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Broad-band radio behaviour of flaring BL Lac (J2202+4216)

ATel #3380; E. Angelakis, L. Fuhrmann, I. Nestoras, R. Schmidt, J. A. Zensus, T. P. Krichbaum (F-GAMMA team, MPIfR, Bonn, Germany), H. Ungerechts, A. Sievers, D. Riquelme (IRAM, Granada, Spain)
on 26 May 2011; 13:53 UT
Credential Certification: Emmanouil Angelakis (angelaki@mpifr-bonn.mpg.de)

Subjects: Radio, Millimeter, Infra-Red, Optical, X-ray, Gamma Ray, AGN, Black Hole, Blazar, Variables

Referred to by ATel #: 3459

Responding to the ATels #3368, #3371, #3375 and #3377 reporting the recent activity of BL Lac (J2202+4216, RA= 22:02:43, DEC=+42:16:39 in J2000) at different high energy bands, we here report its behaviour in the cm-to-mm radio bands as observed by the F-GAMMA program.

Recent activity:
Observations performed with the Effelsberg 100-m and the IRAM 30-m telescope over the last months on May 1, 7, 20 and 25, show a persistent increase in the flux at all frequencies observed. For instance, at 4.85 GHz the flux has increased from 3.96 Jy (May 1, 2011) to 4.20 (May 25, 2011) and at 32 GHz from 4.06 Jy (May 1, 2011) to 4.82 Jy (May 25, 2011). At 86 GHz, its flux density has recently been measured to be 4.5 Jy (May 7, 2011).

Long term behaviour:
BL Lac has been observed since January 2007 showing remarkable variability at all wavelengths between 2.6 and 229 GHz. Interestingly, since a relatively quiet period around 2008.5, the source shows a long term increase in the flux density, underlying a series of short term broad-band events, as one can see in its light curves at low, medium and high radio frequencies. Specifically, there are six prominent events appearing at: 2009.5, 2009.8, 2010.1, 2010.5, 2010.8 and 2011.2 and practically at all wavelengths. It is remarkable that (a) the peaks seem to be appearing at nearly constant intervals and (b) with no apparent time lag between different frequencies. Summarily, the recent activity at high energy bands occurs during an active phase at radio bands.

Evolution of its spectrum:
The same effect can be demonstrated through the temporal evolution of its spectrum. Despite being generally flat, its spectrum varies between being mildly steep and being mildly inverted due to the clearly evident emergence of weak yet noticeable events appearing at high frequencies and fast expanding to lower frequencies.

The source will be continuously monitored and possible future activity will be reported through the current platform.

F-GAMMA program:
F-GAMMA (Fermi-GST AGN Multi-frequency Monitoring Alliance) program is the coordinated effort of several observatories and research teams to probe AGN physics through the multi-frequency monitoring approach. The core program relies on monthly observations with the Effelsberg 100-m radio telescope (operating at 8 frequencies between 2.6 and 43 GHz), the IRAM 30-m telescope (observing at 86 and 142 GHz) and additional measurements with the APEX 12-m telescope (operating at 345 GHz). The core sample consists of roughly 60 Fermi_GST/LAT monitored blazars. The data are taken simultaneously within 40 minutes for Effelsberg and 10 minutes for the IRAM telescope while the cross-station coherency is of order of 10 days. Data products are publicly accessible here. For more details, visit:

F-GAMMA program home page