57 research outputs found
PONDER - A Real time software backend for pulsar and IPS observations at the Ooty Radio Telescope
This paper describes a new real-time versatile backend, the Pulsar Ooty Radio
Telescope New Digital Efficient Receiver (PONDER), which has been designed to
operate along with the legacy analog system of the Ooty Radio Telescope (ORT).
PONDER makes use of the current state of the art computing hardware, a
Graphical Processing Unit (GPU) and sufficiently large disk storage to support
high time resolution real-time data of pulsar observations, obtained by
coherent dedispersion over a bandpass of 16 MHz. Four different modes for
pulsar observations are implemented in PONDER to provide standard reduced data
products, such as time-stamped integrated profiles and dedispersed time series,
allowing faster avenues to scientific results for a variety of pulsar studies.
Additionally, PONDER also supports general modes of interplanetary
scintillation (IPS) measurements and very long baseline interferometry data
recording. The IPS mode yields a single polarisation correlated time series of
solar wind scintillation over a bandwidth of about four times larger (16 MHz)
than that of the legacy system as well as its fluctuation spectrum with high
temporal and frequency resolutions. The key point is that all the above modes
operate in real time. This paper presents the design aspects of PONDER and
outlines the design methodology for future similar backends. It also explains
the principal operations of PONDER, illustrates its capabilities for a variety
of pulsar and IPS observations and demonstrates its usefulness for a variety of
astrophysical studies using the high sensitivity of the ORT.Comment: 25 pages, 14 figures, Accepted by Experimental Astronom
Simultaneous multi-frequency single pulse observations of pulsars
We performed simultaneous observations at 326.5 MHz with the Ooty Radio
Telescope and at 326, 610 and 1308 MHz with the Giant Meterwave Radio Telescope
for a sample of 12 pulsars, where frequency dependent single pulse behaviour
was reported. The single pulse sequences were analysed with fluctuation
analysis, sensitive to both the average fluctuation properties (using longitude
resolved fluctuation spectrum and two-dimensional fluctuation spectrum) as well
as temporal changes in these (using sliding two-dimensional fluctuation
spectrum ) to establish concurrent changes in subpulse drifting over the
multiple frequencies employed. We report subpulse drifting in PSR J09345249
for the first time. We also report pulse nulling measurements in PSRs
J09345249, B1508+55, J18222256, B184519 and J19010906 for the first
time. Our measurements of subpulse drifting and pulse nulling for the rest of
the pulsars are consistent with previously reported values. Contrary to
previous belief, we find no evidence for a frequency dependent drift pattern in
PSR B2016+28 implied by non-simultaneous observations by Oster et al. (1977).
In PSRs B1237+25, J18222256, J19010906 and B204516, our longer and
more sensitive observations reveal multiple drift rates with distinct P3. We
increase the sample of pulsars showing concurrent nulling across multiple
frequencies by more than 100 percent, adding 4 more pulsars to this sample. Our
results confirm and further strengthen the understanding that the subpulse
drifting and pulse nulling are broadband consistent with previous studies
(Gajjar et al. 2014a; Rankin 1986; Weltevrede et al. 2007) and are closely tied
to physics of polar gap.Comment: 22 pages, 44 figures, Single pulse studies of pulsars, accepted by
A&
Detection of long nulls in PSR B170616, a pulsar with large timing irregularities
Single pulse observations, characterizing in detail, the nulling behaviour of
PSR B170616 are being reported for the first time in this paper. Our regular
long duration monitoring of this pulsar reveals long nulls of 2 to 5 hours with
an overall nulling fraction of 312\%. The pulsar shows two distinct phases
of emission. It is usually in an active phase, characterized by pulsations
interspersed with shorter nulls, with a nulling fraction of about 15 \%, but it
also rarely switches to an inactive phase, consisting of long nulls. The nulls
in this pulsar are concurrent between 326.5 and 610 MHz. Profile mode changes
accompanied by changes in fluctuation properties are seen in this pulsar, which
switches from mode A before a null to mode B after the null. The distribution
of null durations in this pulsar is bimodal. With its occasional long nulls,
PSR B170616 joins the small group of intermediate nullers, which lie between
the classical nullers and the intermittent pulsars. Similar to other
intermediate nullers, PSR B170616 shows high timing noise, which could be
due to its rare long nulls if one assumes that the slowdown rate during such
nulls is different from that during the bursts.Comment: Accepted for publication in MNRA
Scatter broadening measurements of 124 pulsars at 327 MHz
We present the measurements of scatter broadening time-scales ()
for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT).
These pulsars lie in the dispersion measure range of 37 503 pc cm
and declination () range of 57. New
estimates for 58 pulsars are presented, increasing the sample of
all such measurements by about 40% at 327 MHz. Using all available
measurements in the literature, we investigate the dependence of on
dispersion measure. Our measurements, together with previously reported values
for , affirm that the ionized interstellar medium upto 3 kpc is
consistent with Kolmogorov spectrum, while it deviates significantly beyond
this distance.Comment: 19 pages, 4 figures, accepted for publication in Ap
The Landscape of C. elegans 3'UTRs.
The 3’ untranslated regions (3’UTRs) of mRNAs have recently been shown to play major roles in gene regulation by interaction with small (21-26nt length) RNAs, such as microRNAs and small interfering RNAs (siRNAs). Recent studies highlight dynamic expression of small RNAs and provide limited evidence of utilization of alternative 3’UTR lengths (3’UTR isoforms) across development and specific cell types. However a comprehensive catalogue of 3’UTRome of an organism had been unavailable. By computational analysis of traditional and novel high-throughput sequence data, chapter two of this dissertation provides annotated 3’UTRs for more than 75% of the genes in the model organism Caenorhabditis elegans across the major stages of development. At the whole-transcriptome level, 3’UTRs express remarkable diversity in utilization of alternative poly-adenylation sites, which define the alternative 3’UTR isoforms, in ~40% of genes in the genome. We identified many isoforms are developmentally stage-specific and many genes show evidence of length switching between longer and shorter isoforms over development to maybe include or escape regulation from small RNAs or other RNA binding proteins. Thus, our study reveals the diversity and temporally regulated expression of 3’UTR isoforms as a complex mechanism in gene regulation at an unprecedented scope. The analysis provides large-scale evidence for multiple alternative 6nt sequence elements (PAS sites) near 3’ ends of 3’UTRs that are enriched in shorter, alternative isoforms. Chapter three of my dissertation also compared and combined the results of a parallel study of 3’UTRs in C. elegans further expanding transcriptome coverage of 3’UTRs. As an example of biological relevance for 3’UTR isoform usage, in chapter four we identified a potential connection between the synaptogenesis pathway and specific 3’UTR isoform usage in C. elegans.
In related work described in chapter five, I analyzed small RNA sequences from isolated sperm and oocytes and identified and characterized a new class of germline-specific siRNAs, 26G-RNAs, which target coding regions and 3’UTRs of genes to regulate their target gene expression. These have been classified into two subclasses: 26G-RNAs generated in the male germline targeting genes involved in spermatogenesis, and maternally inherited 26G-RNAs targeting genes that function in zygotic development.Ph.D.BioinformaticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89776/1/arunpras_1.pd
Detection of radio emission from the gamma-ray pulsar J1732-3131 at 327 MHz
Although originally discovered as a radio-quiet gamma-ray pulsar, J1732-3131
has exhibited intriguing detections at decameter wavelengths. We report an
extensive follow-up of the pulsar at 327 MHz with the Ooty radio telescope.
Using the previously observed radio characteristics, and with an effective
integration time of 60 hrs, we present a detection of the pulsar at a
confidence level of 99.82%. The 327 MHz mean flux density is estimated to be
0.5-0.8 mJy, which establishes the pulsar to be a steep spectrum source and one
of the least-luminous pulsars known to date. We also phase-aligned the radio
and gamma-ray profiles of the pulsar, and measured the phase-offset between the
main peaks in the two profiles to be 0.240.06. We discuss the observed
phase-offset in the context of various trends exhibited by the radio-loud
gamma-ray pulsar population, and suggest that the gamma-ray emission from
J1732-3131 is best explained by outer magnetosphere models. Details of our
analysis leading to the pulsar detection, and measurements of various
parameters and their implications relevant to the pulsar's emission mechanism
are presented.Comment: 8 pages, 6 figures; Accepted for publication in MNRA
Assemblage hétérogène Al/Fe par points par impulsion magnétique
Le soudage par impulsion magnétique est un procédé qui permet l’assemblage rapide (en quelques micro secondes) de matériaux similaires ou dissimilaires à l’état solide. Ce procédé consiste à générer des forces de Laplace dans une pièce conductrice au moyen d’un inducteur parcouru par un courant variable et intense. Pour pouvoir réaliser une soudure il est nécessaire d’accélérer la première pièce. Il faut donc assurer une distance suffisante entre les deux pièces (entrefer). Il est classiquement possible d’effectuer des soudures de tubes et de tôles à condition de ménager un entrefer entre les deux pièces à assembler. Dans le cadre de nos travaux nous avons développé une nouvelle façon de souder par points deux tôles placées l’une sur l’autre sans entrefer (Magnetic Pulse Spot Welding – MPSW). Ce nouveau procédé permet d’envisager l’assemblage hétérogène de structures automobile ou la connexion de batteries entre elles sans chauffage. Le procédé a été validé sur l’assemblage hétérogène Al/Fe. Des essais de traction quasi-statiques et dynamiques nous ont permis de démontrer la qualité des points de soudure
Regular Solar Radio Imaging at Arecibo: Space Weather Perspective of Evolution of Active Regions
The sudden release of magnetic energy on the Sun drives powerful solar flares
and coronal mass ejections. The key issue is the difficulty in predicting the
occurrence time and location of strong solar eruptions, i.e., those leading to
the high impact space weather disturbances at the near-Earth environment. Solar
radio imaging helps identify the magnetic field characteristics of active
regions susceptible to intense flares and energetic coronal mass ejections.
Mapping of the Sun at X-band (8.1 -- 9.3 GHz) with the 12-m radio telescope at
the Arecibo Observatory allows monitoring of the evolution of the brightness
temperature of active regions in association with the development of magnetic
complexity, which can lead to strong eruptions. For a better forecasting
strategy in the future, such ground-based radio observations of high-spatial
and temporal resolution, along with a full polarization capability, would have
tremendous potential not only to understand the magnetic activity of solar
eruptions, but also for revealing the particle acceleration mechanism and
additional exciting science.Comment: 11 pages and 3 figures (White Paper Submitted to `Decadal Survey for
Solar and Space Physics (Heliophysics) 2024-2033'
High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT
Pulsar radio emission undergoes dispersion due to the presence of free
electrons in the interstellar medium (ISM). The dispersive delay in the arrival
time of pulsar signal changes over time due to the varying ISM electron column
density along the line of sight. Correcting for this delay accurately is
crucial for the detection of nanohertz gravitational waves using Pulsar Timing
Arrays. In this work, we present in-band and inter-band DM estimates of four
pulsars observed with uGMRT over the timescale of a year using two different
template alignment methods. The DMs obtained using both these methods show only
subtle differences for PSR 1713+0747 and J19093744. A considerable offset is
seen in the DM of PSR J1939+2134 and J21450750 between the two methods. This
could be due to the presence of scattering in the former and profile evolution
in the latter. We find that both methods are useful but could have a systematic
offset between the DMs obtained. Irrespective of the template alignment methods
followed, the precision on the DMs obtained is about pc cm
using only BAND3 and pc cm after combining data from BAND3 and
BAND5 of the uGMRT. In a particular result, we have detected a DM excess of
about pc cm on 24 February 2019 for PSR J21450750.
This excess appears to be due to the interaction region created by fast solar
wind from a coronal hole and a coronal mass ejection (CME) observed from the
Sun on that epoch. A detailed analysis of this interesting event is presented.Comment: 11 pages, 6 figures, 2 tables. Accepted by A&
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