Fourteen Years of Energetic Neutral Atom Observations from IBEX
Dave McComas (Princeton University)
The Interstellar Boundary Explorer (IBEX) has been observing the outer heliosphere and its interactions with the very local interstellar medium (VLISM) through measurements of energetic neutral atoms (ENAs) for over 14 years. This study makes three major new contributions:
- Validates and analyzes the three most recent years (2020 - 2022) of IBEX-Hi (0.5 - 6 keV FWHM) data.
- Relates the new observations to the prior eleven years of observations and explores long-term variations.
- Provides the first IBEX team validated Ribbon/GDF separation scheme and separated maps.
To download the entire data release as a zip file click the link above. To learn more about the structure and content of the files contained within the release, a detailed description follows. For questions about this or any other release, please email [email protected].
A detailed description and initial analysis of these maps is presented in McComas et al. 2023 (ApJS). Click here to access the paper.
Data Directory Structure and Naming Conventions
The data in this release are separated into six-month and one-year segments, which represent the following IBEX orbits and dates:
The 6-month and annual allsky maps are representative of the following IBEX orbits and dates:
| Year | Skymap Name | Start-End Orbits or Arcs | Dates |
|---|---|---|---|
| 1 | Map2009A | 11-34 | 12/25/2008 – 06/25/2009 |
| 1 | Map2009B | 35-58 | 06/25/2009 – 12/25/2009 |
| 2 | Map2010A | 59-82 | 12/25/2009 – 06/26/2010 |
| 2 | Map2010B | 83-106 | 06/26/2010 – 12/26/2010 |
| 3 | Map2011A | 107-130a | 12/26/2010 – 06/25/2011 |
| 3 | Map2011B | 130b-150a | 06/25/2011 – 12/24/2011 |
| 4 | Map2012A | 150b-170a | 12/24/2011 – 06/22/2012 |
| 4 | Map2012B | 170b-190b | 06/22/2012 – 12/26/2012 |
| 5 | Map2013A | 191a-210b | 12/26/2012 – 06/26/2013 |
| 5 | Map2013B | 211a-230b | 06/26/2013 – 12/26/2013 |
| 6 | Map2014A | 231a-250b | 12/26/2013 – 06/26/2014 |
| 6 | Map2014B | 251a-270b | 06/26/2014 – 12/24/2014 |
| 7 | Map2015A | 271a-290b | 12/24/2014 – 06/24/2015 |
| 7 | Map2015B | 291a-310b | 06/24/2015 – 12/23/2015 |
| 8 | Map2016A | 311a-330b | 12/24/2015 – 06/23/2016 |
| 8 | Map2016B | 331a-351a | 06/24/2016 – 12/26/2016 |
| 9 | Map2017A | 351b-371a | 12/26/2016 – 06/24/2017 |
| 9 | Map2017B | 371b-391a | 06/25/2017 – 12/25/2017 |
| 10 | Map2018A | 391b-411b | 12/25/2017 – 06/28/2018 |
| 10 | Map2018B | 412a-431b | 06/29/2018 – 12/26/2018 |
| 11 | Map2019A | 432a-451b | 12/27/2018 – 06/27/2019 |
| 11 | Map2019B | 452a-471b | 06/28/2019 – 12/26/2019 |
| 12 | Map2020A | 472a-491b | 12/26/2019 – 06/24/2020 |
| 12 | Map2020B | 492a-511b | 06/25/2020 – 12/24/2020 |
| 13 | Map2021A | 512a-531b | 12/24/2020 – 06/24/2021 |
| 13 | Map2021B | 532a-552a | 06/25/2021 – 12/27/2021 |
| 14 | Map2022A | 552b-572a | 12/27/2021 – 06/26/2022 |
| 14 | Map2022B | 572b-592a | 06/26/2022 – 12/26/2022 |
Along with each set of individual maps, we provide the 14-year combined map for that category, as well as a combined set of ENA maps in equatorial and galactic coordinate systems for the broader astrophysical community.
Map directories are named using keywords that indicate the type of data they contain:
- cg - Compton-Getting corrections have been applied to the data to account for the speed of the spacecraft relative to the direction of arrival of the ENAs.
- tabular - survival probability corrections have been applied to the data to account for the loss of ENAs due to radiation pressure, photoionization and ionization via charge exchange with solar wind protons as they stream through the heliosphere. This correction scales the data out from IBEX at 1 AU to ~100 AU.
- noSP - no survival probability corrections have been applied to the data.
- ram - data was collected when the spacecraft was ramming into the incoming ENAs.
- antiram - data was collected when the spacecraft was moving away from the incoming ENAs.
- yyyyA/B - identifies a particular set of orbits spanning 6 months in year yyyy (A - Jan - June, B - July - Dec).
- yyyy - identifies a particular set of orbits spanning year yyyy.
- yyyy-yyyy - data was collected over the course of the specified year range.
- gdf - GDF maps.
- ribbon - ribbon maps.
Filename Description
Data and map files are named using additional keywords that indicate the type of data they contain:
- cnts - total counts data
- desc - description of processing details
- ener - energies data
- fexp - total time exposure data
- flux - flux data
- fsnr - signal/noise (S/N) data
- fvar- flux variances
- hi-n - data from the nth energy bin of IBEX-Hi
- hide - IBEX-Hi direct events
- mono - Compton-Getting corrected data
- numb - samples per pixel
- trp - triple coincidence
File Headers
The first number in the first line of each data file gives the number of lines taken up by the header followed by the number of rows times the number of columns in the data (i.e. 30X60 indicates 30 rows of declination by 60 columns of right ascension values). Row 1 corresponds to the South Ecliptic Pole, while row 30 corresponds to the North Ecliptic Pole. The columns start at ecliptic longitude 0 and step through to ecliptic longitude 360; the values of the first and last columns in each map are identical. The layout of the columns corresponds to Solar Ecliptic East Longitude, right to left as seen outward by IBEX. The keyword “h_title” gives the description of the data and the units used.
Ancillary Files
In addition to the map data the data release also contains attitude and state information for each orbit/arc:
.attdba/.attd2a file
The first column is MET time; the following four columns are a quaternion.
If the file extension is .attd2a the orbit required despinning.
ibex_state_GSE file
The first column is MET time, the next three columns are the x/y/z value of the IBEX position vector (km) and the next three columns are the corresponding velocity vector (km/s). The state vectors are IBEX relative to Earth.
Calculation Notes for Users to Combine Multiple Maps:
Combining different maps is done by accounting for the statistical uncertainties and time exposure weighting. Below is an example of combining three different maps.
ENA Exposure times for the three ENA maps: tau1, tau2, tau3;
ENA fluxes for the three ENA maps: flux1, flux2, flux3;
ENA flux variances for the three ENA maps: var1, var2, var3;
We now calculate the weights from the exposure times as,
wt1=tau1/(tau1+tau2+tau3)
wt2=tau2/(tau1+tau2+tau3)
wt3=tau3/(tau1+tau2+tau3)
Combined fluxes and propagated variances are then determined using:
combined_flux=flux1*wt1 + flux2*wt2 + flux3*wt3
combined_var=var1*(wt1)^2 + var2*(wt2)^2 + var3*(wt3)^2