Research Note

Fermi/LAT detection of extraordinary variability in the gamma-ray emission of the blazar PKS 1510-089

¹ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy
e-mail: luigi.foschini@brera.inaf.it
² INAF – Osservatorio Astrofisico di Torino, via P. Giuria 1, 10125 Torino, Italy
³ INFN – Sezione di Torino, via P. Giuria 1, 10125 Torino, Italy

Received: 10 April 2013
Accepted: 14 June 2013

Abstract

We have reanalyzed the giant outburst of the blazar PKS 1510−089 (z = 0.36) that occurred on 2011 October−November. The γ-ray flux in the 0.1−100 GeV energy range exceeded the value of 10^-5 ph cm^-2 s^-1 for several days. The peak flux was reached on 2011 October 19, with a value of ~4.4 × 10^-5 ph cm^-2 s^-1, which in turn corresponds to a luminosity of ~2 × 10⁴⁹ erg s^-1. A very short timescale variability was measured. Particularly on 2011 October 18, the flux-doubling time was as short as ~20 min. This is the shortest variability ever detected in the MeV-GeV energy band. We compared our analysis with two other outbursts observed in 2009 March and 2012 February−March, when the blazar was also detected by H.E.S.S. and MAGIC to infer information about the emission at hundreds of GeV.