| Name: | Ashish Kalyan |
| Affiliation: | Indian Institute of Technology, Kanpur |
| Conference ID: | ASI2025_260 |
| Title: | VLBA Pulsar Astrometry of J0332+5434 and J1136+1551: Insights into Ionospheric Distortions |
| Authors: | Ashish Kalyan 1,
Adam T. Deller 2,
Pankaj Jain 3,
Javier Moldón 4,5 |
| Authors Affiliation: | 1 Ashish Kalyan, Pankaj Jain - Indian Institute of Technology, Kanpur-208016, India
2 Adam T. Deller - Swinburne University of Technology, John St, Hawthorn, VIC 3122, Australia
4 Javier Moldón - The University of Manchester, Manchester M13 9PL, UK
5 Javier Moldón - Glorieta de la Astronomía s/n, E-18008 Granada, Spain |
| Mode of Presentation: | Oral |
| Abstract Category: | Stars, Interstellar Medium, and Astrochemistry in Milky Way |
| Abstract: | Determining astronomical distances has significant challenges, with different distance scales relying on different methods. A parallax method is a direct approach for distance estimation, forming the foundation of the so-called distance ladder, but its utility is limited to a few kpcs due to small parallax contributions at large distances. The most precise model-independent distance measurements come from VLBI parallax campaigns. VLBI provides the highest angular resolution achievable with ground-based radio telescopes, providing correspondingly precise positions. Relative astrometry offers more precise distances, determining the target position with respect to a background reference source at multiple epochs. In relative astrometry, the possible differences in the atmosphere sampled by the target and calibrator dominantly affect the precision of the position and, hence, the parallax measurements. Fortunately, numerous calibration techniques have been developed to reduce its effect (e.g., In-Beam calibration, 1D, 2D interpolation, and PINPT).
Apart from the thermal noise in the measurements, the primary contribution to systematic uncertainties in L-band VLBI astrometry originates from the ionosphere, which depends on the separation between the target and the calibrator. Recently, a modified mapping function (Petrov23), which converts vertical total electron content (TEC) to slant TEC, aims to better compensate for the dispersive delays. The effectiveness of new approaches to correct dispersive delay using global ionospheric maps on astrometry is still questionable.
In the talk, I will discuss the above-mentioned calibration technique, refined astrometric parameters of the mentioned pulsars, and the effectiveness of the Petrov23 mapping function. |
