PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

We have resolved the scatter-broadened image of PSR B0329+54 and detected substructure within it. These results are not influenced by any extended structure of a source but instead are directly attributed to the interstellar medium. We obtained these results at 324 MHz with the ground-space interferometer RadioAstron which included the space radio telescope (SRT), ground-based Westerbork Synthesis Radio Telescope and 64-m Kalyazin Radio Telescope on baseline projections up to 330,000 km in 2013 November 22 and 2014 January 1 to 2. At short 15,000 to 35,000 km ground-space baseline projections the visibility amplitude decreases with baseline length providing a direct measurement of the size of the scattering disk of 4.8$\pm$0.8 mas. At longer baselines no visibility detections from the scattering disk would be expected. However, significant detections were obtained with visibility amplitudes of 3 to 5% of the maximum scattered around a mean and approximately constant up to 330,000 km. These visibilities reflect substructure from scattering in the interstellar medium and offer a new probe of ionized interstellar material. The size of the diffraction spot near Earth is 17,000$\pm$3,000 km. With the assumption of turbulent irregularities in the plasma of the interstellar medium, we estimate that the effective scattering screen is located 0.6$\pm$0.1 of the distance from Earth toward the pulsar.

[1]  Marc W. Pound,et al.  Astronomical Data Analysis Software and Systems XXVIII. , 2019 .

[2]  Mauricio Solar,et al.  Astronomical data analysis software and systems , 2018, Astron. Comput..

[3]  L. Gurvits,et al.  RADIOASTRON OBSERVATIONS OF THE QUASAR 3C273: A CHALLENGE TO THE BRIGHTNESS TEMPERATURE LIMIT , 2016, 1601.05806.

[4]  L. Gurvits,et al.  EXTREME BRIGHTNESS TEMPERATURES AND REFRACTIVE SUBSTRUCTURE IN 3C 273 WITH RADIOASTRON , 2016, 1601.05810.

[5]  Y. Kovalev,et al.  Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources , 2015, 1507.02459.

[6]  Michael D. Johnson,et al.  THEORY AND SIMULATIONS OF REFRACTIVE SUBSTRUCTURE IN RESOLVED SCATTER-BROADENED IMAGES , 2015, 1502.05722.

[7]  B. C. Joshi,et al.  PSR B0329+54: STATISTICS OF SUBSTRUCTURE DISCOVERED WITHIN THE SCATTERING DISK ON RADIOASTRON BASELINES OF UP TO 235,000 km , 2015, 1501.04449.

[8]  Y. Kovalev,et al.  The RadioAstron project: Measurements and analysis of basic parameters of space telescope in flight in 2011–2013 , 2014 .

[9]  M. Johnson,et al.  DISCOVERY OF SUBSTRUCTURE IN THE SCATTER-BROADENED IMAGE OF SGR A* , 2014, 1409.0530.

[10]  E. Ros,et al.  VLBA observations of a rare multiple quasar imaging event caused by refraction in the interstellar medium , 2013, 1305.6005.

[11]  Interferometric Visibility of a Scintillating Source: Statistics at the Nyquist Limit , 2013, 1304.0803.

[12]  J. A. Zensus,et al.  “RadioAstron”-A telescope with a size of 300 000 km: Main parameters and first observational results , 2013, 1303.5013.

[13]  Adam Deller,et al.  100 μas RESOLUTION VLBI IMAGING OF ANISOTROPIC INTERSTELLAR SCATTERING TOWARD PULSAR B0834+06 , 2009, 0910.5654.

[14]  J. Cordes,et al.  Angular Broadening of Intraday Variable AGNs. II. Interstellar and Intergalactic Scattering , 2007, 0707.1778.

[15]  M. Popov,et al.  Probing cosmic plasma with giant radio pulses , 2007, astro-ph/0703046.

[16]  Scatter Broadening of Scintillating and Nonscintillating AGNs. I. A Multifrequency VLBA Survey , 2006 .

[17]  H. Falcke,et al.  The Intrinsic Size of Sagittarius A* from 0.35 to 6 cm , 2006, astro-ph/0608004.

[18]  D. Stinebring,et al.  Measurements of the interstellar turbulent plasma spectrum of PSR B0329+54 using multi-frequency observations of interstellar scintillation , 2003 .

[19]  W. M. Goss,et al.  Very Long Baseline Array Measurement of Nine Pulsar Parallaxes , 2002 .

[20]  W. M. Goss,et al.  VLBA Measurement of Nine Pulsar Parallaxes , 2002, astro-ph/0204105.

[21]  C. Gwinn,et al.  Interferometric Visibility of a Scintillating Source , 2001 .

[22]  Zhi-qiang Shen,et al.  Intrinsic Size of Sagittarius A*: 72 Schwarzschild Radii , 1998, astro-ph/9809222.

[23]  C. Gwinn,et al.  Angular Broadening of Nearby Pulsars , 1996, astro-ph/9610028.

[24]  J. Cordes,et al.  Angular broadening of pulsars and the distribution of interstellar plasma fluctuations , 1993 .

[25]  Dayton L. Jones,et al.  A speckle hologram of the interstellar plasma , 1992 .

[26]  R. Narayan,et al.  The shape of a scatter-broadened image. II: Interferometric visibilities , 1989 .

[27]  R. Narayan,et al.  The shape of a scatter-broadened image – I. Numerical simulations and physical principles , 1989 .

[28]  J. Cordes,et al.  VLBI observations of a pulsar's scattering disk , 1988 .

[29]  I. Shapiro,et al.  Investigation of radiation from pulsar PSR 0329+54 using Mark III VLBI observations. , 1985 .

[30]  R. Blandford,et al.  Low-frequency variability of pulsars. , 1985 .

[31]  B. Rickett,et al.  Interstellar Scattering and Scintillation of Radio Waves , 1977 .

[32]  F. V. Bunkin,et al.  Laser irradiance propagation in turbulent media , 1975, Proceedings of the IEEE.