20 research outputs found
Detection of gamma-ray quasi-periodic oscillations in non-blazar AGN PKS 0521-36
Quasi-periodic oscillations (QPOs) have been detected in many Fermi-detected
bright blazars. In this letter, we report multiple QPOs detected in a
non-blazar AGN PKS 0521-36 searched over the entire 15 years of Fermi-LAT data.
QPOs are detected at 268 days, at 295 days, and at 806 days timescales with
more than 3 significance. The QPO detected at 806 days happens to be
the third harmonic of QPO at 268 days. The time scales are consistent in both
Lomb-Scargle and Wavelet analysis. Furthermore, the Gaussian Process modeling
of the light curve is performed with stochastically driven damped harmonic
oscillator (SHO) and damped random walk (DRW) modeling to uncover the presence
of QPOs. The constructed power spectral density (PSD) exhibits two QPOs, with
observed timescales of approximately 283 days and 886 days. This is the first
non-blazar AGN where the long-term QPO is detected. Earlier studies show this
source has a weak beamed jet. The exact cause for these QPOs remains unclear.
We also assembled the -ray QPO detected in various blazar and tested
the QPO time scale dependent on the black hole mass. No significant correlation
is found.Comment: 10 pages, 7 figure
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
Quasi-periodic oscillation detected in -rays in blazar PKS 0346-27
We present a variability study of the blazar PKS 0346-27 from December 2018
to January 2022 in its archival -ray observation by Fermi-LAT. We use
the Lomb-Scargle periodogram and the weighted wavelet transform methods in
order to detect the presence of periodicity/quasi-periodicity and localize this
feature in time and frequency space. The significance of the periodicity
feature has been estimated using the Monte-Carlo simulation approach. We have
also determined the global significance of the periodicity to test the
robustness of our claim. To explore the most probable scenario, we modeled the
light curve with both a straight jet and a curved jet model. We detect a
periodicity feature of 100 days duration for the entire period of
observation with a statistical significance of , which amounts to a
99.7\% confidence level. The global significance of this feature is found to be
96.96\%. Based on the Akaike Information Criteria, the most probable
explanation is that the observed emission is enhanced due to the helical motion
of a blob within a curved jet. The origin of this QPO is very likely a region
of enhanced emission moving helically inside a curved jet. This work presents
strong evidence for jet curvature in the source and an independent (albeit a
little serendipitous) procedure to estimate the curvature in blazar jets.Comment: 7 pages, 4 figures, Accepted for publication in A&A, in Pres
Multi-wavelength study of TeV blazar 1ES 1218+304 using gamma-ray, X-ray and optical observations
We report the multi-wavelength study for a high-synchrotron-peaked BL Lac 1ES
1218+304 using near-simultaneous data obtained during the period from January
1, 2018, to May 31, 2021 (MJD 58119-59365) from various instruments including
Fermi-LAT, Swift-XRT, AstroSat, and optical from Swift-UVOT TUBITAK
observatory in Turkey. The source was reported to be flaring in TeV
-ray band during 2019, but no significant variation is observed with
Fermi-LAT. A sub-hour variability is seen in the SXT light curve, suggesting a
compact emission region for their variability. However, hour scale variability
is observed in the -ray light curve. A "softer-when-brighter" trend is
observed in -rays, and an opposite trend is seen in X-rays suggesting
both emissions are produced via two different processes as expected from an HBL
source. We have chosen the two epochs in January 2019 to study and compare
their physical parameters. A joint fit of SXT and LAXPC provides a constraint
on the synchrotron peak, roughly estimated to be 1.6 keV. A clear shift
in the synchrotron peak is observed from 1 keV to above 10 keV revealing
its extreme nature or behaving like an EHBL-type source. The optical
observation provides color-index variation as "blue-when-brighter". The
broadband SED is fitted with a single-zone SSC model, and their parameters are
discussed in the context of a TeV blazar and the possible mechanism behind the
broadband emission.Comment: 13 pages, 10 figures, 5 tables, Accepted for publication in MNRA
Simultaneous multi-wavelength observations of the TeV Blazar Mrk 421 during February - March 2003: X-ray and NIR correlated variability
In the present paper, we have reported the result of simultaneous
multi-wavelength observations of the TeV blazar Mrk 421 during February
March 2003. In this period, we have observed Mrk 421 using Pachmarhi Array of
\v{C}erenkov Telescopes (PACT) of Tata Institute of Fundamental Research at
Pachmarhi, India. Other simultaneous data were taken from the published
literature and public data archives. We have analyzed the high quality X-ray
(2-20 keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We
have seen a possible correlated variability between X-ray and J band (1.25
) near infrared (NIR) wavelength. This is the first case of X-ray and NIR
correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The
correlated variability reported here is indicating a similar origin for NIR and
X-ray emission. The emission is not affected much by the environment of the
surrounding medium around the central engine of the Mrk 421. The observations
are consistent with the shock-in-jet model for the emission of radiations.Comment: 11 pages, 5 figures, Accepted for Publication in ChJA
Cell-surface sensors for real-time probing of cellular environments
Author Manuscript 2012 August 1.The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a signal. The sensor, which is covalently attached to the membranes of mesenchymal stem cells, can quantitatively detect with high spatial and temporal resolution PDGF that is added in cell culture medium or secreted by neighbouring cells. The engineered stem cells retain their ability to find their way to the bone marrow and can be monitored in vivo at the single-cell level using intravital microscopy.National Institutes of Health (U.S.) (Grant HL097172)National Institutes of Health (U.S.) (Grant HL095722)National Institutes of Health (U.S.) (Grant DE019191)National Institutes of Health (U.S.) (Grant NIAID 5RC1AI086152)Charles A. Dana FoundationAmerican Heart Association (Grant 0970178N)National Science Foundation (U.S.) (Graduate Fellowship
Multi-frequency Variability Study of Flat-Spectrum Radio Quasar PKS 0346-27
We have presented a multiwavelength temporal and spectral study of the Blazar
PKS 0346-27 between the time period 2019 January-2021 December (MJD
58484-59575). We analysed the data collected by Fermi-LAT (gamma-rays),
Swift-XRT (x-rays) and Swift-UVOT (ultra-violet). Flaring episodes are
identified by analysing the gamma-ray lightcurve. Flares are fitted using
polynomial fit. We have found rapid variability on time scales of hours during
brightest flaring activity, which implies that the emission region is very
compact. The broadband emission mechanism was studied by modelling the
simultaneous multi waveband Spectral Energy Distributions (SED) using leptonic
emission mechanism. We found that the optical-UV and X-ray data can be
explained by the synchrotron emission. However, the high energy peak is best
fitted with external Compton of disk photon rather than the BLR or DT. Our
modeling also suggest that the flare 1 and flare 5 have more jet power than
flare 2 and 3 which can be caused by different processes. It also suggest that
all the flares are produced in different situation. An auto correlation of
gamma-ray lightcure was done and concluded the possibility of the source being
gravitationally lensed. We have also produced the power spectral density for
this source and a powerlaw seems to produce the best fit with slope 2.15+/-0.87
suggesting variability in this source is dominated by stochastic process. This
source could be a promising target for upcoming CTA for its harder spectrum at
lower energies (tens of GeV)