December 6 2018 to January 29 2019

Pulsar of the week: PSR J0337+1715 Presenter: Ms. Tasha Gautam PDF

Paper of the week: https://arxiv.org/abs/1811.04519 Presenter: Mr. Prajwal Padmanabh

Title: The Frequency Dependence of Scintillation Arc Thickness in Pulsar B1133+16

Abstract: Scintillation arcs have become a powerful tool for exploring scattering in the ionized interstellar medium. There is accumulating evidence that the scattering from many pulsars is extremely anisotropic resulting in highly elongated, linear brightness functions. We present a three-frequency (327~MHz, 432~MHz, 1450~MHz) Arecibo study of scintillation arcs from one nearby, bright, high-velocity pulsar, PSR~B1133+16. We show that a one-dimensional (1D), linear brightness function is in good agreement with the data at all three observing frequencies. We use two methods to explore the broadening of the 1D brightness function B(θ) as a function of frequency: 1) crosscuts of the forward arc at constant delay and 2) a 1D modeling of B(θ) using a comparison between model and observed secondary spectrum as a goodness-of-fit metric. Both methods show that the half-power width of B(θ) deviates from the expected dependence ∝ν−a, where ν is the observing frequency . Our estimates of a have moderately large uncertainties but imply a≲1.8, and so are inconsistent with the expected a=2.0 for plasma refraction or a=2.2 for Kolmogorov turbulence. In addition the shape of B(θ) cuts off more steeply than predicted for Kolmogorov turbulence. Ultimately, we conclude that the underlying physics of the broadening mechanism remains unexplained. Our results place the scattering screen at a distance that is broadly consistent with an origin at the boundary of the Local Bubble.

Pulsar of the week: PSR J1638-4725 and PSR J1259-63 Presenter: Dr. Ralph Eatough PDF

Paper of the week: https://arxiv.org/abs/1811.05766 Presenter: Dr. Robert Main

Title: Unusually bright single pulses from B1744-24A binary: a case of strong lensing?

Abstract: We present a study of unusually bright single pulses (BSPs) from a millisecond pulsar in an ablating binary system, B1744-24A, based on several multi-orbit observations with the Green Bank Telescope. These pulses come predominantly in time near eclipse ingress and egress, have intensities up to 40 times the average pulse intensity, and pulse widths similar to that of the average pulse profile. The average intensity, spectral index of radio emission, and the dispersion measure do not vary in connection with BSP outbursts. The average profile obtained from BSPs has the same shape as the average profile from all pulses. These properties make it difficult to explain BSPs via scintillation in the interstellar medium, as a separate emission mode, or as conventional giant pulses. BSPs from B1744-24A have similar properties to the strong pulses observed from the Black Widow binary pulsar B1957+10, which were recently attributed to strong lensing by the intrabinary material (Main et al. 2018). We argue that the strong lensing likely occurs in B1744-24A as well. For this system, the sizes and locations of the lenses are not well constrained by simple 1D lensing models from Cordes et al. (2017) and Main et al. (2018). This partly stems from the poor knowledge of several important physical parameters of the system.

Pulsar of the week: PSR J0250+5854 Presenter: Mr. Jompoj Wongphecauxson PDF

Paper of the week: https://academic.oup.com/mnras/article/478/2/2835/4999917 [https://arxiv.org/abs/1805.05482] Presenter: Dr. Aris Noutsos PDF

Title: An all-sky survey of circular polarization at 200 MHz

Abstract: We present results from the first all-sky radio survey in circular polarisation. The survey uses the Murchison Widefield Array (MWA) to cover 30900 sq. deg., over declinations south of +30∘ and north of -86∘ centred at 200 MHz (over a 169-231 MHz band). We achieve a spatial resolution of approx. 3' and a typical sensitivity of 3.0 mJy PSF−1 over most of the survey region. We demonstrate a new leakage mitigation technique that reduces the leakage from total intensity into circular polarisation by an order of magnitude. In a blind survey of the imaged region, we detect 14 pulsars in circular polarisation above a 6σ threshold. We also detect six transient sources associated with artificial satellites. A targeted survey of 2376 pulsars within the surveyed region yielded 33 detections above 4σ. Looking specifically at pulsars previously detected at 200 MHz in total intensity, this represents a 35% detection rate. We also conducted a targeted survey of 2400 known flare stars, this resulted in two tentative detections above 4σ. A similar targeted search for 1506 known exoplanets in the field yielded no detections above 4σ. The success of the survey suggests that similar surveys at longer wavelength bands and of deeper fields are warranted.

Pulsar of the week: PSR J0218+4232 Presenter: Mr. Aakash Mantri

Paper of the week: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/sty2945/5151343 [https://arxiv.org/abs/1810.12922] Presenter: Mr. Vishnu Balakrishnan

Title: Ages of radio pulsar: long-term magnetic field evolution

Abstract: We use the Bayesian approach to write the posterior probability density for the three-dimensional velocity of a pulsar and for its kinematic age. As a prior, we use the bimodal velocity distribution found in a recent article by Verbunt, Igoshev & Cator (2017). When we compare the kinematic ages with spin-down ages we find that in general they agree with each other. In particular, maximum likelihood analysis sets the lower limit for the exponential magnetic field decay timescale at 8 Myr with slight preference of t_dec ≈ 12 Myr and compatible with no decay at all. One of the objects in the study, pulsar B0950+08 has kinematic and cooling ages ≈2 Myr which is in strong contradiction with its spin-down age τ ≈ 17 Myr. The 68 per cent credible range for the kinematic age is 1.2–8.0 Myr. We conclude that the most probable explanation for this contradiction is a combination of magnetic field decay and long initial period. Further timing, UV and X-ray observations of B0950+08 are required to better constrain its origin and evolution.

Pulsar of the week: PSR J1723-2837 Presenter: Dr. John Antoniadis

Quick reference on the pulsar, in chronological order:

http://adsabs.harvard.edu/abs/2004MNRAS.355..147F

http://iopscience.iop.org/article/10.1088/0004-637X/776/1/20/pdf

http://iopscience.iop.org/article/10.1088/0004-637X/781/1/6/pdf

http://iopscience.iop.org/article/10.1088/2041-8205/781/1/L21/pdf

http://iopscience.iop.org/article/10.3847/2041-8213/833/1/L12/pdf

http://iopscience.iop.org/article/10.3847/1538-4357/aa6aa2/pdf

Paper of the week: https://link.springer.com/article/10.1007%2Fs10509-018-3322-1 Presenter: Mr. Ashwin Manohar

Title: Timing irregularities of PSR J1705−1906

Abstract:

Timing analysis of PSR J1705−1906 using data from Nanshan 25-m and Parkes 64-m radio telescopes, which span over fourteen years, shows that the pulsar exhibits significant proper motion, and rotation instability. We updated the astrometry parameters and the spin parameters of the pulsar. In order to minimize the effect of timing irregularities on measuring its position, we employ the Cholesky method to analyse the timing noise. We obtain the proper motion of −77(3) \,mas\,yr−1 in right ascension and −38(29) \,mas\,yr−1 in declination. The power spectrum of timing noise is analyzed for the first time, which gives the spectral exponent α=−5.2 for the power-law model indicating that the fluctuations in spin frequency and spin-down rate dominate the red noise. We detect two small glitches from this pulsar with fractional jump in spin frequency of Δν/ν∼2.9×10−10 around MJD~55199 and Δν/ν∼2.7×10−10 around MJD~55953. Investigations of pulse profile at different time segments suggest no significant changes in the pulse profiles around the two glitches.

Pulsar of the week: J1906+0746 Presenter: Dr. Gregory Desvignes

Paper of the week: https://arxiv.org/abs/1809.05064 Presenter: Mr. Jose Martinez

Title: PSR J2234+0611: A NEW LABORATORY FOR STELLAR EVOLUTION

Abstract: We report timing results for PSR J2234+0611, a 3.6-ms pulsar in a 32-day, eccentric (e = 0.13) orbit with a helium white dwarf companion discovered as part of the Arecibo Observatory 327 MHz drift scan survey. The precise timing and the eccentric nature of the orbit allow precise measurements of an unusual number of parameters: a) a precise proper motion of 27.10(3) mas/yr and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; this allows a precise estimate of the transverse velocity, 123(5) km/s. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a full 3-D determination of the system's velocity; b) precise measurements of the rate of advance of periastron, which after subtraction of the contribution of the proper motion yields a total system mass of 1.6518+0.0033−0.0035 solar masses; c) a Shapiro delay measurement, h_3 = 82±14 ns despite the orbital inclination not being near 90 deg; combined with the measurement of the total mass, this yields a pulsar mass of 1.353+0.014−0.017 solar masses and a companion mass of 0.298+0.015−0.012 solar masses; d) we measure precisely the secular variation of the projected semi-major axis and detect significant annual orbital parallax; together these allow a determination of the full 3-D orbital geometry, including an unambiguous orbital inclination (i = 138.7+2.5−2.2 deg) and a position angle for the line of nodes (Omega = 44+5−4 deg). We discuss the component masses to investigate hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the full 3-D position, motion and orbital orientation of the system, plus the precisely measured pulsar and WD mass and the latter's optical detection make this system an unique test of our understanding of white dwarfs and their atmospheres.

Pulsar of the week: PSR J1745-2900 Presenter: Dr. Robert Wharton PDF

Paper of the week: http://science.sciencemag.org/content/362/6411/201 Presenter: Dr. Vivek Venkatraman Krishnan

Title: A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary

Abstract: Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.