Pulse profiles from a pulsar in scalar-tensor gravity

TL;DR

This study investigates how scalar-tensor gravity affects neutron star pulse profiles, finding that the profiles are similar to those in general relativity unless the stellar compactness or scalar coupling significantly differ, which could reveal strong-field gravity effects.

Contribution

It demonstrates that scalar-tensor gravity has minimal impact on pulse profiles unless stellar compactness or scalar coupling constants vary significantly, providing a potential observational test for alternative gravity theories.

Findings

Pulse profiles are similar in scalar-tensor gravity and general relativity for similar compactness.

The ratio of pulse amplitude minima to maxima depends strongly on scalar coupling constants.

Observations of pulse profiles combined with stellar mass measurements can reveal strong-field gravitational effects.

Abstract

The pulse profile from a neutron star in scalar-tensor theory of gravity is examined for several stellar models, where we assume the existence of the antipodal hot spots on the neutron star based on the polar cap model. Then, we find that the pulse profile from the scalarized neutron star in scalar-tensor gravity is almost the same as that in general relativity, i.e., without a scalar field, if the stellar compactness of the both stars is very similar. That is, the existence of the scalar field does not directly change the pulse profile from the neutron star, while the stellar compactness is crucial for determining the pulse shape even in the scalar-tensor gravity. Additionally, we find that the pulse shape from the scalarized neutron star is more or less similar to that from the neutron star with the same mass in general relativity, while the ratio of the minimum amplitude to the maximum amplitude in the pulse profile depend strongly on the coupling constant in scalar-tensor gravity, depending on the angle between the rotational and magnetic axes and the angle between the rotational axis and the direction to the observer. So, the direct observation of the pulse profile together with the additional observation of the stellar mass, one may extract the imprint of the gravitational theory in strong field regime.