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Fermi/LAT detection of a new possible high-z gamma-ray quasar PKS 1915-458

ATEL # 2666; K. V. Sokolovsky (MPIfR/ASC Lebedev), F. K. Schinzel (MPIfR), S. E. Healey (Stanford/KIPAC), D. Donato (NASA/GSFC), E. Wallace (U. Washington), M. Boeck (Remeis Obs./ECAP); on behalf of the Fermi Large Area Telescope Collaboration
on 9 Jun 2010; 8:46 UT
Password Certification: Frank Schinzel (

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Quasars, Transients
Referred to by ATEL #: 2679, 2728

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a new source positionally consistent with PKS 1915-458 (19:19:16.66 -45:43:38.4, J2000) a flat spectrum radio quasar at z=2.47 (Jackson et al. 2002, A&A, 386, 97). The redshift is unusually high for a flaring LAT blazar, however not unprecedented (ATEL #2217).

Preliminary analysis indicates that the source on June 04, 2010 was in a high state with a gamma-ray flux (E>100MeV) of (0.36 +/-0.15) x10^-6 photons cm^-2 s^-1 (errors are statistical only) and a detection significance of slightly greater than 5 sigma. The likelihood analysis for the time interval June 01 00:00 - 05 12:00 (UT) leads to the best fit gamma-ray position: 19:18:17.28 -45:46:17.0 (J2000, with the 68% error circle radius of 13'), ~3.5 deg away from the nearest known gamma-ray source (Abdo et al. 2010, ApJS, 188, 405). The gamma-ray flux for the 5-day time interval is (0.23 +/-0.07) x10^-6 photons cm^-2 s^-1. The source was previously detected on a 5-day timescale at comparable flux levels during the first two weeks of May 2010, and with lower flux on monthly timescale in October 2008.

The redshift of PKS 1915-458 reported by Jackson et al. is taken from a private communication with N. Tasker, no details about the observation technique and reliability of the measurement are provided. We strongly encourage multi-wavelength observations, especially spectroscopy which could confirm the value of the source redshift. For this source the Fermi LAT contact person is F. K. Schinzel (

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.

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R. E. Rutledge , Editor
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