16 research outputs found
Broadband Spectro-temporal Study on Blazar TXS 1700+685
We attempt to present a multiwavelength variability and correlation study as
well as detailed multi-waveband spectral characteristics of the May 2021
-ray flare of the blazar source TXS 1700+685. The multi-wavelength
observation from \textit{Fermi}-LAT, \textit{Swift}-XRT/UVOT as well as radio
archival data are used for our spectro-temporal investigation. We estimate the
variability time-scale of the source from the flux doubling time in different
flaring regions detected in \textit{Fermi}-LAT observation and the shortest
variability time is used to put a constraint on the minimum Doppler factor and
on the size of the emission region. We have detected a statistically
significant quasi-periodic oscillation feature (QPO) at 17 days. The
broad-band emission is satisfactorily represented during its flaring state with
a leptonic synchrotron and inverse Compton component. From the broadband
spectral modeling, we observe the external Comptonization of the seed photons
originating in the broad line region to be dominant compared to the dusty
torus. This is further supported by the fact that the emission region is also
found to be residing within the BLR. The equipartition value implies the energy
density of the magnetic field in the jet comoving frame is weak, and that is
also reflected in the magnetic field and low power corresponding to the
magnetic field component of the jet. In order to produce the high energy hump,
we need the injection of a large population of high energy electrons and/or the
presence of strong magnetic field; and we observe the later component to be
sub-dominant in our case. The flat rising and steep falling profile in the
-ray SED as well as the break or spectral curvature at 1 GeV are
in commensuration with the flat-spectrum radio quasar (FSRQ) nature of the
source
The accretion properties of a low-mass Active Galactic Nucleus: UGC 6728
We present a comprehensive analysis of approximately years ()
of X-ray observations of UGC~6728, a low-mass bare AGN, for the first time. Our
study encompasses both spectral and temporal aspects of this source. The
spectral properties of this source are studied using various phenomenological
and physical models. We conclude that (a) the observed variability in X-ray
luminosity is not attributed to the Hydrogen column density () as UGC~6728
exhibits a bare nucleus, implying a negligible contribution along the
line of sight, and (b) the spectral slope in the X-ray band demonstrates a
systematic variation over time, indicating a transition from a relatively hard
state to a comparatively soft state. We propose that the underlying accretion
dynamics around the central object account for this behavior. By performing
X-ray spectral fitting, we estimate the mass of the central supermassive black
hole (SMBH) in UGC~6728 to be M with
spin and inclination angle degree.
Based on our spectral and temporal analysis, we suggest that UGC~6728 lacks a
prominent Compton hump or exhibits a very subtle hump that remains undetectable
in our analysis. Furthermore, the high-energy X-ray photons in this source are
likely to originate from the low-energy X-ray photons through inverse Compton
scattering in a Compton cloud, highlighting a connection between the emission
in two energy ranges. We notice a strong soft excess component in the initial
part of our observations, which later reduced substantially. This variation of
soft excess is explained in view of accretion dynamics.Comment: 19 pages, 8 figure
Long-term study of the first Galactic ultraluminous X-ray source Swift J0243.6+6124 using NICER
We present the results obtained from detailed X-ray timing and spectral
studies of X-ray pulsar Swift J0243.6+6124 during its giant and normal X-ray
outbursts between 2017 and 2023 observed by the Neutron star Interior
Composition Explorer (NICER). We focused on the timing analysis of the normal
outbursts. A distinct break is found in the power density spectra of the
source. The corresponding break frequency and slope of power-laws around the
break vary with luminosity, indicating the change in accretion dynamics with
mass accretion rate. Interestingly, we detected quasi-periodic oscillations
within a specific luminosity range, providing further insights into the
underlying physical processes. We also studied the neutron star spin period
evolution and a luminosity variation in pulse profile during the recent 2023
outburst. The spectral analysis was conducted comprehensively for the giant and
all other normal outbursts. We identified a double transition at luminosities
of 7.510 and 2.110 erg s in the
evolution of continuum parameters like photon index and cutoff energy with
luminosity. This indicates three distinct accretion modes experienced by the
source mainly during the giant X-ray outburst. A soft blackbody component with
a temperature of 0.08-0.7 keV is also detected in spectra. The observed
temperature undergoes a discontinuous transition when the pulsar evolves from a
sub- to super-Eddington state. Notably, in addition to an evolving 6-7 keV iron
line complex, a 1 keV emission line was observed during the super-Eddington
state of the source, implying the X-ray reflection from the accretion disc or
outflow material.Comment: This paper is accepted now in Astrophysical journa
Survey of Bare Active Galactic Nuclei in the local universe (z < 0.2): I. On the origin of Soft-Excess
We analyse a sample of 21 `bare' Seyfert~1 Active Galactic Nuclei (AGNs), a
sub-class of Seyfert~1s, with intrinsic absorption , in the local universe (z 0.2) using {\it
XMM-Newton} and {\it Swift}/XRT observations. The luminosities of the primary
continuum, the X-ray emission in the 3 to 10 keV energy range and the
soft-excess, the excess emission that appears above the low-energy
extrapolation of the power-law fit of 3 to 10 keV X-ray spectra, are
calculated. Our spectral analysis reveals that the long-term intrinsic
luminosities of the soft-excess and the primary continuum are tightly
correlated . We also found that the
luminosities are correlated for each source. This result suggests that both the
primary continuum and soft excess emissions exhibit a dependency on the
accretion rate in a similar way.Comment: Accepted for publication in ApJ Supplement Series, 37 pages, 12
figures 5 table
Coronal Properties of Low-Accreting AGNs using Swift, XMM-Newton and NuSTAR Observations
We studied the broadband X-ray spectra of {\it Swift}/BAT selected
low-accreting AGNs using the observations from {\it XMM-Newton}, {\it Swift},
and {\it NuSTAR} in the energy range of ~keV. Our sample consists of
30 AGNs with Eddington ratio, . We extracted several
coronal parameters from the spectral modelling, such as the photon index, hot
electron plasma temperature, cutoff energy, and optical depth. We tested
whether there exists any correlation/anti-correlation among different spectral
parameters. We observe that the relation of hot electron temperature with the
cutoff energy in the low accretion domain is similar to what is observed in the
high accretion domain. We did not observe any correlation between the Eddington
ratio and the photon index. We studied the compactness-temperature diagram and
found that the cooling process for extremely low-accreting AGNs is complex. The
jet luminosity is calculated from the radio flux, and observed to be related to
the bolometric luminosity as , which is
consistent with the standard radio-X-ray correlation.Comment: Accepted for publication in MNRA