Quasars with Super Metal Rich Emission Line Regions

We study the degree of chemical enrichment in the Broad Emission Line Regions (BELRs) of two QSOs with unusually strong nitrogen emission lines. The N V 1240/ C IV 1549 intensity ratio is often used as a metallicity indicator for QSOs. The validity of this approach can be tested by studying objects in which the N IV] and N III] lines, in addition to N V, are unusually strong and easily measurable. If all of these ionization states of nitrogen point to the same metallicity, it implies that the large N V strengths observed in most QSOs are not due to some peculiarity of the N V 1240 line. This test had previously been applied to Q0353-383, a QSO long known to have extremely strong N III] and N IV] lines, with the result supporting high metallicity in that object. Here we make the same check in two other QSOs with very strong nitrogen lines, as a step towards using such QSOs to better probe the early chemical enrichment histories of their host galaxies. J1254+0241 has a metallicity of about 10x solar, with good agreement between the abundance results from different line ratios. J1546+5253 has a more moderate metallicity, about 5x solar, but the abundances determined from different line ratios show a much wider scatter than they do for J1254+0241 or Q0353-383. This QSO also has an unusual low-ionization emission line spectrum similar to some low-ionization BAL QSOs and to the unusual AGN I Zw 1. We attribute the peculiarities in its spectrum to some combination of unusual structure and/or unusual physical conditions in its BELR. Our results further affirm the validity of the N V/C IV ratio as an abundance indicator in QSOs.Comment: Accepted for publication in the Astrophysical Journa

High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT

Pulsar radio emission undergoes dispersion due to the presence of free electrons in the interstellar medium (ISM). The dispersive delay in the arrival time of pulsar signal changes over time due to the varying ISM electron column density along the line of sight. Correcting for this delay accurately is crucial for the detection of nanohertz gravitational waves using Pulsar Timing Arrays. In this work, we present in-band and inter-band DM estimates of four pulsars observed with uGMRT over the timescale of a year using two different template alignment methods. The DMs obtained using both these methods show only subtle differences for PSR 1713+0747 and J1909$-$3744. A considerable offset is seen in the DM of PSR J1939+2134 and J2145$-$0750 between the two methods. This could be due to the presence of scattering in the former and profile evolution in the latter. We find that both methods are useful but could have a systematic offset between the DMs obtained. Irrespective of the template alignment methods followed, the precision on the DMs obtained is about $10^{-3}$ pc cm$^{-3}$ using only BAND3 and $10^{-4}$ pc cm$^{-3}$ after combining data from BAND3 and BAND5 of the uGMRT. In a particular result, we have detected a DM excess of about $5\times10^{-3}$ pc cm$^{-3}$ on 24 February 2019 for PSR J2145$-$0750. This excess appears to be due to the interaction region created by fast solar wind from a coronal hole and a coronal mass ejection (CME) observed from the Sun on that epoch. A detailed analysis of this interesting event is presented.Comment: 11 pages, 6 figures, 2 tables. Accepted by A&

Multi-band Extension of the Wideband Timing Technique

The wideband timing technique enables the high-precision simultaneous estimation of Times of Arrival (ToAs) and Dispersion Measures (DMs) while effectively modeling frequency-dependent profile evolution. We present two novel independent methods that extend the standard wideband technique to handle simultaneous multi-band pulsar data incorporating profile evolution over a larger frequency span to estimate DMs and ToAs with enhanced precision. We implement the wideband likelihood using the libstempo python interface to perform wideband timing in the tempo2 framework. We present the application of these techniques to the dataset of fourteen millisecond pulsars observed simultaneously in Band 3 (300 - 500 MHz) and Band 5 (1260 - 1460 MHz) of the upgraded Giant Metrewave Radio Telescope (uGMRT) as a part of the Indian Pulsar Timing Array (InPTA) campaign. We achieve increased ToA and DM precision and sub-microsecond root mean square post-fit timing residuals by combining simultaneous multi-band pulsar observations done in non-contiguous bands for the first time using our novel techniques.Comment: Submitted to MNRA

Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics

Joshi BC, Arumugasamy P, Bagchi M, et al. Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics. Journal of Astrophysics and Astronomy. 2018;39(4): 51.Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-μHz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of μs are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-μHz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined

Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics

Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-μ Hz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of μs are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-μ Hz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined