Pulsar of the week: J1746-2850 (aka Aris' Star) Presenter: Robert Wharton

Paper of the week: https://arxiv.org/abs/1905.05209 Presenter: Vishnu Balakrishnan

Title: Intermediate mass black holes in globular clusters: effects on jerks and jounces of millisecond pulsars

Abstract: Globular clusters may host intermediate mass black holes (IMBHs) at their centres. Here we propose a new method for their identification using millisecond pulsars (MSPs) as probes. We show that measuring the first (jerk) and second (jounce) derivatives of the accelerations of an ensemble of MSPs will let us infer the presence of an IMBH in a globular cluster better than measuring the sole accelerations. We test this concept by simulating a set of star clusters with and without a central IMBH to extract the distributions of the stellar jerks and jounces. We then apply this technique to the ensemble of MSPs in the Galactic globular cluster 47 Tucanae. Current timing observations are insufficient to constrain the presence of an IMBH and can only be used to pose upper limits on its mass. But, with few more years of observations it will be possible to test for the presence of a central IMBH with mass smaller than ∼ 1000 M⊙. We conclude that jerks and jounces help significantly in reducing the upper limit of the mass of IMBHs in Galactic globular clusters.

Cancelled: Lack of interest :(

Pulsar of the week: B0834+06 Presenter: Robert Main PDF

Paper of the week: https://arxiv.org/abs/1904.11618 Presenter: Ms. Tasha Gautam

Title: A Radio Bursts Detection Method Based on Hough Transform

Abstract: We present a simple and fast method for incoherent dedispersion and fast radio burst (FRB) detection based on the Hough transform, which is widely used for feature extraction in image analysis. The Hough transform maps a point in the data maps to a straight line in the parameter space, and points on the same dispersed f−2 curve to a bundle of lines all crossing at the same point, thus the curve is transformed to a single point in the parameter space, enabling a simple way for the detection of radio burst. By choosing an appropriate truncation threshold, the method has a complexity of max(Nt,Nf)Nd where Nf, Nt and Nd are the dimension of the data in frequency, time, and dispersion measure, respectively, this is lower than other existing methods. Using simulation data of different noise levels, we studied how the detected peak varies with different truncation thresholds. We also tested the method with some real pulsar and FRB data.

Special talk: Pulsar evolution on the short and long time scales Presenter: Dr. Simon Johnston

Cancelled: Labour day holiday

Pulsar of the week: PSR J1022+1001 Presenter: Mr. Prajwal Padmanabh PDF

Papers of the week: Jist of M87 black hole papers: https://iopscience.iop.org/issue/2041-8205/875/1 PDF

Presenter: Dr. Roebrt Wharton

Pulsar of the week: PSR J1756-2251 Presenter: Ms. Huanchen Hu PDF

Papers of the week: Astro2020 white papers: https://arxiv.org/abs/1903.08653 https://arxiv.org/abs/1903.08194 https://arxiv.org/abs/1903.08183 https://arxiv.org/abs/1903.07644 https://arxiv.org/abs/1903.06526

Presenter: Dr. Vivek Venkatraman Krishnan

Cancelled: EHT press release

Pulsar of the week: PSR J0737-3039B Presenter: Dr. Aris Noutsos PDF

Paper of the week: https://arxiv.org/abs/1606.00449 Presenter: Mr. Akash Mantri

Title: KNOWN PULSARS IDENTIFIED IN THE GMRT 150 MHz ALL-SKY SURVEY PDF

Abstract: We have used the 150 MHz radio continuum survey (TGSS ADR) from the Giant Metrewave Radio Telescope (GMRT) to search for phase-averaged emission toward all well-localized radio pulsars north of −53° decl. We detect emission toward 200 pulsars with high confidence (5s) and another 88 pulsars at fainter levels. We show that most of our identifications are likely from pulsars, except for a small number where the measured flux density is confused by an associated supernova or pulsar-wind nebula, or a globular cluster. We investigate the radio properties of the 150 MHz sample and find an unusually high number of gamma-ray binary millisecond pulsars with very steep spectral indices. We also note a discrepancy in the measured flux densities between GMRT and LOFAR pulsar samples, suggesting that the flux density scale for the LOFAR pulsar sample may be in error by approximately a factor of two. We carry out a separate search of 30 well-localized gamma-ray, radio-quiet pulsars in an effort to detect a widening of the radio beam into the line of sight at lower frequencies. No steep-spectrum emission was detected either toward individual pulsars or in a weighted stack of all 30 images.

Pulsar of the week: PSR J0737-3039A Presenter: Prof. Michael Kramer PDF

Pulsar of the week: PSR B1257+12 Presenter: Mr. Lorenz Haase PDF

Paper of the week: https://arxiv.org/abs/1902.03814 Presenter: Dr. Eleni Graikou

Title: First detection of frequency-dependent, time-variable dispersion measures

Abstract: Context. High-precision pulsar-timing experiments are affected by temporal variations of the Dispersion Measure (DM), which are related to spatial variations in the interstellar electron content. Correcting for DM variations relies on the cold-plasma dispersion law which states that the dispersive delay varies with the squared inverse of the observing frequency. This may however give incorrect measurements if the probed electron content (and therefore the DM) varies with observing frequency, as is predicted theoretically. Aims. We study small-scale density variations in the ionised interstellar medium. These structures may lead to frequency-dependent DMs in pulsar signals and could inhibit the use of lower-frequency pulsar observations to correct time-variable interstellar dispersion in higher-frequency pulsar-timing data. Methods. We used high-cadence, low-frequency observations with three stations from the German LOng-Wavelength (GLOW) consortium, which are part of the Low Frequency ARray (LOFAR). Specifically, 3.5 years of weekly observations of PSR J2219+4754 are presented. Results. We present the first detection of frequency-dependent DMs towards any interstellar object and a precise multi-year time-series of the time- and frequency-dependence of the measured DMs. The observed DM variability is significant and may be caused by extreme scattering events. Potential causes for frequency-dependent DMs are quantified and evaluated. Conclusions. We conclude that frequency-dependence of DMs has been reliably detected and is caused by small-scale (up to 10s of AUs) but steep density variations in the interstellar electron content. We find that long-term trends in DM variability equally affect DMs measured at both ends of our frequency band and hence the negative impact on long-term high-precision timing projects is expected to be limited.

Paper of the week:: https://arxiv.org/pdf/1903.01573v1.pdf Presenter: Dr. Vivek Venkatraman Krishnan

Title: Mode switching and oscillations in PSR B1828−11

Abstract: The young pulsar PSR B1828−11 has long been known to show correlated shape and spin-down changes with timescales of roughly 500 and 250 days, perhaps associated with large-scale magnetospheric switching. Here we present multi-hour observations with the Parkes and Green Bank Telescopes at multiple phases across the ∼500-day cycle and show that the pulsar undergoes mode-changing between two stable, extreme profile states. The fraction of time spent in each profile state naturally accounts for the observed overall ”shape parameter” (defined to be 0 for wide profiles and 1 for narrow ones); this and the variable rate of the mode transitions are directly related to the spin-down changes. We observe that the mode transition rate could plausibly function as an additional parameter governing the chaotic behaviour in this object which was proposed earlier by Seymour & Lorimer. Free precession is not needed to account for the variations.

Special talk: Millisecond pulsars II Presenter: Dr. Paulo Freire.

Pulsar of the week: J0453+1559, J1411+2551, J0154+1833, J0509+0856, J0709+0458, J0732+2314, J0824+0028, J2204+2700 Presenter: Mr. Joey Martinez PDF

Paper of the week: https://arxiv.org/pdf/1902.03996.pdf Presenter: Dr. Vivek Venkatraman Krishnan

Title: The Period-Width relationship for radio pulsars revisited

Abstract: In the standard picture of radio pulsars, the radio emission arises from a set of open magnetic field lines, the extent of which is primarily determined by the pulsar’s spin period, P, and the emission height. We have used a database of parameters from 600 pulsars to show that the observed profile width, W, follows W ∝ P −0.3 albeit with a large scatter, emission occurs from heights below 400 km and that the beam is underfilled. Furthermore, the prevalence in the data for long period pulsars to have relatively wide profiles can only be explained if the angle between the magnetic and rotation axis decays with time.

Pulsar of the week: PSR B0950+08 Presenter: Ms. Madhuri Gaikwad PDF

Paper of the week: https://arxiv.org/abs/1902.00356 Presenter: Dr. Kuo Liu

Title: A LOFAR search for steep-spectrum pulsars in Supernova Remnants and Pulsar Wind Nebulae

Abstract: Pinpointing a pulsar in its parent supernova remnant (SNR) or resulting pulsar wind nebula (PWN) is key for understanding its formation history, and the pulsar wind mechanism. Yet, only about half the SNRs and PWNe appear associated with a pulsar. We aim to find the pulsars in a sample of eight known and new SNRs and PWNe. Using the LOFAR radio telescope at 150 MHz, each source was observed for 3 hours. We covered the entire remnants where needed, by employing many tied-array beams to tile out even the largest objects. For objects with a confirmed point source or PWN we constrained our search to those lines of sight. We identify a promising radio pulsar candidate towards PWN G141.2+5.0. The candidate, PSR J0337+61, has a period of 94 ms and a DM of 226 pc cm−3. We re-observed the source twice with increased sensitivities of 30% and 50% but did not re-detect it. It thus remains unconfirmed. For our other sources we obtain very stringent upper limits of 0.8-3.1 mJy at 150 MHz. Generally we can rule out that the pulsars travelled out of the remnant. From these strict limits we conclude our non-detections towards point-sources and PWNe are the result of beaming and propagation effects. Some of the remaining SNRs should host a black hole rather than a neutron star.

Paper of the week: https://arxiv.org/abs/1807.07900 Presenter: Dr. Robert Wharton

Title: A Fourier Domain 'Jerk' Search for Binary Pulsars

Abstract: While binary pulsar systems are fantastic laboratories for a wide array of astrophysics, they are particularly difficult to detect. The orbital motion of the pulsar changes its apparent spin frequency over the course of an observation, essentially "smearing" the response of the time series in the Fourier domain. We review the Fourier domain acceleration search (FDAS), which uses a matched filtering algorithm to correct for this smearing by assuming constant acceleration for a small enough portion of the orbit. We discuss the theory and implementation of a Fourier domain "jerk" search, developed as part of the PRESTO software package, which extends the FDAS to account for a linearly changing acceleration, or constant orbital jerk, of the pulsar. We test the performance of our algorithm on archival Green Bank Telescope observations of the globular cluster Terzan~5, and show that while the jerk search has a significantly longer runtime, it improves search sensitivity to binaries when the observation duration is 5 to 15% of the orbital period. Finally, we present the jerk-search-enabled detection of Ter5am (PSR~J1748−2446am), a new highly-accelerated pulsar in a compact, eccentric, and relativistic orbit, with a likely pulsar mass of 1.649+0.037−0.11\,\msun.

Pulsar of the week: PSR J1757-1854 Presenter: Mr.Vishnu Balakrishnan PDF

Paper of the week: https://arxiv.org/pdf/1305.4842.pdf Presenter: Mr. Jompoj Wongphecauxson

Title: Autonomous Spacecraft Navigation With Pulsars

Abstract: An external reference system suitable for deep space navigation can be defined by fast spinning and strongly magnetized neutron stars, called pulsars. Their beamed periodic signals have timing stabilities comparable to atomic clocks and provide characteristic temporal signatures that can be used as natural navigation beacons, quite similar to the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location, the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. The unique properties of pulsars make clear already today that such a navigation system will have its application in future astronautics. In this paper, we describe the basic principle of spacecraft navigation using pulsars and report on the current development status of this novel technology.

Presentation link: https://prezi.com/view/Y7rx4MatCOaw2d3ORvhg/

Paper of the week: https://arxiv.org/abs/1808.09471 Presenter: Dr. Ralph Eatough PDF PDF

Title: Induced Polarization from Birefringent Pulse Splitting in Magnetoionic Media

Abstract: Birefringence in ionized, magnetized media is usually measured as Faraday rotation of linearly polarized radiation. However, pulses propagating through regions with very large Faraday rotation measures (RMs) can split into circularly polarized components with measurable differences in arrival times ∝ν−3RM, where ν is the radio frequency. Differential refraction from gradients in DM (dispersion measure) and RM can contribute a splitting time ∝|∇⊥DM||∇⊥RM|ν−5. Regardless of whether the emitted pulse is unpolarized or linearly polarized, net circular polarization will be measured when splitting is a significant fraction of the pulse width. However, the initial polarization may be inferable from the noise statistics of the bursts. Extreme multipath scattering that broadens pulses can mask splitting effects. We discuss particular cases such as the Galactic center magnetar, J1749−2900, and the repeating fast radio burst source, FRB 121102. Both lines of sight have RM∼105 rad m−2 that yields millisecond splittings at frequencies well below ∼1 GHz. We also consider the splitting of nanosecond shot pulses in giant pulses from the Crab pulsar and the minimal effects of birefringence on precision pulsar timing. Finally, we explore the utility of two-dimensional coherent dedispersion with DM and RM as parameters.

Special talk: Millisecond pulsars I Presenter: Dr. Paulo Freire.