arXiv subjects

Manjari Bagchi

Publications and source records attributed to Manjari Bagchi.

At least 37 records · Page 2Linked to original sources

arXiv2024

Exploring the Impact of Extra Dimensions on Neutron Star Structure and Equation of State

In this work, we explore the impact of higher dimensional spacetime on the stellar structure and thermodynamic properties of neutron stars. Utilizing the density-dependent relativistic hadron field theory, we introduce modifications to incorporate the influence of higher dimensionality, a novel approach not explored in existing literature to our best knowledge. Our methodology involves solving the essential stellar structure equations in D-dimensional spacetime ($D \geq 4$), starting with the modification of the Einstein-Hilbert action, derivation of the Einstein field equation in D dimensions, and application of the resulting exterior Schwarzschild spacetime metric for D-dimension. Our findings reveal that with incremental dimensions, the central density $ρ_{c} G_D$ and central pressure $p_c G_D$ gradually increase, leading to progressively stiffer neutron matter. Incremental dimensionality also results in a gradual increase in the maximum mass attained, limited to our study between $D=4$ and $D=6$, as no maximum mass value is obtained for $D>6$. We consistently observe the criteria $dM/dρ_c>0$ fulfilled up to the maximum mass point, supported by stability analysis against infinitesimal radial pulsations. The validity of our solution is confirmed through causality conditions, ensuring that the matter sound speed remains within the speed of light for all cases. Additionally, our examination indicates that the total mass-to-radius ratio for all discussed D-dimensional cases comfortably resides within the modified Buchdahl limit, which exhibits the physical validity of achieved results.

gr-qc↗

arXiv2023

Multi-band Extension of the Wideband Timing Technique

The wideband timing technique enables the high-precision simultaneous estimation of pulsar 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) with a large band gap of 760 MHz 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.

astro-ph.IM↗

arXiv2023

Discovery and Timing of Millisecond Pulsars with the Arecibo 327 MHz Drift-Scan Survey

We present the discovery and timing solutions of four millisecond pulsars (MSPs) discovered in the Arecibo 327 MHz Drift-Scan Pulsar Survey. Three of these pulsars are in binary systems, consisting of a redback (PSR J2055+1545), a black widow (PSR J1630+3550), and a neutron star-white dwarf binary (PSR J2116+1345). The fourth MSP, PSR J2212+2450, is isolated. We present the multiyear timing solutions as well as polarization properties across a range of radio frequencies for each pulsar. We perform a multiwavelength search for emission from these systems and find an optical counterpart for PSR J2055+1545 in Gaia DR3, as well as a gamma-ray counterpart for PSR J2116+1345 with the Fermi-LAT telescope. Despite the close colocation of PSR J2055+1545 with a Fermi source, we are unable to detect gamma-ray pulsations, likely due to the large orbital variability of the system. This work presents the first two binaries found by this survey with orbital periods shorter than a day; we expect to find more in the 40% of the survey data that have yet to be searched.

astro-ph.HE↗

arXiv2023

A study of the light bending phenomenon under full general relativity for a pulsar in a binary with a Schwarzschild black hole

The values of the bending delays in the signal of a radio pulsar in a binary with a stellar mass black hole as a companion have been calculated accurately within a full general relativistic framework considering the Schwarzchid spacetime near the companion. The results match with the pre-existing approximate analytical expressions unless both of the orbital inclination angle and the orbital phase are close to $90^{\circ}$. For such a case, the approximate analytical expressions underestimate the value of the bending delay. On the other hand, for systems like the double pulsar, those expressions are valid throughout the orbital phase, unless its inclination angle is very close to 90 degrees. For a pulsar-black hole binary, the bending phenomenon also increases the strength of the pulse profile and sometimes can lead to a small low intensity tail.

gr-qc↗

arXiv2023

Noise analysis of the Indian Pulsar Timing Array data release I

The Indian Pulsar Timing Array (InPTA) collaboration has recently made its first official data release (DR1) for a sample of 14 pulsars using 3.5 years of uGMRT observations. We present the results of single-pulsar noise analysis for each of these 14 pulsars using the InPTA DR1. For this purpose, we consider white noise, achromatic red noise, dispersion measure (DM) variations, and scattering variations in our analysis. We apply Bayesian model selection to obtain the preferred noise models among these for each pulsar. For PSR J1600$-$3053, we find no evidence of DM and scattering variations, while for PSR J1909$-$3744, we find no significant scattering variations. Properties vary dramatically among pulsars. For example, we find a strong chromatic noise with chromatic index $\sim$ 2.9 for PSR J1939+2134, indicating the possibility of a scattering index that doesn't agree with that expected for a Kolmogorov scattering medium consistent with similar results for millisecond pulsars in past studies. Despite the relatively short time baseline, the noise models broadly agree with the other PTAs and provide, at the same time, well-constrained DM and scattering variations.

astro-ph.HE↗

arXiv2022

The Indian Pulsar Timing Array: First data release

We present the pulse arrival times and high-precision dispersion measure estimates for 14 millisecond pulsars observed simultaneously in the 300-500 MHz and 1260-1460 MHz frequency bands using the upgraded Giant Metrewave Radio Telescope (uGMRT). The data spans over a baseline of 3.5 years (2018-2021), and is the first official data release made available by the Indian Pulsar Timing Array collaboration. This data release presents a unique opportunity for investigating the interstellar medium effects at low radio frequencies and their impact on the timing precision of pulsar timing array experiments. In addition to the dispersion measure time series and pulse arrival times obtained using both narrowband and wideband timing techniques, we also present the dispersion measure structure function analysis for selected pulsars. Our ongoing investigations regarding the frequency dependence of dispersion measures have been discussed. Based on the preliminary analysis for five millisecond pulsars, we do not find any conclusive evidence of chromaticity in dispersion measures. Data from regular simultaneous two-frequency observations are presented for the first time in this work. This distinctive feature leads us to the highest precision dispersion measure estimates obtained so far for a subset of our sample. Simultaneous multi-band uGMRT observations in Band 3 and Band 5 are crucial for high-precision dispersion measure estimation and for the prospect of expanding the overall frequency coverage upon the combination of data from the various Pulsar Timing Array consortia in the near future. Parts of the data presented in this work are expected to be incorporated into the upcoming third data release of the International Pulsar Timing Array.

astro-ph.IM↗

arXiv2022

Nanohertz Gravitational Wave Astronomy during the SKA Era: An InPTA perspective

Decades long monitoring of millisecond pulsars, which exhibit highly stable rotational periods, in pulsar timing array experiments is on the threshold of discovering nanohertz stochastic gravitational wave background. This paper describes the Indian Pulsar timing array (InPTA) experiment, which employs the upgraded Giant Metrewave Radio Telescope (uGMRT) for timing an ensemble of millisecond pulsars for this purpose. We highlight InPTA's observation strategies and analysis methods, which are relevant for a future PTA experiment with the more sensitive Square Kilometer Array (SKA) telescope. We show that the unique multi-sub-array multi-band wide-bandwidth frequency coverage of the InPTA provides Dispersion Measure estimates with unprecedented precision for PTA pulsars, e.g., ~ 2 x 10{-5} pc-cm{-3} for PSR J1909-3744. Configuring the SKA-low and SKA-mid as two and four sub-arrays respectively, it is shown that comparable precision is achievable, using observation strategies similar to those pursued by the InPTA, for a larger sample of 62 pulsars requiring about 26 and 7 hours per epoch for the SKA-mid and the SKA-low telescopes respectively. We also review the ongoing efforts to develop PTA-relevant general relativistic constructs that will be required to search for nanohertz gravitational waves from isolated super-massive black hole binary systems like blazar OJ 287. These efforts should be relevant to pursue persistent multi-messenger gravitational wave astronomy during the forthcoming era of the SKA telescope, the Thirty Meter Telescope, and the next-generation Event Horizon Telescope.

astro-ph.HE↗

arXiv2022

Magnetar XTE J1810-197: Spectro-temporal evolution of average radio emission

We present the long-term spectro-temporal evolution of the average radio emission properties of the magnetar XTE J1810-197 (PSR J1809-1943) following its most recent outburst in late 2018. We report the results from two and a half years of monitoring campaign with the upgraded Giant Metrewave Radio Telescope carried out over the frequency range of 300 - 1450 MHz. Our observations show intriguing time variability in the average profile width, flux density, spectral index and the broadband spectral shape. While the average profile width appears to gradually decrease at later epochs, the flux density shows multiple episodes of radio re-brightening over the course of our monitoring. Our systematic monitoring observations reveal that the radio spectrum has steepened over time, resulting in evolution from a magnetar-like to a more pulsar-like spectrum. A more detailed analysis reveals that the radio spectrum has a turnover, and this turnover shifts towards lower frequencies with time. We present the details of our analysis leading to these results, and discuss our findings in the context of magnetar radio emission mechanisms as well as potential manifestations of the intervening medium. We also briefly discuss whether an evolving spectral turnover could be an ubiquitous property of radio magnetars.

astro-ph.HE↗

arXiv2022

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

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.

astro-ph.IM↗

arXiv2021

Evidence for profile changes in PSR J1713+0747 using the uGMRT

PSR J1713+0747 is one of the most precisely timed pulsars in the international pulsar timing array experiment. This pulsar showed an abrupt profile shape change between April 16, 2021 (MJD 59320) and April 17, 2021 (MJD 59321). In this paper, we report the results from multi-frequency observations of this pulsar carried out with the upgraded Giant Metrewave Radio Telescope (uGMRT) before and after the event. We demonstrate the profile change seen in Band 5 (1260 MHz - 1460 MHz) and Band 3 (300 MHz - 500 MHz). The timing analysis of this pulsar shows a disturbance accompanying this profile change followed by a recovery with a timescale of $\sim 159$ days. Our data suggest that a model with chromatic index as a free parameter is preferred over models with combinations of achromaticity with DM bump or scattering bump. We determine the frequency dependence to be $\simν^{+1.34}$.

astro-ph.HE↗

arXiv2021

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.

astro-ph.HE↗

arXiv2021

pinta: The uGMRT Data Processing Pipeline for the Indian Pulsar Timing Array

We introduce pinta, a pipeline for reducing the upgraded Giant Metre-wave Radio Telescope (uGMRT) raw pulsar timing data, developed for the Indian Pulsar Timing Array experiment. We provide a detailed description of the workflow and usage of pinta, as well as its computational performance and RFI mitigation characteristics. We also discuss a novel and independent determination of the relative time offsets between the different back-end modes of uGMRT and the interpretation of the uGMRT observation frequency settings, and their agreement with results obtained from engineering tests. Further, we demonstrate the capability of pinta to generate data products which can produce high-precision TOAs using PSR J1909-3744 as an example. These results are crucial for performing precision pulsar timing with the uGMRT.

astro-ph.IM↗

arXiv2020

Understanding the Galactic population of normal pulsars: A leap forward

We revisit the population of normal pulsars in the Galactic field in an `evolutionary' approach. By comparing the distributions of various parameters of synthetic pulsars detectable by the Parkes Multibeam Pulsar Survey, the Pulsar Arecibo L-band Feed Array Survey, and two Swinburne Multibeam surveys with those of the real pulsars detected by the same surveys, we find that a good and physically realistic model can be obtained by using a uniform distribution of the braking index in the range of 2.5 to 3.0, a uniform distribution of the cosine of the angle between the spin and the magnetic axis in the range of 0 to 1, a log-normal birth distribution of the surface magnetic field with the mean and the standard deviation as 12.85 and 0.55 respectively while keeping the distributions of other parameters unchanged from the ones most commonly used in the literature. We have also replaced the universal 'death-line' by a `death-condition' specific to each individual pulsar. We find that our model is better than the most popular model. With our improved model, we predict that an all-sky pulsar survey with phase-I SKA-MID will detect about nine thousand normal pulsars in the Galactic field. Among these pulsars, a considerable number will produce continuous gravitational waves in the operational range of the future ground-based gravitational waves detectors like LIGO A$+$, and in certain cases, the spin-down limit of the gravitational wave strains will be well below the detection sensitivity limit. We also provide a fit for the present-day distributions of the spin periods and 1400 MHz luminosities of the whole normal pulsar population in the Galactic field (which are potentially observable) and those can be used in future population studies under the snapshot approach.

astro-ph.HE↗

arXiv2020

A study of dynamical effects in the observed second time-derivative of the spin or orbital frequencies of pulsars

The observed values of the time-derivatives of the spin or orbital frequency of pulsars are affected by their dynamical properties. We derive thorough analytical expressions for such dynamical contributions in terms of the Galactic coordinates, the proper motion, the pulsar distance, and the radial velocity. We find that the effects of the dynamical terms in the second-derivative of frequencies or parameters based on such second derivatives, e.g., braking index, are usually negligible. However, unique pulsars for which the effects of the dynamical terms are significant can exist. In particular, dynamical effects can make the magnitude of the observed value of the braking index to be in the order of thousand while the true value of it is close to the theoretically expected value three, especially if the pulsars lie close to the Galactic centre. Dynamics can also affect the value of the second derivative of the orbital frequency of a binary pulsar at the first decimal place. We also emphasize the fact that our expressions provide more accurate results than pre-existing approximate ones that exclude some of the terms. Comparison with a set of pulsars showed that the median value of the difference between the results obtained by our method and a pre-existing method is about 50 percent.

astro-ph.HE↗

arXiv2020

A study of neutron stars in $D \ge 4$ dimensions

The relativistic equations of hydrostatic equilibrium for a spherically symmetric star, or the Tolman-Oppenheimer-Volkoff equations are known in higher dimensions. In this paper, these equations have been expressed in terms of parameters of 4 dimensional spacetime and solved numerically for 4, 5, 6, and 7 dimensions using a standard equation of state for the neutron star matter derived for the 4 dimensional spacetime. It has been shown that with the increase of the dimensionality, the maximum value of the mass of the neutron star decreases and the stars become less compact. Thus, although the compactness limit decreases with increased dimensionality, neutron stars never violate this limit. Simultaneous measurements of the mass, radius, and gravitational redshift for a neutron star might enable us to conclude about the central density, equation of state and the dimensionality of the spacetime in and around the star.

gr-qc↗

arXiv2019

Distinct properties of the radio burst emission from the magnetar XTE J1810-197

XTE J1810-197 (PSR J1809-1943) was the first ever magnetar which was found to emit transient radio emission. It has recently undergone another radio and high-energy outburst. This is only the second radio outburst that has been observed from this source. We observed J1810-197 soon after its recent radio outburst at low radio frequencies using the Giant Metrewave Radio Telescope. We present the 650 MHz flux density evolution of the source in the early phases of the outburst, and its radio spectrum down to frequencies as low as 300 MHz. The magnetar also exhibits radio emission in the form of strong, narrow bursts. We show that the bursts have a characteristic intrinsic width of the order of 0.5-0.7 ms, and discuss their properties in the context of giant pulses and giant micropulses from other pulsars. We also show that the bursts exhibit spectral structures which cannot be explained by interstellar propagation effects. These structures might indicate a phenomenological link with the repeating fast radio bursts which also show interesting, more detailed frequency structures. While the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures.

astro-ph.HE↗

arXiv2019

Correcting the measured values of the rate of change of the spin and orbital periods of rotation powered pulsars

For rotation powered pulsars, the rate of change of the spin period is expected to be positive. On the other hand, for a clean binary system (where gravity is the only force acting on the pulsar) the rate of change of the orbital period is expected to be negative. There are, however, some pulsars with the measurements of the rate of change of the spin period as negative quantities. Likewise, there are some pulsars with positive measurements of the rate of change of the orbital period. We investigate these cases by eliminating the external dynamical effects. We also look at those cases where at first, the measured values possess the correct sign, but on subtracting the dynamical effects, the sign changes. We use `GalDynPsr' package to perform these tasks. Moreover, we investigate possible reasons for such anomalies.

astro-ph.HE↗

arXiv2018

Dynamical effects in the observed rate of change of the orbital and the spin periods of radio pulsars: Improvement in the method of estimation and its implications

The observed values of the rate of change of the orbital and the spin periods of pulsars are affected by different dynamical effects, for example, the line-of-sight acceleration and the proper motion of the pulsar relative to the sun. We explore these dynamical effects thoroughly and point out the drawbacks of popular methods. We introduce a package, `GalDynPsr', that evaluates different dynamical effects following traditional as well as improved methods based on the model of the Galactic potential provided in a publicly available package called `galpy'. We argue that the improved methods introduced in this paper should be used for pulsars located 1 kpc or farther away from the solar system, especially when precise values of the rate of change of the periods are required, e.g., while placing limits on alternative theories of gravity, calculating the spin-down limit of the continuous gravitational waves emitted from a rotationally deformed neutron star, understanding pulsar `death-line', etc. GalDynPsr is available online and open for contributions.

astro-ph.IM↗