The Fermi-GBM X-ray burst monitor: thermonuclear bursts from 4U 0614+09

Abstract

Thermonuclear bursts from slowly accreting neutron stars (NSs) have proven difficult to detect, yet they are potential probes of the thermal properties of the neutron star interior. During the first year of a systematic all-sky search for X-ray bursts using the Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope we have detected 15 thermonuclear bursts from the NS low-mass X-ray binary 4U 0614+09, when it was accreting at nearly 1% of the Eddington limit. We measured an average burst recurrence time of 12+/-3 d (68% confidence interval) between March 2010 and March 2011, classified all bursts as normal duration bursts and placed a lower limit on the recurrence time of long/intermediate bursts of 62 d (95% confidence level). We discuss how observations of thermonuclear bursts in the hard X-ray band compare to pointed soft X-ray observations, and quantify such bandpass effects on measurements of burst radiated energy and duration. We put our results for 4U 0614+09 in the context of other bursters and briefly discuss the constraints on ignition models. Interestingly, we find that the burst energies in 4U 0614+09 are on average between those of normal duration bursts and those measured in long/intermediate bursts. Such a continuous distribution in burst energy provides a new observational link between normal and long/intermediate bursts. We suggest that the apparent bimodal distribution that defined normal and long/intermediate duration bursts during the last decade could be due to an observational bias towards detecting only the longest and most energetic bursts from slowly accreting NSs.

Accepted for publication in The Astrophysical Journal (scheduled for the November 10, 2012, v759 - 2 issue). 12 pages, 8 figures, 3 tables

References in corpus (11)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Six new candidate ultracompact X-ray binaries
• Revisiting a fundamental test of the disc instability model for X-ray binaries
• Sedimentation and Type I X-ray Bursts at Low Accretion Rates
• Spitzer Reveals Infrared Optically-Thin Synchrotron Emission from the Compact Jet of the Neutron Star X-Ray Binary 4U 0614+091
• Spectral and timing properties of the accreting X-ray millisecond pulsar IGR J17511-3057
• Time-resolved optical photometry of the ultra-compact binary 4U0614+091
• VLT spectroscopy and non-LTE modeling of the C/O-dominated accretion disks in two ultracompact X-ray binaries
• Long tails on thermonuclear X-ray bursts from neutron stars: a signature of inward heating?
• Hard X-ray Bursts Detected by the IBIS Telescope Onboard the INTEGRAL Observatory in 2003-2004
• The Swift capture of a long X-ray burst from XTE J1701-407

Cited by in corpus (8)

• X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143
• A catalogue of unusually long thermonuclear bursts on neutron stars
• The chemical composition of the accretion disk and donor star in Ultra Compact X-ray Binaries: A comprehensive X-ray analysis
• The Fermi-GBM 3-year X-ray Burst Catalog
• Hard X-ray/Soft gamma-ray experiments and missions: overview and prospects
• GECAM detection of a bright type-I X-ray burst from 4U 0614+09: confirmation its spin frequency at 413 Hz
• X-ray diagnostics of chemical composition of the accretion disk and donor star in ultra-compact X-ray binaries
• Connecting the m-dots: accretion rates and thermonuclear burst recurrence times on neutron stars and white dwarfs