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Optical follow-up of 4C+21.35

ATEL # 2708; Roberto Nesci (University La Sapienza, Roma, Italy), Franco Montagni (Greve in Chianti Observatory, Italy)
on 30 Jun 2010; 17:48 UT
Password Certification: Roberto Nesci (

Subjects: Optical, AGN, Gamma-Ray Bursts, Quasars

The blazar 4C+21.35 (PKS 1222+21) was reported by AGILE (ATel #2686) and FermiGST (ATel #2687) to have a Gamma-ray flare; SWIFT X-ray and UV-optical follow-up was reported in Atel #2698; polarimetry in ATel #2693.

We observed the source with the 31cm telescope of Greve in Chianti equipped with a back-illuminated SITe SIA502A CCD chip and Johnson-Cousins BVR filters. The comparison stars by Raiteri et al. (1998) were used for photometry.

   +----------+-----------+-----------+------------   date               B        V            R
2010-06-21 15.01+-0.05 14.82+-0.02 14.75+-0.02 2010-06-24 15.45+-0.05 14.89+-0.02 14.83+-0.02 +----------+-----------+-----------+------------
Quoted errors are internal; systematic differences between our zero points and other Observatories reports should be checked. The relevant point is that the source fading is faster in the B band (0.15 mag/day), compared to the R band (0.03 mag/day). Given the source redshift z=0.432, the B band is a good tracer of the Big Blue Bump (BBB), while the R band is dominated by the synchrotron emission. Strong emission lines are present in the spectrum (see e.g. SDSS), and spectroscopic follow-up in the near future would be very useful for echo mapping the effects of the Gamma-ray flare.


Raiteri C.M. et al. 1998, A&AS 130, 495.

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