Fermi Mission Epoch (gdt.missions.fermi.time)

The Fermi Mission epoch, also called the Fermi Mission Elapsed Time (MET) is the number of seconds elapsed since January 1, 2001, 00:00:00 UTC, including leap seconds. We have defined a specialized epoch to work with Astropy Time objects so that Fermi MET can be easily converted to/from other formats and time scales.

To use this, we simply import and create an astropy Time object with a ‘fermi’ format:

>>> from gdt.missions.fermi.time import Time
>>> fermi_met = Time(697422649, format='fermi')
>>> fermi_met
<Time object: scale='tt' format='fermi' value=697422649.0>

Now, say we want to retrieve the GPS timestamp:

>>> fermi_met.gps
1359765062.0

The Astropy Time object readily converts it for us. We can also do the reverse conversion:

>>> gps_time = Time(fermi_met.gps, format='gps')
>>> gps_time
<Time object: scale='tai' format='gps' value=1359765062.0>

>>> gps_time.fermi
697422649.0

And we should, of course, get back the Fermi MET we started with. This enables you do do any time conversions already provided by Astropy, as well as time conversions between other missions within the GDT.

In addition to time conversions, all time formatting available in Astropy is also available here. For example, we can format the Fermi MET in ISO format:

>>> fermi_met.iso
'2023-02-07 00:31:53.184'

Finally, there is a specialized format associated with the Fermi epoch, which allows us to output the format for Fermi GBM burst numbers, which is based on time:

>>> fermi_met.gbm_bn
'230207021'

Reference/API

gdt.missions.fermi.time Module

Classes

FermiSecTime(val1, val2, scale, precision, ...)	Represents the number of seconds elapsed since Jan 1, 2001, 00:00:00 UTC, including leap seconds
GbmBurstNumber(val1, val2, scale, precision, ...)	Represent date as Fermi GBM burst number
Time(val[, val2, format, scale, precision, ...])	Represent and manipulate times and dates for astronomy.

Class Inheritance Diagram