M81CXO2 ivo://nasa.heasarc/m81cxo2 NASA/GSFC HEASARC Sell et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source This table contains the source table from an analysis of 15 Chandra ACIS observations of the nearby spiral galaxy M81 taken over the course of six weeks in 2005 May-July. Each observation reaches a sensitivity of ~10<sup>37</sup> erg s<sup>-1</sup>. With these observations and one previous deeper Chandra observation (the properties of which are described in Table 1 and Section 2 of the reference paper), the authors have compiled a master source list of 265 point sources, extracted and fitted their spectra, and differentiated basic populations of sources through their colors. They also carried out variability analyses of individual point sources and of X-ray luminosity functions (XLFs) in multiple regions of M 81 on timescales of days, months, and years. They find that, despite measuring significant variability in a considerable fraction of sources, snapshot observations provide a consistent determination of the XLF of M81. They also fit the XLFs for multiple regions of M81 and, using common parametrization, compare these luminosity functions to those of two other spiral galaxies, M31 and the Milky Way. This table contains the 265 point sources at or above the 99.9% probability level of being real according to AE's PROB_NO_SOURCE statistic (the "master" source list), and 11 additional "borderline" sources which have 99.0-99.9% probability of being real according to AE's PROB_NO_SOURCE statistic, for a total of 276 sources whose properties were described in Tables 3 and 4 of the reference paper. The 265 "master" sources have source numbers from 1 to 265 while the 11 "borderline" sources have source numbers beginning with 'B', e.g., they have source numbers 'B1' to 'B11'. Note that only coordinates are listed for 3 sources in the master source list (source numbers 234, 241 and 262) and 2 sources in the borderline source list (B8 and B9) because they were only in the field of view (on chip) of one observation (ObsID 735). Six additional sources near the center of M81 which were found using maximum likelihood image reconstruction are not included in either the master or borderline source lists contained herein but their positions are listed in table 2 of the reference paper. This table was created by the HEASARC in August 2011 based on electronic versions of Tables 3 and 4 from the reference paper which were obtained from the ApJ web site. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018. This is a service provided by NASA HEASARC . 2011ApJ...735...26S https://heasarc.gsfc.nasa.gov/W3Browse/all/m81cxo2.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=m81cxo2& GET text/xml 180 99999 true 148.77615 68.741468 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=m81cxo2 GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_m81cxo2&Action=More+Options&Action=Parameter+Search&ConeAdd=1 CHANDRA 0.0166666666666667 X-ray public m81cxo2 M 81 Chandra X-Ray Point Source Catalog source_number Sequential Identification Number for Each Source in Catalog meta.id;src char nullable name Source Designation meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable off_axis Average Off-Axis Angle arcmin instr.offset double nullable hb_counts Net Hard (2-8 keV) Counts ct phot;em.X-ray.medium double nullable hb_counts_pos_err Upper Uncertainty for Hard-Band Counts ct stat.error;phot;em.X-ray.medium double nullable hb_counts_neg_err Lower Uncertainty for Hard-Band Counts ct stat.error;phot;em.X-ray.medium double nullable var_stat_1 Variability Statistic 1 stat;src.var double nullable var_stat_2 Variability Statistic 2 stat;src.var double nullable lx The 0.5-8 keV Luminosity (erg/s) erg/s phys.luminosity;em.X-ray double nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable psf_fraction Average PSF Fraction Enclosed by Extraction Region percent instr.det.psf double nullable spectral_norm Model Normalization stat.fit.param;spect double nullable bck_fb_counts Total Background Counts ct phot;instr.background;em.X-ray double nullable best_fit_c_stat Total Best-Fit C-Statistic stat.fit.goodness double nullable mb_counts_neg_err Lower Uncertainty for Medium-Band Counts ct stat.error;phot;em.X-ray.soft double nullable lii Galactic Longitude degree pos.galactic.lon double nullable sb_counts_pos_err Upper Uncertainty for Soft-Band Counts ct stat.error;phot;em.X-ray.soft double nullable spectral_shape_neg_err Lower Uncertainty for Spectral Shape stat.error;stat.fit.param;spect double nullable spectral_norm_neg_err Lower Uncertainty for Model Normalization stat.error;stat.fit.param;spect double nullable lx_pos_err Upper Uncertainty for X-Ray Luminosity (erg/s) erg/s stat.error;phys.luminosity;em.X-ray double nullable spectral_shape Photon Index or kT of Model stat.fit.param;spect double nullable nh The H I Column Density cm^-2 phys.columnDensity double nullable source_flag Flag OC Indicates Source Off-Chip, NA Indicates Not Available meta.code;src char nullable nh_neg_err Lower Uncertainty for NH cm^-2 stat.error;phys.columnDensity double nullable spectral_shape_pos_err Upper Uncertainty for Spectral Shape stat.error;stat.fit.param;spect double nullable spectral_model Model Type meta.code;spect;meta.modelled char nullable comments Comments Concerning Source Extraction meta.note char nullable lx_neg_err Lower Uncertainty for X-Ray Luminosity (erg/s) erg/s stat.error;phys.luminosity;em.X-ray double nullable mb_counts Net Medium (1-2 keV) Counts ct phot;em.X-ray.soft double nullable best_fit_dof Degrees of Freedom of Best Fit stat.fit.dof short nullable spectral_model_flag Flag [ab] Indicates Note on Spectral Model meta.code;spect;meta.modelled char nullable raw_fb_counts Total Source Counts ct phot;em.X-ray int nullable alt_name Alternative Catalog-Based Source Designation meta.id char nullable nh_pos_err Upper Uncertainty for NH cm^-2 stat.error;phys.columnDensity double nullable spectral_norm_pos_err Upper Uncertainty for Model Normalization stat.error;stat.fit.param;spect double nullable bii Galactic Latitude degree pos.galactic.lat double nullable sb_counts Net Soft (0.5-1 keV) Counts ct phot;em.X-ray.soft double nullable var_obsid_nums Two Observations Corresponding to Variability Statistic 1 meta.id;obs char nullable mb_counts_pos_err Upper Uncertainty for Medium-Band Counts ct stat.error;phot;em.X-ray.soft double nullable sb_counts_neg_err Lower Uncertainty for Soft-Band Counts ct stat.error;phot;em.X-ray.soft double nullable