Broadband Spectral Analysis of 1ES2344+514: A Multi-epoch study

TL;DR

This study presents a multi-epoch, broadband analysis of the BL Lac object 1ES 2344+514 using quasi-simultaneous data from 2017 to 2022 across optical/UV, X-ray, and gamma-ray bands. The authors perform joint spectral fits (e.g., SXT-LAXPC, Swift-XRT–NuSTAR) to constrain the synchrotron peak energy $E_p$ and model the SEDs with a one-zone SSC framework, occasionally invoking a two-zone scheme to account for UV excess and host-galaxy contributions. Key findings include a clear synchrotron peak shift into the HSP regime, a harder-when-brighter trend in X-rays, and a softer-when-brighter trend in gamma-rays, with jet energetics indicating a particle-dominated flow ($U_B/U_e \ll 1$) and total jet powers around $P_{jet} \sim 10^{43}$–$10^{44}$ erg s$^{-1}$. The results reinforce leptonic emission scenarios for EHSP BL Lacs and highlight the importance of simultaneous multiwavelength campaigns to disentangle jet physics and potential hadronic contributions.

Abstract

We present the results of the multi-epoch broadband spectral study of 1ES 2344+514 and study the evolution of physical parameters. We used nearly simultaneous data obtained from 2017 June 6 to 2022 August 6 (MJD 57910 -- 59797) in optical, UV, X-ray and $γ$-ray wavebands from various instruments including Swift-UVOT, Swift-XRT, NuSTAR, AstroSat (SXT and LAXPC), Fermi-LAT, and TeV flux from MAGIC. During 2017 July, 1ES 2344+514 appeared to be in the highest flaring state compared to other periods. We used the 0.5 -- 7.0 keV and 3.0 -- 20.0 keV data, respectively, from SXT and LAXPC of AstroSat and also 0.3 -- 8.0 keV and 3.0 -- 79.0 keV data, respectively, from Swift-XRT and NuSTAR. A joint fit between SXT and LAXPC, and between Swift-XRT and NuSTAR has been done for constraining the synchrotron peak. A clear shift in the synchrotron peak has been observed, which included 1ES 2344+514 in the HSP BL Lac family. A `harder-when-brighter' trend is observed in X-rays, and the opposite trend, i.e., `softer-when-brighter', is seen in the $γ$-rays. The multi-epoch broad-band spectral energy distributions (SEDs) of this source were built and studied to get an idea of the radiation processes. The SEDs were fitted using a steady-state leptonic one-zone synchrotron+SSC model, and the fitted parameters of the emission region are consistent with those of other TeV BL Lacs. In this study, we found a weak correlation tendency between bolometric luminosity and magnetic field (B), as well as between bolometric luminosity and the break Lorentz factor ($γ_{break}$).

Figures (14)

• Figure 1: Joint fit for SXT (black) and LAXPC20 (red) spectra for 2017 July 9 observations with the log-parabola model along with the line of sight absorption. Data over energy ranges 0.5-7.0 keV and 3.0-20.0 keV are used for SXT and LAXPC20, respectively. The top panel shows data and model fit, whereas the bottom panel shows the residuals.
• Figure 2: Joint fit for Swift-XRT (black) and NuSTAR FPMA/FPMB (red/green) spectra for 2020 July 22 observations with log-parabola model along with the line of sight absorption. Data over energy ranges 0.3-8 keV and 3-79 keV are used for Swift-XRT and NuSTAR, respectively. The top panel shows data and model fit, whereas the bottom panel shows the residuals.
• Figure 3: The scatter plot of estimated flux data at the synchrotron peak ($S_{\rm p}$) vs peak energy ($E_{\rm p}$) for SXT-LAXPC and XRT-NuSTAR fitted with weighted linear regression and bootstrap linear regression. The grey lines are bootstrapped regression lines, the green dashed line is the mean of them, and the blue line is the weighted linear regression line.
• Figure 4: The scatter plot illustrates the relationship between the power-law photon spectral index and X-ray photon flux. Flux values for Swift-XRT and SXT are calculated over the 0.5–7 keV energy range, while LAXPC and NuSTAR cover the 3–20 keV range. These plots are analyzed using weighted linear regression and bootstrap linear regression. Gray lines represent bootstrapped regression lines for both plots. For the SXT-XRT data (bottom), the red dashed line indicates the mean of bootstrapped regression lines, and the green line shows the weighted linear regression. For the LAXPC-FPMA data (top), the blue dashed line represents the mean of bootstrapped regression lines, and the purple line depicts the weighted linear regression.
• Figure 5: The $\gamma$-ray SED, extracted from the Fermi-LAT data observed on 2017 July 9 and fitted with a log parabola model using the binned likelihood fit method with a bin size of 30 days.