181 research outputs found
A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey
Discoveries of rotating radio transients and fast radio bursts (FRBs) in
pulsar surveys suggest that more of such transient sources await discovery in
archival data sets. Here we report on a single-pulse search for dispersed radio
bursts over a wide range of Galactic latitudes (|b| < ) in data
previously searched for periodic sources by Burgay et al. We re-detected 20 of
the 42 pulsars reported by Burgay et al. and one rotating radio transient
reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into
account this result, and other recent surveys at Parkes, we corrected for
detection sensitivities based on the search software used in the analyses and
the different backends used in these surveys and find that the all-sky FRB
event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be FRBs day sky, where the
uncertainties represent a confidence interval. While this rate is lower
than inferred from previous studies, as we demonstrate, this combined event
rate is consistent with the results of all systematic FRB searches at Parkes to
date and does not require the need to postulate a dearth of FRBs at
intermediate latitudes.Comment: Accepted, 10 pages, 6 figure
GBTrans: A commensal search for radio pulses with the Green Bank twenty metre telescope
We describe GBTrans, a real-time search system designed to find fast radio
bursts (FRBs) using the 20-m radio telescope at the Green Bank Observatory. The
telescope has been part of the Skynet educational program since 2015. We give
details of the observing system and report on the non-detection of FRBs from a
total observing time of 503 days. Single pulses from four known pulsars were
detected as part of the commensal observing. The system is sensitive enough to
detect approximately half of all currently known FRBs and we estimate that our
survey probed redshifts out to about 0.3 corresponding to an effective survey
volume of around 124,000~Mpc. Modeling the FRB rate as a function of
fluence, , as a power law with , we constrain the index at the 90% confidence level. We discuss the implications of this result
in the context of constraints from other FRB surveys.Comment: 7 pages, 6 figure
Simultaneous radio and X-ray observations of PSR B0611+22
International audienceWe report results from simultaneous radio and X-ray observations of PSR B0611+22 which is known to exhibit bursting in its single-pulse emission. The pulse phase of the bursts vary with radio frequency. The bursts are correlated in 327/150 MHz data sets while they are anti-correlated, with bursts at one frequency associated with normal emission at the other, in 820/150 MHz data sets. Also, the flux density of this pulsar is lower than expected at 327 MHz assuming a power law. We attribute this unusual behaviour to the pulsar itself rather than absorption by external astrophysical sources. Using this data set over an extensive frequency range, we show that the bursting phenomenon in this pulsar exhibits temporal variance over a span of few hours. We also show that the bursting is quasi-periodic over the observed band. The anti-correlation in the phase offset of the burst mode at different frequencies suggests that the mechanisms responsible for phase offset and flux enhancement have different dependencies on the frequency. We did not detect the pulsar with XMM–Newton and place a 99 per cent confidence upper limit on the X-ray efficiency of 10 −5
Simultaneous Radio And X-Ray Observations Of Psr B0611+22
We report results from simultaneous radio and X-ray observations of PSR B0611+22 which is known to exhibit bursting in its single-pulse emission. The pulse phase of the bursts vary with radio frequency. The bursts are correlated in 327/150 MHz data sets while they are anti-correlated, with bursts at one frequency associated with normal emission at the other, in 820/150 MHz data sets. Also, the flux density of this pulsar is lower than expected at 327 MHz assuming a power law. We attribute this unusual behaviour to the pulsar itself rather than absorption by external astrophysical sources. Using this data set over an extensive frequency range, we show that the bursting phenomenon in this pulsar exhibits temporal variance over a span of few hours. We also show that the bursting is quasi-periodic over the observed band. The anti-correlation in the phase offset of the burst mode at different frequencies suggests that the mechanisms responsible for phase offset and flux enhancement have different dependencies on the frequency. We did not detect the pulsar with XMM-Newton and place a 99 per cent confidence upper limit on the X-ray efficiency of 10-5
Evidence for an abundant old population of Galactic ultra long period magnetars and implications for fast radio bursts
Two recent discoveries, namely PSR J0901-4046 and GLEAM-X J162759.5-523504.3
(hereafter GLEAM-X J1627), have corroborated an extant population of radio-loud
periodic sources with long periods (76 s and 1091 s respectively) whose
emission can hardly be explained by rotation losses. We argue that GLEAM-X
J1627 is a highly-magnetized object consistent with a magnetar (an ultra long
period magnetar - ULPM), and demonstrate it is unlikely to be either a
magnetically or a rotationally-powered white dwarf. By studying these sources
together with previously detected objects, we find there are at least a handful
of promising candidates for Galactic ULPMs. The detections of these objects
imply a substantial number, and for PSR
J0901--4046 like and GLEAM-X J1627 like objects, respectively, within our
Galaxy. These source densities, as well as cooling age limits from
non-detection of thermal X-rays, Galactic offsets, timing stability and dipole
spindown limits, all imply the ULPM candidates are substantially older than
confirmed Galactic magnetars and that their formation channel is a common one.
Their existence implies widespread survival of magnetar-like fields for several
Myr, distinct from the inferred behaviour in confirmed Galactic magnetars.
ULPMs may also constitute a second class of FRB progenitors which could
naturally exhibit very long periodic activity windows. Finally, we show that
existing radio campaigns are biased against detecting objects like these and
discuss strategies for future radio and X-ray surveys to identify more such
objects. We estimate that more such objects should be detected
with SKA-MID and DSA-2000.Comment: 22 pages, 10 figures. Published in MNRA
Point counting on reductions of CM elliptic curves
We give explicit formulas for the number of points on reductions of elliptic
curves with complex multiplication by any imaginary quadratic field. We also
find models for CM -curves in certain cases. This generalizes
earlier results of Gross, Stark, and others.Comment: Minor corrections. To appear in Journal of Number Theor
The significance of promitochondrial structures in rat liver for mitochondrial biogenesis
1. The heavy, light and fluffy mitochondrial fractions obtained by differential centrifugation were further characterized with respect to their protein synthesizing ability in vitro, their nucleic acid content, buoyant density of their DNA and ultrastructure. 2. The light mitochondrial fraction synthesized proteins in vitro at a rate 4-5 times as high as heavy and fluffy mitochondria. The incorporation ability of this fraction was also maximally affected by the thyroid status of the animal. The radioactivity in leucyl-tRNA of the light mitochondrial fraction was about 3-4 times as high as that of the other two fractions. 3. The heavy, light and fluffy mitochondrial fractions contained small but consistent amounts of RNA and DNA. Although the DNA content was the same in all mitochondria fractions, the light mitochondria contained relatively more RNA. The buoyant density of DNA from all the fractions was 1.701g/cm3. 4. Electron microscopy revealed that the heavy mitochondria have a typical mitochondrial architecture, with densely packed cristae and a well developed double membrane. Light mitochondria were also surrounded by double membranes, but were smaller in size and contained less cristae. The fluffy fraction consisted of a mixture of well formed mitochondria and those in the process of degradation. 5. The significance of these findings in relation to mammalian mitochondrial genesis is discussed
Multi-frequency study of the peculiar pulsars PSR B0919+06 and PSR B1859+07
Since their discovery more than 50 years ago, broadband radio studies of
pulsars have generated a wealth of information about the underlying physics of
radio emission. In order to gain some further insights into this elusive
emission mechanism, we performed a multi-frequency study of two very well-known
pulsars, PSR~B0919+06 and PSR~B1859+07. These pulsars show peculiar radio
emission properties whereby the emission shifts to an earlier rotation phase
before returning to the nominal emission phase in a few tens of pulsar
rotations (also known as `swooshes'). We confirm the previous claim that the
emission during the swoosh is not necessarily absent at low frequencies and the
single pulses during a swoosh show varied behaviour at 220~MHz. We also confirm
that in PSR~B0919+06, the pulses during the swoosh show a chromatic dependence
of the maximum offset from the normal emission phase with the offset following
a consistent relationship with observing frequency. We also observe that the
flux density spectrum of the radio profile during the swoosh is inverted
compared to the normal emission. For PSR~B1859+07, we have discovered a new
mode of emission in the pulsar that is potentially quasi-periodic with a
different periodicity than is seen in its swooshes. We invoke an emission model
previously proposed in the literature and show that this simple model can
explain the macroscopic observed characteristics in both pulsars. We also argue
that pulsars that exhibit similar variability on short timescales may have the
same underlying emission mechanism.Comment: 13 pages, 13 figures, 1 table, accepted for publication in MNRA
Setiburst: A Robotic, Commensal, Realtime Multi-Science Backend For The Arecibo Telescope
Radio astronomy has traditionally depended on observatories allocating time to observers for exclusive use of their telescopes. The disadvantage of this scheme is that the data thus collected is rarely used for other astronomy applications, and in many cases, is unsuitable. For example, properly calibrated pulsar search data can, with some reduction, be used for spectral line surveys. A backend that supports plugging in multiple applications to a telescope to perform commensal data analysis will vastly increase the science throughput of the facility. In this paper, we presen
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