On the Spectral Changes of OJ 287 — I: Particle Spectrum during the Lowest X-ray state — extended at Optical-UV and Hard at X-rays. (arXiv:2305.16144v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kushwaha_P/0/1/0/all/0/1">Pankaj Kushwaha</a> (IISER-Mohali)
Blazar optical-UV emission is synchrotron with the observed spectral shape
directly related to the underlying particle distribution. Here, we report the
finding of an extended optical-UV spectrum with a power-law photon spectral
index of $rm 2.71pm0.03$, continuing to the X-ray band during the lowest
recorded X-ray flux state of the BL Lacetrae object OJ 287 by the Swift
facility. Accounting for the synchrotron contribution at X-rays, we found an
X-ray spectrum with a power-law photon spectral index of $rm 1.22 pm 0.22$,
the hardest reported X-ray spectrum for the source. The inferred X-ray spectrum
is consistent with the spectrum reported at hard energies from the study of the
Swift-BAT data. We further found that this X-ray spectrum naturally reproduces
most of the flat X-ray spectra when combined with the corresponding optical-UV
continuum during the low and intermediate flux states implying synchrotron as
the primary driver of most of the X-ray spectral changes in the LBL state of
the source. Combined with sharp-steepening/cutoff of the optical-UV spectrum
during bright phases, the extended-spectrum indicates a much larger emission
region which may be related to the large-scale jet emission. The optical-UV and
X-ray together trace the complete particle distribution required for the
observed broadband emission with low and high-energy power-law particle
spectral indices of $rm 1.44 pm 0.40$ and $rm 4.42 pm 0.06$ respectively.
Blazar optical-UV emission is synchrotron with the observed spectral shape
directly related to the underlying particle distribution. Here, we report the
finding of an extended optical-UV spectrum with a power-law photon spectral
index of $rm 2.71pm0.03$, continuing to the X-ray band during the lowest
recorded X-ray flux state of the BL Lacetrae object OJ 287 by the Swift
facility. Accounting for the synchrotron contribution at X-rays, we found an
X-ray spectrum with a power-law photon spectral index of $rm 1.22 pm 0.22$,
the hardest reported X-ray spectrum for the source. The inferred X-ray spectrum
is consistent with the spectrum reported at hard energies from the study of the
Swift-BAT data. We further found that this X-ray spectrum naturally reproduces
most of the flat X-ray spectra when combined with the corresponding optical-UV
continuum during the low and intermediate flux states implying synchrotron as
the primary driver of most of the X-ray spectral changes in the LBL state of
the source. Combined with sharp-steepening/cutoff of the optical-UV spectrum
during bright phases, the extended-spectrum indicates a much larger emission
region which may be related to the large-scale jet emission. The optical-UV and
X-ray together trace the complete particle distribution required for the
observed broadband emission with low and high-energy power-law particle
spectral indices of $rm 1.44 pm 0.40$ and $rm 4.42 pm 0.06$ respectively.
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