Abstract:
We report the analysis of simultaneous multiwavelength data of the high-energy-peaked blazar
RGB J0710
+
591 from the Large Area X-ray Proportional Counters, Soft X-ray focusing
Telescope, and Ultraviolet Imaging Telescope (UVIT) instruments onboard
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
β
p
∼
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/
Nu
STAR data where the parameters were
β
p
∼
2.2 or
p
2
∼
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,
γ
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/
Nu
STAR observation, making this as the first well-constrained determination of the
photon energy corresponding to
γ
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.
