The Optical Counterpart of NGC6946 ULX-1 P. Abolmasov, S. Fabrika, O. Sholukhova, V. Afanasiev...
-
Upload
charity-barker -
Category
Documents
-
view
214 -
download
0
Transcript of The Optical Counterpart of NGC6946 ULX-1 P. Abolmasov, S. Fabrika, O. Sholukhova, V. Afanasiev...
The Optical Counterpart of NGC6946 ULX-1
P. Abolmasov,
S. Fabrika, O. Sholukhova, V. Afanasiev
Special Astrophysical Observatory, Russia
(a peculiar ULX nebula MF16)
ULX nebulae:
MH9/10, the optical counterpart of HoIX X-1
(Grise et al., 2006)
-Shock excitation ([SII], [NII], [OI] etc. )
-Large sizes, ~50-500pc
-HeII λ4686 emission (stellar?)
-SNRs? (too powerful)
-Superbubbles? (lack of young stars)
-X-ray ionized nebulae? (requires too much X-rays in some cases!)
What are they?
34pc (~1,˝5)
20p
c (~
1˝)
LLX X ≈≈ 2.5 10 2.5 103939 erg/s erg/s (0.5-8.0 keV)(0.5-8.0 keV)
L(HL(H) ) ≈≈ 2 10 2 103838 erg/s erg/s
L(optical lines, total) L(optical lines, total) ≈≈ 2 10 2 103939 erg/s erg/s
Also a bright radio sourceAlso a bright radio source from Blair&Fesen, 1994
MF16 (counterpart of NGC6946 ULX-1):
But: HeIIλ4686 / Hβ ~ 0.2 !!
(HST ACS, filter F658N)
Radio isophotes
(VLA)
X-ray source coordinates:20h 35m 00s.75 +60˚ 11' 30".9
Observations with the 6m SAO telescopeSpectrograph wavelength range,Å spectral seeing,
resolution arcsec
MPFS (panoramic) 4000-7000 ~1000 1,5
SCORPIO (long-slit) 4000-5700 ~2000 1,5
MPFS FOV
Long Slit
1˝
[OIII]5007
H
HeII4686H
[OIII]4959[OIII]5007
Two-component lines:
V2-V1 120-130 km/s
Broader component width ~ 200-300km/s
(from Dopita&Sutherland, 1996)
,
,
7.69
866 H precursorS
H shock
FkmV s F
Total luminosity in H (if the shock surface area is given);
Shock velocity estimate from the component ratio:
For a single H line
L(Hβ) = (7,2±0,4) 1037 erg/s
Narrow-to-broad components ratio 1,85±0,19kinematics
Additional source of excitation/ionization?
Single Hβ line
nH, cm-3
SHOCK WAVES OR PHOTOIONIZATION?
MF16
MF16
from Evans et al., 1999
Photoionization by power law continuum (labelled by ionization parameter logarithm lgU)
13.6
1
eV
FU d
cn h
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
B/n1/2 =
L(HeII)=1.6 1037 erg/sHeII4686
Cannot be explained by a shock wave, and an EUV source needed with
L<228Å ≥ 1039erg/s
MF16
Photoionization by power law continuum (labelled by ionization parameter logarithm lgU)
Or X-ray source with L ~ 1041 erg/s or larger!
… and other high-excitation lines
Pure photoionization models (CLOUDY 96.01 modeling results):
Photoionization best-fit:
lgT(K) = 5.15±0.05
(T~120 000K)
F = 0.6 ± 0.1 erg/cm2/s
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
=> UV luminosity ~1040erg/s
Central source emitting:
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:
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 (2034 pc) with a SNR-like spectrum [SII] 6717,6731 / H ~ 1; bright [NII] 6548,6583, [OI] 6300, 6364
from Blair&Fesen, 1994
●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
HST images
B
H+[NII]
W50 (VLA)
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)
NGC6946, U-band, CFHT, MegaPrime
(red circle denotes the
coordinates of the X-ray
source, according to
Roberts, Colbert, 2003)
20h 35m 00s.75
+60˚ 11' 30".9
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…
H / H
[OIII](5007+4959) / H
[SII](6717+6731)/ H
[SII]6717 / [SII]6731
AV
ne, cm-3
H
[SII] 6717+6731[OIII] 5007+4959
SCORPIO higher-resolution data (R~1000):
H [OIII]5007+4959
WEWE
Component fluxes and radial velocities
* - red, + - blue
MF16
NGC 6946 galaxy:
D = 5,5 (from 5,1 to 5,9) Mpc
Scd, active star formation
MF16
LH = 6 1037 erg/s,
Lemission lines / LH ~ 400
n > 240cm-3 (!)
Pure shock+precursor model (Dopita&Sutherland 1995)
Vshock~400km/s
Shock power must be than:
3 2
383
1
2
101
pre shock shock
pre shock
L V R
nerg s
cm
R=10pc4
Vsh
ock, k
m/s
B/n1/2 =
Vshock , km/s
B/n1/2 =
The ULX (NGC6946 X-1, X-8, X-11 or ULX-1, ULX-3):
MCD (kT=0.15 keV) + PL (Г = 2.5)L
X=2.5 1039 erg/s (0.5-8.0 keV)
Сhandra observations of NGC 6946 ULX-1 (Roberts, Colbert, 2003)
HeII
H
[OIII]
H+ radio 20cm
Hα
Hβ [SII](6717+6731)
[OIII](5007+4959)
HeII4686 [NII](6548+6583)
Emission lines’ mapping:
Barycenter shift:
line H : -0,111 -0,088 ±0,013 H : -0,11 -0,10 ±0,02 HeII : 0,72 -0,02 ±0,02 [OIII] : 0,058 0,011 ±0,015 [SII] : -0,116 -0,081 ±0,014 [NII] : -0,061 -0,064 ±0,013
1˝