IceCube-240105A and PKS 0446+11

The IceCube neutrino observatory detected a new high-energy event. It will most likely be given the official name “IceCube-240105A”. Its parameters are pretty standard: an energy of around 110 TeV and a probability to be of astrophysical origin (and not atmospheric background) of ~30%. Events like this occur roughly 2.6 times per year due to statistical fluctuations.

What is interesting about this neutrino event is that it comes from a direction that is compatible with the blazar PKS 0446+11. This is a BL Lac object at a redshift of z=2.153 and that has just undergone its highest ever GeV flaring episode. Its gamma-ray flux (as recorded by the Fermi-LAT, named 4FGL J0449.1+1121) increased almost 8-fold over the last two to three months.

=> is this activity period linked to an increased neutrino flux and thus the event detected by IceCube?

All details about the IceCube event (incl. the cone search around its reconstructed direction, which shows the possible spatial link to PKS 0446+11) can be found as usual on Astro-COLIBRI

The Fermi-LAT lightcurve of PKS 0446+11 (cf. also the direct link from the Astro-COLIBRI interface): Fermi LAT Light Curve Repository

A note of caution: the reconstruction of the neutrino event will most likely be updated by the iceCube collaboration using more sophisticated algorithms over the next hours. Let’s see if the spatial link with the blazar is still valid after that.

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In the optical, the blazar is pretty faint: in archival ZTF data it is recorded with magnituded between 19 and 21: SNAD ZTF viewer

It is therefore not surprising that no detection is seen by ASAS-SN over the last year (incl. the recent GeV gamma-ray flaring episode). The upper limits are much lower than the archival ZTF points: ASAS-SN Sky Patrol | Light Curve


The neutrino event has now been confirmed by IceCube. The updated reconstructed direction of the event has an even lower uncertainty and is still compatible with PKS 0446+11.

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For completeness: the surprisingly small reconstruction uncertainties mentioned before did not take into account the systematic uncertainties related to the properties of the ice in the IceCube detector. The updated uncertainties are significantly larger, thus weakening the spatial correlation with PKS 0445+11. :man_shrugging:

Date: 2024-01-05
Time: 12:27:42.57 UT
RA:    72.69 (+1.92, -1.85 deg 90% PSF containment) J2000
Dec: +11.42 (+0.50, -0.44 deg 90% PSF containment) J2000

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And another interesting MWL: Swift observations of PKS 0446+11 show that the source is (still?) in an elevated flux state compared to old archival data from 2015:

Also, some more quantitative discussion of the GeV flaring episode discussed above was given in:

Radio observations also show PKS 0446+11 in an elevated state:

to be continued…

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