Accessing Data

Overview

NICER data are available to the public through the High Energy Astrophysics Science Archive Research Center (HEASARC). This thread provides resources on how to find, access, download, and decrypt the data.

Read this thread if you want to: access, download, and decrypt NICER data.

Last update: 2023-10-02

Introduction

In order to study the objects that NICER has observed, the data files must be accessible to the NICER science tasks. A user must find each desired data set and download it to a location where their processing machine can access it. If the data are encrypted, the user must then decrypt the files before the science tasks can read them.

Prerequisites

Here is what is needed:

• An internet connection
• A way to identify the desired data set, such as target name, target coordinates, or observation ID
• If the data are encrypted: the unique key in order to decyrypt encrypted data

Accessing and Downloading Data

Data can be accessed from the HEASARC in various ways. The Xamin web interface, the Browse search tool, and direct access to the FTP site are all ways in which data are available. Metadata about observations are recorded in a table called nicermastr, which the archive systems use to search for data sets. The cookbook describes ways to find data. If you know the observation, you may also use command line tools to download the desired data set.

• HEASARC Archive links to ways to access and download data
• FTP site

For example, searching in Browse for the target Cas A looks like this:

1: Type in the object name and select NICER.

2: Click on the "nicermastr" link.

3: Select the desired observation data set(s). Here, we choose the August 29, 2021 observation of Cas A with obsid 4010080142. Then click on the link at the bottom of the search results to retrieve the data products.

4: Choose your preferred way to retrieve the data products - with a download script, previewing, retrieving a tar file, or saving to Hera. This example will choose "Retrieve" to download a tar file.

5: Once the tar file is complete, click on the link in order to download it.

Once downloaded, the tar file of the data set is ready to be untarred.

Decrypting Data

If a data set is still inside of its limited-use period, then files in the archive are encrypted. If you have the encryption key, then you will be able to decrypt and access the data. The HEASARC provides a decryption script to decrypt the data.

For example, to decrypt the untarred Cas A 4010080142 observation directory we downloaded above, the command to use the script would be:

$ decrypt_data.pl -d /path/to/4010080142

Note that the path to the data in the above command should be changed to reflect the actual path on your system.

Next Steps

• Set up the NICER analysis environment, including software and calibration.
• Run nicerl2 to process the data.

Related Topics

SciServer offers another way to access and analyze NICER data, without the need to download the data or install the software onto a local machine.

Modifications

• 2023-03-10 - initial draft
• Further changes described here