EXTraS discovery of an 1.2-s X-ray pulsar in M 31

Abstract

During a search for coherent signals in the X-ray archival data of XMM-Newton, we discovered a modulation at 1.2 s in 3XMM J004301.4+413017 (3X J0043), a source lying in the direction of an external arm of M 31. This short period indicates a neutron star (NS). Between 2000 and 2013, the position of 3X J0043 was imaged by public XMM-Newton observations 35 times. The analysis of these data allowed us to detect an orbital modulation at 1.27 d and study the long-term properties of the source. The emission of the pulsar was rather hard (most spectra are described by a power law with $\Gamma <1$) and, assuming the distance to M 31, the 0.3-10 keV luminosity was variable, from $\sim$$3\times 10^{37}$ to $2\times 10^{38}$ erg s${}^{-1}$. The analysis of optical data shows that, while 3X J0043 is likely associated to a globular cluster in M 31, a counterpart with $V\gtrsim 22$ outside the cluster cannot be excluded. Considering our findings, there are two main viable scenarios for 3X J0043: a peculiar low-mass X-ray binary, similar to 4U 1822-37 or 4U 1626-67, or an intermediate-mass X-ray binary resembling Her X-1. Regardless of the exact nature of the system, 3X J0043 is the first accreting NS in M 31 in which the spin period has been detected.

To appear in MNRAS Letters; 2 color figures, 2 tables; 5 pages plus full Table 1 (1 page)

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Cited by in corpus (14)

• The Chandra ACIS Timing Survey Project: glimpsing a sample of faint X-ray pulsators
• The EXTraS Project: Exploring the X-ray transient and variable sky
• The EXOD search for faint transients in XMM-Newton observations: Method and discovery of four extragalactic Type I X-ray Bursters
• Young Accreting Compact Objects in M31: The Combined Power of NuSTAR, Chandra, and Hubble
• EXTraS discovery of two pulsators in the direction of the LMC: a Be/X-ray binary pulsar in the LMC and a candidate double-degenerate polar in the foreground
• The slowest spinning X-ray pulsar in an extragalactic globular cluster
• A LOFAR radio search for single and periodic pulses from M31
• Identification of the Hard X-ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31
• The Orbit of NGC 5907 ULX-1
• Discovery of 3 s pulsations from the Brightest Hard X-ray Source in M31
• Velocity measurement in the extensive [OIII] emission region 1.2° south-east of M31
• A citizen science exploration of the X-ray transient sky using the EXTraS science gateway
• The nature of the X-ray pulsar in M31: an intermediate mass X-ray binary?
• A NuSTAR Census of the X-ray Binary Population of the M31 Disk