Neutron star discovered in center of Supernova 1987A

Science:

Editor summary: The nearby supernova SN 1987A was visible to the naked eye, and its evolution has been observed over the ensuing decades. The explosion is thought to have produced a neutron star or black hole, but none has been directly detected. Fransson et al. observed a remnant of SN 1987A using near- and mid-infrared integral field spectroscopy. They identified emission lines of ionized argon that appear only near the center of the remnant. Photoionization models show that the line ratios and velocities can be explained by ionizing radiation from a neutron star illuminating gas from the inner parts of the exploded star

Nature News:

Astronomers used the [JWST] to finally spot signs of an ultradense ‘neutron star’ lurking in the explosion’s core in a galaxy that orbits the Milky Way. Light from the explosion reached Earth 37 years ago this week, in a supernova that revolutionized modern astrophysics by providing an up-close look at how stars die.

JWST did not observe the neutron star directly, because it remains obscured behind a veil of dust from the explosion. But the telescope detected light coming from argon and sulfur atoms that had been ionized, or electrically charged, by radiation blazing from the long-sought neutron star.

Over the years, astronomers watched as rings of gas and dust expanded outwards from the site of the explosion, usually growing dimmer but sometimes brightening when various ejected materials collided.

One outcome of such a supernova is to leave behind a black hole. But early observations of SN 1987A, such as the wave of neutrinos, suggested that it should have given rise to a neutron star, which can be just 20 kilometres across but is so dense that a teaspoonful weighs millions of tonnes.

Space.com:

Using the James Webb Space Telescope (JWST), astronomers have ended a nearly decade-long game of celestial hide-and-seek after they discovered a neutron star in the wreckage of a stellar explosion.

"For a long time, we've been searching for evidence for a neutron star in the gas and dust of Supernova 1987A," Mike Barlow, an emeritus professor of physics and astronomy and part of the team behind this discovery, told Space.com. "Finally, we have the evidence that we've been seeking."

Barlow suggested that researchers may be able to distinguish between a naked neutron star and one clothed by a pulsar-wind nebula by making further infrared observations of the heart of Supernova 1987A with the JWST's NIRSpec instrument.

"We have a program which is gathering data now, which will be getting data with 3 or 4 times the resolution in the near-infrared," he concluded. "So by obtaining these new data, we may be able to distinguish the 2 models that have been proposed to explain the emission powered by a neutron star.

 

On the Astraveo podcast:

• Supernova 1987A Mystery SOLVED! and more! | Astraveo Coast-to-Coast (Feb 25, 2024)
  
• "No Body, No Crime": Supernova Remains Finally Revealed! (Astraveo Coast-to-Coast Highlight)
  

SN 2023ixf early photometry

This supernova just exploded in the galaxy M101, just 6 Mpc away, making it the closest supernova since SN 2011fe. Research groups around the world are scrambling to conduct analyses of this object. Some have already started popping up on arXiv.

arXiv:

We present the early-stage analysis of the low-resolution (R=1000) optical spectra and the near-infrared light curves of the bright Type II supernova (SN II) 2023ixf in the notable nearby face-on spiral galaxy M101, which are obtained since t=1.7 until 8.0 d.

Compared with SNe II showing the flash-ionized features, we suggest that this SN could be categorized into high-luminosity SNe II with a nitrogen/helium-rich circumstellar material (CSM), e.g., SNe 2014G, 2017ahn, and 2020pni. 

These observational facts support that SN 2023ixf is well consistent with a high-luminosity SN II with the dense nitrogen/helium-rich CSM.

It's great to see the comparisons to previous objects. 23ixf doesn't have too many remarkable qualities aside from some very early flash features (and its proximity), but it's difficult to find good comparisons since we really don't get to observe SNe early this often.

A radio-detected Type Ia supernova with helium-rich circumstellar material

arXiv:

However, despite extensive efforts, no SN Ia has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate WD star. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich CSM, as revealed by its spectral features, infrared emission and, for the first time in a SN Ia, a radio counterpart. Based on our modeling, we conclude the CSM likely originates from a single-degenerate (SD) binary system where a WD accretes material from a helium donor star, an often hypothesized formation channel for SNe Ia. 

nature: 

The CSM interaction in SN 2020eyj is also confirmed, for the first time in a SN Ia, through the detection of a radio counterpart, at a frequency of 5.1 GHz at 605 and 741 days after the first detection. Follow-up in the X-rays did not yield a detection. We model the radio synchrotron emission, which results from the shock interaction between the ejecta and the CSM.

For the SD shell model, the radio detections are best explained with a CSM mass of M_csm = 0.36 M⊙ (see ‘CSM shells’ section in Methods), with the expectation that the radio light curve will start to drop off rapidly at around 900 days. 

 

 Previously on this blog:

• Initial Flash and Spectral Formation of Type Ia Supernovae with An Envelope: Applications to Over-luminous SNe Ia
• Constraining Type Ia Supernova Progenitors the Apian Way
• The core degenerate scenario for the type Ia supernova SN 2020eyj
  

Constraining Type Ia Supernova Progenitors the Apian Way

arXiv:

We present very early photometric and spectroscopic observations of the Type Ia supernova (SN) 2023bee, starting about 8 hours after the explosion, which reveal a strong excess in the optical and nearest UV (U and UVW1) bands during the first several days of explosion.

We find a good match to the Kasen model in which a main-sequence companion star stings the ejecta with a shock as they buzz past. Models of double detonations, shells of radioactive nickel near the surface, interaction with circumstellar material, and pulsational-delayed detonations do not provide good matches to our light curves. We also observe signatures of unburned material, in the form of carbon absorption, in our earliest spectra.

This is an exciting result out of my research group at Las Cumbres Observatory!

Taken together, our observations above suggest that the emission from SN 2023bee during the first few days after explosion consists of typical Type Ia SN spectral features plus an additional hot continuum component. 

This Letter demonstrates the power of using very high-cadence, multiband photometry of young, nearby Type Ia SNe to constrain their progenitor systems, which is only possible with specially designed robotic facilities like the DLT40 Survey, Las Cumbres Observatory, and Swift.  

Previously on this blog:

• The diverse properties of the ejecta and circumstellar matter of Type Icn SNe
• The core degenerate scenario for the type Ia supernova SN 2020eyj

Photometry and spectroscopy of the Type Icn supernova 2021ckj: The diverse properties of the ejecta and circumstellar matter of Type Icn SNe

arXiv:

Spectral modeling of SN 2021ckj reveals that its composition is dominated by oxygen, carbon and iron group elements, and the photospheric velocity at peak is ~10000 km/s. From the light curve (LC) modeling applied to SNe 2021ckj, 2019hgp, and 2021csp, we find that the ejecta and CSM properties of Type Icn SNe are diverse.

The similarity of the emission components of these lines implies that the emitting regions of SNe 2021ckj and 2021csp have similar ionization states, and thus suggests that they have similar properties of the ejecta and CSM, which is inferred also from the LC modeling. Taking into account the difference in the strength of the absorption features, this heterogeneity may be attributed to viewing angle effects in otherwise common aspherical ejecta.

The core degenerate scenario for the type Ia supernova SN 2020eyj

arXiv:

We argue that the core degenerate (CD) scenario of type Ia supernovae (SNe Ia) can explain the compact helium-rich circumstellar material (CSM) of SN 2020eyj...We follow the evolution of two stellar models with initial masses of 5Mo and 7Mo to their asymptotic giant branch phase when they are supposed to engulf the WD companion. We find that there is a sufficiently massive CO core to merge with the WD in the frame of the CD scenario as well as a massive helium-rich layer, ~0.3-1Mo, to account for the helium-rich CSM of SN 2020eyj.

The motivation of our study is the new observations of SN 2020eyj, a SN Ia-CSM with a helium-rich CSM (Kool et al. 2022) and the need to consider all SN Ia scenarios when analysing observations, as the long list of recent papers that study different scenarios suggests.

Building on earlier papers that argue for the CD scenario for SNe Ia-CSM (section 2) we propose the CD scenario also for SN 2020eyj, but we consider a new channel that accounts for the helium-rich CSM (section 3).

James Webb captures an extremely distant triple-lensed supernova

ESA/Webb:

This observation from the NASA/ESA/CSA James Webb Space Telescope contains three different images of the same supernova-hosting galaxy, all of which were created by a colossal gravitational lens. In this case, the lens is the galaxy cluster RX J2129, located around 3.2 billion light-years from Earth in the constellation Aquarius. 

Astronomers discovered the supernova in the triply-lensed background galaxy using observations from the NASA/ESA Hubble Space Telescope, and they suspected that they had found a very distant Type Ia supernova.

SNe Type Ia function as standard candles, so if it really is Type Ia it could be used to determine a cosmic distance to RX J2129. However, I'm curious as to how they made this determination, as I didn't see any conclusive lightcurve or spectra associated with this find. No one has classified the supernova on TNS either. Update: apparently spectroscopy was obtained by NIRSpec but it's not clear if classification was possible.

Digital Trends:

The image features a huge galaxy cluster called RX J2129, located 3.2 billion light-years away, which is acting as a magnifying glass and bending light coming from more distant galaxies behind it. That’s what is causing the stretched-out shape of some of the galaxies toward the top right of the image.

CNET:

Not only does the galaxy appear three times, but it appears at different points in time. A supernova -- a bright exploding star -- is visible in the earliest version of the galaxy. The second and third images, from about 320 days and 1,000 days later, show that the supernova has faded away. An annotated version of the image points out these cool features: 

Mashable:

Astronomers are now adept at spotting the telltale effects of gravitational lensing, but that wasn't always the case. Four decades ago, the concentric arcs of light and stretched celestial objects could be downright confusing. In 1987, an enormous blue arc thought to be hundreds of trillions of miles long was first considered one of the largest objects ever detected in space. The arc was found near the galaxy cluster Abell 370, with another similar object near galaxy cluster 2242-02.

Initial Flash and Spectral Formation of Type Ia Supernovae with An Envelope: Applications to Over-luminous SNe Ia

arXiv:

Over-luminous type Ia supernovae (SNe Ia) show peculiar observational features, for which an explosion of a super-massive white dwarf (WD) beyond the classical Chandrasekhar-limiting mass has been suggested, largely based on their high luminosities and slow light-curve evolution.

In the present work, we suggest a scenario that provides a unified solution to these peculiarities, through hydrodynamic and radiation transfer simulations together with analytical considerations; a C+O-rich envelope (~0.01 - 0.1 Msun) attached to an exploding WD. Strong C II lines are created within the shocked envelope.

The scenario thus can explain some of the key diverse observational properties by a different amount of the envelope, but additional factors are also required; we argue that the envelope is distributed in a disc-like structure, and also the ejecta properties, e.g., the mass of the WD, plays a key role.

Interestingly, the proposed scenario can also be tested for normal (non overluminous) SNe Ia:

Indeed, by combining the expected properties as summarized above, we can comprehensively test this scenario for SNe Ia with intensive observational coverage from the infant to late phases; the present work thus provides one strong motivation for the high-cadence survey and prompt follow-up observation for SNe Ia of various subclasses, especially nearby events that allow longterm monitoring toward the late phase.  

The predicted spectra are shown in Figure 4:

Systematic Near-Infrared Follow-up of Type Ic-BL Supernovae

Came across this interesting paper on the arXiv focusing on Type Ic-BL supernovae and their ability to produce rapid neutron-capture process (r-process) material. Also, they performed their photometric follow-up using the Las Cumbres Observatory, which is pretty neat!

arXiv:

We present the first systematic study of 25 SNe Ic-BL -- discovered with the Zwicky Transient Facility and from the literature -- in the optical/near-infrared bands to determine what quantity of r-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for r-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the r-process mass for these SNe. We also perform independent light curve fits to models without r-process. 

Most of the SNe in our sample show no compelling evidence for r-process production. In our model fits, the general trend we observe is that the best fit consistently under-predicts the peak of the optical light curve, while performing better at predicting the NIR flux. In some cases, the under-prediction is egregious, while in other cases it is more modest. In general under-prediction indicates that the optical-NIR color of the SN is actually bluer than predicted by the models, providing stronger evidence towards favoring r -process-free models over the enriched models.

There is still potentially a link between r-process material and GRBs, but this study was unable to probe it due to the nature of the sample used. 

The fact that none of these SNe are linked to standard, classical long GRBs prevents us from exploring the proposed theoretical connection between the GRB energetics and r -process production. If the GRB jet energy, which scales with the mass accreted by the disk, correlates with the amount of r -process mass produced in the disk winds, then collapsars with no GRBs may not be able to produce detectable r-process signatures.

The work has a few important caveats as well.

First, we note that the r-process enriched and r-process-free models make different predictions about the relationship between nickel mass and SN luminosity...As a result, the amounts of nickel inferred by each model for a given luminosity are inconsistent.

Furthermore, differences between kilonovae and r -process-enriched SN (e.g., in their densities or their compositions) may mean that nebular-phase emission from the former is not a perfect predictor of nebular phase emission from the latter. 

Finally, we acknowledge the limitations of the dataset we present here for testing whether collapsars synthesize r -process elements. Due to the nature of our classical observing runs with WIRC, our NIR light curves are very sparse, and in some cases our upper limits are too shallow to be constraining.

Overall, an exciting paper. Type II/Ib/Ic supernovae have long been potential candidates for detection of prominent r-process influence. This fairly comprehensively presents a case to exclude SNe Type Ic from consideration. 

Carbonaceous dust grains within galaxies seen in the first billion years of cosmic time

 arXiv:

Interstellar dust captures a significant fraction of elements heavier than helium in the solid state and is an indispensable component both in theory and observations of galaxy evolution. However, the astrophysical origin of various types of dust grains remains an open question, especially in the early Universe. Here we report direct evidence for the presence of carbonaceous grain from the detection of the broad UV absorption feature around 2175 Å in deep near-infrared spectra of galaxies up to the first billion years of cosmic time, at a redshift (𝑧) of ∼ 7. 

Our results suggest a more rapid production scenario, likely in supernova (SN) ejecta.

The previous scenario considered was giant branch/AGB stellar evolution. There are some issues with the supernova scenario, particularly in that supernova shock waves tend to vaporize surrounding dust grains produced in previous phases.

Figure 1. Spectrum taken by JWST/NIRSpec of JADES-GS-z6-0 at redshift z = 6.71. a...

I like this figure a lot--it shows the UV bump around 2000 Å extremely clearly.

The Force Explosion Condition is Consistent with Spherically Symmetric CCSN Explosions

 arXiv: 

One of the major challenges in Core-collapse Supernova (CCSN) theory is to predict which stars explode and which collapse to black holes...The collapsing core bounces at the nuclear densities and launches the shock wave. If the blast wave overwhelms the collapsing star, the star explodes as a core-collapse supernova (CCSN) explosion (Li et al. 2011; Horiuchi et al. 2011).

we show that the FEC [(force explosion condition)] is consistent with the explosion condition when using actual neutrino transport in GR1D simulations...since most 1D simulations do not explode, to facilitate this test, we enhance the heating efficiency within the gain region.

With small, yet practical modifications, we show that the FEC predicts the explosion conditions in spherically symmetric CCSN simulations that use neutrino transport.