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arXiv · 1802.01105

FERMI transient J1544-0649: a flaring radio-weak BL Lac

G. Bruni·F. Panessa·G. Ghisellini·V. Chavushyan·H. A. Peña-Herazo·L. Hernández-García·A. Bazzano·P. Ubertini·A. Kraus
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Abstract

On May 15th, 2017, the \emph{FERMI}/LAT gamma-ray telescope observed a transient source not present in any previous high-energy catalogue: J1544-0649. It was visible for two consecutive weeks, with a flux peak on May 21st. Subsequently observed by a \emph{Swift}/XRT follow-up starting on May 26, the X-ray counterpart position was coincident with the optical transient ASASSN-17gs = AT2017egv, detected on May 25, with a potential host galaxy at $z$=0.171. We conducted a 4-months follow-up in radio (Effelsberg-100m) and optical (San Pedro M\'artir, 2.1m) bands, in order to build the overall Spectral Energy Distribution (SED) of this object. The radio data from 5 to 15 GHz confirmed the flat spectrum of the source, favoring a line of sight close to jet axis, not showing significant variability in the explored post-burst time-window. The Rx ratio, common indicator of radio loudness, gives a value at the border between the radio-loud and radio-quiet AGN populations. The Ca$_{\rm{II}}$ H\&K break value (0.29$\pm$0.05) is compatible with the range expected for the long-sought intermediate population between BL Lacs and FRI radio galaxies. An overall SED fitting from Radio to $\gamma$-ray band shows properties typical of a low-power BL Lac. As a whole, these results suggest that this transient could well be a new example of the recently discovered class of radio-weak BL Lac, showing for the first time a flare in the gamma/X-ray bands.

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G. Bruni, F. Panessa, G. Ghisellini, V. Chavushyan, H. A. Peña-Herazo, L. Hernández-García, A. Bazzano, P. Ubertini, A. Kraus. 2018-02-04. FERMI transient J1544-0649: a flaring radio-weak BL Lac. https://doi.org/10.3847/2041-8213%2Faaacfb

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