Remove multiplication/division by 0.2 MeV in generate_time_series and SimpleRate

[Sheshuk]

In the implementation of snowglobes_interface.SimpleRate I see that we're dividing by 0.2 MeV

snewpy/python/snewpy/snowglobes_interface.py

Lines 173 to 175 in b353799

	# Fluence (flux integrated over time bin) in cm^-2
	# (must be divided by 0.2 MeV to compensate the multiplication in generate_time_series)
	fluxs = np.interp(energies, flux[:, 0], flux[:, 1], left=0, right=0)/2e-4

because earlier we multiplied by this value in snowglobes.generate_time_series:

snewpy/python/snewpy/snowglobes.py

Lines 119 to 122 in b353799

	# Generate energy + number flux table.
	for j, E in enumerate(energy):
	for flavor in Flavor:
	osc_fluence[flavor] = osc_spectra[flavor][j] * dt * 0.2 * MeV / (4.*np.pi*(d*1000*3.086e+18)**2)

and snowglobes.generate_fluence:

snewpy/python/snewpy/snowglobes.py

Lines 286 to 288 in b353799

	for j, E in enumerate(energy):
	for flavor in Flavor:
	osc_fluence[flavor] = osc_spectra[flavor][j] * dt * 0.2 * MeV / (4.*np.pi*(d*1000*3.086e+18)**2)

If I understand correctly, this factor exists as an approximation of integral over the energy bin. The problem is that the energy bins can be different, so this hardcoded value is no longer valid in some cases (for example using smaller bins for presupernova flux). And this leads to physically invalid output of the generate_* for those cases - if anyone uses this output apart from feeding it to SimpleRate.

SimpleRate makes it's own approximation of the energy integration, which could be improved (in a separate issue), and doesn't use this

What I suggest

Remove this 0.2 MeV factor everywhere.

[mcolomermolla]

I fully agree, this is always a nightmare when comparing with your separate full simulation.

[JostMigenda]

Originally, the reason for picking these 0.2 MeV bins is that that was the default energy binning in the flux files included with SNOwGLoBES; so the generate_* functions were supposed to use the same binning in the files they write out. Now that we’ve moved to SimpleRate, I agree that we don’t need to stick with that binning.

That said, I would wait to remove this constant factor until we’re also updating the hardcoded energy binning; as you correctly say, updating one without the other would lead to invalid output if anyone uses generate_* without feeding the output to simulate.