atmospheric neutrino flux, and exploring particle physics beyond human-made accelerators. Solving the Muon Puzzle is considered one of the most pressing problems in high-energy cosmic-ray physics.

**Article Reference:**

"Measurement of the mean number of muons with energies above 500 GeV in air showers detected with the IceCube Neutrino Observatory" by R. Abbasi et al. (IceCube Collaboration). Dated June 25, 2025.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: D. Soldin

Join us as we dive into the latest astronomical discovery! Scientists have identified a **new candidate pulsar wind nebula (PWN)**, named XMMU 034124.2+525720, which may be directly linked to **1LHAASO J0343+5254u**, a powerful "PeVatron" in our galaxy.

**What are PeVatrons?** They are the most energetic astrophysical objects in our galaxy, producing cosmic rays (CRs) with energies exceeding 1 PeV (10^15 eV), far surpassing what terrestrial accelerators can achieve. Understanding them is key to solving the mystery of the most energetic galactic cosmic rays and gamma rays.

This potential PWN, discovered through extensive **XMM-Newton observations**, exhibits key characteristics typical of other very high-energy PWNs like the "Eel" and "Boomerang" nebulae. Its X-ray emission shows an **extended, asymmetric morphology** and a **power-law spectrum (ΓX = 1.9)** that becomes notably softer farther from its center.

Using **multiwavelength modeling**, researchers demonstrated that a **fully leptonic model**—involving electron synchrotron radiation and inverse-Compton (IC) scattering of ambient photons—can explain the observed X-ray and gamma-ray emission, especially if there are **elevated infrared (IR) photon fields** in the region. While this model largely accounts for the LHAASO gamma-ray flux, future observations will help explore if hadronic processes in nearby molecular clouds also contribute to the gamma-ray emission and potential neutrino flux.

Though XMM-Newton observations didn't definitively resolve a central pulsar or detect X-ray pulsations, this discovery marks a crucial step in understanding galactic PeVatrons. Future, higher-resolution X-ray observations with missions like Chandra and NuSTAR, along with dedicated radio searches for a pulsar, are planned to solidify this PWN classification and provide deeper insights into these extreme cosmic accelerators.

**Article Reference:**

DiKerby, S., Zhang, S., Ergin, T., et al. 2025, *Discovery of a Pulsar Wind Nebula Candidate Associated with the Galactic PeVatron 1LHAASOJ0343+5254u*, The Astrophysical Journal, 983:21.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Stephen DiKerby et al., 2025 ApJ 983 21

In this episode, we dive into a fascinating new study that performs the **first direct consistency check** between two crucial measurements from the Large High Altitude Air Shower Observatory (LHAASO): the **cosmic-ray (CR) proton spectrum at the "knee"** and the **Galactic diffuse gamma-ray emission**.

The "knee" in the cosmic ray spectrum (around a few PeV) is thought to mark the maximum energy reached by Galactic CR accelerators. Diffuse gamma-ray emission, primarily from CR interactions with interstellar gas, provides a complementary view of the same underlying particle population.

The study reveals a **persistent mismatch**:

* The **predicted gamma-ray flux robustly overshoots the LHAASO data** in both inner and lateral Galactic regions.

* This discrepancy is evident in **both normalization and spectral shape**.

* This is particularly puzzling because while an excess of gamma-rays has been discussed before, **evidence of a deficit in observed emission represents a new and more puzzling feature**.

Key insights from the research:

* The disagreement **challenges conventional scenarios** linking the local cosmic-ray sea to Galactic gamma-ray emission.

* It **calls for a revision of current cosmic ray models** in the TeV-PeV sky.

* The mismatch is **not attributed to the hadronic interaction model** used for calculations; using alternative models would actually increase the tension.

* The findings suggest a **possible tension between the LHAASO gamma-ray observations and the CR proton flux measured by LHAASO itself**.

* One intriguing explanation is that the **CR spectrum measured locally might not be the same as the one responsible for the observed gamma-ray emission** throughout the Galaxy, possibly having a different "knee" location (e.g., around 300 TeV).

* Uncertainties also exist due to the **lack of helium flux measurements** between 100 TeV and a few PeV.

This research highlights the critical importance of evaluating the consistency between these two types of measurements and opens new avenues for understanding cosmic ray propagation in our Galaxy.

**Article Reference:**

Espinosa Castro, L. E., Villante, F. L., Vecchiotti, V., Evoli, C., & Pagliaroli, G. (2025). *LHAASO Protons versus LHAASO Diffuse Gamma Rays: A Consistency Check*. arXiv preprint arXiv:2506.06593.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: LHAASO

In this episode, we dive into the mysterious world of Fast Radio Bursts (FRBs) and the ongoing quest to understand their origins. We discuss a systematic search for **past supernovae (SNe) and other historical optical transients** at the positions of FRB sources, exploring a leading theory that links FRBs to **magnetars**.

The study **found no statistically significant associations** within the 5σ FRB localization uncertainties between the observed CHIME-KKO or literature FRBs and optical transients, *except* for a previously identified potential optical counterpart to FRB 20180916B, named AT 2020hur. AT 2020hur, however, occurred *after* the FRB was first detected, making it inconsistent with the "past SN" progenitor model, though it remains a potential association under other theories.

**Chance Coincidences:** The probability of a chance coincidence (Pcc) between an FRB and a transient was found to be **low (Pcc < 0.1)**. It's estimated that it would take **~22,700 subarcsecond-localized FRBs** to yield one chance association, which translates to roughly **30–60 years** at the projected CHIME/FRB Outrigger detection rate. This means that any robust match found in the near future is highly likely to be a **physical association**.

**Implications of Transparency Time:** The research estimates that **5–7% of matched optical transients** (if all were SNe) are old enough to be associated with a detectable FRB, assuming the 6.4-10 year transparency timescale. More broadly, **23–30% of all cataloged SNe and 32–41% of CCSNe** are currently old enough to have detectable FRB emission.

**The Future with Rubin Observatory:** The upcoming **Vera C. Rubin Observatory (LSST)** is expected to dramatically increase the number of known SNe and the volume over which they can be detected. This will significantly **increase the rate of potential FRB-SN associations** at redshifts below z~1, where most FRBs are discovered.

**Flexible Framework:** The systematic search machinery developed for this work is publicly available and flexible, allowing it to be applied to a wide range of transient timescales, FRB localization sizes, and different optical transient populations in future searches.

**Reference Article:**

* DONG, Y., KILPATRICK, C. D., FONG, W., et al. (2025). **Searching for Historical Extragalactic Optical Transients Associated with Fast Radio Bursts**. arXiv e-prints, arXiv:2506.06420v1.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA - JPL/Caltech

In this episode, we discuss a significant new detection of the Geminga pulsar, a middle-aged, radio-quiet gamma-ray pulsar. The **Large-Sized Telescope (LST-1)**, the first of the Cherenkov Telescope Array Observatory (CTAO) Northern Array, has detected Geminga at energies down to 20 GeV.

Key takeaways from the study:

* The LST-1 detected the Geminga pulsar using 60 hours of data.

* The **second emission peak (P2)** of Geminga was detected with a high significance of **12.2σ** in the energy range between 20 and 65 GeV. This is a doubled significance compared to previous results by the MAGIC Collaboration, achieved with less observation time and a single telescope.

* The first peak (P1) was detected at a lower significance level of 2.6σ.

* The LST-1 analysis has an estimated energy threshold as low as 10 GeV for pulsar analysis, although the peak in reconstructed energy was around 20 GeV.

* The best-fit model for the P2 spectrum was a power law with a spectral index of Γ = 4.5 ± 0.4 (statistical uncertainty). When considering systematic uncertainties, the spectral index is Γ = (4.5 ± 0.4stat)+0.2sys −0.6sys. This is compatible with previous results from the MAGIC Collaboration.

* A joint fit of LST-1 and Fermi-LAT data preferred a power law with a sub-exponential cut-off (PLSEC) over a pure exponential cut-off (PLEC), although the PLSEC model didn't fully match the LST-1 points.

* While no curvature was detected in the LST-1-only spectrum, combining LST-1 and Fermi-LAT data showed a statistical preference for a curved log parabola model at lower minimum energies (10-20 GeV).

* Theoretical models, such as the synchro-curvature (SC) model from Harding et al. (2021), can explain the dominance of the SC component at high energies and the non-detection of the first peak above 20 GeV, although improvements are needed to match the LST-1 SED better.

* These results demonstrate the LST-1's excellent capabilities for observing pulsars at the upper end of their spectra and its overlap with the Fermi-LAT energy range. Future observations with the full CTAO Northern Array are expected to improve sensitivity and allow for more detailed studies of the pulsar peaks and spectra.

**Reference:**

* K. Abe et al. (CTAO LST Project). Detection of the Geminga pulsar at energies down to 20 GeV with the LST-1 of CTAO. *Astronomy & Astrophysics* manuscript no. aa54350-25 ©ESO 2025 May 29, 2025.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Iván Jiménez (IAC)

Astronomers have made a significant discovery, detecting X-ray emission from a rare type of cosmic object known as a **Long-Period Radio Transient (LPT)** for the very first time.

• The object, designated **ASKAP J1832−0911**, is extraordinarily bright in radio, reaching flux densities of 10–20 Jy.
• Crucially, it exhibits **coincident radio and X-ray emission**, both pulsing with a regular period of **44.2 minutes** (2,656.2412 seconds in radio, 2,634 seconds in X-rays).
• This combination of properties – long period, bright coherent radio, and variable X-ray emission – makes ASKAP J1832−0911 **unlike any other known object in our galaxy**.
• Its luminosity is **highly variable**, with both radio and X-ray emission decreasing dramatically over a few months following a 'hyper-active' phase. This variability suggests that the lack of previous X-ray detections from other LPTs might be due to not observing them during such brief bright phases.
• The object is estimated to be located at a distance of approximately **4.5 kpc**.
• Current data suggest potential classifications like an old magnetar or an ultra-magnetized white dwarf, though both interpretations present **theoretical challenges** for existing models. It is not consistent with a classical rotation-powered pulsar or a typical isolated white dwarf.

The discovery of X-ray emission from ASKAP J1832−0911 demonstrates that LPTs can be **more energetic** than previously believed. It also establishes a new class of hour-scale periodic X-ray transients linked to exceptionally bright radio emission.

Reference Article: "Detection of X-ray emission from a bright long-period radio transient" by Ziteng Wang et al..

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Alex Cherney

A recent study utilized **15 years of observations** from the **Fermi Large Area Telescope (LAT)** to analyze the gamma-ray emission from the Sun in its quiet state, meaning when it's not flaring. This is the first study to separately analyze the flux variation of the two distinct components of this quiet-state gamma-ray emission over solar cycles.

According to theoretical understanding, the Sun's steady-state gamma-ray emission arises from interactions with Galactic cosmic rays (CRs). There are two main components:

* The hadronic component, which is primarily confined to the **solar disk**. It's thought to be produced by CR cascades in the solar atmosphere. This component's flux is expected to **anticorrelate with solar activity** (like sunspot number, SSN) and **correlate with the flux of cosmic rays**.

* The **leptonic component**, which is spatially **extended** beyond the solar disk. This is theorized to be an Inverse Compton (IC) component, where CR electrons scatter off solar photons. Like the disk component, its intensity was expected to **vary with the solar cycle**, being highest during solar minimum and lowest during solar maximum, thus anticorrelating with SSN and correlating with CR flux (specifically CR electron flux).

Previous Fermi-LAT observations had shown that the overall solar gamma-ray flux varies with solar activity, anticorrelating with SSN and changing by nearly a factor of two between solar maximum and minimum. However, these studies had not separated the contributions of the disk and extended components.

This new work analyzed Fermi-LAT data from August 2008 to June 2023, carefully selecting data and using an "off-source" method to evaluate background contamination. They were able to distinguish the two components and study their flux variations over Solar Cycle 24 and the beginning of Cycle 25.

The key findings from this analysis reveal both confirmation of expectations and **significant surprises**:

* For the **disk component**, the results align well with theoretical predictions. Its flux variation:

* **Anticorrelates strongly with the sunspot number (SSN)**.

* **Correlates strongly with the flux of cosmic-ray protons** measured near Earth.

* Correlates with the gamma-ray flux from the Moon, supporting similar production mechanisms.

* The variation is **independent of energy** above 250 MeV.

This confirms that the hadronic emission mechanism for the disk component has been correctly identified.

* For the **spatially extended component**, the behavior was **unexpectedly complex**.

* It showed the expected anticorrelation with SSN and correlation with the disk component **only until approximately mid-2012**.

* **After 2013, there was no longer any significant correlation or anticorrelation observed** between the extended component's flux variation and either the SSN or the cosmic-ray electron flux. Correlation coefficients over the entire period are below 0.3.

* Like the disk component, the extended component's variation was also found to be independent of energy above 250 MeV.

This **surprising lack of correlation for the extended component after 2013** is a major finding. The change in behavior coincides with the start of the **reversal of the Sun's polar magnetic field**, which began at the end of 2012. This suggests that the transport and modulation of cosmic rays, particularly electrons, in the **inner heliosphere (close to the Sun)** may be **unexpectedly complex** and possibly different for electrons and protons.

Paper: https://arxiv.org/abs/2505.06348

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Solar Dynamics Observatory/GSFC/NASA

The research investigates how supernovae exploding into dense circumstellar environments, specifically those with dense shells of material, can potentially accelerate particles to energies of a few PeV, thus acting as "PeVatrons" and contributing to the "knee" feature in the cosmic ray spectrum.

Supernova remnants (SNRs) have long been considered prime candidates for the sources of Galactic Cosmic Rays (CRs) up to energies of a few PeV. However, despite decades of gamma-ray astronomy, there hasn't been clear observational proof that standard SNR models can accelerate particles beyond approximately 100 TeV. Young SNRs like Tycho and Casiopeia A, initially expected to be strong accelerators, show even lower cutoff energies.

The presented study explores a different scenario: supernovae that expand into **much denser circumstellar material**, including dense shells ejected by the progenitor star shortly before explosion. These dense shells are thought to be present around massive stars like Luminous Blue Variables (LBVs), which can undergo brief episodes of very high mass-loss rates (up to 1 M⊙/yr). Type IIn supernovae, associated with LBVs, make up about 5% of core-collapse supernovae.

The researchers used spherically symmetric 1D simulations with their time-dependent acceleration code called **RATPaC** (Radiation Acceleration Transport Parallel Code). This code simultaneously solves the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in the test-particle limit. Unlike models that assume a steady state for magnetic turbulence, RATPaC accounts for the time needed for turbulence to build up, which often leads to lower maximum energies in standard scenarios.

**The key finding is that the interaction of the supernova shock front with these dense circumstellar shells can significantly boost the maximum energy** of the accelerated particles.

Specifically, the simulations show that:

* **Interactions with shells that occur earlier post-explosion lead to a greater increase in maximum energy (Emax)**.

* If the interaction happens within the first **5 months (approximately 140 days)** after the explosion, the **Emax can increase to more than 1 PeV**.

* For very early interactions, around **0.1 years**, Emax can even surpass **10 PeV**.

This significant energy boost is attributed to several mechanisms during and after the shock-shell interaction:

1. **Enhanced Particle Escape:** The shock slows down considerably during the interaction with the dense shell, which temporarily enhances the "precursor scale" (the region upstream where particles diffuse back towards the shock, given by D(E)/v_shock). This increased scale provides more time for turbulence to grow. Enhanced particle escape also occurs during the onset of the interaction, boosting the CR current.

2. **Reacceleration in a Pre-amplified Field:** After passing through the shell, the shock propagates into a medium where the magnetic field has been pre-amplified by escaping cosmic rays during the interaction phase. The shock accelerating into this region with an enhanced field boosts Emax.

3. **Interaction with Reflected Shocks:** The collision with the dense shell creates reflected shocks. These can catch up with and interact with the forward shock from behind, leading to sharp increases in the forward shock's velocity and slightly boosting Emax.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: ESO/L. Calçada

The research presents **new observations of the gamma-ray binary system LS 5039 using the High Altitude Water Cherenkov (HAWC) observatory**, revealing significant insights into the nature of this high-energy source.

One of the most striking findings is that **HAWC detected gamma rays from LS 5039 extending up to 200 TeV with no apparent spectral cutoff**. This is a crucial extension of previous observations by the High Energy Stereoscopic System (H.E.S.S.), which had observed the system up to TeV energies. The spectral energy distribution (SED) presented in Figure 2 shows this extension, particularly during the inferior conjunction (INFC). The lower limit on the maximum energy measured by HAWC for LS 5039 is 208 TeV at a 68% confidence level during INFC.

Furthermore, the HAWC data **confirms with a 4.7σ confidence level that the gamma-ray emission between 2 TeV and 118 TeV is modulated by the orbital motion of the binary system**. This modulation, where the emission is more significant during the inferior conjunction (INFC) compared to the superior conjunction (SUPC), strongly suggests that these high-energy photons are produced within or very near the binary orbit. The study notes that despite a longer phase interval for the SUPC data, LS 5039 was more significantly detected during INFC due to a higher flux. This modulation up to 100 TeV provides strong evidence for gamma-ray production inside the binary.

These high-energy observations pose a challenge to purely **leptonic scenarios** for gamma-ray production. In a leptonic scenario, the highest energy photons would be produced by electrons inverse Compton scattering stellar photons. The detection of photons up to 200 TeV would require electrons to be accelerated to at least this energy, demanding an extremely efficient acceleration mechanism within LS 5039, especially given the dense radiation and potentially high magnetic fields within the binary system. The study suggests that achieving such high electron energies within the stellar photosphere would require an acceleration efficiency η close to 1 and a magnetic field not significantly larger than 0.1 Gauss to avoid substantial synchrotron losses.

Alternatively, the HAWC radiation can be interpreted through a **hadronic scenario**. In this case, protons are accelerated to peta-electronvolt (PeV) energies and then produce gamma rays through interactions with either the dense gas (stellar winds) or the intense radiation fields within and close to the binary orbit. The timescale for proton-proton collisions and subsequent pion decay is remarkably close to the binary period, making this a viable explanation. If the gamma rays are of hadronic origin, LS 5039 would be an astronomical accelerator capable of producing PeV-scale hadrons. The required jet power to produce the observed gamma-ray luminosity through proton-proton interactions is estimated, and the study suggests that binary jets powered by either Bondi-type accretion or colliding winds could potentially provide the necessary luminosity.

In conclusion, the HAWC observations provide compelling evidence for **gamma-ray emission beyond 100 TeV from LS 5039 and confirm the orbital modulation of this emission**, suggesting that the production of these very high-energy photons occurs within the binary system. These findings have significant implications for our understanding of particle acceleration and radiation processes in gamma-ray binaries, potentially hinting at a hadronic origin for the highest energy emission and establishing LS 5039 as a candidate PeVatron. Future observations at even higher energies could provide crucial evidence to further elucidate the underlying mechanisms at play.

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: J. Goodman