New IceCube results November 3 (neutrinos from galaxy NGC 1068)

[mfb]

TL;DR Summary

IceCube, the neutrino detector at the South Pole, will announce new results on November 3.

Announcement
Thursday 1 pm CDT, that's 18:00 UTC. This post was made 1:20 UTC. Conversion help.

It's possible they picked up some neutrinos associated with some event observed by other means, or maybe we get an update on extremely high energy neutrinos.

 

[ohwilleke]

What a nice birthday present for me!

 

[Orodruin]

If 42 birthdays taught me anything it is that you should not get too excited before you have opened it.

 

[ohwilleke]

If 42 birthdays taught me anything it is that you should not get too excited before you have opened it.

Yeah! 52 birthdays have taught me the same thing.

"We found evidence for neutrino emission from NGC1068. Results will be published in Science tomorrow." Comes from the vicinity of the supermassive black hole at the center of the galaxy (its AGN) in connection with its ultrafast outflows in the direction of the galaxy's axis. Predicted in 1982 (when I was twelve, which was about the time I started to get interested in astronomy and physics, I'm sure I saw the prediction at the time), seen now, forty years later.

Ho hum.

 

[Vanadium 50]

Hmmm...Cetus is in the south (but near the equator), but Ice Cube looks predominantly north.

 

[berkeman]

but Ice Cube looks predominantly north

Interesting, what is the typical absorption of neutrinos passing through the Earth? I'm off to Google to search...

 

[Vanadium 50]

It's small, But that's not the problem. The problem is that astrophysical neutrinos coming from the south (i.e. up) are swamped by neutrinos from ordinary air showers. Furthermore, there is a veto IceTop) on the top/south. So the instrument is much more sensitive to what's going on in the north.

 

[Orodruin]

Interesting, what is the typical absorption of neutrinos passing through the Earth? I'm off to Google to search...

This depends. At the typical energies the Earth is pretty transparent to neutrinos but for extremely high energies it is essentially opaque. For example, this is the reason the very high energy events of ANITA were surprising.

The problem is that astrophysical neutrinos coming from the south (i.e. up) are swamped by neutrinos from ordinary air showers.

The atmospheric neutrino flux comes from all directions, not only from above, and the flux is not that different from different directions. What is a problem are the charged particles (ie muons) from showers. This is also the reason a veto exists. You could not use a veto to get rid of atmospheric neutrinos. The point of the veto is to veto down-going showers and thus provide at least some sensitivity to the southern sky as well. You do not need a veto for up-going events as the Earth effectively blocks anything but neutrinos coming from the north.

 

[mfb]

IceCube neutrinos give us first glimpse into the inner depths of an active galaxy

80 TeV-scale neutrinos from NGC 1068, 47 million light years away and almost exactly at the horizon for IceCube (Wikipedia says −00° 00′ 47.84″).
Absorption in Earth can become relevant at an energy of a few TeV if the source is far north, above ~300 TeV IceCube has a blind region (plot).

 

[Vanadium 50]

I'd like to see the real paper, and hopefully it's not just a Letter. Auger claimed to have seen cosmic ray sources and it was a statistical fluctuation, made worse by unconventional statistics.

 

[ohwilleke]

I'd like to see the real paper, and hopefully it's not just a Letter. Auger claimed to have seen cosmic ray sources and it was a statistical fluctuation, made worse by unconventional statistics.

Given that it is published in Science today and was the topic of a press conference, I would be very surprised if it was just a Letter.

 

[vanhees71]

https://doi.org/10.1126/science.abg3395

 

[ohwilleke]

Related. https://arxiv.org/abs/2211.01737

 

[Vanadium 50]

The Science article is paywalled and the arXiv version seems not to be up yet. The "related" article is not very closely related - not a sibling or a cousin. More like a eight-times removed granduncle.

 

[ohwilleke]

The Science article is paywalled and the arXiv version seems not to be up yet. The "related" article is not very closely related - not a sibling or a cousin. More like a eight-times removed granduncle.

Paywalls for academic research are evil.

 

[mfb]

The Science article is paywalled and the arXiv version seems not to be up yet. The "related" article is not very closely related - not a sibling or a cousin. More like a eight-times removed granduncle.

The supplementary materials are not behind a paywall and explain the analysis method.

There are a few more interesting spots (Table S2).

 

[Vanadium 50]

The supplementary materials are not behind a paywall and explain the analysis method.

That's actually much more useful.

My thoughts:

(1) M77 is not in a very nice place. It's near IceCube's edge. Not much can be done about that, short of dragging kilometers of ice to the equator. (Centaurus A might have been an even better candidate, but it is unfortunately even further south)

(2) I am not the biggest fan of the trend of ever more complicated statistics. 'We see a signal, but only with a boosted decision tree" is much less convincing than "we see a signal and it doesn't matter which statistical method we use" (got into an argument with an editor about that once). Some of this is taste, I admit, but a lot of it is it becomes very difficult to quantify significance. They say 4.2σ, but I do not believe that the probability that this is an artifact is 1/40,000. It is the probability of rejecting a very complex null hypothesis - no source and we perfectly understand the correlations in our MVA.

Do I think the signal is real? Yes, I do. I trust Francis (we can decide whether that is scientific or not), the result is plausible, and though the statistics are annoying, I doubt they are grossly wrong. I would say that "Evidence" is the right word for the title - that's what CDF used for evidence for the top quark at 2.8σ, and that turned out to be real. That had a p value of 1/400 and this feels about as certain, based on the technique.

It's not like the (now gone) Auger result which smelled fishy from the get go.

 

[ohwilleke]

This is the preprint to the Science article (without final edits). https://arxiv.org/abs/2211.09972 The Science article version can be downloaded without a subscription from https://icecube.wisc.edu/science/publications/