2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable $\gamma$-ray emission

Abstract

We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT) $\gamma$-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric ($e$ = 0.06) 8.133 day orbit with an invisible primary. Modeling the spectroscopy and photometry together lead us to infer a heavy neutron star primary of $\sim 2M_{\odot }$ and a partially stripped giant secondary of $\sim 0.8M_{\odot }$. H$\alpha$ emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find the $\gamma$-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then it has not been detected by \emph{Fermi}. The long period and giant secondary are reminiscent of the $\gamma$-ray bright binary 1FGL J1417.7--4407, which hosts a millisecond pulsar apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of millisecond pulsar binaries that are the likely progenitors of typical field millisecond pulsars.

12 pages, 8 figures, 3 tables. Accepted for publication in ApJ

References in corpus (17)

• Shapiro delay measurement of a two solar mass neutron star
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• A Radio Pulsar/X-ray Binary Link
• The Catalina Surveys Periodic Variable Star Catalog
• Three Millisecond Pulsars in FERMI LAT Unassociated Bright Sources
• Discovery of PSR J1227-4853: A transition from a low-mass X-ray binary to a redback millisecond pulsar
• The Joker: A custom Monte Carlo sampler for binary-star and exoplanet radial velocity data
• A Spectroscopic Study of the Extreme Black Widow PSR J1311-3430
• On the formation of eccentric millisecond pulsars with helium white-dwarf companions
• 1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary
• A new gamma-ray loud, eclipsing low-mass X-ray binary
• Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853
• An active, asynchronous companion to a redback millisecond pulsar
• 1FGL J0523.5-2529: A New Probable Gamma-ray Pulsar Binary
• Discovery of a Redback Millisecond Pulsar Candidate: 3FGL J0212.1+5320
• A Likely Redback Millisecond Pulsar Counterpart of 3FGL J0838.8-2829
• The Quasi-Roche lobe overflow state in the evolution of Close Binary Systems containing a radio pulsar

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