Wednesday, May 17, 2023

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:

Monday, May 8, 2023

Update to: Evidence of near-ambient superconductivity in a N-doped lutetium hydride

Science:

Given the questions, several scientists say Dias should make his data public. “I am unhappy that Dias is supposedly not cooperating with researchers who are questioning his data,” says Marvin Cohen, a theoretical physicist at UC Berkeley. Schilling is blunt: “I told Dias to give [Hirsch] the raw data, for heaven’s sake.”

In his email [responding to Hirsch's request for the raw data], Dias wrote, “Given that you have an active comment on our work, we consider such a request would not be reasonable.” Frustrated, Hirsch requested the data from Nature and the National Science Foundation (NSF), which funded the work. On 30 August, Nature appended an editor’s note to Dias’s paper saying: “The editors of Nature have been alerted to undeclared access restrictions relating to the data behind this paper. We are working with the authors to correct the data availability statement.” NSF and the University of Rochester both tell Science they cannot comment on possible investigative matters.

A theoretical analysis on the theoretical feasibility of superconductivity in lutetium hydride was published. The results add an interesting dimension to the controversy.

AIP:

Recently, room-temperature superconductivity has been reported in a nitrogen-doped lutetium hydride at near-ambient pressure [Dasenbrock-Gammon et al., Nature 615, 244 (2023)]. 

Here, we systematically study the phase diagram of Lu–N–H at 1 GPa using first-principles calculations, and we do not find any thermodynamically stable ternary compounds.

Our theoretical results show that the Tc values of N-doped LuH3 estimated using the Allen–Dynes-modified McMillan equation are much lower than room temperature.

The conclusion seems to be that, based on existing theory, it is not possible to form a stable combination of lutetium, nitrogen, and hydrogen. 

Notably, all predicted potential ternary compounds lie above the convex hull at 1 GPa. Thus, no ternary Lu–N–H compounds can remain thermodynamically stable at this pressure, which is consistent with the main results of Xie et al.26

And even if it were, it seems it would superconduct at far lower than room temperature, in line with existing experiments. 

Our simulations show that the lowest T_c is 4 K for LuH3 without doping. In addition, T_c increases with increasing N-doping concentration; thus, doping N atoms into LuH3 will increase T_c. However, the highest T_c in this VCA calculation is 22 K, obtained with 1% N-doping at 30 GPa, which is much lower than room temperature.

It's worth noting that 30 GPa is about 300 kbar, which is 30 times higher than the pressures reported in Dias et al. (2023). Further investigation is needed, but it seems theoretically unlikely to produce a material like the doped LuNH3 at the reported temperatures and pressures. Certainly even less likely for it to superconduct at room temperatures. This is based on existing theory, so the possibility remains that Dias et al. have discovered an exciting new effect that will require more advanced models to explain.  


Previously on this blog:

Sunday, May 7, 2023

Friends of Pando release 360 degree photographic data

St. George:

Armed with a mission, researchers, volunteers and citizen scientists navigated a trembling giant’s rough terrain, toting high-tech camera equipment and collecting data. Recently, Friends of Pando released the first of many data sets from the survey, allowing individuals from across the globe to study and experience one of the world’s largest organisms — Pando — from the comfort of their living rooms.

The Pando photographic survey is a hugely impressive scientific and artistic accomplishment, cataloging vast swathes of the Pando organism with enough detail and precision to enable rigorous analyses through the exploitation of modern imaging methods. 

Despite its massive size, weighing an estimated 13 million pounds and consisting of over 40,000 trees, Pando is a single organism, according to the Forest Service. The tree, the largest known aspen clone, was germinated from a single seed. It regenerates via “suckering,” where it sends up new shoots, or saplings, from its root system. Pando means “I spread” in Latin.

The tree, first observed in 1976, is thousands of years old and boasts an estimated 47,000 branches, the release states. “Little is known about the workings of the tree,” and the survey will mark the first time the organism has been inventoried.

PRNewsWire:

Developed in collaboration with Fishlake National Forest and Snow College Richfield, the record offers immediate and long-term value for field and remote research efforts. Documenting Pando every 7m with high accuracy, Oditt says the plot map itself has already been used for field research planning. Long-term, the maps and image data sets can be replicated to monitor Pando for generations to come. For remote research, the system offers a flexible model that allows scientists to use the data sets as provided or, mix-and-match recorded locations to design areas of interest. This work, which explores the use of advanced imaging models and statistical techniques, can provide insights on topics such as disease, regeneration and ground cover.

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:

Mysterious Black Hole Twins May Fuel The Brightest Galaxies in Space

ApJ : We propose that AGN flux variability and changes in jet morphology can both be of deterministic nature, i.e., having a geometric/kine...