J/A+A/708/A340 High synchrotron peak blazars X-ray spectral fits (Sibani+, 2026)
Constraining the synchrotron peak and estimating the VHE brightness of a sample
of extreme high synchrotron peak blazars.
Sibani F., Marchesi S., Bronzini E., Ajello M., Doro M., Marcotulli L.,
Prandini E., Vignali C.
<Astron. Astrophys. 708, A340 (2026)>
=2026A&A...708A.340S 2026A&A...708A.340S (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; X-ray sources
Keywords: BL Lacertae objects: general - galaxies: jets - gamma rays: galaxies -
X-rays: galaxies
Abstract:
We present the results of a multi-wavelength study of a
population of X-ray bright (log(F(0.2-12keV))>-12.5), non-Gamma-ray
detected high and extreme high synchrotron peak (HSP, EHSP;
log(Nu,peak,Hz)>16) BL Lacs to i) put stronger constraints on the
synchrotron peak location and shape and ii) model their expected
behaviour in the very high-energy band. First, we performed an X-ray
spectral analysis, using XMM-Newton, Chandra, Swift-XRT, and eROSITA
data, and fitting the spectra using both a power law and a log
parabola model. Out of 78 sources in the initial sample, 17 were best
described by a log parabola model, a result that supports a scenario
where the synchrotron peak falls in the X-ray band. Among these 17
sources, we further selected the 10 objects dominated by the jet
emission, with no significant contamination of the host galaxy. We
performed a gamma-ray analysis of Fermi-LAT data for these objects,
obtaining upper limits providing information on their flux in the
100MeV-300GeV energy range. We then modelled the broadband SED of
these objects with JetSeT using two models: one assuming a log
parabola for the electron distribution and the other one with a broken
power law electron distribution, using parameters consistent with
those describing the emission of the prototypical EHSP 1ES 0229+200.
We found the models to be generally consistent with the available
multi-wavelength detections and upper limits. Furthermore, they
confirmed that a subsample of sources could display relevant emission
in the TeV energy range, even potentially reaching the threshold for
detectability by the Cherenkov Telescope Array Observatory.
Description:
Catalogue of the 78 blazars in the 5th ROMABZCAT catalogue whose X-ray
spectra are analysed in this work. Sources with multiple X-ray spectra
are reported more than once.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 235 95 Catalog of 95 X-ray spectral fits of 78
high synchrotron peak blazars
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See also:
VII/274 : The Roma BZCAT - 5th edition (Massaro+, 2015)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- 5BZCAT 5BZCAT source ID, from Massaro et al.
(2015Ap&SS.357...75M 2015Ap&SS.357...75M, Cat. VII/274)
(ID_5BZCAT)
16- 17 I2 h RAh Right Ascension (J2000),
5BZCAT source (RA_5BZCAT)
19- 20 I2 min RAm Right Ascension (J2000),
5BZCAT source (RA_5BZCAT)
22- 26 F5.2 s RAs Right Ascension (J2000),
5BZCAT source (RA_5BZCAT)
28 A1 --- DE- Declination sign (J2000),
5BZCAT source (DEC_5BZCAT)
29- 30 I2 deg DEd Declination (J2000),
5BZCAT source (DEC_5BZCAT)
32- 33 I2 arcmin DEm Declination (J2000),
5BZCAT source (DEC_5BZCAT)
35- 39 F5.2 arcsec DEs Declination (J2000),
5BZCAT source (DEC_5BZCAT)
41- 47 F7.3 --- z ?=-99 Source redshift (Redshift)
49 I1 --- SpecID Spectrum ID for sources where
multiple X-ray spectra where
analysed; if a single observation
was available, the flag is 0
(Spec_ID)
51- 60 A10 --- Inst X-ray telescope used to obtain the
spectrum (Instrument)
62- 86 A25 --- refsrcID Source ID from the given X-ray source
catalog, when available
(ReferencesrcID)
88- 98 A11 --- ObsID Observation ID for sources with
multiple observations from the same
instrument (ObsID)
100-103 F4.1 [Hz] lognuPeak Logarithm of the blazar SED
synchrotron peak computed using the
Blazar Synchrotron Tool, BlaST.
From Marchesi et al.
(2025A&A...693A.142M 2025A&A...693A.142M,
Cat. J/A+A/693/A142) (nu_peak)
105-110 F6.2 --- Gamma ?=-99 Best-fit photon index from a
power law fit of the X-ray spectrum
(Gamma)
112-116 F5.2 --- e_Gamma [] 90% confidence level lower error
on the photon index (Gammaerrlo)
118-121 F4.2 --- E_Gamma 90% confidence level upper error on
the photon index (Gammaerrup)
123-127 F5.1 --- cstat-pl ?=-99 Best-fit Cstat value from the
power law fit (cstat_pl)
129-132 I4 --- dof-pl ?=-99 Degrees of freedom from the
power law fit (dof_pl)
134-139 F6.2 --- alpha ?=-99 Best-fit alpha parameter from
a logparabola fit of the X-ray
spectrum (alpha)
141-146 F6.2 --- e_alpha [] 90% confidence level lower error
on the alpha parameter
(alphaerrlo)
148-151 F4.2 --- E_alpha 90% confidence level upper error on
the alpha parameter (alphaerrup)
153-160 F8.4 --- beta ?=-99 Best-fit beta parameter from a
logparabola fit of the X-ray
spectrum (beta)
162-167 F6.3 --- e_beta [] 90% confidence level lower error
on the beta parameter (betaerrlo)
169-172 F4.2 --- E_beta 90% confidence level lower error on
the beta parameter (betaerrup)
174-178 F5.1 --- cstat-lp ?=-99 Best-fit Cstat value from the
logparabola fit (cstat_lp)
180-183 I4 --- dof-lp ?=-99 Degrees of freedom from the
logparabola fit (dof_lp)
185-193 E9.3 [10-15W/m2] Flux03-8keV ?=-99 Best-fit value of the observed
0.3-8keV flux from the logparabola
fit (flux038_keV)
195-202 E8.3 [10-15W/m2] b_Flux03-8keV 90% confidence level lower boundary
of the observed 0.3-8keV flux from
the logparabola fit
(flux038keVlow_bound)
204-211 E8.3 [10-15W/m2] B_Flux03-8keV 90% confidence level upper boundary
of the observed 0.3-8keV flux from
the logparabola fit
(flux038keVup_bound)
213-218 F6.2 [10-7W] logLX2-10keV ?=-99 Best-fit value of the logarithm
of the rest-frame, intrinsic 2-10keV
luminosity from the logparabola fit
(logLx210_keV)
220-224 F5.2 [10-7W] e_logLX2-10keV [] 90% confidence level lower error
on the logarithm of the rest-frame,
intrinsic 2-10keV luminosity from
the logparabola fit
(logLx210keVerr_lo)
226-229 F4.2 [10-7W] E_logLX2-10keV 90% confidence level upper error on
the logarithm of the rest-frame,
intrinsic 2-10 keV luminosity from
the logparabola fit
(logLx210keVerr_up)
231-235 F5.1 --- DeltaCstat ?=-99 Difference in Cstat between the
power law and the logparabola best
fits (DeltaCstat)
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Acknowledgements:
Federica Sibani, federica.sibani(at)studio.unibo.it
The research activities described in this paper were carried
out with contribution of the Next Generation EU funds within the
National Recovery and Resilience Plan (PNRR), Mission 4 - Education
and Research, Component 2 - From Research to Business (M4C2),
Investment Line 3.1 - Strengthening and creation of Research
Infrastructures, Project IR0000012 - "CTA+ - Cherenkov Telescope Array
Plus".
(End) Patricia Vannier [CDS] 04-Mar-2026