The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae

2010

Astron Nachr

Self Cite

The first supersoft source (SSS) identification with an optical nova in M 31 was based on ROSAT observations. Twenty additional X-ray counterparts (mostly identified as SSS by their hardness ratios) were detected using archival ROSAT, XMM-Newton and Chandra observations obtained before July 2002. Based on these results optical novae seem to constitute the major class of SSS in M 31. An analysis of archival Chandra HRC-I and ACIS-I observations obtained from July 2004 to February 2005 demonstrated that M 31 nova SSS states lasted from months to about 10 years. Several novae showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The fraction of novae detected in soft X-rays within a year after the optical outburst was more than 30 %. Ongoing optical nova monitoring programs, optical spectral follow-up and an up-to-date nova catalogue are essential for the X-ray work. Re-analysis of archival nova data to improve positions and find additional nova candidates are urgently needed for secure recurrent nova identifications. Dedicated XMM-Newton/Chandra monitoring programs for X-ray emission from optical novae covering the centre area of M 31 continue to provide interesting new results (e.g. coherent 1105 s pulsations in the SSS counterpart of nova M31N 2007-12b). The SSS light curves of novae allow us -together with optical informationto estimate the mass of the white dwarf, of the ejecta and the burned mass in the outburst. Observations of the central area of M 31 allow us -in contrast to observations in the Galaxy -to monitor many novae simultaneously and proved to be prone to find many interesting SSS and nova types.

Section: Ongoing Xmm-newton/chandra Monitoring Of the M 31 Centrementioning

confidence: 73%

Section: Ongoing Xmm-newton/chandra Monitoring Of the M 31 Centrementioning

confidence: 99%

X‐ray emission from optical novae in M 31

2010

Astron Nachr

Self Cite

“…Motivated by that SSS detection, Smirnova et al (2006) found an optical nova at the position of the SSS in archival optical plates which had been overlooked in previous nova searches. Nova M31N 2007-06b has been discussed in Henze et al (2009a). The remaining four novae are discussed individually in more detail below.…”

Section: Correlations With Optical Novaementioning

confidence: 99%

“…The SNR classifications of three other sources from PFH2005 had to be rejected due to the distinct time variability found by SPH2008. Henze et al (2009a) reported on the first two SSSs ever discovered in the M 31 globular cluster system, and Henze et al (2009b) discussed the very short supersoft X-ray state of the classical nova M31N 2007-11a. A comparative study of supersoft sources detected with ROSAT, Chandra and XMMNewton, examining their long-term variability, was presented by Stiele et al (2010).…”

Section: Introductionmentioning

confidence: 99%

The deepXMM-NewtonSurvey of M 31

Stiele

Haberl

et al. 2011

A&A

Self Cite

150

Aims. The largest Local Group spiral galaxy, M 31, has been completely imaged for the first time, obtaining a luminosity lower limit ∼10 35 erg s −1 in the 0.2-4.5 keV band. Our XMM-Newton EPIC survey combines archival observations along the major axis, from The main goal of the paper is to study the X-ray source population of M 31.Methods. An X-ray catalogue of 1897 sources was created, with 914 detected for the first time. Source classification and identification were based on X-ray hardness ratios, spatial extent of the sources, and cross correlation with catalogues in the X-ray, optical, infrared, and radio wavelengths. We also analysed the long-term variability of the X-ray sources and this variability allows us to distinguish between X-ray binaries and active galactic nuclei (AGN). Furthermore, supernova remnant classifications of previous studies that did not use long-term variability as a classification criterion could be validated. Including previous Chandra and ROSAT observations in the long-term variability study allowed us to detect additional transient or at least highly variable sources, which are good candidate X-ray binaries. Results. Fourteen of the 30 supersoft source (SSS) candidates represent supersoft emission of optical novae. Many of the 25 supernova remnants (SNRs) and 31 SNR candidates lie within the 10 kpc dust ring and other star-forming regions in M 31. This connection between SNRs and star-forming regions implies that most of the remnants originate in type II supernovae. The brightest sources in X-rays in M 31 belong to the class of X-ray binaries (XRBs). Ten low-mass XRBs (LMXBs) and 26 LMXB candidates were identified based on their temporal variability. In addition, 36 LMXBs and 17 LMXB candidates were identified owing to correlations with globular clusters and globular cluster candidates. From optical and X-ray colour-colour diagrams, possible high-mass XRB (HMXB) candidates were selected. Two of these candidates have an X-ray spectrum as is expected for an HMXB containing a neutron star primary. Conclusions. While our survey has greatly improved our understanding of the X-ray source populations in M 31, at this point 65% of the sources can still only be classified as "hard" sources; i.e. it is not possible to decide whether these sources are X-ray binaries or Crab-like supernova remnants in M 31 or X-ray sources in the background. Deeper observations in X-ray and at other wavelengths would help classify these sources.

“…For the four XMM-Newton bright state observations of M31N 2007-12b, we analyzed the X-ray spectrum following the procedures used by Henze et al (2009) for the characterization of the SSS counterpart of the nova M31N 2007-06b in the M 31 globular cluster Bol 111. To check for spectral variability during individual observations, we investigated hardness ratios resolving the observations in 1110 s bins, and depending on the 1110 s pulse phase.…”

Section: Resultsmentioning

confidence: 99%

Nova M31N 2007-12b: supersoft X-rays reveal an intermediate polar?

Henze

Haberl

et al. 2011

A&A

Self Cite

Context. In the central part of M 31, a high number of optical novae can be targeted within the field of view of the XMM-Newton EPIC and Chandra HRC-I X-ray detectors. A special monitoring program of the area has allowed us to investigate supersoft emission of individual novae in detail and perform a statistical analysis of the sample. Aims. For the He/N nova M31N 2007-12b, we aimed to constrain the time of appearance of a supersoft source (SSS) and the duration of the SSS state as well as determine the spectral and time variability while the source was bright. Methods. We analyzed XMM-Newton EPIC and Chandra HRC-I observations of our monitoring program performed at intervals of ten days and added results of a XMM-Newton target of opportunity observation and Swift XRT observations. We performed source detection, determined long-term time and spectral variation of M31N 2007-12b, and searched for shorter-term time variability in the individual observations when the source was bright, using fast Fourier and folding techniques to analyze periodicities. Results. The SSS emission started between 21 and 30 d after the optical outburst and ended between 60 and 120 d after outburst, making M31N 2007-12b one of the few novae with the shortest SSS phase known. The X-ray spectrum was supersoft and can be fitted with a white dwarf (WD) atmosphere model with solar abundances absorbed by the Galactic foreground. The temperature of the WD atmosphere seems to increase at the beginning of the SSS phase from ∼70 to ∼80 eV. The luminosity of M31N 2007-12b during maximum was at the Eddington limit of a massive WD and dropped by ∼30% in the observation 60 d after outburst. The radius of the emission region is ∼6 × 10 8 cm. In the four bright state observations, we detected a stable 1110 s pulsation, which we interpret as the WD rotation period. In addition, we detect dips in three observations that might represent a 4.9 h or 9.8 h binary period of the system. Conclusions. Nova envelope models with < ∼ 50% mixing between solar-like accreted material and the degenerate core of the WD can be used to describe the data. We derive a WD mass of 1.2 M , as well as an ejected and burned mass of 2.0×10 −6 M and 0.2×10 −6 M , respectively. The observed periodicities indicate that nova M31N 2007-12b erupted in an intermediate polar (IP) system. The WD photospheric radius seems to be larger than expected for a non-magnetic WD but in the range for magnetic WDs in an IP system.