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An increase in the millimeter and centimeter band flux density of Mrk421

ATel #5107; Talvikki Hovatta (Caltech), Mislav Balokovic (Caltech), Joseph L. Richards (Purdue), Walter Max-Moerbeck (NRAO), Anthony C. S. Readhead (Caltech)
on 5 Jun 2013; 18:45 UT
Credential Certification: Talvikki Hovatta (thovatta@caltech.edu)

Subjects: Radio, Millimeter, Blazar

We have observed an increase in the 15 GHz and 95 GHz flux density of Mrk421, a high-synchrotron-peaked (HSP) BL Lac object. In April the source underwent extreme flaring in X-rays (seen by NuSTAR, ATel #4974), gamma rays (Fermi-LAT and Swift, ATel #4977) and in the very high energy gamma-rays (MAGIC and VERITAS, ATel #4976). Since the major high-energy flaring, we have been monitoring the source on a daily basis at 15 GHz with the Owens Valley Radio Observatory (OVRO) 40m Telescope and 2-3 times a week with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 95 GHz.

Since mid-May we have detected a steady increase in the flux density at both bands. Our preliminary data reduction indicates that on 16 May 2013 the 95 GHz flux density was at the typical levels of (0.57 +/- 0.09) Jy, increasing to (0.71 +/- 0.11) Jy by 1 June 2013. We have several observations in between the dates confirming the increase. At 15 GHz the flux density has increased from (0.65 +/- 0.01) Jy on 12 May 2013 to (0.72 +/- 0.01) on 2 June 2013. The OVRO light curve is available on the program website (log in with username 'guest' and no password).

These flux density levels are still lower than the peak value observed during the previous 15 GHz flare of the source in September 2012 (ATel #4451). The flare in September also followed a major gamma-ray flare detected 2 months earlier by the Fermi-LAT telescope (ATel #4261). We will continue observing the source with the same cadence at OVRO and CARMA. Despite the source getting closer to the sun, we strongly encourage further multiwavelength observations of this source during the possible flare, especially in the radio wavelengths.

The OVRO 40m monitoring program is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. Support for CARMA construction was derived from the states of California, Illinois, and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology, and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities.