ON THE COOLING TAILS OF THERMONUCLEAR X-RAY BURSTS: THE IGR J17480-2446 LINK

Journal Article · Wed Jun 01 00:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/733/2/L17· OSTI ID:21562660

Linares, M; Chakrabarty, D ^[1]; Van der Klis, M ^[2]

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1. Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States)
2. Astronomical Institute 'Anton Pannekoek', University of Amsterdam and Center for High-Energy Astrophysics, P.O. Box 94249, 1090 GE Amsterdam (Netherlands)

The neutron star transient and 11 Hz X-ray pulsar IGR J17480-2446, recently discovered in the globular cluster Terzan 5, showed unprecedented bursting activity during its 2010 October-November outburst. We analyzed all X-ray bursts detected with the Rossi X-ray Timing Explorer and find strong evidence that they all have a thermonuclear origin, despite the fact that many do not show the canonical spectral softening along the decay imprinted on type I X-ray bursts by the cooling of the neutron star photosphere. We show that the persistent-to-burst power ratio is fully consistent with the accretion-to-thermonuclear efficiency ratio along the whole outburst, as is typical for type I X-ray bursts. The burst energy, peak luminosity, and daily-averaged spectral profiles all evolve smoothly throughout the outburst, in parallel with the persistent (non-burst) luminosity. We also find that the peak-burst to persistent luminosity ratio determines whether or not cooling is present in the bursts from IGR J17480-2446, and argue that the apparent lack of cooling is due to the 'non-cooling' bursts having both a lower peak temperature and a higher non-burst (persistent) emission. We conclude that the detection of cooling along the decay is a sufficient, but not a necessary condition to identify an X-ray burst as thermonuclear. Finally, we compare these findings with X-ray bursts from other rapidly accreting neutron stars.

• OSTI ID: 21562660
• Journal Information: Astrophysical Journal Letters, Vol. 733, Issue 2; Other Information: DOI: 10.1088/2041-8205/733/2/L17; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
COOLING
COSMIC X-RAY BURSTS
DETECTION
LUMINOSITY
NEUTRON STARS
PULSARS
COSMIC RADIATION
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
IONIZING RADIATIONS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PRIMARY COSMIC RADIATION
RADIATIONS
STARS