A Search for New Galactic Magnetars in Archival Chandra and XMM-Newton Observations

Abstract

We present constraints on the number of Galactic magnetars, which we have established by searching for sources with periodic variability in 506 archival Chandra observations and 441 archival XMM-Newton observations of the Galactic plane (|b|<5 degree). Our search revealed four sources with periodic variability on time scales of 200-5000 s, all of which are probably accreting white dwarfs. We identify 7 of 12 known Galactic magnetars, but find no new examples with periods between 5 and 20 s. We convert this non-detection into limits on the total number of Galactic magnetars by computing the fraction of the young Galactic stellar population that was included in our survey. We find that easily-detectable magnetars, modeled after persistent anomalous X-ray pulsars, could have been identified in 5% of the Galactic spiral arms by mass. If we assume there are 3 previously-known examples within our random survey, then there are 59 (+92,-32) in the Galaxy. Transient magnetars in quiescence could have been identified throughout 0.4% of the spiral arms, and the lack of new examples implies that <540 exist in the Galaxy (90% confidence). Similar constraints are found by considering the detectability of transient magnetars in outburst by current and past X-ray missions. For assumed lifetimes of 1e4 yr, we find that the birth rate of magnetars could range between 0.003 and 0.06 per year. Therefore, the birth rate of magnetars is at least 10% of that for normal radio pulsars. The magnetar birth rate could exceed that of radio pulsars, unless the lifetimes of transient magnetars are >1e5 yr. Obtaining better constraints will require wide-field X-ray or radio searches for transient X-ray pulsars similar to XTE J1810--197, AX J1845.0--0250, CXOU J164710.2--455216, and 1E 1547.0-5408.

16 pages, 10 figures, one with a bit of color. submitted to ApJ

References in corpus (11)

• The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis
• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Transient pulsed radio emission from a magnetar
• The Magnificent Seven: Magnetic fields and surface temperature distributions
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• Supernova remnant energetics and magnetars: no evidence in favour of millisecond proto-neutron stars
• The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
• The Compact X-ray Source 1E 1547.0-5408 and the Radio Shell G327.24-0.13: A New Proposed Association between a Candidate Magnetar and a Candidate Supernova Remnant
• Exciting the Magnetosphere of the Magnetar CXOU J164710.2-455216 in Westerlund 1
• The first XMM-Newton observations of the Soft Gamma-ray Repeater SGR 1900+14
• A tale of two populations: Rotating Radio Transients and X-ray Dim Isolated Neutron Stars

Cited by in corpus (12)

• On the birthrates of Galactic neutron stars
• The Stellar Ancestry of Supernovae in the Magellanic Clouds - I. the Most Recent Supernovae in the Large Magellanic Cloud
• A VLT/FLAMES survey for massive binaries in Westerlund 1. IV. Wd1-5 - binary product and a pre-supernova companion for the magnetar CXOU J1647-45?
• Sign of hard X-ray pulsation from the gamma-ray binary system LS 5039
• Origin and evolution of magnetars
• Accretion-Induced Collapse of Neutron Stars in the Disks of Active Galactic Nuclei
• The isolated neutron star candidate 2XMM J104608.7-594306
• X-ray and radio observations of the magnetar Swift J1834.9-0846 and its dust-scattering halo
• The Chandra ACIS Timing Survey Project: glimpsing a sample of faint X-ray pulsators
• Expected number of supergiant fast X-ray transients in the Milky Way
• Searching for Magnetar Binaries Disrupted by Core-Collapse Supernovae
• The Northern Cross Fast Radio Burst project: V. Search for transient radio emission from Galactic magnetars