2. Chandra Observations of the Norma Region Bodaghee et al. 2012 Search for new HMXBs and study hard X-ray populations Twenty-seven 20 ks pointings Red: 0.5-2 keV Green: 2-4.5 keV Blue: 4.5-10 keV HEAD 13th Meeting, 2013 338° l 337° -0.4° b 0.4° HMXB Magnetar PWN Supernova Remnants Young Massive Clusters

3. Now I wonder what you are Two main analyses to help classify X-ray sources: Dividing sources into spectral groups Making stacked spectra, analyzing variability and counterparts of sources in each group Near-IR follow-up of individual sources 30 J, H, K spectra obtained using OSIRIS on the SOAR telescope Selected sources based on X-ray brightness, spectral hardness, variability, and IR counterpart reliability and magnitude HEAD 13th Meeting, 2013

4. Now I wonder what you are Two main analyses to help classify X-ray sources: Dividing sources into spectral groups Making stacked spectra, analyzing variability and counterparts of sources in each group Near-IR follow-up of individual sources 30 J, H, K spectra obtained using OSIRIS on the SOAR telescope Selected sources based on X-ray brightness, spectral hardness, variability, and IR counterpart reliability and magnitude HEAD 13th Meeting, 2013

5. Defining Spectral Groups Quantile grid method developed by Hong et al. 2004 HEAD 13th Meeting, 2013 Broadness Hardness >3σ sources (0.5-10 keV)

6. Defining Spectral Groups HEAD 13th Meeting, 2013 Broadness Hardness

7. Defining Spectral Groups HEAD 13th Meeting, 2013 Hardness Broadness Soft, low absorption Soft, high absorption Hard, high absorption Hard, moderate absorption Hard, low absorption

8. Group D Probably dominated by intermediate polars in the far Norma arm. HMXBs are most likely to be in this group. Power-law: Γ = 0.7±0.1 N H = 6.8±0.6 x 10 22 cm -2 Fe line: Line = 6.62±0.03 keV Eq width = 360±70 eV HEAD 13th Meeting, 2013

9. Dominant X-Ray Populations HEAD 13th Meeting, 2013 Hardness Broadness X-ray active stars, RS CVn CVs, RS CVnCVs IPs, HMXBs Colliding wind binaries, high-mass stars

10. >3σ sources (2-10 keV) Broadness Hardness LogN-logS HEAD 13th Meeting, 2013 Corrected for differences in sensitivity across surveyed area and Eddington bias as discussed in Georgakakis et al. 2008

11. Now I wonder what you are Two main analyses to help classify X-ray sources: Dividing sources into spectral groups Making stacked spectra, analyzing variability and counterparts of sources in each group Near-IR follow-up of individual sources 30 J, H, K spectra obtained using OSIRIS on the SOAR telescope Selected sources based on X-ray brightness, spectral hardness, variability, and IR counterpart reliability and magnitude HEAD 13th Meeting, 2013

12. Low-mass counterparts 13 show CO lines typical of low-mass stars and cool giants consistent with a dominant CV population 1 shows accretion disk signatures > magnetic CV Γ = 1.1 ± 0.1, N H = 1.2 ± 0.1 x 10 21 cm -2, P ≈ 3500 sec, L 2-10 ~ 10 32 erg/s HEAD 13th Meeting, 2013 K band Near-IR diagnostics: Wallace & Hinkle 1996, Meier et al. 1998, Förster Schreiber 2000, Ivanov et al. 2004, Rayner et al. 2009

13. High-mass counterparts 6 spectra show lines typical of O, B, Be, or WR stars 2 are possible HMXBs in the far Norma arm 2 are likely massive stars in the far Norma arm 2 are sources in the Scutum- Crux or near Norma arm HEAD 13th Meeting, 2013 K bandH band Hardness Broadness Near-IR diagnostics: Hanson & Conti 1996, Morris et al. 1996, Hanson et al. 1998, Meier et al. 1998, Hanson et al. 2005

14. Summary and Outlook Magnetic CVs are the dominant X-ray population in the Norma spiral arm, many of which appear to be intermediate polars. The potential HMXBs we have discovered are faint and could be useful in constraining the faint end of the HMXB luminosity function. Ongoing IR follow-up and a NuSTAR survey of this region will help to uncover other potential HMXBs and to constrain their hard X-ray spectral properties. HEAD 13th Meeting, 2013

15. IR counterparts from VISTA VVV survey Low-mass, foreground stars Cool giants and high mass stars, near arm Cool giants and high mass stars, far arm Other clues for classifying sources HEAD 13th Meeting, 2013

16. Other clues for classifying sources Short-timescale variability 21 of 28 variable sources (95% confidence) belong to groups A and B > consistent with foreground flaring stars Long-timescale variability RS CVn systems can flare by factor of 10 in amplitude HMXBs and X-rays from high-mass winds are variable Intermediate polars have fairly constant emission HEAD 13th Meeting, 2013

17. Group A Dominated by low-mass X-ray active stars, RS CVn systems in the foreground. Red dashed: kT = 2.1 +0.3 -0.1 keV N H = 5 +5 -4 x 10 20 cm -2 Blue dotted: kT = 0.76±0.04 keV N H = 3±1 x 10 21 cm -2 HEAD 13th Meeting, 2013

18. Group B Mixture of foreground active stars and magnetic CVs in the Scutum/near Norma arms. Red dashed component: kT = 5.9 keV N H = 3.0 x 10 21 cm -2 Blue dotted component: kT = 1.0 keV N H < 4 x 10 20 cm -2 HEAD 13th Meeting, 2013

19. Group C Dominated by magnetic CVs in the Scutum/near Norma arms. Red dashed component: Γ = 1.2 N H = 1.5 x 10 22 cm -2 Blue dotted component: Line = 6.8 keV Eq width = 400 eV HEAD 13th Meeting, 2013

20. Group E Mixture of isolated high-mass stars, colliding wind binaries, symbiotic binaries in the far Norma arm. Possible contamination from group D IPs. Red dashed component: kT = 1.8 keV N H = 2.3 x 10 23 cm -2 Blue dotted component: kT = 1.45 keV N H = 4.1 x 10 22 cm -2 HEAD 13th Meeting, 2013

21. AGN Contribution HEAD 13th Meeting, 2013

22. LogN-logS for all groups HEAD 13th Meeting, 2013

23. >3σ sources (2-10 keV) Broadness Hardness LogN-logS HEAD 13th Meeting, 2013 Sensitivity curve method developed by Georgakakis et al. 2008

24. HMXB Luminosity Function Blue: if all 4 potential HMXBs are HMXBs HEAD 13th Meeting, 2013 17-60 keV ––– INTEGRAL: Lutovinov et al. 2013 – – Swift BAT: Voss & Ajello 2010 - - - Chandra: Grimm et al. 2002