added time delays and observer times for time series predictions

sim_pipeline/galaxy_galaxy_lens.py

@@ -276,6 +276,41 @@ def deflector_magnitude(self, band):
         band_string = str("mag_" + band)
         return self._lens_dict[band_string]
 
+    def point_source_arrival_times(self):
+        """Arrival time of images relative to a straight line without lensing. Negative
+        values correspond to images arriving earlier, and positive signs correspond to
+        images arriving later.
+
+        :return: arrival times for each image [days]
+        :rtype: numpy array
+        """
+        lens_model_list, kwargs_lens = self.lens_model_lenstronomy()
+        lens_model = LensModel(
+            lens_model_list=lens_model_list,
+            cosmo=self.cosmo,
+            z_lens=self.lens_redshift,
+            z_source=self.source_redshift,
+        )
+        x_image, y_image = self.image_positions()
+        arrival_times = lens_model.arrival_time(
+            x_image, y_image, kwargs_lens=kwargs_lens
+        )
+        return arrival_times
+
+    def image_observer_times(self, t_obs):
+        """Calculates time of the source at the different images, not correcting for
+        redshifts, but for time delays. The time is relative to the first arriving
+        image.
+
+        :param t_obs: time of observation [days]
+        :return: time of the source when seen in the different images (without redshift
+            correction)
+        :rtype: numpy array
+        """
+        arrival_times = self.point_source_arrival_times()
+        observer_times = t_obs + arrival_times - np.min(arrival_times)
+        return observer_times
+
     def point_source_magnitude(self, band, lensed=False):
         """Point source magnitude, either unlensed (single value) or lensed (array) with
         macro-model magnifications.

tests/test_galaxy_galaxy_lens.py

@@ -1,4 +1,6 @@
 import pytest
+import numpy as np
+from numpy import testing as npt
 from astropy.cosmology import FlatLambdaCDM
 from astropy.table import Table
 from sim_pipeline.galaxy_galaxy_lens import (
@@ -86,6 +88,18 @@ def test_los_linear_distortions(self):
         losd = self.gg_lens.los_linear_distortions()
         assert losd != 0
 
+    def test_point_source_arrival_times(self):
+        dt_days = self.gg_lens.point_source_arrival_times()
+        assert np.min(dt_days) > -1000
+        assert np.max(dt_days) < 1000
+
+    def test_image_observer_times(self):
+        t_obs = 1000
+        dt_days = self.gg_lens.image_observer_times(t_obs=t_obs)
+        arrival_times = self.gg_lens.point_source_arrival_times()
+        observer_times = t_obs + arrival_times - np.min(arrival_times)
+        npt.assert_almost_equal(dt_days, observer_times, decimal=5)
+
 
 if __name__ == "__main__":
     pytest.main()