Low-frequency wideband timing of InPTA pulsars observed with the uGMRT

Abstract

High-precision measurements of the pulsar dispersion measure (DM) are possible using telescopes with low-frequency wideband receivers. We present an initial study of the application of the wideband timing technique, which can simultaneously measure the pulsar times of arrival (ToAs) and DMs, for a set of five pulsars observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) as part of the Indian Pulsar Timing Array (InPTA) campaign. We have used the observations with the 300 – 500 MHz band of the uGMRT for this purpose. We obtain high precision in DM measurements with precisions of the order 10−6 cm−3 pc. The ToAs obtained have sub-μs precision and the root-mean-square of the post-fit ToA residuals are in the sub-μs range. We find that the uncertainties in the DMs and ToAs obtained with this wideband technique, applied to low-frequency data, are consistent with the results obtained with traditional pulsar timing techniques and comparable to high-frequency results from other PTAs. This work opens up an interesting possibility of using low-frequency wideband observations for precision pulsar timing and gravitational wave detection with similar precision as high-frequency observations used conventionally.

Wide-band Timing of GMRT-discovered Millisecond Pulsars

“…We have scaled the ToA uncertainties by a factor of bandwidth 100 MHz duration 30 min ( ) ´(following scaling similar to that of Nobleson et al 2022;Alam et al 2021b) to compare the ToA precision obtained in our work with the values from other highprecision timing studies. We have also scaled the raw ToA uncertainties reported in Krishnakumar et al (2021).…”

“…We have also scaled the raw ToA uncertainties reported in Krishnakumar et al (2021). Table 6 shows a comparison of scaled ToA and raw DM precision obtained from Krishnakumar et al (2021;InPTA), Nobleson et al (2022;InPTA), Alam et al (2021b;NANOGrav), and this work. Krishnakumar et al (2021) reported ToA and DM precision for five PTA pulsars, including J1713+0747, J1909−3744, and J2145−0750, from simultaneous 400-500 MHz (with five antennas of the uGMRT array) and 1360-1460 MHz (with 12 antennas of the uGMRT array) observations using the multiple-subarray mode of the uGMRT.…”

“…Krishnakumar et al (2021) reported ToA and DM precision for five PTA pulsars, including J1713+0747, J1909−3744, and J2145−0750, from simultaneous 400-500 MHz (with five antennas of the uGMRT array) and 1360-1460 MHz (with 12 antennas of the uGMRT array) observations using the multiple-subarray mode of the uGMRT. Recently, Nobleson et al (2022) reported DM and ToA precision from WB analysis for the same three pulsars using 10 antennas of the uGMRT array at 300-500 MHz.…”

“…The Giant Metrewave Radio Telescope (GMRT) is one of the most sensitive radio telescopes at low radio frequencies, covering a frequency range from 120 to 1460 MHz. The GMRT, being an IPTA telescope, can provide sensitive low-frequency timing measurements, which are already demonstrated by Jones et al (2021) with the legacy GMRT (Roy et al 2010) and by Krishnakumar et al (2021) and Nobleson et al (2022) with the upgraded GMRT (uGMRT; Reddy et al 2017;Gupta et al 2017). The current observing setup for the observations presented in this paper aims to utilize the maximum possible sensitivity at the low frequencies with the GMRT, and it is different from the regular Indian PTA (InPTA) monitoring program.…”

“…Section 3 contains the details of the NB and WB timing techniques. Section 4 contains the measurements obtained from two timing analyses and comparisons with some of the existing results (Krishnakumar et al 2021;Alam et al 2021b andNobleson et al 2022). In Section 5 we summarize the improvements seen with the WB timing analysis.…”