J/ApJ/879/112 Chandra multi-epoch study of the spiral gal. NGC7331 (Jin+, 2019)
A multi-epoch X-ray study of the spiral galaxy NGC 7331.
Jin R., Kong A.K.H.
<Astrophys. J., 879, 112 (2019)>
=2019ApJ...879..112J 2019ApJ...879..112J
ADC_Keywords: Galaxies, nearby; X-ray sources; Supernovae; Binaries, X-ray;
Optical
Keywords: galaxies: individual (NGC 7331) ; supernovae: individual (SN 2014C) ;
X-rays: binaries ; X-rays: galaxies
Abstract:
X-ray point sources in galaxies are dominated by X-ray binaries (XRBs)
that are variables or transients, and whether their variability would
alter the X-ray luminosity functions (XLFs) is still in debate. Here
we report on NGC 7331 as an example to test this with seven Chandra
observations. Their detection limit is 7x1037erg/s in the energy
range 0.3-8.0keV by assuming a power-law (PL) spectral model with a
photon index of 1.7. We detected 55 X-ray sources. Thirteen of them
are variables, of which three are transients, and some of the sources
possess a bimodal feature in their luminosity-hardness ratio, which is
often observed among XRBs. Nine more ultraluminous X-ray sources are
found in comparison with previous studies and eight are likely to be
low-mass or high-mass XRBs. Twenty-one optical counterpart candidates
are found based on the Hubble Space Telescope images, but we cannot
rule out the possibility of positional coincidence. The spectral
analysis of SN 2014C shows a trend of increasing soft photons and
decreasing hydrogen column densities as its outer shell expands. We
fit the seven incompleteness-corrected XLFs to both a PL and a PL with
an exponential cut-off (PLC) model using the Bayesian method, which is
used for the first time in XLF fitting. The hierarchical PLC model can
describe the XLF of NGC 7331 best with a slope of ∼0.5 and a
luminosity cut-off around 8x1038erg/s. This study proves that
multi-epoch observations decrease the deviation due to the variable
luminous sources in XLFs.
Description:
In this study, we use seven X-ray observations of NGC 7331 taken by
the Advanced CCD Imaging Spectrometer S-array (ACIS-S) of Chandra from
2001 to 2016 (ObsIDs 2198, 16005, 17569, 17570, 17571, 18340 and 18341).
The first Chandra X-ray observation (ObsID 2198) of the field of
SN2014C was taken before its explosion with an exposure time of
29.5ks. The first Chandra detection after the explosion was at t=308d
(ObsID 16005); we analyzed five pairs of Chandra and NuSTAR
observations in this study from t=397d to t=1029d. See Section 2.4.
In order to search for optical counterparts of the X-ray sources found
in NGC 7331, we select five HST observations from 1994 to 2015 that
contain its D25 isophote region. There are three observations with
the HST Wide Field Planetary Camera-2 (WFPC2) (ObsID 07450, 11128, and
11966) and two with the Wide Field Camera 3 (WFC3) (ObsID 14202 and
14668) taken between 1997 and 2016.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 81 55 Chandra source properties
--------------------------------------------------------------------------------
See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/hst : HST Archived Exposures Catalog (STScI, 2007)
VIII/10 : Bell Laboratories H I Profiles (Stark+ 1992)
VIII/28 : Bell Laboratories H I Survey (Stark+ 1992)
J/ApJS/79/77 : Bell Lab. H I Survey - High Velocity Clouds (Stark+ 1992)
J/A+AS/131/317 : NGC 7331 HII regions catalogue (Petit 1998)
J/AJ/122/2810 : Chandra Deep Field North Survey. V. (Brandt+, 2001)
J/ApJ/577/738 : M31 Chandra X-ray point sources (Kong+, 2002)
J/ApJ/589/225 : Chandra X-ray sources toward Galactic Center (Muno+, 2003)
J/ApJ/599/218 : Chandra LMXB in NGC 4365 and NGC 4382 (Sivakoff+, 2003)
J/ApJS/144/213 : Chandra X-ray observations of M81 (Swartz+, 2003)
J/ApJ/602/231 : Chandra X-ray point sources in nearby gal. (Colbert+, 2004)
J/ApJS/161/271 : The X-ray binary population in M33. I (Grimm+, 2005)
J/ApJS/173/572 : GALEX/Spitzer photometry in NGC 7331 (Thilker+, 2007)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/ApJ/735/26 : Chandra observations of M81 (Sell+, 2011)
J/ApJ/741/49 : ULX candidates in nearby galaxies (Swartz+, 2011)
J/ApJ/836/50 : Chandra observations of IC 10 (Laycock+, 2017)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/55] Source number
4- 5 I2 h RAh [22] Hour of Right Ascension (J2000)
7- 8 I2 min RAm [36/37] Minute of Right Ascension (J2000)
10- 15 F6.3 s RAs Second of Right Ascension (J2000)
17 A1 --- DE- [+] Sign of the Declination (J2000)
18- 19 I2 deg DEd [34] Degree of Declination (J2000)
21- 22 I2 arcmin DEm [23/28] Arcminute of Declination (J2000)
24- 28 F5.2 arcsec DEs Arcsecond of Declination (J2000)
30- 33 I4 ct Ncts [9/1437] Net counts (1)
35- 38 F4.2 10-2ct/s CR [0.04/5.2] Count rate (2)
40- 43 F4.2 10-2ct/s e_CR [0.02/0.3] Lower uncertainty in CR (2)
45- 48 F4.2 10-2ct/s E_CR [0.02/0.3] Upper uncertainty in CR (2)
50- 54 F5.2 10-14mW/m2 Flux [0.4/63] Flux; 10-14erg/s/cm2 (3)
56- 59 F4.2 10-14mW/m2 e_Flux [0.1/2.8] Lower uncertainty in Flux
61- 64 F4.2 10-14mW/m2 E_Flux [0.2/3] Upper uncertainty in Flux
66- 73 E8.2 10-7W Lx [1e+38/1.7e+40] X-ray luminosity; erg/s (4)
75- 81 A7 --- Class Class (5)
--------------------------------------------------------------------------------
Note (1): The net counts are background scaled net counts in the source regions.
Note (2): The count rates and the uncertainties are obtained by computing the
Bayesian background-marginalized posterior probability distribution
function (PDF) using the aprates tool.
Note (3): The 0.3-8keV maximum unabsorbed model fluxes in these seven
observations by assuming a power law model with a photon index of
1.7 and an absorption of Galactic NH, which is evaluated by an
interactive program COLDEN. COLDEN is supported by the datasets
provided by Bell Laboratories (Stark 1992, VIII/28) and
National Radio Astronomy Observatory (NRAO) HI Survey
(Dickey and Lockman 1990ARA&A..28..215D 1990ARA&A..28..215D).
Note (4): The 0.3-8keV maximum luminosity estimated from the unabsorbed
maximum fluxes by assuming a distance of 14.7Mpc.
Note (5): The sources classified as variables according to Section 2.2 are
denoted with "v" and the transients (with maximum to minimum
flux >10) are added with a letter "T". The variables possess
low/hard and high/soft bimodal characters in flux and HR variation
are denoted in "B". "L", "H", and "a" are the classification
determined by the X-ray colors adopted from
Prestwich (2003ApJ...595..719P 2003ApJ...595..719P); L: Low mass X-ray binary,
H: High-mass X-ray binary, a: Absorbed sources. SN: SN 2014C.
c: The sources located within less than 1.5" radius of the central
region of NGC 7331.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Dec-2020