scholarly journals LOFAR radio search for single and periodic pulses from M 31

2020 ◽  
Vol 634 ◽  
pp. A3 ◽  
Author(s):  
Joeri van Leeuwen ◽  
Klim Mikhailov ◽  
Evan Keane ◽  
Thijs Coenen ◽  
Liam Connor ◽  
...  
Keyword(s):  
Low Frequency ◽  
Crab Pulsar ◽  
Radio Bursts ◽  
Pulse Emission ◽  
Giant Pulses ◽  
Wide Range ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
M 31 ◽  
Pulsar Populations

Bright short radio bursts are emitted by sources at a wide range of distances: from the nearby Crab pulsar to remote fast radio bursts (FRBs). FRBs are likely to originate from distant neutron stars, but our knowledge of the radio pulsar population has been limited to the Galaxy and the Magellanic Clouds. In an attempt to increase our understanding of extragalactic pulsar populations and their giant-pulse emission, we employed the low-frequency radio telescope LOFAR to search the Andromeda galaxy (M 31) for radio bursts emitted by young Crab-like pulsars. For direct comparison we also present a LOFAR study on the low-frequency giant pulses from the Crab pulsar; their fluence distribution follows a power law with slope 3.04 ± 0.03. A number of candidate signals were detected from M 31, but none proved persistent. FRBs are sometimes thought of as Crab-like pulsars with exceedingly bright giant pulses; based on our sensitivity, we can rule out that M 31 hosts pulsars that are more than an order of magnitude brighter than the Crab pulsar if their pulse scattering follows that of the known FRBs.

scholarly journals Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition

2020 ◽  
Vol 494 (2) ◽  
pp. 2948-2968 ◽  
Author(s):  
E J Polzin ◽  
R P Breton ◽  
B Bhattacharyya ◽  
D Scholte ◽  
C Sobey ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Low Frequency ◽  
Line Of Sight ◽  
Observational Constraints ◽  
Main Body ◽  
Theoretical Studies ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Mechanism Transition ◽  
Hubble Time

ABSTRACT We present a comparative study of the low-frequency eclipses of spider (compact and irradiating binary) PSRs B1957+20 and J1816+4510. Combining these data with those of three other eclipsing systems we study the frequency dependence of the eclipse duration. PSRs B1957+20 and J1816+4510 have similar orbital properties, but the companions to the pulsars have masses that differ by an order of magnitude. A dedicated campaign to simultaneously observe the pulsed and imaged continuum flux densities throughout the eclipses reveals many similarities between the excess material within the two binaries, irrespective of the companion star properties. The observations show that the pulsar fluxes are removed from the line of sight throughout the main body of the eclipses. For PSR J1816 + 4510, we present the first direct evidence of an eclipse mechanism that transitions from one that removes the pulsar flux from the line of sight to one that merely smears out pulsations, and claim that this is a consequence of scattering in a tail of material flowing behind the companion. Inferred mass-loss rates from the companion stars are found to be $\dot{M}_{\text{C}} \sim 10^{-12}$ and $\sim 2 \times 10^{-13}\,\mathrm{M}_\odot$ yr−1 for PSR B1957+20 and PSR J1816 + 4510, respectively; seemingly too low to evaporate the stars within Hubble time. Measurements of eclipse durations over a wide range of radio frequencies show a significant dependence of eclipse duration on frequency for all pulsars, with wider eclipses at lower frequencies. These results provide a marked improvement in the observational constraints available for theoretical studies of the eclipse mechanisms.

scholarly journals Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). VIII. A less biased view of the early co-evolution of black holes and host galaxies

2019 ◽  
Vol 71 (6) ◽  
Author(s):  
Takuma Izumi ◽  
Masafusa Onoue ◽  
Yoshiki Matsuoka ◽  
Tohru Nagao ◽  
Michael A Strauss ◽  
...  
Keyword(s):  
Black Holes ◽  
Far Infrared ◽  
Supermassive Black Holes ◽  
Host Galaxies ◽  
Star Forming ◽  
Wide Range ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
Local Relation ◽  
Almost All

Abstract We present ALMA [C ii] line and far-infrared (FIR) continuum observations of three $z \gt 6$ low-luminosity quasars ($M_{\rm 1450} \gt -25$ mag) discovered by our Subaru Hyper Suprime-Cam (HSC) survey. The [C ii] line was detected in all three targets with luminosities of $(2.4\mbox{--}9.5) \times 10^8\, L_{\odot }$, about one order of magnitude smaller than optically luminous ($M_{\rm 1450} \lesssim -25$ mag) quasars. The FIR continuum luminosities range from $\lt 9 \times 10^{10}\, L_{\odot }$ (3 $\sigma$ limit) to ${\sim } 2 \times 10^{12}\, L_{\odot }$, indicating a wide range in star formation rates in these galaxies. Most of the HSC quasars studied thus far show [C ii]/ FIR luminosity ratios similar to local star-forming galaxies. Using the [C ii]-based dynamical mass ($M_{\rm dyn}$) as a surrogate for bulge stellar mass ($M_{\rm\, bulge}$), we find that a significant fraction of low-luminosity quasars are located on or even below the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation, particularly at the massive end of the galaxy mass distribution. In contrast, previous studies of optically luminous quasars have found that black holes are overmassive relative to the local relation. Given the low luminosities of our targets, we are exploring the nature of the early co-evolution of supermassive black holes and their hosts in a less biased way. Almost all of the quasars presented in this work are growing their black hole mass at a much higher pace at $z \sim 6$ than the parallel growth model, in which supermassive black holes and their hosts grow simultaneously to match the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation at all redshifts. As the low-luminosity quasars appear to realize the local co-evolutionary relation even at $z \sim 6$, they should have experienced vigorous starbursts prior to the currently observed quasar phase to catch up with the relation.

scholarly journals Super-giant pulses from the Crab pulsar: energy distribution and occurrence rate

2019 ◽  
Vol 490 (1) ◽  
pp. L12-L16 ◽  
Author(s):  
Apurba Bera ◽  
Jayaram N Chengalur
Keyword(s):  
Energy Distribution ◽  
Power Law ◽  
Pulse Energy ◽  
Occurrence Rate ◽  
Crab Pulsar ◽  
Limited Sample ◽  
Pulse Emission ◽  
High Fluences ◽  
Giant Pulses ◽  
Power Law Index

ABSTRACT We present statistical analysis of a fluence-limited sample of over 1100 giant pulses from the Crab pulsar, with fluence > 130 Jy ms at ∼1330 MHz. These were detected in ∼260 h of observation with the National Centre for Radio Astrophysics (NCRA) 15 m radio telescope. We find that the pulse-energy distribution follows a power law with index $\rm \alpha \approx -3$ at least up to a fluence of ∼5 Jy s. The power-law index agrees well with that found for lower-energy pulses in the range 3–30 Jy ms. The fluence distribution of the Crab pulsar hence appears to follow a single power law over ∼3 orders of magnitude in fluence. We do not see any evidence for the flattening at high fluences reported by earlier studies. We also find that, at these fluence levels, the rate of giant-pulse emission varies by as much as a factor of ∼5 on time-scales of a few days, although the power-law index of the pulse-energy distribution remains unchanged. The slope of the fluence distribution for Crab giant pulses is similar to that recently determined for the repeating FRB 121102. We also find an anti-correlation between the pulse fluence and the pulse width, so that more energetic pulses are preferentially shorter.

scholarly journals A LOW FREQUENCY SURVEY OF GIANT PULSES FROM THE CRAB PULSAR

2016 ◽  
Vol 829 (2) ◽  
pp. 62 ◽  
Author(s):  
T. Eftekhari ◽  
K. Stovall ◽  
J. Dowell ◽  
F. K. Schinzel ◽  
G. B. Taylor
Keyword(s):  
Low Frequency ◽  
Crab Pulsar ◽  
Giant Pulses ◽  
Frequency Survey

scholarly journals Narrow-band giant pulses from the Crab pulsar

2021 ◽  
Vol 508 (2) ◽  
pp. 1947-1953
Author(s):  
Parasar Thulasiram ◽  
Hsiu-Hsien Lin
Keyword(s):  
Narrow Band ◽  
Crab Pulsar ◽  
Radio Bursts ◽  
Propagation Effect ◽  
Emission Mechanism ◽  
Radio Observatory ◽  
Spectral Fitting ◽  
Giant Pulses ◽  
Intrinsic Emission

ABSTRACT We used a new spectral-fitting technique to identify a subpopulation of 6 narrow-band giant pulses from the Crab pulsar out of a total of 1578. These giant pulses were detected in 77 min of observations with the 46-m dish at the Algonquin Radio Observatory at 400–800 MHz. The narrow-band giant pulses consist of both main- and inter-pulses, thereby being more likely to be caused by an intrinsic emission mechanism as opposed to a propagation effect. Fast radio bursts (FRBs) have demonstrated similar narrow-band features, while only little has been observed in the giant pulses of pulsars. We report the narrow-band giant pulses with Δν/ν of the order of 0.1, which is close to the value of 0.05 reported for the repeater FRB 20190711A. Hence, the connection between FRBs and giant pulses of pulsars is further established.

scholarly journals Radio emission physics in the Crab pulsar

2016 ◽  
Vol 82 (3) ◽  
Author(s):  
Jean A. Eilek ◽  
Timothy H. Hankins
Keyword(s):  
High Altitude ◽  
Low Frequency ◽  
High Time Resolution ◽  
Emission Model ◽  
Crab Pulsar ◽  
Radio Observations ◽  
Wide Range ◽  
Cascade Models ◽  
Standard Picture ◽  
Radio Power

We review our high-time-resolution radio observations of the Crab pulsar and compare our data to a variety of models for the emission physics. The Main Pulse and the Low Frequency Interpulse come from regions somewhere in the high-altitude emission zones (caustics) that also produce pulsed X-ray and${\it\gamma}$-ray emission. Although no emission model can fully explain these two components, the most likely models suggest they arise from a combination of beam-driven instabilities, coherent charge bunching and strong electromagnetic turbulence. Because the radio power fluctuates on a wide range of time scales, we know the emission zones are patchy and dynamic. It is tempting to invoke unsteady pair creation in high-altitude gaps as the source of the variability, but current pair cascade models cannot explain the densities required by any of the likely models. It is harder to account for the mysterious High Frequency Interpulse. We understand neither its origin within the magnetosphere nor the striking emission bands in its dynamic spectrum. The most promising models are based on analogies with solar zebra bands, but they require unusual plasma structures which are not part of our standard picture of the magnetosphere. We argue that radio observations can reveal much about the upper magnetosphere, but work is required before the models can address all of the data.

scholarly journals Long-term study of extreme giant pulses from PSR B0950+08 with AARTFAAC

2020 ◽  
Vol 497 (1) ◽  
pp. 846-854
Author(s):  
Mark Kuiack ◽  
Ralph A M J Wijers ◽  
Antonia Rowlinson ◽  
Aleksandar Shulevski ◽  
Folkert Huizinga ◽  
...  
Keyword(s):  
Time Scale ◽  
Low Frequency ◽  
Transient Detection ◽  
Term Study ◽  
Long Term Study ◽  
Giant Pulses ◽  
Order Of Magnitude ◽  
Radio Transients ◽  
Detection Instrument

ABSTRACT We report on the detection of extreme giant pulses (GPs) from one of the oldest known pulsars, the highly variable PSR B0950+08, with the Amsterdam-ASTRON Radio Transient Facility And Analysis Centre (AARTFAAC), a parallel transient detection instrument operating as a subsystem of the LOw Frequency ARray (LOFAR). During processing of our Northern Hemisphere survey for low-frequency radio transients, a sample of 275 pulses with fluences ranging from 42 to 177 kJy ms were detected in one-second snapshot images. The brightest pulses are an order of magnitude brighter than those previously reported at 42 and 74 MHz, on par with the levels observed in a previous long-term study at 103 MHz. Both their rate and fluence distribution differ between and within the various studies done to date. The GP rate is highly variable, from 0 to 30 per hour, with only two 3-h observations accounting for nearly half of the pulses detected in the 96 h surveyed. It does not vary significantly within a few-hour observation, but can vary strongly one from day to the next. The spectra appear strongly and variably structured, with emission sometimes confined to a single 195.3 kHz subband, and the pulse spectra changing on a time-scale of order 10 min.

scholarly journals Spectral Flattening of Crab Giant Pulses at Low Frequencies

2017 ◽  
Vol 13 (S337) ◽  
pp. 378-379
Author(s):  
Bradley W. Meyers ◽  
Steven E. Tremblay ◽  
N. D. Ramesh Bhat ◽  
Ryan M. Shannon
Keyword(s):  
Crab Pulsar ◽  
Giant Pulse ◽  
Pulse Emission ◽  
Low Frequencies ◽  
Pulsar Radio ◽  
Giant Pulses ◽  
Spectral Behaviour ◽  
The Mean ◽  
Murchison Widefield Array ◽  
Pulsar Radio Emission

AbstractThe frequency dependence of normal pulsar radio emission is typically observed to be a power law, with some indications of a flattening or turnover at low frequencies (≲ 100 MHz). The spectrum of the Crab pulsar’s giant pulse emission has not been examined as closely. We conducted simultaneous wideband observations of the Crab pulsar, with the Parkes radio telescope and the Murchison Widefield Array, to study the spectral behaviour of its giant pulses. Our analysis shows that the mean spectral index of Crab giant pulses flattens at low frequencies, from −2.6 ± 0.5 between the Parkes bands, to −0.7 ± 1.4 between the lowest MWA subbands.

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

2009 ◽  
Vol 23 (4) ◽  
pp. 191-198 ◽  
Author(s):  
Suzannah K. Helps ◽  
Samantha J. Broyd ◽  
Christopher J. James ◽  
Anke Karl ◽  
Edmund J. S. Sonuga-Barke
Keyword(s):  
Brain Activity ◽  
Sampling Rate ◽  
Low Frequency ◽  
Future Research ◽  
Adhd Symptoms ◽  
Default Mode ◽  
Very Low Frequency ◽  
Wide Range ◽  
Interference Hypothesis ◽  
Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

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