Photometry of the blazars AO 0235+164 and 3C 345

ATel #16320; Boyko M. Mihov (Institute of Astronomy and NAO, Bulgarian Academy of Sciences), Lyuba Slavcheva-Mihova (Institute of Astronomy and NAO, Bulgarian Academy of Sciences)
on 6 Nov 2023; 13:25 UT
Credential Certification: Boyko Mihov (bmihov@astro.bas.bg)

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We observed the blazars AO 0235+164 and 3C 345 following the recent reports about their flaring activity.

Our observations of the blazar AO 0235+164 in October 2023 were obtained using the same observational setup and were processed following the same procedure as described previously (ATel #16253). Here we report our BVRI-band measurements:

UT	JD	band	mag	err	N
Oct 23.0121	2460240.512113	B	20.120	0.090	6
Oct 23.0299	2460240.529884	V	19.063	0.076	5
Oct 23.0168	2460240.516765	R	18.240	0.053	6
Oct 23.0072	2460240.507164	I	17.282	0.037	7

The reported JDs are a median over the N frames got during the night in the corresponding band; the frame JD is calculated at the mid-exposure.

The blazar 3C 345 was recently reported in a flaring state (ATel #16274, ATel #16305, ATel #16306, ATel #16309). We obtained R-band observations during the night of 24/25 October 2023 using the 50/70 cm Schmidt telescope at the Rozhen National Astronomical Observatory, Bulgaria. The telescope was equipped with a FLI PL16803 model CCD camera (a pixel size of 1.079 arcsec) and a set of Johnson-Cousins BVRI filters. Multiple frames of the blazar field with integrations of 120/240 sec were obtained followed by the corresponding dark current frames; we also acquired a set of twilight flat fields.

The instrumental magnitudes of the objects of interest were derived using 4 arcsec radius aperture photometry. The calibration was performed using the reference stars 4, 10, 12, and 19 from the standard sequence of González-Pérez et al. (2001, AJ, 122, 2055); the star 15 was used as a control star. Below is our R-band photometry of 3C 345:

UT	JD	band	mag	err	N
Oct 24.7594	2460242.259433	R	16.565	0.045	4

Our new observations of AO 0235+164 detect a brightness decrease in R-band of about 2.2 mag compared to our previous measurements, that is the blazar seems to go back to its typical brightness level (ATel #16190). Regarding 3C 345, our photometry does not show significant difference compared to the last reported measurement (ATel #16306). Further multi-wavelength observations of the blazars are needed in order to follow-up their brightness evolution in details.