Fermi and Swift observations of increased activity in blazar PMN J2141-6411

ATel #6547; Stefano Ciprini (ASDC and INAF OAR, Rome, Italy), Sara Cutini (ASDC and INAF OAR, Rome, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 6 Oct 2014; 19:05 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the blazar of unknown type PMN J2141-6411, with radio counterpart coordinates (J2000.0) R.A.: 325.44346 deg, Dec.: -64.18733 deg (Healey at al. 2007, ApJS, 171, 61).

Preliminary analysis indicates that PMN J2141-6411 on September 22, 2014, was in a high state with a daily averaged gamma-ray flux (E>100MeV) of (1.0+/-0.4)X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) and a gamma-ray photon energy index of (1.8+/-0.2). This source is not in any published LAT catalog.

Two follow-up target of opportunity Swift observations were made on September 24 and September 25 for 4.0ks and 2.9ks respectively. XRT data were taken in Photon Counting mode. The X-ray spectrum (0.3-10 keV) can be fit by an absorbed power law model with an HI column density set to the Galactic value of 3.1X10^20 cm^-2 (Kalberla et al. 2005, A&A, 440, 775). The unabsorbed fluxes were (1.1+/-0.4)X10^-12 erg cm^-2 s^-1 and (1.3+/-0.6)X10^-12 erg cm^-2 s^-1 respectively, and the photon indexes 1.6+/-0.3 and 1.3+/-0.6 respectively.

The nearby source PKS 2136-642 was also observed by Swift and not detected by XRT, thus strengthening the association of this LAT flare with PMN J2141-6411.

Simultaneous Swift/UVOT observations using all the filters are shown below.

The optical-UV spectral energy distribution of PMN J2141-6411 has brightened with respect to archival observations at optical bands (in particular the B-band magnitudes in DENIS and USNO catalog) and with respect to the NUV-band magnitude observed by GALEX.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact persons are Stefano Ciprini (stefano.ciprini@asdc.asi.it) and Sara Cutini (sara.cutini@asdc.asi.it).

We thank the Swift Team for making these observations possible, in particular C. J. Mountford as the Swift Observatory Duty Scientist.

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.