A Multiwavelength View of the Neutron Star Binary 1FGL J1417.7–4402: A Progenitor to Canonical Millisecond Pulsars

Abstract

The Fermi γ-ray source 1FGL J1417.7-4407 (J1417) is a compact X-ray binary with a neutron star primary and a red giant companion in a ∼5.4 day orbit. This initial conclusion, based on optical and X-ray data, was confirmed when a 2.66 ms radio pulsar was found at the same location (and with the same orbital properties) as the optical/X-ray source. However, these initial studies found conflicting evidence about the accretion state and other properties of the binary. We present new optical, radio, and X-ray observations of J1417 that allow us to better understand this unusual system. We show that one of the main pieces of evidence previously put forward for an accretion disk-the complex morphology of the persistent Hα emission line-can be better explained by the presence of a strong, magnetically driven stellar wind from the secondary and its interaction with the pulsar wind. The radio spectral index derived from VLA/ATCA observations is broadly consistent with that expected from a millisecond pulsar, further disfavoring an accretion disk scenario. X-ray observations show evidence for a double-peaked orbital light curve, similar to that observed in some redback millisecond pulsar binaries and likely due to an intrabinary shock. Refined optical light curve fitting gives a distance of 3.1±0.6 kpc, confirmed by a Gaia DR2 parallax measurement. At this distance the X-ray luminosity of J1417 is (1.0 +0.4 −0.3 ) ×10 33 erg s −1 , which is more luminous than all known redback systems in the rotational-powered pulsar state, perhaps due to the wind from the giant companion. The unusual phenomenology of this system and its differing evolutionary path from redback millisecond pulsar binaries points to a new eclipsing pulsar "spider" subclass that is a possible progenitor of normal field millisecond pulsar binaries.

PSR J1306-40: An X-Ray Luminous Redback with an Evolved Companion

“…Using our best hot spot model, the inferred mass of the primary is M 1 = 1.77 +0.07 −0.03 , fairly massive for a typical neutron star, but fully consistent with the neutron star masses found in many redback MSPs (e.g., Kaplan et al 2013;Romani et al 2015b;Bellm et al 2016;Strader et al 2016;Sanchez & Romani 2017;Shahbaz et al 2017;Linares et al 2018;Swihart et al 2018). The secondary has a mass of M 2 = 0.51 +0.02 −0.01 , placing it in the highmass tail of the redback companion mass distribution (Strader et al 2019).…”

“…For the remainder of this paper, we adopt this value for the distance. We note that this method has proven successful in the past at estimating reliable distances to similar systems (e.g., Swihart et al 2018). However, due to systematic effects such as the unknown metallicity and precise evolutionary state of the star, our estimate is likely uncertain by at least 20%.…”

“…Another piece of evidence for an unusually luminous shock is the X-ray luminosity in this system (∼ 10 33 erg s -1 ), which is higher than other redbacks in the pulsar state. Swihart et al (2018) discuss the possibility that the shock luminosity in 1FGL J1417.7-4407 is enhanced over typical redbacks by a strong, magnetically driven wind from the tidally-locked red giant secondary. The candidate MSP binary 2FGL J0846.0+2820 shows many similarities to 1FGL J1417.7-4407, making it a possible second member of the huntsman subclass, though no radio pulsar has yet been confirmed in this system (Swihart et al 2017).…”

A New Likely Redback Millisecond Pulsar Binary with a Massive Neutron Star: 4FGL J2333.1–5527

“…Nearly all of the spectra cover both Hα and Hβ, and while there is Balmer absorption present in most of the warmer spectra, there is no clear evidence for emission in any of the spectra. This is unlike some other redbacks, where the Balmer emission is attributed to a wind or shock (Swihart et al 2018).…”

A compact X-ray emitting binary in likely association with 4FGL J0935.3+0901

“…This system would have been in the disc state all the time, since our optical spectrum was taken recently and J0935 has been in its low-flux period since 2013 August based on the long-term γ-ray light curve. However it has been noted that several redbacks (and a black widow; PSR J1740−5340A, Sabbi et al 2003;3FGL J0838.8−2829, Halpern et al 2017; 2FGL J0846.0+2820, Swihart et al 2018;PSR J1048+2339, Strader et al 2019PSR J1311−3430, Romani et al 2015 can have strong variable emission lines and the lines (notable the Hα line) can appear to be double-peaked. This feature is interpreted as the indication of material driven from the heated side of a companion by the pulsar wind and possibly plus an intrabinary shock between the companion and the pulsar wind (Strader et al 2019 and references therein).…”