Galactic X-ray Surveys and Galactic X-ray Source Populations Bob - - PowerPoint PPT Presentation

X-ray Astronomy Group

Bob Warwick University of Leicester

Galactic X-ray Surveys and Galactic X-ray Source Populations

PART I - Galactic X-ray Surveys A Brief Overview

THE FOURTH UHURU CATALOG OF X-RAY SOURCES Forman et al (1978) 339 sources THE ARIEL V (3A) CATALOGUE OF X-RAY SOURCES: Warwick et al (1981) McHardy et al (1981) 250 sources

X-RAY ALL-SKY SURVEYS circa late-1970’s

Galactic Coordinates “Classical” hard X-ray 2-10 keV band

Wood et al. (1984)

HEAO 1 A1 All-Sky Survey

Aug 1977-Jan 1979 2-10 keV

842 sources

SS Cyg V711 Tau

“Pseudo” All-Sky coverage of XMM Slew-Survey (0.3-12 keV)

Saxton, Read et al XMMSL1- Delta6 ~65% sky coverage total of ~20000 sources 2160 in 2-10 keV band

XMM Slew-Survey – Source Catalogue

INTEGRAL/IBIS All-sky Survey

Krivonos et. al., 2007 plus up-dates Krivonos et al. 2012 – the low latitude sample

17-60 keV

The 70 month Swift-BAT All-sky X-ray Survey

Baumgartner et al. 2013 14-195 keV 1171 sources

Galactic Source Statistics: High Mass X-ray Binary (HMXB) - 85 Low Mass X-ray Binary (LMXB) - 84 Other binary - 17 Star - 14 Supernova Remnant (SNR) - 6 Cataclysmic variables (CV) - 55 Pulsars - 20

ROSAT All-Sky Survey in the soft X-ray (0.1-2.4 keV) band

ROSAT BSC - 18,811 sources- Voges et al. 1999

X-ray emission across the HR diagram

Gudel 2004

Active Coronae Stellar Winds RS CVn Binaries

The "next-generation" all-sky survey

Spectrum-Roentgen-Gamma Satellite Prospective Launch date: 2017

eROSITA

LMXB HMXB Doroshenko et al. 2014

Galactic X-ray Surveys via Multiple Pointings ASCA Galactic Plane Survey within | l | < 45o

ASCA Galactic Plane Survey (-45<l<45); Sugizaki et al. (2001) 0.7-7 keV 163 sources with Fx > 10-13 erg/s/cm2

Studying the Galactic Plane with XMM-Newton

XGPS Survey I = 19-22o ; Hands et al 2004; 424 sources; Fx > 2 x 10-14 erg/s/cm2 XMM-Newton SSC programme included a ground-based follow-up programme focused on a bright subset of the XGPS sources - Motch et al. (2010)

Combination of three surveys

ASCA – Sugizaki et al 2001 XMM – Hands et al 2004

l = 19o-22o

Chandra – Ebisawa et al 2005

l = 28.5o 2 x 100 ks

Observed 2-10 keV Source Counts in the Galactic Plane

Chandra XMM ASCA extragalactic (abs. corrected)

Point sources detected by Chandra in the Galactic Centre

Muno et al. 2004 > 30,000 sources per

• sq. deg

The ChamPlane Survey of the Galactic Bulge Region

X-ray Glimpse 3.6 micron J,H,K Grindlay et al 2005; Koenig et al 2008; Hong et al 2009; van den Berg et al. 2009; van den Berg et al. 2012

Chandra Survey of the Norma Spiral Arm

Fornasini et al. 2014

20 ks pointings covering 2o x 0.8o 1415 sources

Serendipitous Source Catalogues

Swift  1SXPS 1905 deg2 151,524 sources Evans P. et al. 2014 XMM  3XMM-DR5 877 deg2 396910 sources Rosen et al. 2015 Chandra  CSC-V1.1 106,528 sources Evans I. et al. 2010

PART II - Galactic X-ray Source Populations1

1focusing on the 2-10 keV band

and intermediate-to-low Lx sources

The Diversity of Source Types

High luminosity (Lx ~ 1035-39 erg/s) X-ray binaries powered by accretion onto either a NS or BH

• HMXB (Supergiant XRBs, SFTs, Be-star XRBs etc..)
• LMXB (Atoll, Z; Bursters, Dippers, ADC etc..)

The Diversity of Source Types

Intermediate-to-low (Lx ~ 1027-35 erg/s) luminosity sources:

• XRBs (qLMXB, γ Cas, Symbiotics)
• CVs (Dwarf Novae, IPs, Polars, Symbiotics)
• SNRs + PWN + PULSARS (radio, msec, AXPs, SGRs)
• HOT STARS (WR, O Supergiants, Col. Wind Binaries)
• COOL STARS (F-M, Active binaries - BY Dra, RS CVn)
• Pre-MS (Protostars, T-Tauri )

• Detailed X-ray properties – spectra & timing
• Nature of the Optical/IR counterparts 
• Distances  intrinsic properties such as LX
• "Completely" identified samples combined

with a spatial distribution model 

• X-ray Luminosity Function(XLF)

[ dN/dLX = No. of sources per unit LX per pc3 ]

What we would like to know about each defined sub-class:

Within the Galaxy: There is the wide angular scale and the high extinction and high stellar density in the Galactic Plane. These hamper the definition of "complete" samples, the identification of the counterparts in the optical/IR and the determination of the source distance. For external galaxies: The distance is known but only the most luminous X-ray sources are resolved1 and the optical/IR follow-up is limited to high-mass stellar counterparts.

1 For Chandra the threshold Lx outside of the Local Group is typically > 1036-37 erg/s.

Observational Hurdles

The XLF of Galactic LMXB & HMXB – follow the "Universal" form

Gilfanov 2004

HMXB Trace star formation Tevol ~ 1-10 Myr LMXB Trace stellar mass Tevol ~ 1-10 Gyr

2-10 keV XLFs of the Intermediate/Old Binary Source Populations in the Galaxy

Sazonov et al., 2006 Revnivtsev et al., 2006

Number of sources in the Galaxy per log Lx bin Contribution to total 2-10 keV luminosity of the Galaxy LMXB + CVs + Active Stellar Binaries (ABs)

~3%

2-10 keV

The Galactic Ridge X-ray Emission (GRXE)

EXOSAT RXTE - contours HEAO-1 circa ~1985 circa ~1982 circa ~2006

X-ray Spectrum of the GRXE

Cool component kT ~0.8 keV Kaneda et al. 1997 Cosmic X-ray Background ASCA GIS

6.7 keV iron line kT ~ 8 keV kT ~ 0.8 keV

Above 4 keV:

• Hard thermal continuum (kT ~ 5 keV)
• He-like and H-like Fe Kα lines (6.67/6.96 keV)

Origin of the GRXE

Cool component kT ~0.8 keV

Very hot diffuse plasma Emission of unresolved sources

Unbound  Needs 1043 erg s-1 to replenish? What Galactic source population(s)?

Sources – Integrated Spectrum

Revnivtsev et al., 2009

Resolving the Galactic Ridge X-ray Emission in a 1 Msec Chandra Observation

Revnivtsev et al., 2009 ~ 80,000 sources per deg2

Resolved Fraction of GRXE

[Hong 2012; Morihana et al. 2013]

Exploring the X-ray Source Population in the Galactic Plane at Faint Fluxes (in the 2-10 keV band)

• We assume that coronally active single

stars and active binaries (ASBs) and cataclysmic variables (CVs) dominate.

• Use a new hard-band selected sample

taken from the high-latitude (|b| > 10o) XMM Slew Survey [Warwick 2014]

• Transpose the results to the Galactic

Plane assuming a 150 pc z-scale height and Rdisc=2.2 kpc for both populations

46 ASBs 16 CVs Spectral Assumptions: Count/s  X-ray flux  X-ray luminosity ASBs: kT = 3.5 x 107 K (3 keV) apec plasma with Z=0.4 Z CVs: kT = 10 keV thermal bremsstrahlung + Fe lines

46 ASBs  coronally- active stars and binary systems 16 CVs  magnetic & non-magnetic cataclysmic variables

The XSS hard-band selected sample

★★★ The coronally-active stars and binaries are preferentially

• bserved in the 2-10

keV band during flare states. ★★★

Derived X-ray Luminosity Functions

Warwick 2014 Lx / pc3 / M 46 ASBs 16 CVs Local volume emissivity of ASBs: = 1.08 ± 0.16 x 1028 erg/s (2-10 keV) / M Local volume emissivity of CVs: = 2.5 ± 0.6 x 1027 erg/s (2-10 keV) / M

[Referenced to a local mass density of 0.04 M/ pc3

Local space density

• f ASBs:

= 3.4±0.5 x 10-3 pc-3 Local space density

• f CVs:

= 3.4±0.7 x 10-5 pc-3

"Template" 2-10 keV X-ray Luminosity Functions

Warwick 2014 Lx / pc3 / M

ASBs CVs XRBs  Sazanov et al (2006) XLF [Referenced to a local mass density of 0.04 M/ pc3

Predicted 2-10 keV Source Counts in the Galactic Plane (at l = 28.5o)

Warwick 2014

ASBs CVs XRBs  extragalactic sources TOTAL

coronally-active stars and binaries dominate at faint levels

Observed 2-10 keV Source Counts [normalized to (SX/10-14)-1.5]

Warwick 2014

Chandra ASCA XMM ~600 per deg2 (raw) ~1600 per deg2 (corrected)

Observed Versus Predicted Source Counts [normalized to (SX/10-14)-1.5]

Warwick 2014

ASBs CVs XRBs   extragalactic sources TOTAL

Matching the measured intensity of the GRXE in the 2-10 keV band

(= 4.8 x 10-11 erg/s/cm2 /deg2 - Ebisawa et al 2008)

Warwick 2014

ASBs CVs XRBs Total

Active Stars  78 +/- 12 % CVs  16 +/- 4 % Total  94 +/- 13%

Matching the X-ray spectrum of the GRXE

Suzaku l=28.46o b=-0.2o Ebisawa et al. 2008

Fe-K Line Equivalent Widths 6.4-keV line  80 +/- 20 eV 6.67-keV line  350 +/- 40 eV 6.96-keV line  70 +/- 30 eV

Matching the measured equivalent widths

• f the 6.4 keV/6.7/6.9-keV Fe-K lines
• 20% contribution from CVs

[EW6.4 ~ 75 eV; EW6.7 ~ 150 eV; EW6.9 ~ 100 eV]

• 60%+ contribution from ASBs1

[EW6.4 ~ 0 eV; EW6.7 ~ 400 eV; EW6.9 ~ 70 eV]

39

• 10%+ contribution from scattered

radiation in the ISM [Molaro et al. 2014]

[EW6.4 ~ 1000 eV; EW6.7 ~ 0 eV; EW6.9 ~ 0 eV]

1 Assumes kT ~3-5 keV and Z ~ 0.4 for the coronal flares

Part III - The challenge of identifying IR/optical counterparts in the Galactic Plane

Stellar density in the Galactic Plane as a function of the Ks magnitude

Stars in a 3 arcsec radius error circle

0.17 15 1.7 18

Kaplan et al 2004

Make-up of the X-ray source population

• n the Galactic Plane

Warwick 2014

ASBs CVs XRBs GALACTIC TOTAL

Fraction of Total Detections

~ 32% of the hard X-ray sources in the Ebisawa Chandra fields have plausible NIR counterparts with Ks < 15

2-10 keV

AGN seen through the Galactic Plane

Rovilos et al 2011 Correction for absorption NH~6 x 1022 cm-2 A

V~33

AK~3.7

Track of a "typical" CV LX ~ 1032 erg/s (~9 kpc) LX ~ 1030 erg/s (~900 pc)

NIR colour-magnitude diagram for X-ray emitting CVs

LX ~ 1031 erg/s (~3 kpc)

X-ray survey at Sx ~ 10-14 erg/s/cm2 (2-10 keV)

Assumes reddening: Av = 2 mag/kpc AJ-AK = 0.34 mag/kpc

K3III Giant B0I Supergiant M6V Dwarf F0V Dwarf Plotted data based on Ebisawa et al 2005 NIR measurements

NIR colour-magnitude diagram for X-ray emitting stars

X-ray survey at Sx ~ 10-14 erg/s/cm2 (2-10 keV) Solid Lines for:

Lx = 1029-32 erg/s (0.3 - 9 kpc)

active binaries active dwarf stars

active binaries active dwarf stars K3III Giant B0I Supergiant M6V Dwarf F0V Dwarf Plotted data based on Anderson et al 2014 NIR measurements

NIR colour-magnitude diagram for X-ray emitting stars

X-ray survey at Sx ~ 3 x 10-13 erg/s/cm2 (2-10 keV) Solid Lines for:

Lx = 1029-32 erg/s (50 – 1700 pc)

HMXB Be stars WR stars

Nebot Gomez-Moran et al 2015 173 hard X-ray sources with likely IR (2MASS and Glimpse) counterparts >80% remain of "unconstrained" nature

IR Follow-up of 3XMM Sources

K3III Giant B0I Supergiant M6V Dwarf F0V Dwarf Plotted data based on Nebot Gomez-Moran 2015 X-ray & IR sample

NIR colour-magnitude diagram for X-ray emitting stars

X-ray survey at Sx ~ 3 x 10-14 erg/s/cm2 (2-10 keV) Solid Lines for:

Lx = 1029-32 erg/s (170 – 5000 pc)

active binaries active dwarf stars

Conclusions

• Our knowledge of the statistical properties of

the various Galactic X-ray Source Populations (high-Lx XRBs excepted) is still very limited.

• Based on current estimates of their XLF it

seems likely that CVs and coronally-active stars and binaries (ASBs) dominate at faint fluxes in the 2-10 keV band and produce a significant fraction of the GRXE.

• This hypothesis (at least the ASB part) is

readily testable with current data.