PKS 1502+106: A NEW AND DISTANT GAMMA-RAY BLAZAR IN OUTBURST DISCOVERED BY THEFERMILARGE AREA TELESCOPE

Abstract

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope discovered a rapid (∼5 days duration), high-energy (E > 100 MeV) gamma-ray outburst from a source identified with the blazar PKS 1502+106 (OR 103, S3 1502+10, z = 1.839) starting on 2008 August 5 (∼23 UTC, MJD 54683.95), and followed by bright and variable flux over the next few months. Results on the gamma-ray localization and identification, as well as spectral and temporal behavior during the first months of the Fermi all-sky survey, are reported here in conjunction with a multiwaveband characterization as a result of one of the first Fermi multifrequency campaigns. The campaign included a Swift ToO (followed up by a 16 day observation on August 7-22, MJD 54685-54700), VLBA (within the MOJAVE program), Owens Valley Radio Observatory (OVRO) 40 m, Effelsberg-100 m, Metsähovi-14 m, RATAN-600, and Kanata-Hiroshima radio/optical observations. Results from the analysis of archival observations by INTEGRAL, XMM-Newton, and Spitzer space telescopes are reported for a more complete picture of this new gamma-ray blazar. PKS 1502+106 is a sub-GeV peaked, powerful flat spectrum radio quasar (luminosity at E > 100 MeV, L γ , is about 1.1 × 10 49 erg s −1 , and black hole mass likely close to 10 9 M ), exhibiting marked gamma-ray bolometric dominance, in particular during the asymmetric outburst (L γ /L opt ∼ 100, and 5 day averaged flux F E>100 MeV = 2.91 ± 1.4 × 10 −6 ph cm −2 s −1 ), which was characterized by a factor greater than 3 of flux increase in less than 12 hr. The outburst was observed simultaneously from optical to X-ray bands (F 0.3−10 keV = 2.18 +0.15 −0.12 × 10 −12 erg cm −2 s −1 , and hard photon index ∼1.5, similar to past values) with a flux increase of less than 1 order of magnitude with respect to past observations, and was likely controlled by Comptonization of external-jet photons produced in the broad-line region (BLR) in the gamma-ray band. No evidence of a possible blue bump signature was observed in the optical-UV continuum spectrum, while some hints for a possible 4 day time lag with respect to the gamma-ray flare were found. Nonetheless, the properties of PKS 1502+106 and the strict optical/UV, X-, and gamma-ray cross-correlations suggest the contribution of the synchrotron self-Compton (SSC), in-jet, process should dominate from radio to X-rays. This mechanism may also be responsible for the consistent gamma-ray variability observed by the LAT on longer timescales, after the ignition of activity at these energies provided by the BLR-dissipated outburst. Modulations and subsequent minor, rapid flare events were detected, with a general fluctuation mode between pink-noise and a random-walk. The averaged gamma-ray spectrum showed a deviation from a simple power law, and can be described by a log-parabola curved model peaking around 0.4-0.5 GeV. The maximum energy of photons detected from the 812 ABDO ET AL.Vol. 710 source in the first four months of LAT observations was 15.8 GeV, with no significant consequences ...

Search for the shortest variability at gamma rays in flat-spectrum radio quasars

“…The best examples measured by CGRO/EGRET during nineties are PKS 1622−29 (∼4 h, Mattox et al 1997) and3C 279 (∼8 h, Wherle et al 1998). The early results from Fermi satellite obtained in the latest years have confirmed such time scales: PKS 1454−354 ), PKS 1502+106 (Abdo et al 2010a), PKS B1510−089 ), 3C 454.3 (Foschini et al 2010Tavecchio et al 2010;Ackermann et al 2010) and 3C 273 (Abdo et al 2010b).…”

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

“…Since the 90 • jump is seen only during the first epoch, this option is not applicable too. It is more likely that 90 • flip is resulted from opacity change as a precursor of radio outburst (see, e.g., Abdo et al 2010;Orienti et al 2011). Since the core of S4 1030+61 is only partially opaque (see Fig.…”

PKS 1502+106: A high-redshiftFermiblazar at extreme angular resolution

“…In 2008 August, the Fermi-GST (Gamma-ray Space Telescope, hereafter Fermi, Ritz 2007;Atwood et al 2009) detected the blazar PKS 1502+106, which showed a rapid and strong γ-ray outburst followed by high and variable flux over the next months (Ciprini 2008;Abdo et al 2010). This activity at high energies triggered an intensive multi-wavelength campaign, covering the radio, optical, UV, and X-ray bands.…”