We present 41 bursts from the first repeating fast radio burst (FRB) discovered (FRB 121102). A deep search has allowed us to probe unprecedentedly low burst energies during two consecutive ...observations (separated by one day) using the Arecibo telescope at 1.4 GHz. The bursts are generally detected in less than one-third of the 580 MHz observing bandwidth, demonstrating that narrowband FRB signals may be more common than previously thought. We show that the bursts are likely faint versions of previously reported multi-component bursts. There is a striking lack of bursts detected below 1.35 GHz and simultaneous Very Large Array observations at 3 GHz did not detect any of the 41 bursts, but did detect one that was not seen with Arecibo, suggesting preferred radio emission frequencies that vary with epoch. A power-law approximation of the cumulative distribution of burst energies yields an index −1.8 0.3, which is much steeper than the previously reported value of ∼−0.7. The discrepancy may be evidence for a more complex energy distribution. We place constraints on the possibility that the associated persistent radio source is generated by the emission of many faint bursts (∼700 ms−1). We do not see a connection between burst fluence and wait time. The distribution of wait times follows a log-normal distribution centered around ∼200 s; however, some bursts have wait times below 1 s and as short as 26 ms, which is consistent with previous reports of a bimodal distribution. We caution against exclusively integrating over the full observing band during FRB searches, because this can lower signal to noise.
Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin. The only known repeating fast radio burst source-FRB 121102-has been localized to a star-forming ...region in a dwarf galaxy at redshift 0.193 and is spatially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1.46 × 10
radians per square metre to +1.33 × 10
radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole. The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula or supernova remnant surrounding a young neutron star.
This book is like a time capsule containing a selection of interviews that aired on Hromadske Radio’s Ukraine Calling show. They capture what people were thinking during a critical time in the ...country’s history, from the July 2016 NATO Summit through to Volodymyr Zelenskyy’s 2019 landslide election victories. Decision makers, opinion makers, and other interesting people commented on events of the day as well as larger issues. Topics range from politics to sports, religion, history, war, books, diplomacy, health, business, art, holidays, foreign policy, anniversaries, public opinion to freedom of speech. Interview guests include Canada’s then Foreign Minister Chrystia Freeland, writer Andrey Kurkov, Crimean political prisoner Hennadii Afanasiev, who was tortured in 2014, Ukraine’s acting Health Minister Ulana Suprun, American analyst/journalist Brian Whitmore, UNHRC’s Pablo Mateu, ethnologist Ihor Poshyvailo, investment banker Olena Bilan, Tufts University’s Daniel Drezner, a cameo appearance by Boris Johnson, and many more. Together these interviews provide a unique, diverse, and kaleidoscopic perspective conveying the substance, atmosphere, and flavor of Ukraine while it was on the receiving end of a hybrid war from Russia.
Reseña del libro de Luis Miguel Pedrero Esteban y José María García Lastra-Núñez (eds.) (2019), La transformación digital de la radio. Diez claves para su comprensión profesional y académica. ...Valencia: Tirant Humanidades, 307 páginas.
This paper introduces a new solution to improve the performance for secondary systems in radio frequency (RF) powered cognitive radio networks (CRNs). In a conventional RF-powered CRN, the secondary ...system works based on the harvest-then-transmit protocol. That is, the secondary transmitter (ST) harvests energy from primary signals and then uses the harvested energy to transmit data to its secondary receiver (SR). However, with this protocol, the performance of the secondary system is much dependent on the amount of harvested energy as well as the primary channel activity, e.g., idle and busy periods. Recently, ambient backscatter communication has been introduced, which enables the ST to transmit data to the SR by backscattering ambient signals. Therefore, it is potential to be adopted in the RF-powered CRN. We investigate the performance of RF-powered CRNs with ambient backscatter communication over two scenarios, i.e., overlay and underlay CRNs. For each scenario, we formulate and solve the optimization problem to maximize the overall transmission rate of the secondary system. Numerical results show that by incorporating such two techniques, the performance of the secondary system can be improved significantly compared with the case when the ST performs either harvest-then-transmit or ambient backscatter technique.
La creación del reggaetón tiene sus raíces en diferentes elementos musicales que lo hacen un género transnacional -ya que proviene del hip-hop estadounidense, el reggae jamaiquino, rap panameño, ...cubano, y puertorriqueño, así como una infinidad de ritmos caribeños-; sin embargo, este se desarrolla mayormente en Puerto Rico (Marshall et al.; Rivera-Rideau). Es decir, esa obsesión de lo nacional dentro de la música popular y los elementos culturales es privilegiada cuando se habla de Ricky Martin, Héctor Lavoe, o Jennifer López, entre otros; sin embargo, cuando se habla de Daddy Yankee, Tego Calderón, Wisin y Yandel, o Arcangel, entre otros, muchos de los puertorriqueños tienden a pensarlo como un elemento de "mal gusto" ya que atenta con su concepción imaginada de nación en el contexto puertorriqueño. Sin embargo, al final del video podemos observar como los millonarios en motora no son Jowell y Randy, sino que son dos hombres blancos. En el 2017, durante una entrevista en los Billboard Latin Music, Residente argumentaba que todas las canciones que suenan en la radio son lo mismo y agrega que "si tú me das 30 minutos, te preparo un hit de lo que está sonando".
XTE J1810−197 (PSR J1809-1943) was the first magnetar that was found to emit transient radio emission. It has recently undergone another radio and high-energy outburst. This is only the second radio ...outburst that has been observed from this source. We observed J1810−197 soon after its recent radio outburst at low radio frequencies using the Giant Metrewave Radio Telescope. We present the 650 MHz flux density evolution of the source in the early phases of the outburst, and its radio spectrum down to frequencies as low as 300 MHz. The magnetar also exhibits radio emission in the form of strong, narrow bursts. We show that the bursts have a characteristic intrinsic width of the order of 0.5-0.7 ms, and discuss their properties in the context of giant pulses and giant micropulses from other pulsars. We also show that the bursts exhibit spectral structures that cannot be explained by interstellar propagation effects. These structures might indicate a phenomenological link with the repeating fast radio bursts that also show interesting, more detailed frequency structures. While the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures.
Abstract
Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active ...constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO
J
> 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 <
z
< 2.1, namely MRC 0114-211 (
z
= 1.41), MRC 0156-252 (
z
= 2.02), and MRC 2048-272 (
z
= 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1–0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large sample of high-
z
radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with
r
2−1/1−0
and
r
3−2/1−0
values ≲0.2. This could be part of the circumgalactic medium.
Abstract
We present the largest and deepest late-time radio and millimeter survey to date of superluminous supernovae (SLSNe) and long-duration gamma-ray bursts (LGRBs) to search for associated ...nonthermal synchrotron emission. Using the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), we observed 43 sources at 6 and 100 GHz on a timescale of ∼ 1–19 yr post-explosion. We do not detect radio/millimeter emission from any of the sources, with the exception of a 6 GHz detection of PTF10hgi, as well as the detection of 6 GHz emission near the location of the SLSN PTF12dam, which we associate with its host galaxy. We use our data to place constraints on central engine emission due to magnetar wind nebulae and off-axis relativistic jets. We also explore nonrelativistic emission from the SN ejecta, and place constraints on obscured star formation in the host galaxies. In addition, we conduct a search for fast radio bursts (FRBs) from some of the sources using VLA phased-array observations; no FRBs are detected to a limit of 16 mJy (7
σ
; 10 ms duration) in about 40 minutes on source per event. A comparison to theoretical models suggests that continued radio monitoring may lead to detections of persistent radio emission on timescales of ≳ a decade.
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