19 research outputs found
Low-frequency radio study of MACS clusters at 610 and 235 MHz using the GMRT
Studies have shown that mergers of massive galaxy clusters produce shocks and turbulence in the intra-cluster medium, the possible event that creates radio relics, as well as the radio halos. Here we present GMRT dual-band (235 and 610~MHz) radio observations of four such clusters from the MAssive Cluster Survey (MACS) catalogue. We report the discovery of a very faint, diffuse, elongated radio source with a projected size of about 0.5~Mpc in cluster MACSJ0152.5-2852. We also confirm the presence of a radio relic-like source (about 0.4~Mpc, previously reported at 325~MHz) in MACSJ0025.4-1222 cluster. Proposed relics in both these clusters are found apparently inside the virial radius instead of their usual peripheral location, while no radio halos are detected. These high-redshift clusters (z=0.584 and 0.413) are among the earliest merging systems detected with cluster radio emissions. In MACSJ1931-2635 cluster, we found a radio mini-halo and an interesting highly bent pair of radio jets. Further, we present here a maiden study of low frequency (GMRT 235&610~MHz) spectral and morphological signatures of a previously known radio cluster MACSJ0014.3-3022 (Abell~2744). This cluster hosts a relatively flat spectrum (α610235∼−1.15), giant (∼1.6~Mpc each) halo-relic structure and a close-by high-speed (1769±148359~km~s−1) merger-shock (M=2.02±0.170.41) originated from a possible second merger in the cluster
The radio source in Abell 980: A Detached-Double-Double Radio Galaxy?
It is argued that the new morphological and spectral information gleaned from
the recently published LoFAR Two meter Sky Survey data release 2 (LoTSS-2 at
144 MHz) observations of the cluster Abell 980 (A980), in combination with its
existing GMRT and VLA observations at higher frequencies, provide the
much-needed evidence to strengthen the proposal that the cluster's radio
emission comes mainly from two double radio sources, both produced by the
brightest cluster galaxy (BCG) in two major episodes of jet activity. The two
radio lobes left from the previous activity have become diffuse and developed
an ultra-steep radio spectrum while rising buoyantly through the confining hot
intra-cluster medium (ICM) and, concomitantly, the host galaxy has drifted to
the cluster centre and entered a new active phase manifested by a coinciding
younger double radio source. The new observational results and arguments
presented here bolster the case that the old and young double radio sources in
A980 conjointly represent a `double-double' radio galaxy whose two lobe-pairs
have lost colinearity due to the (lateral) drift of their parent galaxy, making
this system by far the most plausible case of a `Detached-Double-Double Radio
Galaxy' (dDDRG).Comment: Accepted for publication by Publications of the Astronomical Society
of Australia (PASA); 10 pages, 6 figure
Radio-relic and the diffuse emission trail discovered in a low mass galaxy cluster Abell 1697
We report the discovery of a putative radio relic, 830 kpc in length and
found toward the outskirts of galaxy cluster Abell 1697 (), using the
LOFAR Two Meter Sky Survey (LoTSS) at 144 MHz. With an X-ray-inferred mass of
, this places
Abell 1697 among the least massive relic hosts. The relic is also detected at
325 MHz in the Westerbork Northern Sky Survey (WENSS) and at 1.4 GHz in the
NRAO VLA Sky Survey (NVSS) with an average spectral index of
and magnetic field of
G. This relic, located in the northeast periphery of the
cluster, is 300 kpc wide, exhibits a gradual spectral steepening across the
width ( to ), as well as indications of a
co-spatial X-ray (ROSAT) shock and the radio relic emission. The radio power of
the relic is , which is
found to be in good agreement with the expected empirical correlation between
the radio power and Largest Linear Size (LLS) of relics. The relic is trailed
by extended ( kpc) diffuse radio emission towards the cluster
center, that is likely an ultra-steep spectrum () radio source. This structure is also found to
be older by at least 190 Myrs, has a very low surface brightness of Jy
arcsec and magnetic field G, similar to that of a
radio phoenix. Finally, we discuss the possible mechanisms responsible for the
relic and the trailing diffuse radio emission, invoking re-acceleration due to
wake turbulence, as well as the revival of fossil electrons from an old AGN
activity by the cluster merger shocks.Comment: 9 pages, 8 figures, Accepted for publication in A&
GMRT observations of extragalactic radio sources with steeply inverted spectra
We report quasi-simultaneous GMRT observations of seven extragalactic radio
sources at 150, 325, 610 and 1400 MHz, in an attempt to accurately define their
radio continuum spectra, particularly at frequencies below the observed
spectral turnover. We had previously identified these sources as candidates for
a sharply inverted integrated radio spectrum whose slope is close to, or even
exceeds = +2.5, the theoretical limit due to synchrotron
self-absorption (SSA) in a source of incoherent synchrotron radiation arising
from relativistic particles with the canonical (i.e., power-law) energy
distribution. We find that four out of the seven candidates have an inverted
radio spectrum with a slope close to or exceeding +2.0, while the critical
spectral slope is exceeded in at least one case. These sources,
together with another one or two reported in very recent literature, may well
be the archetypes of an extremely rare class, from the standpoint of violation
of the SSA limit in compact extragalactic radio sources. However, the
alternative possibility that free-free absorption is responsible for their
ultra-sharp spectral turnover cannot yet be discounted.Comment: Accepted for publication in MNRAS. Comments are welcom
GMRT observations of a first sample of Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS) candidates in the Northern sky
We present an extension of our search for Extremely Inverted Spectrum
Extragalactic Radio Sources (EISERS) to the northern celestial hemisphere. With
an inverted radio spectrum of slope > +2.5, these rare sources would
either require a non-standard particle acceleration mechanism (in the framework
of synchrotron self-absorption hypothesis), or a severe free-free absorption
which attenuates practically all of their synchrotron radiation at metre
wavelengths. By applying a sequence of selection filters, a list of 15 EISERS
candidates is extracted out by comparing two large-sky radio surveys, WENSS
(325 MHz) and TGSS-ADR1 (150 MHz), which overlap across 1.03 steradian of
the sky. Here we report quasi-simultaneous GMRT observations of these 15 EISERS
candidates at 150 MHz and 325 MHz, in an attempt to accurately define their
spectra below the turnover frequency. Out of the 15 candidates observed, two
are confirmed as EISERS, since the slope of the inverted spectrum between these
two frequencies is found to be significantly larger than the critical value
= +2.5: the theoretical limit for the standard case of synchrotron
self-absorption (SSA). For another 3 sources, the spectral slope is close to,
or just above the critical value . Nine of the sources have GPS type
radio spectra. The parsec-scale radio structural information available for the
sample is also summarised.Comment: Accepted for publication in MNRAS. Comments are welcom
Phytochemical screening and In Vitro Antioxidant potential of Memecylon umbellatum Burm leaf extracts
Objective: Different dry extracts of Memecylon umbellatum Burm leaf obtained by various solvents such as petroleum ether, chloroform, ethyl acetate, acetone, methanol and chloroform water (IP) was screened to reap the benefits of its antioxidant and free radical scavenging properties using ascorbic acid as standard antioxidants. Methods: The in vitro free radical scavenging activity was evaluated using diphenyl picryl hydrazyl (DPPH) radical method using various concentrations of dry extract in distilled water (1, 2, 4, 8, 16, 20 μg/ml) against blank with ascorbic acid as a standard in same concentrations. Results: Among the all extracts, Methanol leaf extract has showed higher Antioxidant activity (84.65 ± 0.064 %) having IC50 Value 11.81 ± 0.033 μg/ml at 20 μg/ml. While, IC50 value for ascorbic acid was found to be 8.91 ± 0.084 μg/ml. Conclusion: The results clearly indicate that Methanol leaf extract of Memecylon umbellatum is effective in free radical scavenging. So in future, this may emerge as promising natural herbal source of powerful antioxidant. Keywords: Memecylon umbellatum, DPPH reagent, Antioxidant activity, Ascorbic acid, IC50
Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA
Diffuse radio emission has been detected in a considerable number of galaxy
clusters and groups, revealing the presence of pervasive cosmic magnetic
fields, and of relativistic particles in the large-scale structure (LSS) of the
Universe. Since cluster radio emission is faint and steep spectrum, its
observations are largely limited by the instrument sensitivity and frequency of
observation, leading to a dearth of information, more so for lower-mass
systems. The unprecedented sensitivity of recently commissioned low-frequency
radio telescope arrays, aided by the development of advanced calibration and
imaging techniques, have helped in achieving unparalleled image quality. At the
same time, the development of sophisticated numerical simulations and the
availability of supercomputing facilities have paved the way for
high-resolution numerical modeling of radio emission, and the structure of the
cosmic magnetic fields in LSS, leading to predictions matching the capabilities
of observational facilities. In view of these rapidly-evolving scenerio in
modeling and observations, in this review, we summarise the role of the new
telescope arrays and the development of advanced imaging techniques and discuss
the detections of various kinds of cluster radio sources. In particular, we
discuss observations of the cosmic web in the form of supercluster filaments,
studies of emission in poor clusters and groups of galaxies, and of ultra-steep
spectrum sources. We also review the current theoretical understanding of
various diffuse cluster radio sources and the associated magnetic field and
polarization. As the statistics of detections improve along with our
theoretical understanding, we update the source classification schemes based on
their intrinsic properties. We conclude by summarising the role of the upgraded
GMRT and our expectations from the upcoming Square Kilometre Array (SKA)
observatories.Comment: 32 pages, 10 figures, accepted for publication in the Journal of
Astrophysics and Astronomy (JoAA) (to appear in the special issue on "Indian
participation in the SKA"
Deciphering the ultra-steep-spectrum diffuse radio sources discovered in the cool-core cluster Abell 980
Clusters of galaxies are excellent laboratories for studying recurring nuclear activity in galactic nuclei since their hot gaseous medium can vastly prolong the detectability of their radio lobes via better confinement. We report here a multi-band study of the sparsely studied galaxy cluster Abell 980, based on our analysis of Chandra X-ray data and GMRT (150 and 325 MHz) and EVLA (1.5 GHz) radio archival data, revealing an unusually rich phenomenology. It is shown to be a quasi-relaxed cluster with a cool core (T ∼ 4.2 keV) surrounded by a hot and extensive intracluster medium (ICM) at T ∼ 6.8 keV. The radio emission shows a rich diversity, having (i) two large diffuse sources of ultra-steep spectrum (USS) extending to opposite extremities of the ICM, each associated with an X-ray brightness discontinuity (cold front); (ii) a bright radio-double of size ∼55 kpc coinciding with the central BCG; and (iii) a diffuse radio source, likely a mini-halo of size ∼110 kpc around the BCG which possesses a huge ellipsoidal stellar halo of extent ∼80 kpc. The association of cold fronts with two highly aged (∼260 Myr) USS sources in a cool-core cluster makes it a very rare system. These USS sources are probably radio lobes from a previous episode of jet activity in the BCG, driven buoyantly towards the outskirts of the X-ray halo, thereby creating the cold fronts. A deeper radio image of this cluster may provide a rare opportunity to verify the recently proposed alternative model which explains radio mini-haloes as the aggregate radio emission from Type Ia supernova remnant occurring in the giant stellar halo extended across the cluster core
Implementation of time release technology in formulation development and evaluation of sustained release tablet of Lornoxicam
In present study, the attempts have been made to formulate sustained release tablets of lornoxicam by direct compression method. Based on viscosity grades different proportions of hydrophilic polymers (HPMC K4M, HPMC K15M, HPMC K100M) are used for preparation of lornoxicam sustained release matrix tablet. The drug excipient mixtures were subjected to preformulation studies comprising of micromeritic properties. The tablets were subjected to various studies like as physicochemical studies, in vitro drug release, kinetic studies, etc. FTIR studies shown there was no interaction between drug and polymers. The physicochemical properties of tablets were found within the limits. Lornoxicam is a first generation analgesic, inflammatory and antipyretic agent used in relieving symptoms of osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, acute sciatica and low back pain. From developed formulations batch F1 have shown zero order drug release behavior and prolong drug release over a period of 12 h which was deemed as suitable and optimum formulation for sustained drug delivery. Results of the present study indicated the suitability of the low viscous polymer in the proportion of (drug:polymer) 1:1 in the preparation of sustained release formulation of lornoxicam
uGMRT detection of cluster radio emission in low-mass Planck Sunyaev–Zel’dovich clusters
International audienceLow-mass (M_500 < 5 × 10^14 M_⊙) galaxy clusters have been largely unexplored in radio observations, because of the inadequate sensitivity of existing telescopes. However, the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Low Frequency ARray (LoFAR), with unprecedented sensitivity at low frequencies, have paved the way to study less massive clusters more closely than before. We have started the first large-scale programme to systematically search for diffuse radio emission from low-mass galaxy clusters, chosen from the Planck Sunyaev–Zel’dovich cluster catalogue. We report here the detection of diffuse radio emission from four of the 12 objects in our sample, shortlisted from the inspection of the LoFAR Two-Meter Sky Survey data release 1 (LoTSS-I), followed up by uGMRT Band 3 deep observations. The clusters PSZ2 G089 (Abell 1904) and PSZ2 G111 (Abell 1697) are detected with relic-like emission, while PSZ2 G106 is found to have an intermediate radio halo and PSZ2 G080 (Abell 2018) seems to be a halo-relic system. PSZ2 G089 and PSZ2 G080 are among the lowest-mass clusters discovered with a radio-relic and a halo-relic system, respectively. A high (||) detection rate, with powerful radio emission (P_1.4 GHz ∼ 10^23 W Hz^−1) found in most of these objects, opens up prospects of studying radio emission in galaxy clusters over a wider mass range, to much lower-mass systems