J/ApJ/719/L79 BH spin-orbit misalignment in Galactic XRBs (Fragos+, 2010)
Black hole spin-orbit misalignment in Galactic X-ray binaries.
Fragos T., Tremmel M., Rantsiou E., Belczynski K.
<Astrophys. J., 719, L79-L83 (2010)>
=2010ApJ...719L..79F 2010ApJ...719L..79F
ADC_Keywords: Models ; Binaries, X-ray
Keywords: binaries: close - Galaxy: stellar content - stars: evolution -
X-rays: binaries
Abstract:
In black hole (BH) X-ray binaries (XRBs), a misalignment between the
spin axis of the BH and the orbital angular momentum can occur during
the supernova explosion that forms the compact object. In this Letter,
we present population synthesis (PS) models of Galactic BH XRBs and
study the probability density function of the misalignment angle and
its dependence on our model parameters. In our modeling, we also take
into account the evolution of the misalignment angle due to accretion
of material onto the BH during the XRB phase. The major factor that
sets the misalignment angle for XRBs is the natal kick that the BH may
receive at its formation. However, large kicks tend to disrupt
binaries, while small kicks allow the formation of XRBs and naturally
select systems with small misalignment angles. Our calculations
predict that the majority (>67%) of Galactic field BH XRBs have rather
small (≲10°) misalignment angles, while some systems may reach
misalignment angles as high as ∼90° and even higher. These results
are robust among all PS models. The assumption of small misalignment
angles is extensively used to observationally estimate BH spin
magnitudes, and for the first time we are able to confirm this
assumption using detailed PS calculations.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 58 245 The 67%, 95.4%, and 99.7% confidence levels of
BH spin-orbit misalignment angle probability
density function (PDFs) of selected population
synthesis (PS) models
--------------------------------------------------------------------------------
See also:
J/ApJ/699/453 : Determination of black hole masses (Shaposhnikov+, 2009)
J/ApJ/687/471 : Observational comparison between ULXs and XRBs (Berghea+, 2008)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Model Population synthesis (PS) model (1)
11- 14 F4.1 --- 2M67 The 67% confidence level for M≤2M☉
16- 19 F4.1 --- 2M95 The 95.4% confidence level for M≤2M☉
21- 25 F5.1 --- 2M99 The 99.7% confidence level for M≤2M☉
27- 30 F4.1 --- 2-5M67 The 67% confidence level for 2M☉<M<5M☉
32- 35 F4.1 --- 2-5M95 The 95.4% confidence level for 2M☉<M<5M☉
37- 41 F5.1 --- 2-5M99 The 99.7% confidence level for 2M☉<M<5M☉
43- 46 F4.1 --- 5M67 The 67% confidence level for ≥5M☉
48- 52 F5.1 --- 5M95 The 95.4% confidence level for ≥5M☉
54- 58 F5.1 --- 5M99 The 99.7% confidence level for ≥5M☉
--------------------------------------------------------------------------------
Note (1): Model names with no exponents correspond to the post-SN BH spin-orbit
misalignment, right after the BH formation. For model names with
exponents the BH spin evolution due to accretion was taken into
account. PS models are defined in table1 as below:
---------------------------------------------------------
Model alphaCE IMF.Exponent ηwind σVkick
---------------------------------------------------------
1 0.5 -2.35 1.0 265
2 0.3 -2.35 1.0 265
3 0.7 -2.35 1.0 265
4 0.5 -2.35 1.0 50
5 0.5 -2.35 1.0 150
6 0.5 -2.35 1.0 400
7 0.5 -2.7 1.0 265
8 0.5 -2.7 1.0 50
9 0.5 -2.7 1.0 150
10 0.5 -2.7 1.0 400
11 0.5 -2.35 0.25 265
12 0.5 -2.35 0.25 50
13 0.5 -2.35 0.25 150
14 0.5 -2.35 0.25 400
15 0.5 -2.7 0.25 265
16 0.5 -2.7 0.25 50
17 0.5 -2.7 0.25 150
18 0.5 -2.7 0.25 400
19 0.5 -2.35 1.0 265
---------------------------------------------------------
- ηwind is the stellar wind strength parameter for
the late evolutionary stages of massive stars.
- σVkick is the σ parameter of the Maxwellian
distribution of asymmetric kick magnitudes.
---------------------------------------------------------
For each of the models listed in this table, we applied two types of
asymmetric kicks, one with an isotropic distribution for the direction
of the kicks (denoted by the letter "i" after the model number) and
one with polar kicks, where the kick is always directed perpendicular
to the orbital plane (denoted by the letter "p" after the model
number). In addition, we considered different distributions for the
initial BH spin magnitude: constant spin with a value of 0.2, 0.5,
or 0.9 across the whole BH population (denoted by an exponent "C0.2",
"C0.5" or "C0.9" correspondingly), or spin magnitudes in the range
between 0 and 1 drawn from a Maxwellian distribution with a maximum
at 0.2, 0.5, or 0.9 (denoted by an exponent "M0.2", "M0.5" or "M0.9"
correspondingly).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 21-Jun-2012