scholarly journals Limits on absorption from a 332-MHz survey for fast radio bursts

2020 ◽  
Vol 493 (3) ◽  
pp. 4418-4427 ◽  
Author(s):  
K M Rajwade ◽  
M B Mickaliger ◽  
B W Stappers ◽  
C G Bassa ◽  
R P Breton ◽  
...  
Keyword(s):  
Radio Emission ◽  
Compton Scattering ◽  
Low Frequency ◽  
Radio Bursts ◽  
Intensity Mapping ◽  
The Past ◽  
Upper Limit ◽  
Shock Region ◽  
Absorption Models ◽  
Post Shock

ABSTRACT Fast radio bursts (FRBs) are bright, extragalactic radio pulses whose origins are still unknown. Until recently, most FRBs have been detected at frequencies greater than 1 GHz with a few exceptions at 800 MHz. The recent discoveries of FRBs at 400 MHz from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope have opened up possibilities for new insights about the progenitors while many other low-frequency surveys in the past have failed to find any FRBs. Here, we present results from an FRB survey recently conducted at the Jodrell Bank Observatory at 332 MHz with the 76-m Lovell telescope for a total of 58 d. We did not detect any FRBs in the survey and report a 90${{\ \rm per\ cent}}$ upper limit of 5500 FRBs per day per sky for a Euclidean Universe above a fluence threshold of 46 Jy ms. We discuss the possibility of absorption as the main cause of non-detections in low-frequency (<800 MHz) searches and invoke different absorption models to explain the same. We find that Induced Compton Scattering alone cannot account for absorption of radio emission and that our simulations favour a combination of Induced Compton Scattering and Free-Free Absorption to explain the non-detections. For a free–free absorption scenario, our constraints on the electron density are consistent with those expected in the post-shock region of the ionized ejecta in superluminous supernovae.

scholarly journals Inverse Compton Scattering in pulsar physics

1996 ◽  
Vol 160 ◽  
pp. 159-162
Author(s):  
G.J. Qiao
Keyword(s):  
Radio Emission ◽  
Compton Scattering ◽  
Low Frequency ◽  
Position Angle ◽  
High Energy ◽  
Particle Energy ◽  
Important Process ◽  
Frequency Wave ◽  
Inverse Compton Scattering ◽  
Inverse Compton

AbstractInverse Compton Scattering (ICS) is a very important process not only in inner gap physics, but also for radio emission. ICS of high energy particles with thermal photons is the dominant and a very efficient mechanism of the particle energy loss above the neutron star surface, and is an important process in causing gap breakdown. The pulsar distribution in theP−Pdiagram and the observed mode changing phenomenon of some pulsars can be expained by the sparking conditions due to ICS. ICS of the secondary particles with the low frequency wave from the inner gap sparking can be responsible for radio emission. In this ICS model, many observational features of pulsar radio emission can be explained, such as: one core and two conal emission components, their different emission altitudes and relative time delay effects; spectral behavior of pulse profiles; the behavior of the linear polarization and position angle.

scholarly journals The spectacular cluster chain Abell 781 as observed with LOFAR, GMRT, and XMM-Newton

2019 ◽  
Vol 622 ◽  
pp. A19 ◽  
Author(s):  
A. Botteon ◽  
T. W. Shimwell ◽  
A. Bonafede ◽  
D. Dallacasa ◽  
F. Gastaldello ◽  
...  
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Thermal Emission ◽  
Low Frequency ◽  
Current Data ◽  
Mass Relation ◽  
Radio Halo ◽  
Main Cluster ◽  
Upper Limit ◽  
Main Component

Context. A number of merging galaxy clusters show the presence of large-scale radio emission associated with the intra-cluster medium (ICM). These synchrotron sources are generally classified as radio haloes and radio relics. Aims. Whilst it is commonly accepted that mergers play a crucial role in the formation of radio haloes and relics, not all the merging clusters show the presence of giant diffuse radio sources and this provides important information concerning current models. The Abell 781 complex is a spectacular system composed of an apparent chain of clusters on the sky. Its main component is undergoing a merger and hosts peripheral emission that is classified as a candidate radio relic and a disputed radio halo. Methods. We used new LOw Frequency ARay (LOFAR) observations at 143 MHz and archival Giant Metrewave Radio Telescope (GMRT) observations at 325 and 610 MHz to study radio emission from non-thermal components in the ICM of Abell 781. Complementary information came from XMM-Newton data, which allowed us to investigate the connection with the thermal emission and its complex morphology. Results. The origin of the peripheral emission is still uncertain. We speculate that it is related to the interaction between a head tail radio galaxy and shock. However, the current data allow us only to set an upper limit of ℳ <  1.4 on the Mach number of this putative shock. Instead, we successfully characterise the surface brightness and temperature jumps of a shock and two cold fronts in the main cluster component of Abell 781. Their positions suggest that the merger is involving three substructures. We do not find any evidence for a radio halo either at the centre of this system or in the other clusters of the chain. We place an upper limit to the diffuse radio emission in the main cluster of Abell 781 that is a factor of 2 below the current radio power-mass relation for giant radio haloes.

scholarly journals The search for radio emission from exoplanets using LOFAR beam-formed observations: Jupiter as an exoplanet

2019 ◽  
Vol 624 ◽  
pp. A40 ◽  
Author(s):  
Jake D. Turner ◽  
Jean-Mathias Grießmeier ◽  
Philippe Zarka ◽  
Iaroslavna Vasylieva
Keyword(s):  
Radio Emission ◽  
Low Frequency ◽  
Scaling Factor ◽  
Theoretical Studies ◽  
Radio Bursts ◽  
Post Processing ◽  
Sensitivity Limit ◽  
Circularly Polarized ◽  
Peak Flux ◽  
Emission Detection

Context. The magnetized solar system planets are strong radio emitters and theoretical studies suggest that the radio emission from nearby exoplanets in close-in orbits could reach intensity levels 103–107 times higher than Jupiter’s decametric emission. Detection of exoplanets in the radio domain would open up a brand new field of research, however, currently there are no confirmed detections at radio frequencies. Aims. We investigate the radio emission from Jupiter, scaled such that it mimics emission coming from an exoplanet, with low-frequency beam-formed observations using LOFAR. The goals are to define a set of observables that can be used as a guideline in the search for exoplanetary radio emission and to measure effectively the sensitivity limit for LOFAR beam-formed observations. Methods. We observe “Jupiter as an exoplanet” by dividing a LOFAR observation of Jupiter by a down-scaling factor and adding this observation to beam-formed data of the “sky background”. Then we run this artificial dataset through our total intensity (Stokes-I) and circular polarization (Stokes-V) processing and post-processing pipelines and determine up to which down-scaling factor Jupiter is still detected in the dataset. Results. We find that exoplanetary radio bursts can be detected at 5 pc if the circularly polarized flux is 105 times stronger than the typical level of Jupiter’s radio bursts during active emission events (~4 × 105 Jy). Equivalently, circularly polarized radio bursts can be detected up to a distance of 20 pc (encompassing the known exoplanets 55 Cnc, Tau Boötis, and Upsilon Andromedae) assuming the level of emission is 105 times stronger than the peak flux of Jupiter’s decametric burst emission (~6 × 106 Jy).

scholarly journals The FRATS project: real-time searches for fast radio bursts and other fast transients with LOFAR at 135 MHz

2019 ◽  
Vol 621 ◽  
pp. A57 ◽  
Author(s):  
S. ter Veen ◽  
J. E. Enriquez ◽  
H. Falcke ◽  
J. P. Rachen ◽  
M. van den Akker ◽  
...  
Keyword(s):  
Real Time ◽  
Low Frequency ◽  
Radio Bursts ◽  
Pilot Survey ◽  
Upper Limit ◽  
Previous Decade ◽  
Fast Transients ◽  
Radio Transients ◽  
The Individual ◽  
Galactic Sources

Context. In the previous decade, two new classes of fast radio transients were detected: the Galactic, rotating radio transients (RRATs) and the extragalactic fast radio bursts (FRBs). If the detectable emission of these objects extends to lower radio frequencies, the LOw Frequency ARray (LOFAR) is ideally suited to seek and localize these transients at frequencies of 10–250 MHz. This is due to LOFAR’s sensitivity, diverse beamform capabilities, and transient buffers for the individual elements that allow post-event imaging of events, potentially at arcsecond resolution. Aims. Our aim is to identify and localize pulses at frequencies below 250 MHz and, in the case of nondetections, derive upper limits on the sky and volume rates of FRBs. Methods. A real-time search program for fast radio transients is installed on the LOFAR systems which runs commensally with other observations, and uses the wide incoherent LOFAR beam (11.25 deg2 at 150 MHz). Buffered data from hundreds of dipoles are used to reconstruct the direction and polarization information of the event, and to distinguish between celestial, terrestrial, and instrumental origins. Results. Observations were taken covering either the frequency range 119–151 MHz or in four frequency bands, each of 2 MHz in width, centered at 124, 149, 156, and 185 MHz. A first pilot survey covered a range of dispersion measures (DM) below 120 pc cm−3, focusing on Galactic sources, and resulted in an upper limit on the transient rate at LOFAR frequencies of less than 1500 events per sky per day above a fluency of 1.6 kJy ms for an 8-ms pulse. A second pilot survey covered a range of DMs below 500 pc cm−3, focusing on extragalactic sources to about 1 Gpc, and resulted in an upper limit of 1400 events per sky per day above a fluency of 6.0 kJy ms for an 8-ms pulse. Using a model for the distance-DM relationship, this equates to an upper limit of 134 events per Gpc3 per day.

scholarly journals Murchison Widefield Array rapid-response observations of the short GRB 180805A

2021 ◽  
Vol 38 ◽  
Author(s):  
G. E. Anderson ◽  
P. J. Hancock ◽  
A. Rowlinson ◽  
M. Sokolowski ◽  
A. Williams ◽  
...  
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Response Times ◽  
Low Frequency ◽  
Rapid Response ◽  
Gamma Ray Burst ◽  
Upper Limit ◽  
Emission Models ◽  
Murchison Widefield Array ◽  
Prompt Emission

Abstract Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a $3\sigma$ persistent flux density upper limit of 40.2 mJy beam–1. Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3\sigma$ limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam–1, respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a $6\sigma$ fluence upper-limit range from 570 Jy ms at DM $=3\,000$ pc cm–3 ( $z\sim 2.5$ ) to 1 750 Jy ms at DM $=200$ pc cm–3 ( $z\sim 0.1)$ , corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.

Hyperfine Polarization Structure of Jupiter’s Radio Bursts

1976 ◽  
Vol 3 (1) ◽  
pp. 49-51 ◽  
Author(s):  
P. S. Whitham
Keyword(s):  
Fine Structure ◽  
Radio Emission ◽  
Preliminary Report ◽  
Low Frequency ◽  
Incident Radiation ◽  
Radio Bursts ◽  
Polarization Structure ◽  
Yield Information ◽  
Linearly Polarized ◽  
Elliptically Polarized

Observations of Jupiter’s decametric radio burst have established that above 20 MHz more than 90% of the emission is elliptically polarized in the RH sense, but below this frequency the proportion of the LH polarization increases (Sherrill 1965) until at 10 MHz nearly 40% of the emission is LH polarized (Dowden 1963). The best time and frequency resolutions so far obtained when examining the polarization of the spectra of Jupiter’s bursts have been 10 ms and 50 kHz respectively (Gordon and Warwick 1967, Riihimaa 1975). To study the fine structure of Jupiter’s emission as observed by the linearly polarized Llanherne low frequency radio telescope (Ellis 1972), spectrum analysers with resolutions in the ranges 0.3 — 1 msec and 2–10 kHz have been used (Ellis 1973a, 1973b, 1974, 1975). A new telescope at Llanherne, which is capable of detecting the RH and LH circular components of incident radiation, is being used in conjunction with these analysers to yield information of the hyperfine polarization structure of Jupiter’s decametric radio emission. This paper is a preliminary report of this investigation.

scholarly journals The corona of GJ 1151 in the context of star–planet interaction

2020 ◽  
Vol 497 (1) ◽  
pp. 1015-1019
Author(s):  
G Foster ◽  
K Poppenhaeger ◽  
J D Alvarado-Gómez ◽  
J H M M Schmitt
Keyword(s):  
Radio Emission ◽  
Low Frequency ◽  
Mass Star ◽  
Coronal Temperature ◽  
X Ray ◽  
Upper Limit ◽  
Radio Signals ◽  
Low Mass ◽  
Time Periods

ABSTRACT The low-mass star GJ 1151 has been reported to display variable low-frequency radio emission, which has been interpreted as a signpost of coronal star–planet interactions with an unseen exoplanet. Here we report the first X-ray detection of GJ 1151’s corona based on the XMM–Newton data. We find that the star displays a small flare during the X-ray observation. Averaged over the observation, we detect the star with a low coronal temperature of 1.6 MK and an X-ray luminosity of LX = 5.5 × 1026 erg s−1. During the quiescent time periods excluding the flare, the star remains undetected with an upper limit of $L_{\mathrm{ X},\, \mathrm{ qui}} \le 3.7\times 10^{26}$ erg s−1. This is compatible with the coronal assumptions used in a recently published model for a star–planet interaction origin of the observed radio signals from this star.

scholarly journals Digital Glomus Tumor: Bibliographic Review of the Studies Published over the Past 10 Years

2021 ◽  
Vol 49 (01) ◽  
pp. 046-055
Author(s):  
Victoria Hernández ◽  
Tania Lena ◽  
Eliana Camacho ◽  
Matías Craviotto
Keyword(s):  
Glomus Tumor ◽  
Case Reports ◽  
Low Frequency ◽  
Benign Neoplasm ◽  
Surgical Excision ◽  
Soft Tissue Tumors ◽  
Glomus Tumors ◽  
The Past ◽  
Pubmed Search ◽  
Magnetic Resonance Imaging Mri

AbstractGlomus tumors are a mostly benign neoplasm that constitutes less than 4% of upper-limb soft-tissue tumors. Its unspecific clinical presentation, added to its low frequency, leads to a late diagnosis.The objective of the present study is to update the clinical-paraclinical approach and the surgical technique used in the treatment.We carried out a literature review from 2014 to 2019 on digital glomus tumor in the hand in adult patients using the PubMed search engine.In most of the publications analyzed, the diagnosis was clinical, with a delay of 1 to 10 years. Plain radiography is the most requested study; of the 16 articles reporting its indication, only half evidenced compatible changes. Magnetic resonance imaging (MRI) was requested in 15 articles, presenting normal results in 3 of them. The treatment of choice was surgical excision using a transungual approach. Only 4 articles report recurrence after excision.Although there is diversity in the approach to these tumors, we conclude that the diagnosis is clinical, and the treatment surgical, and there is no consensus regarding the paraclinical indication. The information available comes mainly from case reports, publications that contribute to the generation of evidence for the clinical practice in rare diseases such as this one.

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

2019 ◽  
Vol 15 (S356) ◽  
pp. 375-375
Author(s):  
Sarah White
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Visual Inspection ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Relativistic Jets ◽  
The Galaxy ◽  
Murchison Widefield Array ◽  
Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

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