[Paper Review] RXTE observations of single pulses of PSR B0531+21: II Test for radio behavior

M. Vivekanand|ArXiv.org|May 13, 2002

Pulsars and Gravitational Waves Research25 references3 citations

TL;DR

This study analyzes 1.87 million X-ray pulses from the Crab pulsar (PSR B0531+21) using RXTE/PCA data to test whether three radio pulsar phenomena—pulse nulling, subpulse drifting, and mode changing—occur at X-ray energies. The key result is that none of these phenomena are observed in the X-ray data, suggesting that the X-ray emission likely originates from a different emission mechanism than the radio, possibly the outer gap, and implying that radio nulling may involve microphysical processes rather than global current disruptions.

ABSTRACT

This article is the second in the series that analyze about 1.87 million periods of Crab pulsar, observed by the PCA detector aboard the RXTE x-ray observatory. At these energies the pulsar displays none of the three phenomena that are often seen in normal radio pulsars -- ``pulse nulling'', ``systematic sub pulse drifting'' and ``mode changing''. Presence or absence of these three behavior in the Crab pulsar, at radio wavelengths, something that has not been rigorously established yet, might be important for a satisfactory understanding of the above three phenomena.

Motivation & Objective

• To test whether radio pulsar phenomena—pulse nulling, subpulse drifting, and mode changing—occur at X-ray energies in the Crab pulsar.
• To investigate the connection between coherent radio emission and incoherent X-ray emission in rotation-powered pulsars.
• To determine whether the absence of these phenomena in X-rays supports or contradicts inner-gap versus outer-gap emission models.
• To provide observational constraints on theoretical models of pulsar emission, particularly regarding the role of relativistic charge bunching and current flow.
• To assess whether nulling at radio and X-ray energies is simultaneous or decoupled, which could reveal the interplay between inner and outer gaps.

Proposed method

• Data were collected from 23 RXTE/PCA observations (ObsIDs 10203-01-01-00 to 10203-01-03-01) in EVENT mode, combining photons from all five PCUs and both anode layers of each.
• Energy channels 50–249 (13.3–58.4 keV) were used to isolate the X-ray band of interest.
• The analysis used FTOOLS and custom-developed software to process and analyze single-pulse light curves over 1.87 million periods.
• Integrated pulse profiles were constructed and compared with radio data from PSR J0437−4715 to assess statistical behavior.
• Logarithmic counts (LOG(N)) were compared between X-ray and radio data to evaluate pulse intensity distributions.
• The study focused on detecting nulling (absence of pulses), systematic subpulse drifting, and profile instability (mode changing) in the X-ray regime.

Experimental results

Research questions

• RQ1 Does the Crab pulsar exhibit pulse nulling at X-ray energies, as it does at radio wavelengths?
• RQ2 Are systematic subpulse drifts observed in the X-ray emission, consistent with inner-gap models?
• RQ3 Is there evidence of mode changing or profile instability in the X-ray light curves?
• RQ4 Do the absence of these phenomena in X-rays imply that radio emission arises from a different emission region than X-ray emission?
• RQ5 Can the simultaneous presence or absence of nulling at radio and X-ray energies help distinguish between microphysical and global physical causes of radio nulling?

Key findings

• The Crab pulsar shows no evidence of pulse nulling in X-ray observations, with no significant drop in pulse intensity across 1.87 million periods.
• No systematic subpulse drifting is detected in the X-ray light curves, indicating that such behavior is not present at these energies.
• The integrated X-ray pulse profile remains stable over time, with no signs of mode changing or profile instability.
• The absence of these phenomena in X-rays suggests that the X-ray emission is not coherently modulated like radio emission, supporting incoherent emission mechanisms.
• The results are consistent with the outer-gap model, where X-ray emission originates from relativistic pairs in the outer magnetosphere, while radio emission may stem from a different region.
• The lack of nulling at X-rays, despite possible nulling at radio, implies that radio nulling is likely due to microphysical processes (e.g., loss of coherence) rather than global current disruption.