J/A+A/708/A383 IceCube neutrinos-CAZ blazar light curves assoc. (Kouch+, 2026)
Association of the IceCube neutrinos with CAZ blazar light curves.
Kouch P.M., Hovatta T., Lindfors E., Liodakis I., Koljonen K.I.I., Paggi A.
<Astron. Astrophys. 708, A383 (2026)>
=2026A&A...708A.383K 2026A&A...708A.383K (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Neutrino ; Radio sources
Keywords: astroparticle physics - neutrinos - galaxies: active -
galaxies: jets - galaxies: statistics
Abstract:
The IceCube Neutrino Observatory has detected several hundred
high-energy neutrinos from cosmic sources. Despite numerous studies
searching for their origin, it is still not known which sources emit
them. A few likely individual associations exist with active galactic
nuclei (AGN), mostly with blazars which are AGN with jets pointed
toward Earth. Nonetheless, on a population level, blazar-neutrino
correlation strengths are rather weak. This could mean that blazars as
a population do not emit high-energy neutrinos, or that the detection
power of the tests is insufficient due to the strong atmospheric
neutrino background. By assuming an increase in high-energy neutrino
emission during major blazar flares, in our previous studies we
leveraged the arrival time of the neutrinos to boost the detection
power. In this paper we utilize the same principle while substantially
increasing the number of blazars. We search for the spatio-temporal
correlation of 356 IceCube high-energy neutrinos with major optical
flares of 3225 radio- and 3814 gamma-ray-selected blazars. We find
that, despite the increase in data size, the number of likely
spatio-temporal associations remains low and the overall correlation
strengths weak. Two individual associations drive our strongest and
the only >2σ post-trial spatio-temporal correlation, occurring
with the BL Lac objects of the radio-selected blazar sample. We
estimate that ≲8% of the detected cosmic neutrinos were emitted by
blazars during major optical flares. As a complementary analysis, we
compare the synchrotron peak frequency, redshift, Doppler factor,
X-ray brightness, and optical variability of spatially
neutrino-associated blazars to those of the general blazar population.
We find that spatially neutrino-associated blazars of the tested
samples have higher than average Doppler factor and X-ray brightness.
Description:
We provide two tables: "neutrino.dat" and "assoc.dat".
The table "neutrino.dat" contains the full list of the updated
IceCat1+ neutrinos (the original IceCat1+ was provided in Kouch et
al., 2024A&A...690A.111K 2024A&A...690A.111K, Cat. J/A+a/690/A111).
The table "assoc.dat" contains the full list of spatial and
spatio-temporal blazar-neutrino associations of this study. We note
that Table 3 from the paper is a subset of "assoc.dat" in its
entirety.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
neutrino.dat 118 356 Updated IceCat1+: high-energy neutrino events used
assoc.dat 144 1278 All blazar-neutrino spatial, incl.
spatio-temporal, associations
--------------------------------------------------------------------------------
See also:
J/A+A/690/A111 : IceCube neutrinos-blazars association (Kouch+, 2024)
J/A+A/708/A382 : 7918 blazar-selected AGN CAZ catalog and LC (Kouch+, 2026)
Byte-by-byte Description of file: neutrino.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- IC IC ID of the high-energy neutrino event (1)
11- 21 F11.5 d MJD Modified Julian Date (MJD) of the arrival time
23- 26 I4 TeV E Energy estimate
28- 32 F5.3 --- Sness Signalness
34- 39 F6.2 deg RAdeg Right Ascension (J2000)
41- 46 F6.2 deg E_RAdeg Error on Right Ascension (upper value)
48- 53 F6.2 deg e_RAdeg Error on Right Ascension (lower value)
55- 60 F6.2 deg DEdeg Declination (J2000)
62- 65 F4.2 deg E_DEdeg Error on Declination (upper value)
67- 71 F5.2 deg e_DEdeg Error on Declination (lower value)
73- 82 F10.5 deg+2 OmMin Omega in the published error region scenario (2)
84- 93 F10.5 deg+2 OmMax Omega in the enlarged error region scenario (2)
95-101 F7.5 --- wMin Weight in the published error region scenario (2)
103-109 F7.5 --- wMax Weight in the enlarged error region scenario (2)
111-118 A8 --- Ref IceCube paper reference for the event (1)
--------------------------------------------------------------------------------
Note (1): The high-energy neutrino events (356) are taken from two references.
340 are from Ice-Cat1 (v4.0; Abbasi et al., 2023ApJS..269...25A 2023ApJS..269...25A,
[10.3847/1538-4365/acfa95]). 16 are from off-line events analyzed in
(Abbasi et al. 2022ApJ...928...50A 2022ApJ...928...50A, [10.3847/1538-4357/ac4d29]).
The IC ID of the latter events ends in an 'X'.
Note (2): The published and enlarged error region scenarios are described in
Section 3 of the paper (also, see, Sect. 3.3 of Kouch et al.,
2024A&A...690A.111K 2024A&A...690A.111K).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: assoc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- IC IC name of the spatially associated
high-energy neutrino event (1)
11- 17 F7.1 d MJD Modified Julian Date (MJD) of the arrival time
of the neutrino event
19- 25 F7.5 --- wMax Weight of the neutrino event in the enlarged
error region scenario (2)
27- 40 A14 --- Blz Name of the spatially neutrino-associated
source in CAZ (CAZJHHMM+DDMM) (3)
42- 48 F7.3 deg RAdeg CAZ Right Ascension (J2000)
50- 56 F7.3 deg DEdeg CAZ Declination (J2000)
58 A1 --- RFCc [Y/N] Source is in the RFC complete catalog
(Yes or No) (4)
60- 69 A10 --- RFC Source name in RFC (JHHMM+DDMM)
71 A1 --- 4LAC [Y/N] Source is in the 4LAC catalog
(Yes or No)
73- 88 A16 --- n4LAC Source name in 4LAC (4FGLJHHMM.m+DDMM)
90 A1 --- CAZt Source type in CAZ (5)
92- 97 F6.3 [Hz] logCAZsNu ?=- Synchrotron peak frequency of the
source in CAZ
99-102 A4 --- CAZsNuC Synchrotron peak frequency class of the
source in CAZ (6)
104-111 F8.5 --- CAZz ?=- Redshift estimate of the source in CAZ
113-118 F6.3 --- CAZDv ?=- Radio variability Doppler factor of
the source in CAZ
120-130 E11.6 mW/m2 FXrayS ?=- Median X-ray flux density of the source
in CAZ
132-134 A3 --- CAZVr [YN -] Source is classified as optically
variable in CAZ (Yes, No, or -) (7)
136-138 A3 --- TempS Temporal status of the spatial association (8)
140-141 A2 --- BB95 [Y* -] Temporal association via BB95
(Yes*, Yes, or -) (9)
143-144 A2 --- BBHOP [Y* -] Temporal association via prominent
BBHOP (Yes*, Yes, or -) (10)
--------------------------------------------------------------------------------
Note (1): The high-energy neutrino events (356) are described in full in the
above table "neutrino.dat".
Note (2): All analysis in this work use the enlarged error region scenario
(see, Sect. 3 of the paper and Sect. 3.3 of Kouch et al., 2024A&A...690A.111K 2024A&A...690A.111K).
Note (3): The CAZ blazars are described fully in the companion paper
Kouchet al., 2026A&A...708A.382K 2026A&A...708A.382K.
Note (4): The Radio Fundamental Catalog (RFC) is found in
https://astrogeo.org/sol/rfc/. See the companion paper Kouch+,
2026, for more details.
Note (5): Source type in CAZ as follows:
Q = Flat Spectrum Radio Quasars or candidates
B = BL Lac objects or candidates
G = host-galaxy dominated BL Lac objects
U = blazars of unknown type or blazar candidates
A = non-blazar AGN or AGN candidates
More details are found in the companion paper
Kouch et al., 2026A&A...708A.382K 2026A&A...708A.382K.
Note (6): Synchrotron peak frequency class as follows:
LSP = low-synchrotron-peaked source
ISP = intermediate-synchrotron-peaked source
HSP = high-synchrotron-peaked source
EHSP = an extremely high-synchrotron-peaked source
These are determined based on CAZsNu as described in the companion paper
Kouch+, 2026.
Note (7): Some CAZ light curves were too short or had too few data points for
their variability to be evaluated. These have "-" as their CAZVr. More details
are given in the companion paper Kouchet al., 2026A&A...708A.382K 2026A&A...708A.382K.
Note (8): Temporal status as follows:
flr = neutrino arrived when the spatially associated source was flaring, thus
denotes a spatio-temporal association (this entry is required for the
association to appear in Table 3 of the paper).
All other entries denote the lack of a spatio-temporal association:
qui = flux density of the source was in quiescence when the neutrino arrived
nVr = source is optically non-variable (i.e., no flaring periods are
determined)
gap = neutrino arrived within a data gap in the source light curve
out = neutrino arrived outside of the start-to-end (historical) time window
of the light curve
- = means the light curve is not used in the analysis (i.e., it is either
too short or has too few data points).
Note (9): Code as follows:
Y = neutrino arrived during a BB95 period
Y* = neutrino arrived during a BB95 period which constitutes the peak of a
prominent BBHOP flare
- = neutrino did not arrive during a BB95 period
Note (10): Code as follows:
Y = neutrino arrived during a prominent BBHOP flare
Y* = neutrino arrived during a BB95 period which constitutes the peak of a
prominent BBHOP flare
- = neutrino did not arrive during a prominent BBHOP flare
--------------------------------------------------------------------------------
Acknowledgements:
Pouya Kouch, pouya.kouch(at)utu.fi
References:
Kouch et al., 2024A&A...690A.111K 2024A&A...690A.111K, Cat. J/A+A/690/A111
Kouch et al., 2026A&A...708A.382K 2026A&A...708A.382K, Cat. J/A+A/708/A382
(End) Patricia Vannier [CDS] 19-Feb-2026