EDP Sciences
Free Access
Issue
A&A
Volume 544, August 2012
Article Number A144
Number of page(s) 33
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/201219025
Published online 15 August 2012

Online material

Appendix A: XMM-Newton and LGGS images

thumbnail Fig. A.1

XMM-Newton three-colour image (red 0.2–1.0 keV, green 1.0–2.0 keV, blue 2.0–4.5 keV), continuum-subtracted LGGS Hα, [S ii], and [O iii] images, and an [S ii]/Hα ratio image with XMM-Newton 3σ positional error circle (solid). The dashed circle shows the extraction region for the optical emission. If no dashed circle is shown, the X-ray error circle was used. The shown area has a size of  ~1′  ×  1′. The label gives the source number of the XMM-Newton catalogue (SPH11), followed by the coordinates. The positions of all detected XMM-Newton sources are marked in the XMM-Newton images (left) with crosses.

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Appendix B: Supernova remnants and candidates in the XMM-Newton M 31 large survey catalogue

Table B.1

X-ray SNRs and candidates in the XMM-Newton M 31 survey catalogue by Stiele et al. (2011).

Appendix C: SDSS images

thumbnail Fig. C.1

SDSS-III images (upper left: u band, upper right: r band, lower left: i band, lower right: z band) of [SPH11] 1669, 1748, and 1796. The shown area has a size of  ~1′  ×  1′.

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Appendix D: Sources with unchanged classification

D.1. SNRs

D.1.1. [SPH11] 182: XMMM31 J003923.50+404419.1

[SPH11] 182 is a soft X-ray source with hardness ratios indicative of an SNR. No foreground star was found at its position. The X-ray source is coincident with the optical SNR [DDB80] 1-4, which corresponds to [BA64] 474 and [PAV78] 118. On the basis of these results, the source was classified as an SNR by SPH11.

The optical source is clearly visible in all three emission-line images of the LGGS (Fig. 2) and has a limb-brightened shell that is bright in the southeast. The diameter of the optical SNR is  ~16′′. We confirm the SNR classification based on the [S ii]/Hα flux ratio (Table 3). The LGGS UBVRI band images show several blue point-like sources at the position of the SNR, indicating a group of young stars.

D.1.2. [SPH11] 474: XMMM31 J004047.19+405524.6

[SPH11] 474 has hardness ratios indicative of an SNR and is coincident with the optical SNR [DDB80] 1-7. A radio counterpart [GLG04] 68 was found with α =  −0.25, which might indicate a PWN (GLG05).

From the analysis of the LGGS narrow-band images, we derived an [S ii]/Hα flux ratio of 1.0 ± 0.5 (Fig. A.1), which thus confirms the SNR identification. The source is rather compact with a diameter of  ~5′′, corresponding to  ~18 pc.

D.1.3. [SPH11] 883: XMMM31 J004224.41+411729.8

[SPH11] 883 has hardness ratios indicative of an SNR and is coincident with the Chandra source [KGP02] r2-57, which was identified as an SNR by WSK04 based on additional studies of LGGS and Very Large Array radio data.

Its optical line flux ratio is [S ii]/Hα = 0.9 ± 0.2, corroborating an SNR nature. The optical source has an arc-like structure with an extent of  ~9′′ (Fig. A.1). It is brightest in the east. This source is the second closest SNR to the centre of M 31 with a galactocentric distance of about 860 pc.

D.1.4. [SPH11] 1040: XMMM31 J004249.11+412406.6

[SPH11] 1040 is coincident with the Chandra source [KGP02] r3-84, which was identified as an SNR by WSK04, as well as the radio source [B90] 97. It was therefore classified as an SNR by PFH05 and SPH11.

There is significant Hα, [S ii], and [O iii] emission at its position and the flux ratio of [S ii]/Hα = 0.8 ± 0.2 confirms its SNR nature (Fig. A.1). The optical SNR has a patchy, ring-like morphology with an extent of  ~6′′ and is brightest in the north. It is surrounded by faint, diffuse Hα emission.

D.1.5. [SPH11] 1050: XMMM31 J004250.47+411556.7

[SPH11] 1050 is a soft source and is coincident with the Chandra source [KGP02] r2-56, which was identified as an SNR by Kong et al. (2003). Therefore, the XMM-Newton source was classified as an SNR by SPH11. The source also has an extended radio counterpart [B90] 101. It is located at a distance of about 70′′ from the galactic centre (i.e., about 250 pc).

In the optical, the SNR is a rather compact source with an extent of  ~3′′ (Fig. A.1). On the LGGS images, it is located at the edge of the central part of M 31 where the subtracted continuum images are saturated, as can be seen in the [S ii]/Hα ratio image.

D.1.6. [SPH11] 1066: XMMM31 J004253.53+412551.0

[SPH11] 1066 is a bright X-ray source with a detection likelihood of ML = 1400. It is coincident with a Chandra source that was classified as an SNR by KGP02 (r3-69), the optical SNR [DDB80] 1-13 ([BA64] 521), and its radio counterpart [B90] 106. Therefore, the XMM-Newton source was classified as an SNR by PFH05 and SPH11.

There is significant Hα, [S ii], and [O iii] emission at its position and the flux ratio of [S ii]/Hα = 0.9 ± 0.2 confirms its SNR nature (Fig. A.1). It is slightly elongated in the north-south direction with a size of  ~4′′  ×  8′′, being brighter in the south. The relatively hard X-ray spectrum and the rather small extent of the source seen in the optical suggest that it is a young SNR.

D.1.7. [SPH11] 1234: XMMM31 J004327.93+411830.5

[SPH11] 1234 is the brightest source in our list with ML = 6300 and is a soft X-ray source. It is coincident with the Chandra source [KGP02] r3-63, which was identified as an SNR by Kong et al. (2002a), with the optical SNR [MPV95] 2-033, and the radio source [B90] 142. Therefore, it was classified as an SNR by PFH05 and SPH11.

Its XMM-Newton spectrum is best fitted with a combination of two thermal components (see Sect. 3.1). The soft X-ray spectrum indicates that the source is not strongly absorbed. In addition, since there is significant emission even below 0.5 keV but almost no emission above 1 keV, it might be a rather old SNR. The optical source seen in the LGGS Hα, [S ii], and [O iii] images has a horse-shoe shaped structure with an extent of  ~8′′, corresponding to 50–60 pc (see Fig. A.1). It is brighter on one side (northwest) and open on the other side (southeast), which is typical of SNRs evolving in a medium with a density gradient. There is also significant extended diffuse emission visible in the optical emission-line images around the SNR, which indicates that the SNR might be embedded in a superbubble. The X-ray spectrum of the SNR might therefore have been contaminated by thermal emission from the interstellar gas in its environment.

D.1.8. [SPH11] 1275: XMMM31 J004339.27+412653.0

[SPH11] 1275 is a bright source (ML = 1200) embedded in a region with soft diffuse emission. The X-ray position agrees very well with the optical SNR [MPV95] 3-059, which is also a radio source ([B90] 158). Therefore, the source was classified as an SNR by PFH05 and SPH11.

Its [S ii]/Hα flux ratio is 0.9 ± 0.2. The SNR has a half-circular shape in the optical, which is open to the northwest and has an extent of  ~7′′ (Fig. A.1).

D.1.9. [SPH11] 1291: XMMM31 J004343.97+411232.7

[SPH11] 1291 is a soft X-ray source and has been classified as an SNR based on its positional coincidence with the radio source [B90] 166, which is an extended continuum source. O06 also discussed the possibility of this source being an SNR ([O06] 4).

In the optical, it is located in-between two diffuse sources in the east and the south visible in Hα, which are most likely H ii regions (Fig. A.1). Neither [S ii] nor [O iii] emission is significant. Therefore, the source is most likely a non-radiative SNR.

D.1.10. [SPH11] 1328: XMMM31 J004353.69+411204.4

[SPH11] 1328 is a soft X-ray source coincident with the optical SNR [BW93] K230A (Fig. A.1) and was thus classified as an SNR by PFH05 and SPH11. Radio emission that fills the western half of the gap between the optical line emission was also found.

In the optical, the source consists of brighter regions to the north and the south, which are both extended in the east-west direction, thus form a parallel structure. The entire structure has an extent of  ~15′′.

D.1.11. [SPH11] 1351: XMMM31 J004358.25+411328.7

[SPH11] 1351 is a soft source coincident with the optical SNR [BW93] K252 ([DDB80] 18) and the radio source [B90] 199. It was therefore classified as an SNR by PFH05 and SPH11.

In the optical, the source has an extent of  ~12′′ and is located on the southern edge of the more extended structure visible in the Hα image (Fig. A.1). The [S ii]/Hα flux ratio of 0.8 ± 0.2 fulfils the criterion for SNRs. In the optical, the source has a half-shell structure in the south with filaments extending to the north. In general, it has a patchy morphology.

D.1.12. [SPH11] 1386: XMMM31 J004409.53+413320.9

[SPH11] 1386 is a soft X-ray source. In the catalogues of PFH05 and SPH11, it was classified as an SNR based on its positional coincidence with the radio source [B90] 217.

It is located inside the H ii region [WB92] 315, which can also be seen in the LGGS images (Fig. A.1). The [S ii]/Hα flux ratio at the X-ray position is low ( ≈ 0.2). Therefore, the source is likely a non-radiative SNR.

D.1.13. [SPH11] 1410: XMMM31 J004413.55+411954.3

[SPH11] 1410 is a soft source coincident with the optical SNR [BW93] K327 with the radio counterpart [B90] 224. Therefore, it was classified as an SNR by SPH11.

The X-ray position coincides with a knot with an extent of  ~4′′ in the optical emission-line images located at the southern edge of a more extended diffuse emission (Fig. A.1). The extended emission is likely an H ii region, whereas the optical SNR has a flux ratio of [S ii]/Hα = 0.9 ± 0.2.

D.1.14. [SPH11] 1497: XMMM31 J004438.91+412528.8

[SPH11] 1497 is a faint soft source and has been classified as an SNR by PFH05 and SPH11 based on its coincidence with an SNR candidate suggested by [MPV95]. It is the counterpart of the optical and radio SNR [BW93] K506A, [B90] 278.

The morphology of its optical line emission is that of a circular shell with a diameter of  ~12′′ and is most clearly seen in the [S ii] image (Fig. A.1). There is a bright blob-like Hα source east to the SNR. While the SNR shell has an [S ii]/Hα flux ratio of  ~1.0, the Hα blob reduces the [S ii]/Hα ratio of the total SNR (0.5 ± 0.1).

D.1.15. [SPH11] 1522: XMMM31 J004447.19+412918.7

[SPH11] 1522 is a soft X-ray source and coincides with the optical SNR [BW93] K548 and was thus identified as an SNR by PFH05 and SPH11.

A shell with an extent of  ~10′′ is seen in the LGGS images, which is slightly elongated in the east-west direction (Fig. A.1) and is brighter to the west. Its [S ii]/Hα flux ratio of 1.0 ± 0.2 is clearly indicative of an SNR. A nebula that is bright only in Hα with a similar size is located northeast of the SNR.

D.1.16. [SPH11] 1539: XMMM31 J004452.82+415458.1

[SPH11]1539 is the X-ray counterpart of the optical SNR [BW93] K594 and its radio counterpart [B90] 316. It was therefore identified as an SNR by PFH05 and SPH11.

It has an extent of  ~8′′ in the optical and is brighter in the north (Fig. A.1). Its [S ii]/Hα flux ratio is 1.0 ± 0.4.

D.1.17. [SPH11] 1587: XMMM31 J004510.59+413251.3

[SPH11] 1587 is a faint, soft X-ray source and is positionally coincident with a shell-type radio source [B90] 354 with an offset of  ~3′′. It was thus classified as an SNR by SPH11.

No optical emission is detected at its position. Therefore, the SNR seems to be non-radiative.

D.1.18. [SPH11] 1593: XMMM31 J004512.31+420029.6

[SPH11] 1593 is a faint, soft X-ray source and is coincident with a radio source [B90] 365 with an amorphous shape and was thus classified as an SNR by SPH11.

Faint shell-like emission can be seen in the Hα, [S ii], [O iii] images (Fig. A.1) that has a diameter of about 30′′. Its optical flux ratio [S ii]/Hα is 1.0 ± 0.4, indicative of an SNR. We therefore also classify this source as an SNR, most likely a highly evolved SNR. It is so far the largest X-ray SNR detected in M 31.

D.1.19. [SPH11] 1599: XMMM31 J004513.94+413615.5

[SPH11] 1599 is the X-ray counterpart of the optical SNR [DDB80] 19 ([BW93] K717) and the radio source [B90] 367. It was identified as an SNR by PFH05 and SPH11.

The optical SNR has an extent of  ~10′′. It is bright in the west and has a diffuse extension to the east (Fig. A.1). The X-ray poisition coincides with the bright part in the optical.

D.1.20. [SPH11] 1793: XMMM31 J004624.71+415541.6

[SPH11] 1793 is a soft X-ray source coincident with the source [PFH05] 745. The X-ray source has an extended radio counterpart [B90] 472 and was thus classified as an SNR by PFH05 and SPH11.

Only faint emission is seen in the LGGS images (Fig. A.1). The optical flux ratio [S ii]/Hα is 0.7 ± 0.3. On the basis of the X-ray properties and the coincidence with a radio continuum source, we also classify this source as an SNR, which is most likely non-radiative.

D.1.21. [SPH11] 1805: XMMM31 J004627.91+420806.7

[SPH11] 1805 is a soft X-ray source coincident with the radio source [B90] 476 and was thus classified as an SNR by PFH05, O06, and SPH11.

Very faint optical line-emission is detected in the LGGS images. The [S ii]/Hα flux ratio of 3.0 ± 1.1 is indicative of an SNR.

D.2. SNR candidates

D.2.1. [SPH11] 294: XMMM31 J003958.28+402726.2

[SPH11] 294 is a bright X-ray source with hardness ratios typical of an SNR. As no foreground star is detected, it was proposed as an SNR candidate by PFH05 and SPH11.

We determined its Hα and [S ii] fluxes from the LGGS images, even though the source is very faint (Fig. A.1). We therefore keep the classification of this source as an SNR candidate. If it is an SNR, the optical fluxes indicate that it is likely non-radiative.

D.2.2. [SPH11] 414: XMMM31 J004030.46+402756.0

[SPH11] 414 is a hard source and thus was not classified as an SNR candidate based on its hardness ratios but was instead suggested as an SNR candidate based on its positional coincidence with the radio source [GLG04] 198 with a radio spectral index of α =  −0.08. Its radio properties indicate emission from a PWN (GLG05).

We detect neither Hα, [S ii], nor [O iii] emission in the LGGS images (Fig. A.1). Therefore, if the source is an SNR, it has to be non-radiative. A PWN can produce hard X-ray emission. On the basis of the radio-source coincidence, we retain its identification as an SNR candidate.

D.2.3. [SPH11] 419: XMMM31 J004031.92+405837.4

[SPH11] 419 is a soft X-ray source with hardness ratios indicative of an SNR. No optical source is detected at its position that might be a foreground star. Therefore, it was classified as an SNR candidate by SPH11.

We do not detect any emission in the narrow-band filter images of the LGGS (Fig. A.1). If the source is an SNR, it has to be non-radiative. Because of a lack of additional information, we keep the SNR candidate classification.

D.2.4. [SPH11] 441: XMMM31 J004040.39+403012.3

[SPH11] 441 is a soft X-ray source with hardness ratios indicative of an SNR. No foreground star was found at its position. It was therefore classified as an SNR candidate by PFH05 and SPH11.

Faint Hα and [S ii] emission was detected in the LGGS images (see Table 4 and Fig. A.1) on the northwestern side. However, this emission does not help us to classify the optical source as an SNR. Therefore, the XMM-Newton source remains an SNR candidate.

D.2.5. [SPH11] 521: XMMM31 J004058.94+410300.6

[SPH11] 521 is one of the faintest X-ray sources with a detection likelihood of ML = 10. Its hardness ratios suggest that it is an SNR candidate. No optical counterpart was found that could be a foreground star. It was therefore proposed as an SNR candidate by PFH05 and SPH11.

The X-ray source seems to be surrounded by a very extended optical source, which is visible in the Hα, [S ii], and [O iii] images (Fig. A.1) and has a low flux ratio [S ii]/Hα = 0.3 ± 0.2, hence is an H ii region. The X-ray source therefore remains an SNR candidate.

D.2.6. [SPH11] 560: XMMM31 J004108.08+403142.4

[SPH11] 560 is a soft X-ray source, which was classified as an SNR candidate by PFH05 and SPH11 based on its hardness ratios and the lack of a foreground star as a possible optical counterpart.

Faint Hα and [S ii] emission was measured at its position in the LGGS images. This source thus remains an SNR candidate.

D.2.7. [SPH11] 969: XMMM31 J004239.82+404318.8

[SPH11] 969 is a bright X-ray source with a detection likelihood of ML = 4800. Its hardness ratios suggest that it is an SNR candidate. As no foreground star was found, the XMM-Newton source was suggested to be an SNR candidate by SPH11. The X-ray source was also detected with Chandra ([WGK04] s1-84).

There is neither a point source nor significant extended emission in the optical at and around the source. Without any confirmation in optical or radio, this source is still classified as an SNR candidate.

D.2.8. [SPH11] 1083: XMMM31 J004256.78+405718.5

[SPH11] 1083 is a soft X-ray source with no foreground star at its position and hence has been classified as an SNR candidate by SPH11.

No optical source is detected at its position in the LGGS images. Therefore, if it is an SNR, it is non-radiative. The source remains an SNR candidate.

D.2.9. [SPH11] 1282: XMMM31 J004341.57+413406.6

[SPH11] 1282 is a soft X-ray source with no foreground star as a possible counterpart and thus was classified as an SNR candidate by SPH11. PFH05 classified the X-ray as a candidate super-soft source.

There is faint optical line-emission in the LGGS image with an extent of  ~14′′ (Fig. A.1). The flux ratio of 0.5 ± 0.1 is insignificantly high to classify the optical source as an SNR. It is very diffuse and patchy, similar to [SPH11] 1148 and 1328. This source still remains an SNR candidate based on its X-ray hardness ratios.

D.2.10. [SPH11] 1332: XMMM31 J004354.13+412047.3

[SPH11] 1332 is a soft X-ray source with no foreground star as a possible counterpart, which was classified as an SNR candidate by PFH05 and SPH11 based on its hardness ratios.

There is faint Hα and [O iii] emission confirmed in the LGGS data, even though no [S ii] emission was detected (see Table 4 and Fig. A.1). A filament in Hα is visible with an extent of  ~5′′. This source remains an SNR candidate.

D.2.11. [SPH11] 1669: XMMM31 J004538.26+411246.9

[SPH11] 1669 is a faint soft X-ray source, which was classified as an SNR candidate by SPH11 based on its hardness ratios and the lack of a foreground star as its possible counterpart.

The position of the X-ray source was not observed by the LGGS. No optical counterpart is found in the SDSS-III images (Fig. C.1, upper left). Radio emission has not been detected at its position so far either. This source remains an SNR candidate based on its X-ray properties.

D.2.12. [SPH11] 1748: XMMM31 J004606.34+412923.6

[SPH11] 1748 is a faint soft X-ray source, which marginally fulfilled the hardness ratio criterion for SNR candidates and has no optical counterpart that is likely to be a star. Therefore, it was classified as an SNR candidate by SPH11.

The LGGS did not cover the position of the X-ray source. The SDSS-III images show no source at the XMM-Newton position inside the error circle (Fig. C.1, upper right). A radio counterpart is not known either. Therefore, this source remains an SNR candidate.

D.2.13. [SPH11] 1796: XMMM31 J004625.39+410938.7

[SPH11] 1796 was classified as an SNR candidate by PFH05 and SPH11 based on HR1 and HR2 and the lack of a foreground star at its position.

The source was not covered by the LGGS. The SDSS-III images show no source inside the XMM-Newton positional error circle (Fig. C.1, lower panel). A radio counterpart is similarly unknown. With no additional information available, this source remains an SNR candidate.

D.3. No SNRs

D.3.1. [SPH11] 1121: XMMM31 J004303.70+413717.2

[SPH11] 1121 is a hard source and was not proposed as an SNR candidate by SPH11. Nevertheless, we studied this source because of coincident diffuse optical emission seen in Hα and [S ii].

Diffuse emission is seen in both the Hα and [S ii] LGGS images (Fig. A.1). However, the flux ratio is [S ii]/Hα = 0.2 ± 0.1, which is not indicative of an SNR. The diffuse optical source at and north of the X-ray emission is most likely an H ii region. As this source is hard in X-rays and there is no optical counterpart indicative of an SNR, we do not classify it as an SNR candidate and keep the classification as a hard source.

D.3.2. [SPH11] 1461: XMMM31 J004428.62+414948.7

[SPH11] 1461 is a soft source and was classified as a foreground star candidate by SPH11 because stars with characteristic log(fX/fopt) values are found in the X-ray error circle, with an optically red object located close to the centre of the X-ray error circle. However, the Hα image also revealed a diffuse source right next to the X-ray source in the north.

The diffuse optical source is visible in Hα, [S ii], and [O iii] emission (Fig. A.1). The flux ratio [S ii]/Hα = 0.2 ± 0.1, which is typical of an H ii region. Therefore, the origin of the soft X-ray emission seems to be either a star or an H ii region and the source is not an SNR candidate.

D.3.3. [SPH11] 1468: XMMM31 J004430.56+412306.2

[SPH11] 1468 is a hard X-ray source. As diffuse Hα emission was found in the optical, we considered this source for further studies.

The LGGS images show an extended diffuse source in Hα and [S ii] (Fig. A.1). The [S ii]/Hα flux ratio is 0.4 ± 0.1. This value is at the border between SNRs and H ii regions. While the more extended optical source seems to be an H ii region, we cannot rule out that there is an SNR located at the same position. However, as the X-ray emission does not correspond to an SNR, we do not classify [SPH11] 1468 as an SNR candidate.

D.3.4. [SPH11] 1611: XMMM31 J004518.44+413936.3

[SPH11] 1611 is a hard X-ray source coincident with [PFH2005] 626 and [SBK2009] 220 and was classified as a hard source by SPH11. Diffuse optical Hα  [S ii], and [O iii] emission was found around the X-ray source.

The largely extended optical source can be seen in the LGGS emission-line images (Fig. A.1). The X-ray source is located close to the northern rim of the optical source and is coincident with a brighter shell-like structure. The entire optical source has a flux ratio of [S ii]/Hα = 0.4–0.5. The optical source is most likely a large H ii region. The X-ray hardness ratios are not even marginally representative of an SNR. Therefore, we do not consider this source to be an SNR candidate.


© ESO, 2012

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