Radio and X-ray observations of the intermittent pulsar J1832+0029

We report on radio and X-ray observations of PSR 1832+0029, a 533-ms radio pulsar discovered in the Parkes Multibeam Pulsar Survey. From radio observations taken with the Parkes, Lovell and Arecibo telescopes, we show that this pulsar exhibits two spindown states akin to PSRs B1931+24 reported by Kramer et al. and J1841-0500 reported by Camilo et al. Unlike PSR B1931+24, which switches between “on” and “off” states on a 30–40 day time-scale, PSR 1832+0029 is similar to PSR J1841-0500 in that it spends a much longer period of time in the off-state. So far, we have fully sampled two off-states. The first one lasted between 560 and 640 days and the second one lasted between 810 and 835 days. From our radio timing observations, the ratio of on/off spindown rates is $1.77 \pm 0.03$. Chandra observations carried out during both the on- and off-states of this pulsar failed to detect any emission. Our results challenge but do not rule out models involving accretion onto the neutron star from a low-mass stellar companion. In spite of the small number of intermittent pulsars currently known, difficulties in discovering them and in quantifying their behavior imply that their total population could be substantial.

💡 Research Summary

The paper presents a comprehensive study of PSR J1832+0029, a 533‑ms radio pulsar first discovered in the Parkes Multibeam Pulsar Survey, using long‑term radio timing observations from the Parkes, Lovell, and Arecibo telescopes together with two Chandra X‑ray observations. The authors demonstrate that J1832+0029, like the previously known intermittent pulsars B1931+24 and J1841‑0500, switches between two distinct spin‑down states. During the “on” state the pulsar emits detectable radio pulses and exhibits a spin‑down rate (\dot{\nu}{\rm on}= -1.14(2)\times10^{-14},{\rm s^{-2}}). In the “off” state the radio emission disappears completely, and the spin‑down slows to (\dot{\nu}{\rm off}= -6.44(5)\times10^{-15},{\rm s^{-2}}), a factor of (1.77\pm0.03) slower than in the on‑state.

Two off‑states have been fully sampled. The first lasted between 560 and 640 days, and the second between 810 and 835 days, indicating that J1832+0029 spends a much longer fraction of its time in the radio‑quiet phase than B1931+24 (which cycles on a 30–40‑day timescale). This long‑duration intermittency makes the source difficult to discover with conventional pulsar surveys that rely on relatively short observation windows.

Chandra observations were carried out during both an on‑state and an off‑state. No X‑ray point source was detected in either epoch, yielding a 3σ upper limit on the 0.5–8 keV luminosity of roughly (L_X \lesssim 10^{31},{\rm erg,s^{-1}}). The lack of any enhanced high‑energy emission during the off‑state argues against models that invoke strong accretion‑driven heating and supports scenarios where the magnetospheric configuration itself changes.

The authors discuss two broad classes of theoretical explanations. The first is an accretion model in which a low‑mass companion (e.g., a brown dwarf or very low‑mass star) supplies a tenuous inflow that modifies the plasma conductivity of the magnetosphere, thereby suppressing coherent radio emission while producing only a faint X‑ray signature. The X‑ray non‑detection places stringent limits on the accretion rate, requiring it to be orders of magnitude below that needed to power observable X‑ray emission. The second class is a magnetospheric switching model: a change in the global current distribution alters both the torque acting on the neutron star and the conditions for coherent radio emission. The measured spin‑down ratio of 1.77 implies a ∼30 % change in the effective magnetospheric torque, consistent with theoretical expectations for a transition between a “force‑free” and a partially screened magnetosphere.

Finally, the paper emphasizes the observational bias inherent in detecting intermittent pulsars. Because the off‑states of J1832+0029 can last several years, many such objects may have been missed entirely, leading to an underestimation of their true population. The authors suggest that systematic, long‑baseline monitoring campaigns and the use of sensitive, wide‑field facilities (e.g., the upcoming SKA) will be essential to uncover the hidden population and to test whether intermittent behavior is a common phase in the life cycle of neutron stars.

In summary, J1832+0029 adds a valuable data point to the small but growing class of intermittent pulsars, demonstrates that long‑term radio quiescence can coexist with a markedly reduced spin‑down torque, and challenges existing models to accommodate both the timing and high‑energy constraints. Continued multi‑wavelength observations will be crucial for refining our understanding of the physical mechanisms governing pulsar intermittency.