Studying the Extreme Behaviour of 1ES 2344+51.4

A. Arbet-Engels; M. Manganaro; M. Cerruti; V. Fallah Ramazani; D. Dorner; V. Sliusar; A. V. Filippenko; T. Hovatta; V. Larionov; J. A. Acosta-Pulido; C. M. Raiteri; W. Zheng

arXiv · 1908.10089

Studying the Extreme Behaviour of 1ES 2344+51.4

A. Arbet-Engels·M. Manganaro·M. Cerruti·V. Fallah Ramazani·D. Dorner·V. Sliusar·A. V. Filippenko·T. Hovatta·V. Larionov·J. A. Acosta-Pulido·C. M. Raiteri·W. Zheng

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Abstract

The BL Lac type object 1ES 2344+51.4 (redshift $z=0.044$) was one of the first sources to be included in the extreme high-peaked BL Lac (EHBL) family. EHBLs are characterised by a broadband spectral energy distribution (SED) featuring the synchrotron peak above $\sim 10^{17}$ Hz. From previous studies of 1ES 2344+51.4 in the very-high-energy (VHE, $>$100 GeV) gamma-ray range, its inverse Compton (IC) peak is expected around 200 GeV. 1ES 2344+51.4 was first detected in the VHE range by Whipple in 1995 during a very bright outburst showing around 60 % of the flux of the Crab Nebula above 350 GeV. In 1996, during another flare in the X-ray band, observations with Beppo-SAX revealed a large 0.1-10 keV flux variability on timescales of a few hours and an impressive frequency shift of the synchrotron peak to above $10^{18}$ Hz. Later on, this extreme behaviour of the source motivated several multiwavelength campaigns, during most of which the source appeared to be in a low state and showing no clear signs of "extremeness". In August 2016, FACT detected 1ES 2344+51.4 in a high state and triggered multiwavelength observations. The VHE observations show a flux level similar to the historical maximum of 1995. The combination of MAGIC, FACT, and Fermi-LAT spectra provides an unprecedented characterisation of the IC peak. It is the first time that simultaneous HE and VHE data are presented for this object during a flaring episode. We find an atypically hard spectrum in the VHE $\gamma$-rays as well as a hard X-ray spectrum, revealing a renewed extreme behaviour.

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A. Arbet-Engels, M. Manganaro, M. Cerruti, V. Fallah Ramazani, D. Dorner, V. Sliusar, A. V. Filippenko, T. Hovatta, V. Larionov, J. A. Acosta-Pulido, C. M. Raiteri, W. Zheng. 2019-08-27. Studying the Extreme Behaviour of 1ES 2344+51.4. https://arxiv.org/abs/1908.10089

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