Long-term multi-wavelength variability and extreme spectral properties of the TeV-detected blazar 1ES 0033+595

Abstract

Context. The multi-wavelength (MWL) properties of some TeV-detected blazars are still poorly understood. By studying the MWL properties of the BL Lacertae source 1ES 0033+595, we make further progress in our understanding of the instable physical processes responsible for particle acceleration to ultra-relativitic energies and the observed emission properties. Aims. This paper presents the results of a detailed X-ray timing and spectral analysis of the source 1ES 0033+595, allowing us to draw conclusions about the physical mechanisms responsible for particle acceleration and the generation of X-ray emission. We also examined the long-term MWL behaviour of the source and interband cross-correlations. Methods. Our study focused on the observations performed with the X-Ray Telescope on board the Neil Gehrels Swift Observatory (Swift-XRT) in the period 2005-2022. The MWL data sets were obtained with several space and ground-based instruments. We analysed the MWL flaring behaviour during the entire period, as well as in particular subperiods selected on the basis of the X-ray flaring activity of the target; constructed histograms characterising the distributions of the different spectral parameters and MWL fluxes; and checked cross-correlations between these parameters and/or MWL fluxes. The obtained results are compared with the predictions of the various theoretical studies and simulations presented by the different authors to date. Results. The source showed extreme spectral properties with dominance of high spectral curvature, frequent occurrence of very and extremely hard photon indices, and the presence of a synchrotron spectral energy distribution (SED) peak in the hard X-ray range (sometimes at energies beyond 10 keV). These properties reveal the importance of first-order Fermi acceleration with very low initial particle energy distribution, along with the co-existence of stochastic acceleration and hadronic processes. The source was characterised by very uneven and erratic flaring activity in diverse epochs: the period of strong flares (2013)(2014)(2015)(2016) was preceded by a moderate variability and followed by a gradual long-term decrease in MWL flaring activity. We detected a number of instances of intraday 0.3-10 keV variability, which were sometimes observed within a few hundred seconds and explained by the interaction between the relativistic shock front and jet inhomogeneities with strong magnetic fields. The X-ray and γ-ray fluxes showed a lognormal distribution, which hints at the imprint of accretion disc instabilities on the blazar jet.

Long-term X-Ray Outburst in the TeV-detected Blazar Mrk 501 in 2021–2022: Further Clues for the Emission and Unstable Processes

“…´, where F 1 and F 2 are the initial and final flux values, respectively, and Δt is the corresponding time interval. However, the source did not show such instances on intraday timescales, in contrast to other bright HBLs (Mrk 421, 1ES 1959+650, and 1ES 0033 +595; see, e.g., Kapanadze et al 2016Kapanadze et al , 2018Kapanadze & Gurchumelia 2022). In the case of the 120 s binned count rates, the fastest observed flux-doubling instance occurred within 3.97 days (MJD 59,261.50), which corresponds to τ d = 1.28 days.…”

“…However, the distributions of the photon index in these periods were significantly softer than that shown by 1ES 0033 +595 during the XRT observations performed in 2005-2022: it was the hardest source among HBLs with more than half of the curved spectra showing very hard and extremely hard values (Kapanadze & Gurchumelia 2022). Nevertheless, this source showed α ∼ 1 for 13 spectra, which has not been reported for any other HBL to date.…”

“…sync n = E p /h Hz (where h is Planck's constant), which is the widest range reported for BL Lac object sources to date. Among other HBLs, the most extreme position of the synchrotron SED peak has been reported for 1ES 0033+595 (E p = 23.19 ± 1.98; Kapanadze & Gurchumelia 2022).…”

Gamma-ray Emission and Variability Processes in High-Energy-Peaked BL Lacertae Objects

“…The corresponding SEDs (whenever the VHE spectral points were available) were modeled by using a two-zone SSC scenario: two co-moving blobs (with δ ∼10) characterized by the narrow power-law and relativistic Maxwellian EEDs, established by means of the first and second-order Fermi mechanisms, respectively. We also found a number of the instances of very hard LAT-band photon index for Mrk 501, as well as for another HBL source 1ES 0033+595 ( [69,187]; see also Figure 4). Note that these objects showed the features of the efficient stochastic acceleration, as well as very fast X-ray variability explained by presence of small scale jet inhomogeneities with strong turbulent magnetic fields (see [68,187]).…”

“…We also found a number of the instances of very hard LAT-band photon index for Mrk 501, as well as for another HBL source 1ES 0033+595 ( [69,187]; see also Figure 4). Note that these objects showed the features of the efficient stochastic acceleration, as well as very fast X-ray variability explained by presence of small scale jet inhomogeneities with strong turbulent magnetic fields (see [68,187]). The 2-D MHD modellings of a mildly relativistic shock propagating through a jet inhomogeneous medium showed that the post-shock jet regions may become highly turbulent if there are pre-shock density inhomogeneities.…”