The Astronomer's Telegram
Telegram Index | Search
To The Parent Site

[ Previous | Next ]

Fermi LAT detection of a GeV flare from OX 169 (S3 2141+17)

ATEL # 2393; K. V. Sokolovsky (MPIfR/ASC Lebedev), F. K. Schinzel (MPIfR); on behalf of the Fermi Large Area Telescope Collaboration, and Y. Y. Kovalev (ASC Lebedev/MPIfR)
on 20 Jan 2010; 21:11 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Frank Schinzel (

Subjects: Gamma Ray, >GeV, AGN, Quasars

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed an increased gamma-ray flux from a source positionally coincident with OX 169 (also known as S3 2141+17, CGRaBS J2143+1743; VLBI position R.A.=21:43:35.54457 Dec.=+17:43:48.7875, J2000, Beasley et al. 2002, ApJS, 141, 13) - a relatively bright V~15.7 (Ramirez et al. 2009, AJ, 138, 991) flat spectrum radio quasar at z=0.211 (Marziani et al. 1996, ApJS, 104, 37; Ho et al. 2009, ApJS, 184, 398). The source is listed as having a Seyfert 1.0 type optical spectrum in the catalog of Veron-Cetty & Veron (2006, A&A, 455, 773).

Our preliminary analysis of the Fermi/LAT data indicates that on January 18, 2010, the source was in a high state, with a gamma-ray flux (E>100MeV) of (1.4 0.4)*10^-6 photons/cm^2/s (statistical uncertainty only), about seven times above its average flux during the first 11 months of Fermi observations.

OX 169 has a peculiar radio spectrum with a peak around 6.3 GHz (flux ~1 Jy) visible in simultaneous 1-22 GHz RATAN-600 observations between 2003 and 2008 (the program is described in Kovalev et al. 1999, A&AS, 139, 545). At frequencies below 1 GHz the spectrum is dominated by a power-law as indicated by flux density measurements listed in the CATS database ( Despite its complex spectral shape the source can be classified as a flat spectrum radio quasar (see e.g. Drinkwater et al. 1997, MNRAS, 284, 85, for typical classification criteria). VLBA observations at 15 GHz in the course of the MOJAVE survey (Lister et al., 2009, AJ, 137, 3718) reveal a core-dominated parsec-scale structure with a short (~4 mas/14 pc) jet extended in a north-northeast direction.

Since Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Multi-wavelength observations are encouraged. The source is currently only 45 degrees from the Sun (and approaching). The Fermi LAT contact person for this source is Kirill Sokolovsky (ksokolov [at]

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.

MOJAVE page of the source

Radio spectrum
(red points represent simultaneous RATAN-600 observations, green points are the measurements collected by the CATS database)

[ Telegram Index ]

R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates