J/MNRAS/414/1329 M82 X-ray sources long-term variability (Chiang+, 2011)
The long-term variability of the X-ray sources in M82.
Chiang Y.-K., Kong A.K.H.
<Mon. Not. R. Astron. Soc., 414, 1329-1338 (2011)>
=2011MNRAS.414.1329C 2011MNRAS.414.1329C
ADC_Keywords: Galaxies, nearby ; X-ray sources
Keywords: galaxies: individual: M82 - X-rays: binaries - X-rays: galaxies
Abstract:
We investigate the long-term variability exhibited by the X-ray point
sources in the starburst galaxy M82. By combining nine Chandra
observations taken between 1999 and 2007, we detect 58 X-ray point
sources within the D25 isophote of M82 down to a luminosity of
∼1037erg/s. Of these 58 sources, we identify three supernova remnant
candidates and one supersoft source. 26 sources in M82 exhibit
long-term (i.e. days to years) flux variability and three show
long-term spectral variability. Furthermore, we classify 26 sources as
variables and 10 as persistent sources. Among the total 26 variables,
17 varied by a flux ratio of >3 and six are transient candidates. By
comparing with other nearby galaxies, M82 shows extremely strong
long-term X-ray variability that 47 per cent of the X-ray sources are
variables with a flux ratio of >3. The strong X-ray variability of M82
suggests that the population is dominated by X-ray binaries.
Description:
Since the X-ray sources in the central region of M82 are crowded, a
high spatial resolution instrument like the Chandra X-ray Observatory
is needed to resolve the images. M82 has been observed 13 times
between 1999 and 2007 with Chandra; some of them were designed to
observe M82 X-1 with special configurations. To study the long-term
variability of the whole galaxy, we used nine Chandra data sets with
relatively long exposure time and large field of view from the Chandra
Data Archive.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 104 59 Chandra source properties for M82
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 18 A15 --- CXOU Source name, HHMMSS.s+DDMMSS (CXOU J)
20- 28 F9.5 deg RAdeg Right ascension in decimal degrees (J2000)
30- 38 F9.6 deg DEdeg Declination in decimal degrees (J2000)
40- 46 F7.2 10+31W LX Maximum X-ray luminosity (1)
48 A1 --- l_Sflux Limit flag on SFlux
49- 54 F6.2 --- Sflux Significance parameter of long-term flux
variability (2)
56 A1 --- l_R Limit flag on R
57- 62 F6.2 --- R Fmax/Fmin ratio (3)
64- 68 F5.2 --- e_R ? rms uncertainty in R
70- 73 F4.2 --- SHR1 ?=- Significance parameter of HR1 variability (4)
74 A1 --- n_SHR1 [gi] Note on SHR1 (5)
76- 79 F4.2 --- SHR2 ?=- Significance parameter of HR2 variability (6)
80 A1 --- n_SHR2 [hjk] Note on SHR2 (5)
82-104 A23 --- Notes Notes (7)
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Note (1): The highest luminosity in 0.3-7keV of a source among the nine
observations we used, assuming an absorbed power-law model
with a photon index of 1.7, NH=3x1022cm-2 and d=3.6Mpc.
Note (2): Sflux=maxi,j(|Fi-Fj|/sqrt((σHR1i)2+(σHR1j)2)
Note (3): R=Fmax/Fmin with a standard error if the lowest flux is detected or
a 90 per cent lower bound if the lowest flux is an upper limit.
Note (4): SHR1=maxi,j(|HR1i-HR1j|/sqrt((σHR1i)2+(σHR1j)2)
of the five Chandra ACIS observations.
Note (5): Individual notes as follows:
g, i = The SHR1 and SHR2 with a different extraction of colours in observation
5 using a pile-up spectral fitting. This source suffers from mild
pile-up in observation 5 with a pile-up fraction of ∼26 per cent.
h, j = The SHR1 and SHR2 excluding observation 5
k = Considering the strong contamination from the diffuse emission, this
significant level is overestimated
Note (6): SHR2=maxi,j(|HR2i-HR2j|/sqrt((σHR2i)2+(σHR2j)2)
of the five Chandra ACIS observations
Note (7): Codes as follows:
P = persistent source
V = variable
V3 = variable with flux ratio >3
T = transient candidate
SV = spectral variable
SSS = supersoft source candidate
RSN = source coincides with a radio-selected SNR in the list of
Fenech et al. (2008, Cat. J/MNRAS/391/1384)
IOV(Obs. No.) = intra-observation variability detected in the specified
observation
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 02-Feb-2012