4.7 Article

MEASURING THE COOLING OF THE NEUTRON STAR IN CASSIOPEIA A WITH ALL CHANDRA X-RAY OBSERVATORY DETECTORS

Journal

ASTROPHYSICAL JOURNAL
Volume 777, Issue 1, Pages -

Publisher

IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/777/1/22

Keywords

dense matter; neutrinos; pulsars: general; stars: neutron; supernovae: individual (Cassiopeia A); X-rays: stars

Funding

  1. NSERC
  2. Alberta Ingenuity New Faculty Award
  3. STFC in the UK
  4. RFBR [11-02-00253-a]
  5. RF Presidential Programm NSh [4035.2012.2]
  6. Ministry of Education and Science of Russian Federation [8409]
  7. STFC [ST/J00135X/1] Funding Source: UKRI
  8. Science and Technology Facilities Council [ST/J00135X/1] Funding Source: researchfish

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The thermal evolution of young neutron stars (NSs) reflects the neutrino emission properties of their cores. Heinke & Ho measured a 3.6% +/- 0.6% decay in the surface temperature of the Cassiopeia A (Cas A) NS between 2000 and 2009, using archival data from the Chandra X-ray Observatory ACIS-S detector in Graded mode. Page et al. and Shternin et al. attributed this decay to enhanced neutrino emission from a superfluid neutron transition in the core. Here we test this decline, combining analysis of the Cas A NS using all Chandra X-ray detectors and modes (HRC-S, HRC-I, ACIS-I, ACIS-S in Faint mode, and ACIS-S in Graded mode) and adding a 2012 May ACIS-S Graded mode observation, using the most current calibrations (CALDB 4.5.5.1). We measure the temperature changes from each detector separately and test for systematic effects due to the nearby filaments of the supernova remnant. We find a 0.92%-2.0% decay over 10 yr in the effective temperature, inferred from HRC-S data, depending on the choice of source and background extraction regions, with a best-fit decay of 1.0% +/- 0.7%. In comparison, the ACIS-S Graded data indicate a temperature decay of 3.1%-5.0% over 10 yr, with a best-fit decay of 3.5% +/- 0.4%. Shallower observations using the other detectors yield temperature decays of 2.6% +/- 1.9% (ACIS-I), 2.1% +/- 1.0% (HRC-I), and 2.1% +/- 1.9% (ACIS-S Faint mode) over 10 yr. Our best estimate indicates a decline of 2.9% +/- 0.5%(stat) +/- 1.0(sys)% over 10 yr. The complexity of the bright and varying supernova remnant background makes a definitive interpretation of archival Cas A Chandra observations difficult. A temperature decline of 1%-3.5% over 10 yr would indicate extraordinarily fast cooling of the NS that can be regulated by superfluidity of nucleons in the stellar core.

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