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Swift observations of the new gamma-ray quasar PKS 1915-458

ATEL # 2679; K. V. Sokolovsky (MPIfR/ASC Lebedev), F. D'Ammando (INAF - IASF Palermo), F. K. Schinzel (MPIfR) on behalf of the Fermi Large Area Telescope Collaboration.
on 16 Jun 2010; 11:04 UT
Password Certification: Frank Schinzel (

Subjects: Optical, X-ray, Request for Observations, AGN, Quasars

Following the Fermi-LAT detection of a new gamma-ray source positionally consistent with the possible high-z (z=2.47, Jackson et al. 2002, A&A, 386, 97) quasar PKS 1915-458 (ATel #2666), Swift Target of Opportunity observations were performed on June 13 and 14, 2010, with a total exposure time of 8.3 ksec. A single X-ray source was detected within the Swift/XRT field of view (covering ~50% of the LAT error circle). The X-ray source position coincides with PKS 1915-458 and its spectrum is described by an absorbed power law (N_H fixed to 6.14 x10^20 cm^-2; Kalberla et al. 2005, A&A, 440, 775) with an unabsorbed flux (0.3-10 keV) of (1.72 +/-0.26) x10^-12 erg cm^-2 s^-1 and a photon index Gamma = 1.48 +/-0.18.

The 1WGA catalog, generated from ROSAT/PSPC pointed observations (White et al. 2000), lists a flux for the source (0.24-2.0 keV) more than a factor of 3 lower than the value in the same energy range derived from the Swift/XRT measurement. The increased X-ray flux supports association of the gamma-ray source with PKS 1915-458. Swift/UVOT has detected PKS 1915-458 at a magnitude of U = 18.50 +/-0.02. Unfortunately, for comparison no archival observations were found in this band.

Further multiwavelength observations are strongly encouraged, especially spectroscopy which could confirm the value of the redshift of PKS 1915-486. For this source the Fermi LAT contact person is is F. K. Schinzel (

We thank the Swift Team for their rapid scheduling of these observations.

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