![Page 1: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/1.jpg)
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)
![Page 2: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/2.jpg)
Five Years of Chandra Observations of the Galactic
Center
Sgr A*
5 pcGalactic Plane
0.1% of the Galactic stellar mass!
![Page 3: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/3.jpg)
X-ray Sources within 25 pc of Sgr A*
• Previous wide-field surveys were only sensitive to LX>1036 erg s-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 sources have LX>1034 to 1036 erg s-1. These are a bit unexpected. . .
Sgr A*
5 pc
![Page 4: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/4.jpg)
X-ray Sources within 25 pc of Sgr A*
• Previous wide-field surveys were only sensitive to LX>1036 erg s-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 sources have LX>1034 to 1036 erg s-1. These are a bit unexpected. . .
Sgr A*
New Transient
5 pc
![Page 5: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/5.jpg)
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.
One Solar Radius
Image c
reate
s w
ith b
insi
m,
by R
ob H
yn
es
Location ofCompact Object
![Page 6: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/6.jpg)
Thermonuclear Bursts from a Neutron Star Low-Mass X-ray
Binary
Sgr A*
New Transient
5 pc An X-ray burst lasting 100 swas produced by unstable Heburning on the neutron star.
![Page 7: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/7.jpg)
Another LMXB (0.1 pc from Sgr A*) with Periodic Eclipses
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)
To Sgr A*(0.1 pc)
![Page 8: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/8.jpg)
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.
![Page 9: 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](https://reader035.vdocuments.mx/reader035/viewer/2022072007/56649d345503460f94a0b2b2/html5/thumbnails/9.jpg)
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.