Optical spectrum and photometry of PKS 0446+11 located inside the IceCube-240105A error region with GRANDMA
ATel #16534; A. Coleiro (APC, France), T. Pradier (Unistra/IPHC, France), M. Masek (FZU), S. Karpov (FZU), M. Prouza (FZU), C. Adami (Pytheas/LAM, France), J. Schmitt, (Pytheas/OHP, France), S. Antier (OCA), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), D. Turpin (CEA-Saclay/Irfu), M. Coughlin (UMN), C. Andrade (UMN), P-A Duverne (APC), N. Guessoum (AUS), D. Dornic (CPPM), M. Lamoureux (UCLouvain)
on 15 Mar 2024; 17:30 UT
Credential Certification: Alexis Coleiro (alexis.coleiro@u-paris.fr)
Subjects: Optical, Neutrinos, AGN, Blazar
We report optical observations of the flat-spectrum radio quasar PKS 0446+11 located within the 90% error region of the neutrino event IceCube-240105A (GCN #35485 and #35498).
We obtained optical spectra of PKS 0446+11 between 2024-01-31 and 2024-02-03 using the MISTRAL spectrograph on the 1.93-m telescope of the Observatoire de Haute-Provence (OHP).
The spectra cover the wavelength range 4,200 - 8,000 Angstrom (blue arm) and 6,000 - 10,000 Angstrom (red arm) with a resolution R~700 and a total exposure time of 180 min and 270 min in the blue and red arm respectively.
With a preliminary data reduction, the spectrum shows no clear emission or absorption line. After preliminary flux calibration and correction from Galactic extinction, the optical spectrum can be fitted by a single power law with a spectral index of -1.3 +/- 0.3, compatible with the value provided in Shaw et al. 2012, ApJ, 748, 49. The overall spectrum seems compatible with the classification of PKS 0446+11 as a low-synchrotron peaked blazar (as reported e.g. by Linford et al., ApJ, 757:25, 2012).
On another hand, optical B, V, R, z photometry was performed between 2024-01-22 and 2024-02-22, using FRAM CTA-N for the GRANDMA collaboration. We measured the following uncorrected AB magnitudes during the first observation in each band :
B = 18.63 +/- 0.72 mag on MJD = 60334.93
V = 18.55 +/- 0.26 mag on MJD = 60332.92
R = 17.58 +/-0.16 mag on MJD = 60331.88
z = 16.15 +/-0.15 mag on MJD = 60334.93
The lightcurve with GRANDMA measurements, the extinction corrected fluxes vs frequency, together with the derived epoch-dependent spectral indices are available here.
Preliminary data analysis shows small magnitude variation through the observations, consistent with the observations reported in ATel #16402 and #16407. However, there is no clear evidence for varying spectral index between the observations.
We acknowledge the excellent support from Observatoire de Haute-Provence, in particular Stephane Favard and Yoann Degot Longhi for the MISTRAL observations.
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518).
