J/ApJ/643/238 Chandra/2MASS sources in Cygnus OB2 (Butt+, 2006)
Deeper Chandra follow-up of Cygnus TeV source perpetuates mystery.
Butt Y.M., Drake J., Benaglia P., Combi J.A., Dame T., Miniati F.,
Romero G.E.
<Astrophys. J., 643, 238-244 (2006)>
=2006ApJ...643..238B 2006ApJ...643..238B
ADC_Keywords: Clusters, open ; X-ray sources ; Infrared sources
Keywords: acceleration of particles - cosmic rays - gamma rays: observations -
ISM: bubbles - open clusters and associations: individual (Cygnus OB2)
Abstract:
A 50ks Chandra observation of the unidentified TeV source in Cygnus
reported by the HEGRA collaboration reveals no obvious diffuse X-ray
counterpart. However, 240 point-like X-ray sources are detected within
or nearby the extended TeV J2032+4130 source region, of which at least
36 are massive stars and two may be radio emitters. That the HEGRA
source is a composite, having as a counterpart the multiple point-like
X-ray sources we observe, cannot be ruled out. Indeed, the
distribution of point-like X-ray sources appears nonuniform and
concentrated broadly within the extent of the TeV source region. We
offer a hypothesis for the origin of the very high energy gamma-ray
emission in Cyg OB2 based on the local acceleration of TeV-range
cosmic rays and the differential distribution of OB versus less
massive stars in this association.
Description:
TeV J2032+4130 was observed by Chandra on 2004 July 12 at UT 02:04:33
for a total effective exposure time of 48728s using the Advanced CCD
Imaging Spectrometer-Imager (ACIS-I) detector in its standard Timed
Exposure Very Faint mode. All four imaging chips were active, in
addition to spectroscopy chips S3 and S4.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 72 240 Detected sources in Cyg OB2
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [BDB2006] Running X-ray identification number
5- 6 I2 h RAh Chandra Hour of Right Ascension (J2000)
8- 9 I2 min RAm Chandra Minute of Right Ascension (J2000)
11- 16 F6.3 s RAs Chandra Second of Right Ascension (J2000)
17 A1 --- DE- Chandra Sign of Declination (J2000)
18- 19 I2 deg DEd Chandra Degree of Declination (J2000)
21- 22 I2 arcmin DEm Chandra Arcminute of Declination (J2000)
24- 28 F5.2 arcsec DEs Chandra Arcsecond of Declination (J2000)
30- 35 F6.3 --- SNR Signal-to-noise of source
37- 42 F6.3 --- HR Hardness ratio (1)
44- 48 F5.1 ct Ct Source counts from ACIS-I
50- 51 I2 h RA2h ? 2MASS Hour of Right Ascension (J2000)
53- 54 I2 min RA2m ? 2MASS Minute of Right Ascension (J2000)
56- 60 F5.2 s RA2s ? 2MASS Second of Right Ascension (J2000)
61 A1 --- DE2- 2MASS Sign of Declination (J2000)
62- 63 I2 deg DE2d ? 2MASS Degree of Declination (J2000)
65- 66 I2 arcmin DE2m ? 2MASS Arcminute of Declination (J2000)
68- 72 F5.2 arcsec DE2s ? 2MASS Arcsecond of Declination (J2000)
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Note (1): Defined as (2-10keV)/(0.5-2keV).
For reasons of computational expediency, we employed a binning by 4
pixels in both image dimensions for these calculations. This process
was carried out for images made from event lists filtered in the
energy ranges 0.5-2 and 2-10keV. These particular energy ranges were
chosen so as to contain approximately one half of the X-ray photon
events in each. The resulting images were then binned by a further
factor of 32 in order to accumulate sufficient counts in each bin to
estimate a meaningful hardness ratio.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 26-Sep-2008