Which M15 Source Is Now in Outburst?
Abstract
On May 16, MAXI detected an X-ray burst from the globular cluster M15. Today (5/18) Swift confirmed that either the edge-on ADC source AC 211 or the ultracompact (22-min period) M15 X-2 is flaring (L~1.3E37). It is unlikely that AC 211 is responsible as one does not expect to see bursts from ADC sources. The standard paradigm for ultracompact XRBs like M15 X-2 is that they "should" show stable mass transfer. The few Chandra observations of M15 X-2 have not showed significant variations, but today's measured luminosity was 10 times that typically measured. The 17-minute ultracompact XRB in NGC 1851 has shown variability by factors of >10 (Maccarone et al. 2010, MNRAS, 406, 2087), a behavior that remains unexplained. Determining that a second ultracompact exhibits large variations would significantly challenge the standard paradigm for accretion in ultracompact XRBs.
- Publication:
-
Chandra Proposal
- Pub Date:
- September 2010
- Bibcode:
- 2010cxo..prop.3292S