SLIDE 1 Radio continuum searches for black holes in globular clusters
Jay Strader (Michigan St)
Laura Chomiuk (Michigan St) Laura Shishkovsky (Michigan St) Tom Maccarone (Texas Tech) James Miller-Jones (Curtin) Anil Seth (Utah) Craig Heinke (Alberta) Greg Sivakoff (Alberta) Nadine Neumayer (MPIA) Eva Noyola (UNAM)
with
SLIDE 2
Low-mass X-ray binaries
Accretion onto a compact object (neutron star or black hole) produces X-ray, optical, and radio emission
SLIDE 3 Radio & X-ray for BHs
Corbel et al. 2013
For BHs with low accretion rates, radio detection increasingly efficient
Lr ~ Lx0.6 Lx Lr
Jonker/Hynes
SLIDE 4
Why Now? The VLA upgrade
Bandwidth is 20x higher than old VLA: an enormous upgrade for radio continuum observations just by changing the electronics
SLIDE 5
How Non-detections Look
M19 VLA
1 pc
SLIDE 6 M22: Central sources
flat spectrum: S ~ v0.0-0.2 no X-rays
Strader et al. 2012
central spatial location flux density ~ 55-60 uJy VLA Chandra
SLIDE 7
Still not X-ray detected
in new simultaneous Chandra data, have LX < 5 x 1029 erg/s
SLIDE 8 Radio & X-ray
radio/X-ray ratio suggests these are BHs
Miller-Jones, JS et al., 2015
SLIDE 9 Radio & X-ray
transitional MSP/LMXB appear to follow offset relation
Miller-Jones, JS et al., 2015
SLIDE 10 Optical Counterparts?
~ 0.34 M
Strader et al. 2012
WD?
SLIDE 11 Radio Proper Motions for M22 Sources
Would completely rule
46 +/- 6 uJy
Keep trying (and being foiled) at getting a clean 2nd epoch of data
SLIDE 12 M62: A nicer BH candidate
VLA Chandra 25”
Chomiuk et al 2013
(only 19 uJy!)
power-law X-ray spectrum:
SLIDE 13 Radio & X-ray Redux
similar to V404 Cyg (longish period for BHXB)
match is a red giant
Miller-Jones, JS et al., 2015
possible to get AO RVs: first set taken
SLIDE 14 A candidate in 47 Tuc
ATCA Chandra 20”
Miller-Jones, JS, et al 2015
SLIDE 15 Radio & X-ray
Miller-Jones, JS et al., 2015
SLIDE 16 Optical Data
HST (275W) HST (814W) Optical counterpart is well-known UV- bright variable, with a UV HST spectrum
CIV
no He 1640
Knigge et al. 2008
SLIDE 17 X-ray Data
Unusual X-ray spectrum, consistent with the presence of OVIII emission
Heinke et al 2005
SLIDE 18
47 Tuc X9
in addition, there is a good upper limit on H- alpha emission from narrow-band HST photometry presence of C/O emission with no H/He emission suggests donor is a CO WD an HST broadband spectrum could rule out H emission and provide more evidence for ultracompact interpretation
SLIDE 19
M10
flat-spectrum radio source within core of cluster deep Chandra data will be taken this cycle (LX < 6 x 1032) red giant counterpart
POSTER BY LAURA SHISHKOVSKY
SLIDE 20
Population Conclusions?
among BH candidate secondaries: 2 RGB stars, 1 MS star, 1-2 WDs, 1 sub-subgiant median distance of GC with BH candidates is 4 kpc: suggests search is sensitivity limited, and thus a large population of candidate BHs
