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Strong Millimeter-Band Flaring of 3C454.3 Underway

ATEL # 2150; Mark A. Gurwell (Harvard-Smithsonian Center for Astrophysics, MA, USA)
on 6 Aug 2009; 14:17 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Mark A. Gurwell (

Subjects: Millimeter, Sub-Millimeter, Request for Observations, AGN, Quasars
Referred to by ATEL #: 2155

The Submillimeter Array (SMA) performs ongoing flux density monitoring of quasars that are typically bright in the mm/submm bands, in order to optimally choose quasars for use as interferometric calibration sources. Through this monitoring effort, we report that the quasar 3C454.3 (J2253+161) is currently flaring strongly at millimeter wavelengths.

After reaching 1.3 mm band flux densities of 27 +/- 1.8 Jy on October 3 2008, the quasar showed a substantial long term drop in intensity, reaching a measured nadir of 3 +/- 0.2 Jy on April 3, 2009 (though observations in 2009 are particularly sparse prior to May, and it is possible that the source dipped below 3 Jy during this time). We note that this drop in millimeter flux density is strongly correlated with a drop in the gamma ray intensity as measured by the Fermi Large Area Telescope (LAT) monitoring program (see ).

Since April, 3C454.3 has been steadily increasing in 1.3 mm band flux density, nearly doubling by July 10 (to 5.4 +/- 0.3 Jy), equivalent to a growth rate of about 4.3% per week. However, monitoring observations over the past 25 days show a dramatic increase in the rate of brightening. On August 3, the flux density was measured to be 10.3 +/- 0.6 Jy, and on August 4 the flux density had grown to 11.3 +/- 1.1 Jy, equivalent to a growth rate of 21-23% per week; this is over 5 times the rate seen in the preceding three month period. Figures showing SMA measurements of 3C454.3 in 2009, including the current flare, as well as observations over the past 5 years (including the major flares of 2005, 2007, and 2008) can be accessed at the link provided at the bottom of this ATel.

Past flares (e.g. 2005, 2007, 2008) have typically proceeded for several weeks, followed by a variably-long period of relatively steady flux density, finally succumbing with a rapid decrease to a background state near 3 Jy. This suggests that 3C454.3 may continue to brighten in the millimeter (and submillimeter) bands in the weeks to come. Fermi LAT monitoring, as provided through the website above, may also have detected an increase in gamma ray intensity when looking at the weekly averaged light curve (see ) that could be related to this millimeter flare. It is our opinion that increased monitoring of the source at all wavelengths is warranted as this flare progresses.

[The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics, and is funded by the Smithsonian Institution (USA) and the Academia Sinica (Taiwan).]

Submillimeter Array Observations of a 3C454.3 Millimeter-Band Flare

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