The blazar PKS 0446+11: a possible correlation of optical flares with neutrino and gamma-rays

ATel #17008; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 31 Jan 2025; 19:07 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

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The blazar PKS 0446+11 inspired a significant interest of astrophysicists in 2024 January after its prompt identification as "the blazar inside the IceCube-240205A error region", being the known gamma-ray source located at 0.4 degree from best-fit position of this event (ATel #16398). The agreement between epochs of neutrino event and gamma-rays flare was not too reliable, so the authors supposed that the blazar was in the descending phase of the flare reported a few months before on 2023 November.

First multi-wavelength studies of PKS 0446+11 did not reveal any evident signatures on optical flux density variations (ATel #16402, #16534). Optical spectroscopy of blazar performed with the GTC+OSIRIS allowed to confirm its redshift (z = 2.153) and detect strong variation of CIV 1550 emission line between earlier spectra and last result (Paiano et al., 2024, ApJ).

Our monitoring campaign with 1-meter and 0.5-meter SAO RAS reflectors allowed us to detect 2 epochs of optical brightening in 2024: January 10 (MJD 60319.8) and last night of the year --- December 31 (MJD 60676.8) with R-magnitudes 17.60 and 17.52 respectively. The behavior of optical flux density around these dates was some different: the plateau in 2024 January spanned over 45 days and was completed by 1-magnitude break within 2 days: from R = 17.88 down to R = 18.81 on the last days of February. This result is in a good agreement with data from ATels # 16402 and #16534. The New Year night flare spanned 70 days to reach R = 17.52 from R = 19.87 and to return to this level back. If take into account the monthly interval between our estimates, this flare coincides well with epoch of elevated gamma-ray emission state on January 6, as it was noted in ATel #16970. More frequent flux density data will refine this conclusion.

The monitoring of PKS 0446+11 is in progress; most of the data were taken under good weather conditions (seeing (FWHM) < 2 arcsec with normal transparency) and have typical accuracy about 0.05 mags. We strongly encourage further multi-wavelength studies.