2017A&A...608A..47K


Query : 2017A&A...608A..47K

2017A&A...608A..47K - Astronomy and Astrophysics, volume 608A, 47-47 (2017/12-1)

ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources.

KOLIOPANOS F., VASILOPOULOS G., GODET O., BACHETTI M., WEBB N.A. and BARRET D.

Abstract (from CDS):

Aims. In light of recent discoveries of pulsating ultraluminous X-ray sources (ULXs) and recently introduced theoretical schemes that propose neutron stars (NSs) as the central engines of ULXs, we revisit the spectra of eighteen well known ULXs, in search of indications that favour this newly emerging hypothesis.
Methods. We examine the spectra from high-quality XMM-Newton and NuSTAR observations. We use a combination of elementary black body and multicolour disk black body (MCD) models, to diagnose the predictions of classic and novel theoretical models of accretion onto NSs. We re-interpret the well established spectral characteristics of ULXs in terms of accretion onto lowly or highly magnetised NSs, and explore the resulting parameter space for consistency.
Results. We confirm the previously noted presence of the low-energy (≤6keV) spectral rollover and argue that it could be interpreted as due to thermal emission. The spectra are well described by a double thermal model consisting of a "hot" (≥1keV) and a "cool" (≤0.7keV) multicolour black body (MCB). Under the assumption that the "cool" MCD emission originates in a disk truncated at the neutron star magnetosphere, we find that all ULXs in our sample are consistent with accretion onto a highly magnetised (B≥1012 G) neutron star. We note a strong correlation between the strength of the magnetic field, the temperature of the "hot" thermal component and the total unabsorbed luminosity. Examination of the NuSTAR data supports this interpretation and also confirms the presence of a weak, high-energy (≥15keV) tail, most likely the result of modification of the MCB emission by inverse Compton scattering. We also note that the apparent high-energy tail, may simply be the result of mismodelling of MCB emission with an atypical temperature (T) versus radius (r) gradient, using a standard MCD model with a fixed gradient of T∼r–0.75.
Conclusions. We have offered a new and robust physical interpretation for the dual-thermal spectra of ULXs. We find that the best-fit derived parameters of our model, are in excellent agreement with recent theoretical predictions that favour super-critically accreting NSs as the engines of a large fraction of ULXs. Nevertheless, the considerable degeneracy between models and the lack of unequivocal evidence cannot rule out other equally plausible interpretations. Deeper broadband observations and time-resolved spectroscopy are warranted to further explore this newly emerging framework.

Abstract Copyright: © ESO, 2017

Journal keyword(s): X-rays: binaries - accretion, accretion disks - accretion, accretion disks

Simbad objects: 39

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Number of rows : 39
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 55 GiG 00 14 53.602 -39 11 47.86 8.54 8.58 7.87 7.84   ~ 743 2
2 [BWE2015] NGC 55 119 ULX 00 15 28.89 -39 13 18.8           ~ 54 0
3 RX J004732.9-251748 ULX 00 47 32.97 -25 17 50.2           ~ 33 0
4 NGC 253 SyG 00 47 33.134 -25 17 19.68   8.03   6.94 8.1 ~ 3160 2
5 [PFP2004] J005431.9-373825 SNR 00 54 31.79 -37 38 15.9           ~ 8 0
6 [FWB2009] HLX-1 ULX 01 10 28.30 -46 04 22.3     24.5 23.80   ~ 176 1
7 ChASeM33 J013350.89+303936.6 SNR 01 33 50.8965749232 +30 39 36.630403128           ~ 89 1
8 M 33 GiG 01 33 50.8965749232 +30 39 36.630403128 6.17 6.27 5.72     ~ 5538 1
9 RX J031820.3-662911 UX? 03 18 20.00 -66 29 10.9           ~ 192 1
10 2E 756 ULX 03 18 22.00 -66 36 04.3   23.5 23.6     O9.5 220 3
11 [SST2011] J034555.61+680455.3 ULX 03 45 55.612 +68 04 55.29           ~ 155 1
12 IC 342 SBG 03 46 48.514 +68 05 45.98   10.5       ~ 1458 1
13 UGC 4305 IG 08 19 04.9864630512 +70 43 13.086910452 12.06 11.72 11.39 11.11   ~ 733 2
14 [SST2011] J081929.00+704219.3 ULX 08 19 28.99 +70 42 19.4           ~ 174 2
15 [FK2005] 7 SNR 09 55 32.95 +69 00 33.6   23.87 23.89     ~ 81 1
16 M 81 Sy2 09 55 33.1726556496 +69 03 55.062505368   7.89 6.94     ~ 4214 3
17 NAME M82 ULX-1 UX? 09 55 50.01 +69 40 46.0           ~ 260 1
18 [KCF2005] M82 G ULX 09 55 51.040 +69 40 45.49           ~ 206 1
19 UGC 5336 G 09 57 32.1 +69 02 46 15.19 15.15 14.10 14.12   ~ 303 4
20 RX J0957.9+6903 ULX 09 57 53.290 +69 03 48.20           ~ 216 4
21 NGC 4190 LSB 12 13 44.1717362856 +36 37 53.374557468 13.88 13.40 13.25 12.86   ~ 196 0
22 CXO J121345.2+363754 ULX 12 13 45.41 +36 37 55.2           ~ 12 0
23 RX J123551+27561 ULX 12 35 51.71 +27 56 04.1           ~ 71 1
24 NGC 4559 H2G 12 35 57.6402869976 +27 57 35.859278160   10.46 10.01     ~ 582 1
25 2XMM J125048.6+410743 ULX 12 50 48.6 +41 07 43           ~ 7 0
26 M 94 SyG 12 50 53.0737971432 +41 07 12.900884628 9.15 8.96 8.24 7.78   ~ 1316 2
27 IXO 72 X 12 59 00.9 +34 50 42           ~ 7 1
28 NGC 4861 H2G 12 59 02.340 +34 51 33.98   12.90 12.32     ~ 369 2
29 NGC 5204 LSB 13 29 36.508 +58 25 07.43   11.84   11.37   ~ 448 0
30 [FK2005] 23 ULX 13 29 38.62 +58 25 05.6           ~ 121 2
31 M 83 SBG 13 37 00.91920 -29 51 56.7400 8.85 8.11 7.52 7.21   ~ 2423 2
32 CXOU J133705.1-295207 ULX 13 37 05.13 -29 52 07.1           ~ 12 0
33 [FK2005] 25 ULX 14 03 19.63 -41 22 58.7           ~ 217 0
34 NGC 5906 GiG 15 15 53.687 +56 19 43.86   11.4       ~ 727 1
35 NAME NGC 5907 ULX ULX 15 15 58.60 +56 18 10.0           ~ 122 0
36 4U 1705-44 LXB 17 08 54.470 -44 06 07.35           ~ 373 0
37 V* V1405 Aql LXB 19 18 47.871 -05 14 17.09 20.90 21.40 21.0     ~ 460 0
38 NGC 7793 GiG 23 57 49.7540045856 -32 35 27.701550744 10.26 9.74 9.28 9.06 9.7 ~ 1035 2
39 NAME NGC 7793 P13 ULX 23 57 50.90 -32 37 26.6           ~ 163 0

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2022.09.26-02:02:00

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