Fermi LAT detection of increased gamma-ray activity of two blazars PKS 0420-01 and BL Lacertae
ATel #2402; K. V. Sokolovsky (MPIfR/ASC Lebedev), F. K. Schinzel (MPIfR) and E. Wallace (Uni. Washington); on behalf of the Fermi Large Area Telescope Collaboration
on 25 Jan 2010; 16:22 UT
Credential Certification: Frank Schinzel (email@example.com)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Quasar
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope
has observed an increasing gamma-ray flux from sources positionally consistent
with PKS 0420-01 (VLBI position: R.A.=04:23:15.80073 Dec.=-01:20:33.0655,
J2000; z=0.914, Wills & Lynds 1978, ApJS, 36, 317) and BL Lacertae (VLBI
position: R.A.=22:02:43.29137 Dec.=+42:16:39.9799, J2000; z=0.0686
Vermeulen et al., 1995, ApJ, 452L, 5). The VLBI positions are from Beasley et al.
2002, ApJS, 141, 13.
Preliminary analysis indicates that PKS 0420-01 on January 21, 2010, was in
a high state with a gamma-ray flux (E>100MeV) of (0.8 +/-0.2)*10^-6 photons/cm^2/s,
which represents an increase of a factor of six with respect to the average
source flux level in the first eleven months of Fermi observations (see http://fermi.gsfc.nasa.gov/ssc/data/access/lat/1yr_catalog/ ).
The current gamma-ray flare has been preceded by a gradual flux rise
lasting for ~40 days. A recent, rapid optical and radio brightening
of this source was reported by Bach et al. (2010) in ATEL #2395.
Our preliminary analysis indicates that BL Lacertae was in a
high gamma-ray state on January 21, 2010, with a flux (E>100MeV) of
(0.8 +/-0.2)*10^-6 photons/cm^2/s, five times above the average level.
Most of the photons were detected in a six-hour interval centered on
2010 January 21.375 (UT). The estimated source flux during this six-hour
interval was (1.1 +/-0.5)*10^-6 photons/cm^2/s. BL Lacertae was also
marginally detected recently on a six-hour timescale around 2010 January
10.875 (UT) with a flux of (0.8 +/-0.5)*10^-6 photons/cm^2/s.
All uncertainties mentioned in this telegram are statistical only.
Because Fermi operates in an all-sky scanning mode, regular gamma-ray
monitoring of these sources will continue. We encourage multi-wavelength
observations. For PKS 0420-01 the Fermi LAT contact person is
Frank Schinzel (schinzel at mpifr-bonn.mpg.de), for BL Lacertae the
LAT contact person is Davide Donato (donato at milkyway.gsfc.nasa.gov).
The Fermi LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.