Remarkable X-Ray Source Populations

Summary

Spectra of the optical counterparts of serendipitous x-ray sources identified by Chandra

Finding Targets

An object whose ANCILLARY_TARGET1 value include one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS-III bitmasks to learn how to use these values to identify objects in this ancillary target program.

Sub-program (bit name)	Bit Number
CXOBRIGHT	58
CXOGRIZt	59
CXORED	60

Description

This program targets remarkable serendipitous X-ray sources from the Second XMM-Newton Serendipitous Source Catalog (2XMMi; Watson et al. 2009) and the Chandra Source Catalog (CSC; Evans et al. 2010) that do not already have available identification spectra. Source types of primary interest include AGN (often obscured), X-ray binaries, magnetic cataclysmic variables, and strongly flaring stars.

XMM-Newton sources were required to lie within 14' of the pointing center of an XMM-Newton observation, to have a 2XMMi detection likelihood greater than 12 as defined in Watson et al. (2009), to have a statistically significant match to an SDSS photometric counterpart, and not to have any 2XMMi problem flags set. Similarly, Chandra sources were required to have an SDSS counterpart and not to have any indication of Chandra source confusion. All XMM-Newton and Chandra sources having Galactic latitudes of |b| < 20 degrees w ere furthermore removed to emphasize extragalactic sources.

Target Selection Details

The four XMM-Newton source types for this program were all selected using SDSS model magnitudes and are determined as follows:

XMMHR:
- 1030 XMM-Newton sources were selected that have unusual 2XMMi hardness ratios in the HR2-HR3 plane.
- i < 20.5 (to ensure reasonable BOSS spectral quality)
- 2-12 keV X-ray to i-band flux ratios greater than 0.03 (to minimize stellar contamination).
Optical fluxes are defined as f_ν Δν, where Δν is the width of the bandpass.
XMMBRIGHT:
- 826 XMM-Newton sources were selected that have bright 2-12 keV fluxes (brighter than 5 x 10^-14 erg cm^-2 s^-1).
- i < 20.0
XMMRED:
- 627 optically red XMM-Newton sources were selected that have SDSS colors of g - i > 1.0.
- i < 19.3
- 2-12 keV X-ray to i-band flux ratios greater than 0.03.
XMMGRIZ:
- 149 XMM-Newton sources were selected that have "outlier" SDSS colors: SDSS point-source counterparts that have g - r > 1.2 or r - i > 1.0 or i - z > 1.4.
- i < 18-21.3
- 0.5-2 keV X-ray to i-band flux ratios greater than 0.1.

There is some overlap among these XMM-Newton source-selection approaches ( e.g., a bright XMM-Newton source might also have optically red colors). At each selection step, we removed sources already selected in previous XMMNewton selection steps (following the ordering above). There are 2632 selected XMM-Newton sources in total.

As with the XMM-Newton sources, Chandra source types were all selected using SDSS model magnitudues and are determined as follows:

CXOBRIGHT:
- 387 Chandra sources were selected that have bright 2-8 keV fluxes (brighter than 5 x 10^-14 erg cm^-2 s^-1).
- i < 20.0
CXORED:
- 635 optically red Chandra sources were selected that have SDSS colors of (g-i) > 1.0.
- i < 19.3
- 2-8 keV X-ray to i-band flux ratios greater than 0.03.
CXOGRIZ :
- 66 Chandra sources were selected that have "outlier" SDSS colors: SDSS point-source counterparts that have g - r > 1.2 or r - i > 1.0 or i - z > 1.4.
- i < 18-21.3
- 0.5-2 keV X-ray to i-band flux ratios greater than 0.1.

Again, there is some overlap among these Chandra source-selection approaches, and again at each step we removed sources already selected in previous Chandra selection steps (following the ordering above). There are 1088 selected Chandra sources in total. We furthermore removed selected Chandra sources that were also selected XMM-Newton sources; this reduced the number of selected Chandra sources to 952.

Primary contact

Niel Brandt
Pennsylvania State University
niel -at- astro.psu.edu

REFERENCES

Watson, M. G., et al., 2009, A&A, 493, 339 article
Evans, I. N., et al., 2010, ApJS, 189, 37 doi:10.1088/0067-0049/189/1/37