Download MF16

The Optical Counterpart of NGC6946 ULX-1
(a peculiar ULX nebula MF16)
P. Abolmasov,
S. Fabrika, O. Sholukhova, V. Afanasiev
Special Astrophysical Observatory, Russia
ULX nebulae:
-Shock excitation ([SII], [NII], [OI] etc. )
-Large sizes, ~50-500pc
-HeII λ4686 emission (stellar?)
What are they?
-SNRs? (too powerful)
-Superbubbles? (lack of young stars)
-X-ray ionized nebulae? (requires too much
X-rays in some cases!)
MH9/10, the optical
counterpart of HoIX X-1
(Grise et al., 2006)
MF16
(counterpart of NGC6946 ULX-1):
34pc (~1,˝5)
X-ray source
coordinates:
20h 35m 00s.75
+60˚ 11' 30".9
(HST ACS,
filter F658N)
20pc (~1˝)
But: HeIIλ4686 / Hβ ~ 0.2 !!
Radio isophotes
(VLA)
LX ≈ 2.5 1039 erg/s (0.5-8.0 keV)
L(H) ≈ 2 1038 erg/s
L(optical lines, total) ≈ 2 1039 erg/s
Also a bright radio source
from Blair&Fesen, 1994
Observations with the 6m SAO telescope
Spectrograph
wavelength range,Å
spectral
resolution
seeing,
arcsec
MPFS (panoramic)
4000-7000
~1000
1,5
SCORPIO (long-slit) 4000-5700
~2000
1,5
Long
Slit
MPFS
FOV
1˝
Two-component lines:
HeII4686
H
[OIII]4959
[OIII]5007
V2-V1  120-130 km/s
[OIII]5007
Broader component width ~ 200-300km/s
H
For a single H line
(from Dopita&Sutherland, 1996)
Total luminosity in H (if the shock surface area is given);
Shock velocity estimate from the component ratio:
 FH  , precursor
VS  866 km  
s  F
 H  , shock



7.69
L(Hβ) = (7,2±0,4) 1037 erg/s
Single Hβ line
Narrow-to-broad components ratio 1,85±0,19
kinematics
Additional source of
excitation/ionization?
nH, cm-3
SHOCK WAVES OR
PHOTOIONIZATION?
from Evans et al., 1999

Only lgU~-5 can be provided by the extrapolated
model for X-ray spectrum (Chandra data, taken from
Roberts&Colbert, 2003), lgU~-2.7 needed
MF16
MF16
B/n1/2 =
Photoionization by power law continuum
(labelled by ionization parameter logarithm lgU)

F
1
U
d
cn 13.6eV h
HeII4686
L(HeII)=1.6 1037 erg/s
Cannot be explained by a
shock wave, and an EUV
source needed with
L<228Å ≥ 1039erg/s
MF16
Or X-ray source
with L ~ 1041 erg/s
or larger!
Photoionization by power
law continuum (labelled by
ionization parameter
logarithm lgU)
… and other high-excitation lines
Pure photoionization models (CLOUDY 96.01 modeling
results):
Central source emitting:
fixed X-ray spectrum (best-fit from
Roberts&Colbert, 2003), with dilution
corresponding to 13pc
+
black body with temperatures
(3-30) 104K and integral flux
densities 0.3-7.0 erg/cm2/s
Photoionization best-fit:
lgT(K) = 5.15±0.05
(T~120 000K)
F = 0.6 ± 0.1 erg/cm2/s
=> UV luminosity ~1040erg/s
Conclusions:
MF16 remains an enigma, but it is clearly much more than a SNR
●
We estimate the expansion velocity for the nebula as 50-100 km/s, that is close
●
to the late-Sedov SNR expansion rate in a moderately-dense ISM (nH~1 cm-3)
Shock waves seem to be short in explaining the observed optical emission-line
●
spectrum
We suggest a photoionizaing source in H-ionizing UV (~1040erg/s) and He+-
●
ionizing EUV (>1039erg/s), needed to explain the high-excitation emission line
luminosities
Thank you for attention!
References:
● Holt, S. S., Schlegel E. M., Hwang, U., & Petre, R. 2003, ApJ, 588, 792
● Dunne, C. D., Gruendl, R. A., & Chu, Y.-H. 2001, AJ, 119, 1172
● Liu, Z.-F. & Bregman, J. N., 2005, ApJSS, 157, 59
● Roberts, T. P. & Colbert, E. J. M., 2003, MNRAS, 341, L49
● Blair, W. P., Fesen, R. A., Schlegel, E. M., 2001, AJ, 121, 1497
● Schlegel, E. M., Blair, W. P., Fesen, R. A., 2000, AJ, 120, 791
● Blair, W. P., Fesen, R. A., 1994, ApJ, 424, L103
● Lira, P., Lawrence, R. A., Johnson, A., 2000, MNRAS, 319, 17
● Pakull, M. W., Mirioni, L., 2003 RevMexAA, 15, 197
● Van Dyk, S. D., 1994, ApJ, 425, L77
● Lehmann, I. et al., 2005, A&A, 431, 847
MF16 – main properties:
total x-ray luminosity > 1039 erg/s (>> Cas A)
●“ULX-like” X-ray spectrum, i e, soft MCD+PL
●short-timescale variability (minutes)
●point source (with Chandra resolution, d < 0.7 arcsec)
●
in X-rays
X-rays not from the SNR! –
Roberts & Colbert, 2003
Bright (L ~ 2 1039 erg/s in optical emission lines only) emission line region
1×1.5arcsec (2034 pc) with a SNR-like spectrum [SII] 6717,6731 / H ~ 1;
bright [NII] 6548,6583, [OI] 6300, 6364
from Blair&Fesen, 1994

HST images
B
W50 (VLA)
H+[NII] 
Observations held 17/18 January 2005, with MultiPupil Fiber
Spectrograph on 6m telescope BTA, 8 exposures, total exposure 5829s
seeing ~1".5, spectral resolution R~650 (~8Å at H wavelength)
(red circle denotes the
coordinates of the X-ray
source, according to
Roberts, Colbert, 2003)
20h 35m 00s.75
+60˚ 11' 30".9
NGC6946, U-band, CFHT, MegaPrime 
Data reduction:
MPFS-data reduction system developed in IDL environment, prior
versions written by V. L. Afanasiev, A. V. Moiseev
Reconsidered and rewritten:
-
Extraction using 2 etalon files (different for object and spectral standard)
Cosmic hits removal (because of non-negligible probability of cosmic particles’
overlapping for different frames for new 2k×2k CCD)
●
Added flat field extraction (data cubes rather than initial frames are corrected by flat
fields)
●
Included:
Atmospheric dispersion correction (better than 0,1 arcsec accuracy, using spectral
standard)
●
Arbitrary correction for interstellar absorption, using CCM (Cardelli, Clayton & Mathis,
1998) absorption curve
●
Some other features…
●
AV
H / H
[OIII](5007+4959) / H
[SII](6717+6731)/ H
ne, cm-3
[SII]6717 / [SII]6731
[OIII]
[SII] 6717+6731
5007+4959
H
SCORPIO higher-resolution data (R~1000):
* - red, + - blue
[OIII]5007+4959
H
E
Component fluxes and
radial velocities
W
E
W
NGC 6946 galaxy:
D = 5,5 (from 5,1 to 5,9) Mpc
Scd, active star formation
MF16
Pure shock+precursor model (Dopita&Sutherland 1995)
R=10pc
MF16
B/n1/2 =
B/n1/2 =
4
Vshock~400km/s
Shock power must be
than:
1
3
L   pre  shockVshock
R 2 
2
 n pre  shock 
38
 10 erg s 
3 
1
cm


LH = 6 1037 erg/s,
Lemission lines / LH ~ 400
n > 240cm-3 (!)
The ULX (NGC6946 X-1, X-8, X-11 or ULX-1, ULX-3):
MCD (kT=0.15 keV) + PL (Г = 2.5)
LX=2.5 1039 erg/s (0.5-8.0 keV)

Сhandra observations of NGC 6946 ULX-1 (Roberts, Colbert, 2003)
H
[OIII]
H+ radio 20cm
HeII
Emission lines’ mapping:


-0,111 -0,088
-0,11 -0,10
0,72 -0,02
0,058 0,011
-0,116 -0,081
-0,061 -0,064
[OIII]
(5007+4959)
Barycenter shift:
line
H
:
H
:
HeII :
[OIII] :
[SII] :
[NII] :
Hα
1˝
±0,013
±0,02
±0,02
±0,015
±0,014
±0,013
Hβ
[SII]
(6717+6731)
HeII4686
[NII]
(6548+6583)