Swift simultaneous observations of the VHE flare of S3 1227+25

ATel #7526; Luigi Pacciani (INAF-IAPS)
on 18 May 2015; 12:58 UT
Credential Certification: Luigi Pacciani (luigi.pacciani@iaps.inaf.it)

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We detected a gamma-ray flare from the low-synchrotron-peaked BL Lac (z=0.135) S3 1227+25, triggering on FERMI-LAT data at E > 10 GeV with TS ~35, from 2015-05-06 to 2015-05-15, following the prescription of Pacciani et al. 2014, ApJ, 790, 45. The gamma-ray flux was (41+/-4)E-8 ph cm^-2 s^-1, photon index 1.94+/-0.07, TS ~ 450 (E>0.1 GeV). The FERMI-LAT revealed gamma-ray emission up to 14 GeV.

We triggered a ToO campaign with Swift, started on 2015-05-16.

VERITAS detected the source (ATEL#7516) simultaneous to the first Swift observation.

The preliminary Swift-UVOT photometry on 2015-05-16 08:06 is:

V = 14.63 +/- 0.03

B = 14.94 +/- 0.02

U = 14.06 +/- 0.02

UVW1 = 14.00 +/- 0.02

UVM2 = 13.93 +/- 0.01

UVW2 = 14.07 +/- 0.01.

Magnitudes are in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and have not been corrected for Galactic extinction.

The simultaneous Swift-XRT observation gives a counting rate of 0.43 cps, flux (0.3-10 KeV): (1.5+-0.1) E-11erg/cm2/s, photon index 2.30+-0.07.

These Optical and X-ray observations show the source almost at its brightest state (see also ATEL#7523, ATEL#7365).

The Swift observation on 2015-05-17 show the source ~20% fainter.

We thank the Swift team and Swift Observatory Duty Scientist for rapidly scheduling our observations.