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Mission Overview

Space Telescope and Optical Reverberation Mapping of Mrk 817 (STORM2)

Primary Investigator: Gerard Kriss, Gisella de Rosa

HLSP Authors: Rachel Plesha, Gerard Kriss, Gisella de Rosa, Yasaman Homayouni

Released: 2023-03-03

Updated: 2023-03-03

Primary Reference(s): Homayouni et al. 2023

DOI: 10.17909/n734-k698

Citations: See ADS Metrics

Read Me

Source Data:

The top panel shows changes in C IV emission line flux across the entire STORM2 campaign. The bottom panel shows the 1180 Å continuum lightcurve where the red dot indicates the corresponding spectrum shown in the top panel.


Calibrated spectra and light curves are provided for the HST/COS observations of the Seyfert 1 galaxy Mrk 817 in the Space Telescope and Optical Reverberation Mapping 2 (STORM 2) campaign. The STORM 2 campaign used HST/COS, Swift, NICER, XMM-Newton, and ground-based facilities in a 15-month long reverberation-mapping experiment. HST observations were made in 165 single-orbit COS visits with a mean cadence of two days from 2020 November 24 through 2022 February 24. In each visit, the team used the G130M and G160M gratings to observe the UV spectrum over the range 1070-1750 Angstroms in eight separate exposures. Exposure times were selected to provide S/N > 100 when measured over velocity bins of ~500 km/s. During each visit, the team obtained four 60-second exposures with G130M centered at 1222 Angstroms, two exposures of 175 s and 180 s using the G160M grating centered at 1533 Angstroms, and two 195 s exposures with G160M at 1577 Angstroms. As described in Homayouni et al. (2023), the team customized the calibrations of these spectra to provide more accurate and repeatable flux calibrations. These reprocessed spectra obtained with the various central wavelength and FPPOS settings were then combined for each individual observation into single spectra for G130M and G160M, single merged G130M+G160M spectra, a merged spectrum for the whole data set, and extracted continuum and emission-line light curves.


Data Products

Calibrated spectra and light curves are provided in FITS format. They are available for download in the tables below and as a tar bundle which includes the following:

  1. A spectrum that combines all available visits across both gratings at several levels of binning in the top-level directory.
  2. A “night only” spectrum to exclude airglow from the O I 1304 geocoronal emission line that combines all available visits across both gratings in the top-level directory.
  3. A single fits file containing both continuum and emission line light curves in the top-level directory.
  4. Combined and binned spectra that merge all grating settings in a subdirectory called “combined_and_binned/“.
  5. A time dependent sensitivity reference file and twelve flux reference files containing updated response functions are available in a subdirectory called “reference_files/“.

In the different data extensions of the spectra, multiple levels of bin sizes are delivered to allow for different science use cases and to preserve the correct error propagation. Further details about the different bin sizes can be found in the table below. For reference, a bin size of 4 pixels was used to create light curves.


Data files are named according to the following convention:



  • <visit> is the visit number from the HST GO-16196 program, e.g., "v01", "v0n", or "v74"
  • <filter> is the filter used, one of "g130m" or "g130m-g160m"
  • <exten> is the type of product; consult the table below for descriptions

Data file types:


Grating-combined spectra for a given visit, binned by 4 pixels (ext1), no additional binning (ext2), and 8 pixels (ext3)


Grating-combined spectra for all available visits, binned by 3 pixels (ext1), no additional binning (ext2), and 8 pixels (ext3)


Grating-combined spectra for all available visits where SUN_ALT < 20 deg, binned by 3 pixels


Flux reference file in the expected COS format


Time dependent sensitivity reference file in in the expected COS format


All emission-line and continuum data extensions have three columns giving the observation time in Heliocentric Julian Days - 2400000, the observed flux in 1.e-13 erg cm-1 s-2, and the 1-sigma error in flux in 1.e-13 erg cm-1 s-2. For the emission line extensions, the wavelength intervals used for integrating the line flux are given in the extension name. For the continuum extensions, the continuum level used for each line is a linear fit to its bracketing continuum windows.

  •   ext1 : CONTINUUM-1180; Averaged over 1173-1185 Angstroms
  •   ext2 : LYA-1235-1248;   Lyman alpha Flux
  •   ext3 : NV-1268-1290;   NV 1238,1242 Flux
  •   ext4 : CONTINUUM-1398; Averaged over 1394.2-1401.6 Angstroms
  •   ext5 : SIIV-1424-1460; SiIV 1393,1402 Flux
  •   ext6 : CONTINUUM-1502; Averaged over 1493-1511 Angstroms
  •   ext7 : CIV-1590-1638;  CiIV 1548, 1550 Flux
  •   ext8 : HEII-1680-1700; HeII 1640 Flux
  •   ext9 : CONTINUUM-1739; Averaged over 1736-1741.5 Angstroms

Data Access

Tar bundles of STORM2 files (<0.5 GB each) can be downloaded from the links in the table below:

STORM2 tar Bundles
Data Files
Reference Files


Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.