Deep XMM-Newton observations of the northern disc of M 31

Abstract

Context. We carried out new observations of two fields in the star-forming northern ring of M 31 with XMM-Newton with each one of them consisting of two exposures of about 100 ks each. A previous XMM-Newton survey of the entire M 31 galaxy revealed extended diffuse X-ray emission in these regions. Aims. We study the population of X-ray sources in the northern disc of M 31 by compiling a complete list of X-ray sources down to a sensitivity limit of ∼7 × 10 34 erg s −1 (0.5-2.0 keV) and improve the identification of the X-ray sources. The major objective of the observing programme was the study of the hot phase of the interstellar medium (ISM) in M 31. The analysis of the diffuse emission and the study of the ISM is presented in a separate paper. Methods. We analysed the spectral properties of all detected sources using hardness ratios and spectra if the statistics were high enough. We also checked for variability. In order to classify the sources detected in the new deep XMM-Newton observations, we cross-correlated the source list with the source catalogue of a new survey of the northern disc of M 31 carried out with the Chandra X-ray Observatory and the Hubble Space Telescope (Panchromatic Hubble Andromeda Treasury, PHAT) as well as with other existing catalogues.Results. We detected a total of 389 sources in the two fields of the northern disc of M 31 observed with XMM-Newton. We identified 43 foreground stars and candidates and 50 background sources. Based on a comparison with the results of the Chandra/PHAT survey, we classify 24 hard X-ray sources as new candidates for X-ray binaries. In total, we identified 34 X-ray binaries and candidates and 18 supernova remnants (SNRs) and candidates. We studied the spectral properties of the four brightest SNRs and confirmed five new X-ray SNRs. Three of the four SNRs, for which a spectral analysis was performed, show emission mainly below 2 keV, which is consistent with shocked ISM. The spectra of two of them also require an additional component with a higher temperature. The SNR [SPH11] 1535 has a harder spectrum and might suggest that there is a pulsar-wind nebula inside the SNR. For all SNRs in the observed fields, we measured the X-ray flux or calculated upper limits. We also carried out short-term and long-term variability studies of the X-ray sources and found five new sources showing clear variability. In addition, we studied the spectral properties of the transient source SWIFT J004420.1+413702, which shows significant variation in flux over a period of seven months (June 2015 to January 2016) and associated change in absorption. Based on the likely optical counterpart detected in the Chandra/PHAT survey, the source is classified as a low-mass X-ray binary.

Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185

“…Based on the images in different energy bands and according to its hardness hardness ratio, we conclude that VIEM 8 is a soft X-ray source. The obtained results, HR 1 > 0 and HR 2 < 0, are in accordance with the conclusions stated in Sasaki et al (2018) for SNRs in the northern disk of the galaxy M31. Soft X-rays indicate a thermal origin, as expected for an SNR, and enhance the likelihood that are detecting emission from a remnant.…”

Supernova remnants in nearby galaxies

“…Since SNRs predominantly emit soft X‐rays, they are ideal targets for XMM‐Newton. We have studied the SNR population in M 31 (Sasaki et al , ) using the data of the XMM‐Newton survey of M 31 (Stiele et al ), the XMM‐Newton large program on the northern disk of M 31, and the H α [S II] and [O III] emission line images as well as the UBVRI band images of the Local Group galaxy survey (Massey et al ) in the optical band. A recent X‐ray study of the SNR population in M 33 has been performed by Garofali et al () based on an XMM‐Newton survey.…”

“…Since SNRs predominantly emit soft X-rays, they are ideal targets for XMM-Newton. We have studied the SNR population in M 31 (Sasaki et al 2012(Sasaki et al , 2018 (Massey et al 2002) in the optical band. A recent X-ray study of the SNR population in M 33 has been performed by Garofali et al (2017) based on an XMM-Newton survey.…”

AstroSat UVIT Detections of Chandra X-ray Sources in M31

“…Leahy & Chen AGN identifications. Sasaki et al (2018) gave X-ray identifications for the XMM-Newton survery of the northern disk of M31 4 . Their X-ray sources were classified as: foreground star (fgstar), X-ray binary (XRB), supernova remnant (SNR), Galaxy, or hard, using a combination of methods.…”

“…is given as LMXB, AGN, or otherwise blank; the Class fromSasaki et al (2018) is given as XRB, fgStar, and v is attached if the source is variable. d For column Optical Ctpt, the counterpart type from Johnson et al (2015) is listed as C for star cluster, or otherwise blank; the counterpart type from Williams et al (2018) is listed as n for none, p for point/star, f for foreground, s for SNR, c for cluster; GD indicates that there is a Gaia DR2 parallax (Gaia Collaboration et al 2018) and a distance measurement (Bailer-Jones et al 2018).…”