Transcript What Are the Faint X-ray Transients Near the Galactic Center?

What Are the Faint X-ray
Transients Near the
Galactic Center?
Michael Muno (UCLA/Hubble Fellow)
Fred Baganoff (MIT), Eric Pfahl (UVa),
Niel Brandt, Gordon Garmire (Penn State)
Mark Morris, Andrea Ghez,
Jessica Lu, Seth Hornstein (UCLA)
Five Years of Chandra Observations
of the Galactic Center
Sgr A*
5 pc
Galactic Plane
0.1% of the Galactic stellar mass!
X-ray Sources within 25 pc of
Sgr A*
• Previous wide-field
surveys were only
sensitive to LX>1036 erg s1.
• Most of the Chandra X-ray
sources have LX=1031 to
1033 erg s-1. These are
likely to be CVs.
• Seven transient X-ray
5 pc
sources have LX>1034 to
1036 erg s-1. These are a
bit unexpected. . .
Sgr A*
X-ray Sources within 25 pc of
Sgr A*
• Previous wide-field
surveys were only
sensitive to LX>1036 erg s-
New Transient
1.
• Most of the Chandra X-ray
sources have LX=1031 to
1033 erg s-1. These are
likely to be CVs.
• Seven transient X-ray
5 pc
sources have LX>1034 to
1036 erg s-1. These are a
bit unexpected. . .
Sgr A*
Location of
Compact Object
One Solar Radius
Image creates with binsim, by Rob Hynes
Your Standard Transient
X-ray Source
• Most bright, transient X-ray sources are accreting
black holes and neutron stars.
• When accretion occurs at low rates, the disk tends
to be unstable, producing outbursts with LX>1037 erg
s-1.
Thermonuclear Bursts from a
Neutron Star Low-Mass X-ray Binary
New Transient
Sgr A*
5 pc
An X-ray burst lasting 100 s
was produced by unstable He
burning on the neutron star.
Another LMXB (0.1 pc from Sgr A*)
with Periodic Eclipses
To Sgr A*
(0.1 pc)
The X-ray light curve displays
partial eclipses at the 8 hour
orbital period.
Infrared images reveal no infrared
companion with K<15, ruling out a
high-mass star.
Muno et al. (2005b)
Other Transients also have
Unusual Properties
• Transient outbursts
last anywhere from
less than a month,
to the full five years.
• The long, slow
transient to the left
has a soft spectrum
reminiscent of
transient magnetars.
Making Progress on
Faint X-ray Transients
• We need better X-ray coverage, to identify new
examples and to measure outburst time scales and
spectral evolution.
• Radio observations can reveal jets, which are
common from X-ray binaries.
– Likewise, we need to determine whether the radio transients
seen near the Galactic center have X-ray counterparts.
• Infrared observations can detect accreting
companions.
• TeV instruments will soon have the baseline to
identify transients.