The Highest Historical X-ray Brightness State in HBL Source 1ES 1218+304
ATel #12365; Vandad Fallah Ramazani (Tuorla Observatory, University of Turku), Giacomo Bonneli (Universita degli Studi di Siena), Matteo Cerruti (Institut de Ciencies del Cosmos - Universitat de Barcelona)
on 7 Jan 2019; 18:53 UT
Credential Certification: Vandad Fallah Ramazani (vafara@utu.fi)
Subjects: X-ray, AGN, Blazar
1ES 1218+304, a TeV-detected HBL object, located at redshift z=0.182 is showing flaring activity in very high energy (VHE, E > 100 GeV) gamma-rays and R-band optical. An unprecedented activity from the blazar 1ES 1218+304 at VHE gamma rays was reported by the MAGIC collaboration (ATel #12354) and later confirmed by the VERITAS collaboration (ATel #12360). The data from KVA telescope also show a record flux (2.35+/-0.05 mJy) in R-band optical (Tuorla Blazar Monitoring).
Since 2017-01-01, the Neil Gehrels Swift observatory (Swift) has pointed to the source 20 times in photon counting mode. The multi-epoch (20) event lists for the period from 2017 January 1 to 2019 January 6 with a total exposure time of ?6 h were downloaded from the publicly available SWIFTXRLOG (Swift-XRT Instrument Log). These observations have an average integration time of 1.1 ks each. They were processed using the analysis procedure described by Evans P. A., et al. (2009, MNRAS, 397, 1177) and the configuration described by Fallah Ramazani et al. (2017, A&A, 608A, 68F), assuming fixed equivalent Galactic hydrogen column density nH = 1.94e20 cm^-2 reported by Kalberla et al. (2005, A&A, 440, 775). The hard index indicates that the peak of the synchrotron component is located beyond the Swift energy band.
Our analysis reveals that the X-ray Flux of the source is also in a historical flaring state with the highest flux in the range of 2-to-10 keV reaching to (1.83+/-0.14)e-10 [erg cm^-2 s^-1] on the 2019-01-06T01:31:32 which is a factor of ~5 times higher than the average flux in our analysis period. Moreover, a harder-when-brighter behavior is clear in the analyzed data with the hardest spectral index (Gamma= 1.60 +/- 0.06) observed on the night of highest flux (2019-01-06T01:31:32). The spectrum can be well described by power-law with chi-squared/dof = 34.96/35.
The Swift ToO observations will continue until 2019/01/14 with every-other-day schedule. Multi-wavelength observations, especially in hard X-ray bands (>10keV), are encouraged. The contact persons for this analysis is V. Fallah Ramazani (vafara@utu.fi).
Acknowledgment: We want to thank Swift PIs (C. Gronwall and M. H. Siegel) during the holiday season for they fruitful collaboration.
