Table 1: Measured, assumed, and derived values for different physical quantities at the innermost starburst region of NGC 253 (IS), a cylindrical disk with height 70 pc, and its surrounding disk (SD).
Physical parameters Symbol Value Units Comment

Distance
D 2.5 Mpc ST

Inclination
i 78 degrees ST

Infrared Luminosity of the innermost starburst (IS)
$L_{\rm IR}$ $2\times 10^{10}$ $L_\odot$ ST

Radius of the IS
- 100 pc ST

Radius surrounding disk (SD)
- 1000 pc ST

Uniform density of the IS
$n_{\rm IS}$ $\sim$ 600 cm^-3 ST

Uniform density of the SD
$n_{\rm SD}$ $\sim$ 50 cm^-3 ST

Gas mass of the IS
$M_{\rm IS}$ $\sim$ $3 \times 10^7$ $M_\odot$ ST

Gas mass of the SD
$M_{\rm SD}$ $\sim$ $2.5 \times 10^8$ $M_\odot$ ST

Supernova explosion rate of the IS
${\cal R}$ $\sim$ 0.08 SN yr^-1 ST

Supernova explosion rate of the SD
- $\sim$ 0.01 SN yr^-1 ST

Typical supernova explosion energy
- 10⁵¹ erg ST

SN energy transferred to cosmic rays
$\eta$ $\sim$ 10 % ST

Convective velocity
V 300-600 km s^-1 ST

Dust emissivity index
$\sigma$ 1.5 - OM

Dust temperature
$T_{\rm dust}$ 50 K OM

Emission measure
EM $5 \times 10^5$ pc cm^-6 OM

Ionized gas temperature
T 10⁴ K OM

Magnetic field of the IS
B 300 $\mu$ G OM

Slope of primary injection spectrum
p 2.2-2.3 - A

Maximum energy considered for primaries
- 100 TeV A

Diffusion coefficient slope
$\mu$ 0.5 - A

Proton to electron primary ratio
$N_{\rm p}/N_{\rm e}$ 50 - A

Diffusive timescale
$\tau _0$ 1-10 Myr A

**Table 1:** Measured, assumed, and derived values for different physical quantities at the innermost starburst region of NGC 253 (IS), a cylindrical disk with height 70 pc, and its surrounding disk (SD).
Physical parameters	Symbol	Value	Units	Comment
Distance	D	2.5	Mpc	ST
Inclination	i	78	degrees	ST
Infrared Luminosity of the innermost starburst (IS)	$L_{\rm IR}$	$2\times 10^{10}$	$L_\odot$	ST
Radius of the IS	-	100	pc	ST
Radius surrounding disk (SD)	-	1000	pc	ST
Uniform density of the IS	$n_{\rm IS}$	$\sim$ 600	cm^-3	ST
Uniform density of the SD	$n_{\rm SD}$	$\sim$ 50	cm^-3	ST
Gas mass of the IS	$M_{\rm IS}$	$\sim$ $3 \times 10^7$	$M_\odot$	ST
Gas mass of the SD	$M_{\rm SD}$	$\sim$ $2.5 \times 10^8$	$M_\odot$	ST
Supernova explosion rate of the IS	${\cal R}$	$\sim$ 0.08	SN yr^-1	ST
Supernova explosion rate of the SD	-	$\sim$ 0.01	SN yr^-1	ST
Typical supernova explosion energy	-	10⁵¹	erg	ST
SN energy transferred to cosmic rays	$\eta$	$\sim$ 10	%	ST
Convective velocity	V	300-600	km s^-1	ST
Dust emissivity index	$\sigma$	1.5	-	OM
Dust temperature	$T_{\rm dust}$	50	K	OM
Emission measure	EM	$5 \times 10^5$	pc cm^-6	OM
Ionized gas temperature	T	10⁴	K	OM
Magnetic field of the IS	B	300	$\mu$ G	OM
Slope of primary injection spectrum	p	2.2-2.3	-	A
Maximum energy considered for primaries	-	100	TeV	A
Diffusion coefficient slope	$\mu$	0.5	-	A
Proton to electron primary ratio	$N_{\rm p}/N_{\rm e}$	50	-	A
Diffusive timescale	$\tau _0$	1-10	Myr	A

Source LaTeX | All tables | In the text

	1 Introduction
	2 CANGAROO observations of NGC 253
	3 Phenomenology of the central region of NGC 253
	4 Diffuse modelling
	5 Results
	6 HESS observations
	7 Concluding remarks
	References
	Online Material
	Appendix: Parameterizations of proton-proton cross sections for neutral pion decay