MAGIC detects an unprecedented high VHE gamma-ray emission from the blazar PG 1553+113

ATel #4069; Juan Cortina (IFAE Barcelona) for the MAGIC collaboration
on 26 Apr 2012; 14:22 UT
Credential Certification: Juan Cortina (cortina@ifae.es)

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The source PG 1553+113 is a well-known TeV emitter, likely located at redshift 0.4-0.5 (Danforth et al. 2010). Its state has been monitored by MAGIC since February 2005. In March 2012, a high emission state at VHE, X-ray, optical, and infrared wavelengths was reported (ATel #3977).

During the night of April 19-20th (MJD 56037), the source was observed by MAGIC for a total of 1.1 hour of good quality data. A strong signal corresponding to a statistical significance above 15 standard deviations in the VHE range was detected. The level obtained with the preliminary analysis reaches the Crab Nebula flux level at ~100 GeV. It is the highest state of PG 1553+113 ever detected at these energies. The mean flux at 100 GeV measured by MAGIC between 2005 and 2009 was ~50% of the Crab Nebula flux (J. Aleksic et al., 2012). Follow up observations carried out in the following nights confirm that the source persists in this high state.

Simultaneous optical observations performed in the R band by the KVA telescope also show increased emission. The maximum flux reached is 13.14 ± 0.01 mJy (MJD 56040). The source is brighter than during the high state reported one month ago (12.2 ± 0.2 mJy; http://users.utu.fi/kani/1m/PG_1553+113_jy.html ). Optical polarimetric observations were taken with the Liverpool telescope as part of a joint observational program with MAGIC.

Preliminary photometric observations in the J, H and K bands with the REM telescope show an increasing activity of the source during the last week. In addition, automatic analysis procedures applied to Swift/XRT data collected on April 17th and 21st indicate that the source is also brightening in X rays. The preliminary Swift/XRT lightcurve is publicly available at: http://www.swift.psu.edu/monitoring/data/PG1553+113/lightcurve.png. Dedicated analyses are in progress. Given the high activity detected, we strongly encourage multi-wavelength observations of the source.

For this MWL campaign the MAGIC contact persons are: E. Prandini (prandini@pd.infn.it), J. Cortina (cortina@ifae.es); for KVA observations: E. Lindfors (elilin@utu.fi); for REM observations: S. Covino (stefano.covino@brera.inaf.it). We thank the Swift Monitoring Program for the online preliminary analysis results.