TY - GEN
T1 - An Exceptional Radio Flare in Markarian 421
AU - Richards, Joseph L.
AU - Hovatta, Talvikki
AU - Lister, Matthew L.
AU - Readhead, Anthony C. S.
AU - Max-Moerbeck, Walter
AU - Savolainen, Tuomas
AU - Angelakis, Emmanouil
AU - Fuhrmann, Lars
AU - Aller, Margo F.
AU - Aller, Hugh D.
AU - Myserlis, Ioannis
AU - Karamanavis, Vassilis
PY - 2013
Y1 - 2013
N2 - In September 2012, the high-synchrotron-peaked (HSP) blazar Markarian
421 underwent a rapid wideband radio flare, reaching nearly twice the
brightest level observed in the centimeter band in over three decades of
monitoring. In response to this event we carried out a five epoch
centimeter- to millimeter-band multifrequency Very Long Baseline Array
(VLBA) campaign to investigate the aftermath of this emission event.
Rapid radio variations are unprecedented in this object and are
surprising in an HSP BL Lac object. In this flare, the 15 GHz flux
density increased with an exponential doubling time of about 9 days,
then faded to its prior level at a similar rate. This is comparable with
the fastest large-amplitude centimeter-band radio variability observed
in any blazar. Similar flux density increases were detected up to
millimeter bands. This radio flare followed about two months after a
similarly unprecedented GeV gamma-ray flare (reaching a daily E > 100
MeV flux of (1.2 ± 0.7) × 10-6 ph
cm-2 s-1) reported by the Fermi Large Area
Telescope (LAT) collaboration, with a simultaneous tentative TeV
detection by ARGO-YBJ. A cross-correlation analysis of long-term 15 GHz
and LAT gamma-ray light curves finds a statistically significant
correlation with the radio lagging ~40 days behind, suggesting that the
gamma-ray emission originates upstream of the radio emission.
Preliminary results from our VLBA observations show brightening in the
unresolved core region and no evidence for apparent superluminal motions
or substantial flux variations downstream.
AB - In September 2012, the high-synchrotron-peaked (HSP) blazar Markarian
421 underwent a rapid wideband radio flare, reaching nearly twice the
brightest level observed in the centimeter band in over three decades of
monitoring. In response to this event we carried out a five epoch
centimeter- to millimeter-band multifrequency Very Long Baseline Array
(VLBA) campaign to investigate the aftermath of this emission event.
Rapid radio variations are unprecedented in this object and are
surprising in an HSP BL Lac object. In this flare, the 15 GHz flux
density increased with an exponential doubling time of about 9 days,
then faded to its prior level at a similar rate. This is comparable with
the fastest large-amplitude centimeter-band radio variability observed
in any blazar. Similar flux density increases were detected up to
millimeter bands. This radio flare followed about two months after a
similarly unprecedented GeV gamma-ray flare (reaching a daily E > 100
MeV flux of (1.2 ± 0.7) × 10-6 ph
cm-2 s-1) reported by the Fermi Large Area
Telescope (LAT) collaboration, with a simultaneous tentative TeV
detection by ARGO-YBJ. A cross-correlation analysis of long-term 15 GHz
and LAT gamma-ray light curves finds a statistically significant
correlation with the radio lagging ~40 days behind, suggesting that the
gamma-ray emission originates upstream of the radio emission.
Preliminary results from our VLBA observations show brightening in the
unresolved core region and no evidence for apparent superluminal motions
or substantial flux variations downstream.
U2 - 10.1051/epjconf/20136104010
DO - 10.1051/epjconf/20136104010
M3 - Conference article in proceedings
VL - 61
BT - EPJ Web of Conferences
PB - EDP Sciences
ER -