diff --git a/src/km3irf/utils.py b/src/km3irf/utils.py
index 08e470f304b8b8783c0d9bff219972c0d0686e65..5380badb04060e29674b4ddf5d354491b264ad45 100644
--- a/src/km3irf/utils.py
+++ b/src/km3irf/utils.py
@@ -1,10 +1,41 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
-from .calc import Calculator
+# from .calc import Calculator
+from astropy.io import fits
 
 
-def print_multiplication_table(base):
-    """Prints the multiplication table for a given base"""
-    calculator = Calculator()
-    for i in range(1, 11):
-        print("{} x {} = {}".format(base, i, calculator.multiply(base, i)))
+# def print_multiplication_table(base):
+#     """Prints the multiplication table for a given base"""
+#     calculator = Calculator()
+#     for i in range(1, 11):
+#         print("{} x {} = {}".format(base, i, calculator.multiply(base, i)))
+
+
+def merge_fits(aeff_fits="./data/aeff.fits", 
+               psf_fits="./data/psf.fits", 
+               edisp_fits="./data/edisp.fits",
+               bkg_fits="./data/bkg_nu.fits",
+               output_file='all_in_one.fits'):
+    """Merge separated fits files into one, which can be used in gammapy"""
+    hdu_list = []
+    hdu_list.append(fits.PrimaryHDU())
+
+    with fits.open(aeff_fits) as file_aeff:
+        hdu_list.append(file_aeff[1])
+    hdu_list[1].name = 'EFFECTIVE AREA'
+
+    with fits.open(psf_fits) as file_psf:
+        hdu_list.append(file_psf[1])
+    hdu_list[2].name = 'POINT SPREAD FUNCTION'
+
+    with fits.open(edisp_fits) as file_edisp:
+        hdu_list.append(file_edisp[1])
+    hdu_list[3].name = 'ENERGY DISPERSION'
+
+    with fits.open(bkg_fits) as file_bkg:
+        hdu_list.append(file_bkg[1])
+    hdu_list[4].name = 'BACKGROUND'
+
+    new_fits_file = fits.HDUList(hdu)
+    new_fits_file.writeto(f'./data/{output_file}', overwrite=True)
+