Unravelling the unusually curved X-ray spectrum of RGB J0710+591 using AstroSat observations

Abstract

We report the analysis of simultaneous multi-wavelength data of the high energy peaked blazar RGB J0710+591 from the LAXPC, SXT and UVIT instruments on-board AstroSat. The wide band X-ray spectrum (0.35 -- 30 keV) is modelled as synchrotron emission from a non-thermal distribution of high energy electrons. The spectrum is unusually curved, with a curvature parameter ${\beta }_p\sim 6.4$ for a log parabola particle distribution, or a high energy spectral index $p_2>4.5$ for a broken power-law distribution. The spectrum shows more curvature than an earlier quasi-simultaneous analysis of Swift-XRT/NuSTAR data where the parameters were ${\beta }_p\sim 2.2$ or $p_2\sim 4$. It has long been known that a power-law electron distribution can be produced from a region where particles are accelerated under Fermi process and the radiative losses in acceleration site decide the maximum attainable Lorentz factor, ${\gamma }_{max}$. Consequently, this quantity decides the energy at which the spectrum curves steeply. We show that such a distribution provides a more natural explanation for the AstroSat data as well as the earlier XRT/NuSTAR observation, making this as the first well constrained determination of the photon energy corresponding to ${\gamma }_{max}$. This in turn provides an estimate of the acceleration time-scale as a function of magnetic field and Doppler factor. The UVIT observations are consistent with earlier optical/UV measurements and reconfirm that they plausibly correspond to a different radiative component than the one responsible for the X-ray emission.

9 pages, 3 figures. Accepted for publication in MNRAS

References in corpus (7)

• IACHEC Cross-Calibration of Chandra, NuSTAR, Swift, Suzaku, and XMM-Newton with 3C 273 and PKS 2155-304
• Discovery of VHE gamma-rays from the distant BL Lac 1ES 0347-121
• Large Area X-ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its performance in the orbit
• AstroSat/LAXPC observation of Cygnus X-1 in the hard state
• Models for the Spectral Energy Distributions and Variability of Blazars
• AstroSat - a multi-wavelength astronomy satellite
• A Hot Companion to a Blue Straggler in NGC188 as Revealed by the Ultra-violet Imaging Telescope (UVIT) on ASTROSAT

Cited by in corpus (1)

• Correlations between X-ray spectral parameters of Mkn 421 using long-term Swift-XRT data