192 research outputs found
Long term study of the light curve of PKS 1510-089 in GeV energies
We have analyzed data from the Flat Spectrum Radio Quasar PKS 1510-089
collected over a period of 8 years from August 2008 to December 2016 with the
Fermi-LAT. We have identified several flares of this highly variable source,
studied their temporal and spectral properties in detail and compared with
previous works on flares of PKS 1510-089. Five major flares and few
sub-flares/sub-structures have been identified in our study. The fastest
variability time is found to be 1.300.18 hr between MJD 55852.063 and
55852.188 where we estimate the minimum size of the emission region to be cm. In most of the flares the spectral energy distributions are
better fitted with Logparabolic distribution compared to simple Power law or
Power law with exponential cut-offs. This has strong physics implications
regarding the nature of the high energy gamma-ray emission region.Comment: 29 pages, 29 figures, Accepted in Ap
The detection of possible transient Quasi-Periodic Oscillations in the -ray light curve of PKS 0244-470 and 4C+38.41
The continuous monitoring capability of Fermi-LAT has enabled the exploration
of Quasi-Periodic Oscillations (QPOs) in the -ray light curve of blazar
that has given a new perspective to probe these source and jet physics over a
wide range of time scales. We report the presence of transient QPOs in the
long-term -ray light curve of blazars PKS 0244-470 \& 4C +38.41. We
first identified different flux states using the Bayesian Block algorithm and
then explored the possible transient QPOs in the segments of each flux phase
where the flux level changes over fairly regular intervals. Combining this with
source intrinsic variance, we identified two flux phases for PKS 0244-470: one
activity (AP-1) and one quiescent phase (QP-1). For 4C+38.41, we similarly
identified four activity (AP-1, AP-2, AP-3, and AP-4) and two quiescent (QP-1
and QP-2) phases. AP-1 phase of PKS 0244-470 shows QPO of 225 days
persisting for 8 cycles ( 4.1 ). In 4C+38.41, AP-1 and AP-2
phases show QPO of 110 days and 60 days, respectively, persisting
for 5 cycles. In AP-3, we identified three sub-phases, and all show a
week scale recurrent rise with five complete cycles, while in QP-1, we could
identify 2 sub-phases (Q1 and Q2). Q1 phase shows a significant period of
104 days with six complete cycles. Q2 phase also shows significant QPO
but with only 3.7 cycles. All the detections are locally significant
with at least four or more cycles. We discuss the possible origin and argue
that the current driven kink instability and curved jet model seem the most
likely cause for shorter and longer QPOs though the latter requires continuous
acceleration or injection of particles to explain these
Fermi-Large Area Telescope observations of the brightest Gamma-ray flare ever detected from CTA 102
We present a multi-wavelength study of the FSRQ CTA 102 using Fermi-LAT and
simultaneous Swift-XRT/UVOT observations. The Fermi-LAT telescope detected one
of the brightest flares from this object during Sep, 2016 to Mar, 2017. In the
190 days of observation period the source underwent four major flares. A
detailed analysis of the temporal and spectral properties of these flares
indicates the flare at MJD 57751.594 has a -ray flux of
(30.124.48) ph cm s (from 90 minutes
binning) in the energy range of 0.1--300 GeV. This has been found to be the
highest flux ever detected from CTA 102. Time dependent leptonic modelling of
the pre-flare, rising state, flares and decaying state has been done. A single
emission region of size cm has been used in our work to
explain the multi-wavelength spectral energy distributions. During flares the
luminosity in electrons increases nearly seventy times compared to the
pre-flare state.Comment: 19 pages, 7 figures, Accepted for Publication in Ap
Multiwavelength temporal and spectral study of TeV blazar 1ES 1727+502 during 2014 to 2021
One of the most important questions in blazar physics is the origin of
broadband emission and fast-flux variation. In this work, we studied the
broadband temporal and spectral properties of a TeV blazar 1ES 1727+502 and
explore the one-zone synchrotron-self Compton (SSC) model to fit the broadband
spectral energy distribution (SED). We collected the long-term (2014-2021)
multiband data which includes both the low and high flux states of the source.
The entire light curve is divided into three segments of different flux states
and the best-fit parameters obtained by broadband SED modeling corresponding to
three flux states were then compared. The TeV blazar 1ES 1727+502 has been
observed to show the brightest flaring episode in X-ray followed by optical-UV
and gamma-ray. The fractional variability estimated during various segments
behaves differently in multiple wavebands, suggesting a complex nature of
emission in this source. This source has shown a range of variability time from
days scale to month scale during this long period of observations between
2014-2021. A "harder-when-brighter" trend is not prominent in X-ray but seen in
optical-UV and an opposite trend is observed in gamma-ray. The complex nature
of correlation among various bands is observed. The SED modeling suggests that
the one-zone SSC emission model can reproduce the broadband spectrum in the
energy range from optical-UV to very high energy gamma-ray.Comment: 14 pages, 8 figure, 2 table. Accepted for publication in MNRA
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
- …