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تسجيل مستخدم جديدThe XMM-Newton survey of the Small Magellanic Cloud: XMMUJ010633.1-731543 and XMMUJ010743.1-715953, two new Be/X-ray binary systems
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تأليف
M.J. Coe
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In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), two new bright X-ray sources were discovered exhibiting the spectral characteris- tics of High Mass X-ray Binaries - but revealing only weak evidence for pulsations in just one of the objects(at 153s in XMMUJ010743.1-715953). The accurate X- ray source locations permit the identification of these X-ray source with Be stars, thereby strongly suggesting these systems are new Be/X-ray binaries. From blue spectra the proposed classification for XMMUJ010633.1-731543 is B0.5-1Ve and for XMMUJ010743.1-715953 it is B2IV-Ve.
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One of the goals of the XMM-Newton survey of the Small Magellanic Cloud is the study of the Be/X-ray binary population. During one of our first survey observations a bright new transient - XMMUJ004814.0-732204 - was discovered. We present the analysi
s of the EPIC X-ray data together with optical observations, to investigate the spectral and temporal characteristics of XMMUJ004814.0-732204. We found coherent X-ray pulsations in the EPIC data with a period of (11.86642 +/- 0.00017) s. The X-ray spectrum can be modelled by an absorbed power-law with indication for a soft excess. Depending on the modelling of the soft X-ray spectrum, the photon index ranges between 0.53 and 0.66. We identify the optical counterpart as a B = 14.9mag star which was monitored during the MACHO and OGLE-III projects. The optical light curves show regular outbursts by ~0.5 mag in B and R and up to 0.9 mag in I which repeat with a time scale of about 1000 days. The OGLE-III optical colours of the star are consistent with an early B spectral type. An optical spectrum obtained at the 1.9 m telescope of the South African Astronomical Observatory in December 2009 shows H_alpha emission with an equivalent width of 3.5 +/- 0.6 A. The X-ray spectrum and the detection of pulsations suggest that XMMUJ004814.0-732204 is a new high mass X-ray binary pulsar in the SMC. The long term variability and the H_alpha emission line in the spectrum of the optical counterpart identify it as a Be/X-ray binary system.
Although numerous archival XMM-Newton observations existed towards the Small Magellanic Cloud (SMC) before 2009, only a fraction of the whole galaxy was covered. Between May 2009 and March 2010 we carried out an XMM-Newton survey of the SMC, in order
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and temporal characteristics. We detected X-ray pulsations with a period of 25.550(2) s from the second-brightest source in the field, which we designate XMMU J004814.1-731003. The X-ray spectrum is well modelled by a highly absorbed (NH = 5x10^22) powerlaw with photon index 1.33+/-0.27. The precise X-ray position allows us to identify a Be star as the optical counterpart. XMMU J004814.1-731003 is located within the error circle of the transient ASCA source AX J0048.2-7309, but its position is inconsistent with that of the proposed optical counterpart of AX J0048.2-7309 (the emission line star [MA93] 215). It remains unclear if XMMU J004814.1-731003 is associated with AX J0048.2-7309. XMMU J004814.1-731003 might be identical to an RXTE pulsar that was discovered with a period of 25.5 s, but which is listed as 51 s pulsar in the recent literature.
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