Colliding Magnetospheres: X-ray Observations and Data Extraction

10 May 2024

This paper is available on arxiv under CC 4.0 license.


(1) Konstantin V. Getman, Department of Astronomy & Astrophysics, Pennsylvania State University;

(2) Agnes Kospal, Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, E¨otv¨os Lor´and Research Network (ELKH), MTA Centre of Excellence, Max Planck Institute for Astronomy, and ELTE E¨otv¨os Lor´and University, Institute of Physics;

(3) Nicole Arulanantham, Space Telescope Science Institute;

(4) Dmitry A. Semenov, Konkoly Observatory, Research Centre for Astronomy and Earth Sciences;

(5) Grigorii V. Smirnov-Pinchukov, Konkoly Observatory, Research Centre for Astronomy and Earth Sciences;

(6) Sierk E. van Terwisga, Konkoly Observatory, Research Centre for Astronomy and Earth Sciences.


2.1. NuSTAR Data

We conducted a single observation (ObsID 30801011002; PI K. Getman) of this system with NuSTAR (Harrison et al. 2013) from 04:51:09 UTC on July 28, 2022, to 19:36:09 UTC on July 31, 2022. This time window covers the orbital phase range of Φ = (0.9 − 1.13) around the periastron passage on July 30, 2022 (Φ = 1.0). The science exposure of the observation, taking into account Earth occultations, is 156 ksec.

The data obtained from focal plane modules A and B (FPMA and FPMB), covering similar energy ranges, were processed using tools from the NuSTAR Data Analysis Software package NuSTARDAS (v. 2.1.2), which is incorporated into HEASOFT (v. 6.31.1) as detailed in (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc) 2014). NuSTAR’s calibration database (CALDB) v. 20221229 was utilized. The data went through calibration and screening using the nupipeline tool. Parameters saamode=OPTIMIZED and tentacle=yes were employed to screen the data for elevated count rates resulting from the spacecraft’s passages through the South Atlantic Anomaly. Subsequently, the nuproducts tool was utilized to generate various outputs, including the source and background lightcurves and spectra, as well as response and response matrix files.

Figures 1(a,b) present images of the combined FPMA and FPMB event lists for the (3 − 10) keV and (10 − 50) keV energy bands, respectively. The source counts were obtained from a circular region with a radius of 40′′ (indicated by the green circle in Figure 1), representing 60% of the energy within the point spread function. The background measurement was performed locally in an area devoid of sources. Within the source extraction circle, there are 771 X-ray events with energies ranging from 3 to 10 keV, approximately one third of which are background events. The source is not detected in the (10 − 20) keV band (not shown) or the (10 − 50) keV band (Figure 1b), nor at higher energies.

2.2. Swift Data

Using the Neil Gehrels Swift observatory (Gehrels et al. 2004), we conducted 16 short observations of DQ Tau near periastron over a time period of July 28 to August 2, 2022. These observations are part of our joint NuSTAR/Swift program. The observations were spaced several hours apart, with durations ranging from 1 to 1.7 ksec, totaling 22.5 ksec. The target ID for these observations is 14857. The X-ray Telescope (XRT) operated in the PC mode, while the Ultraviolet/Optical Telescope (UVOT) operated in the 0x30ed standard sixfilter blue-weighted mode. The Swift-XRT data product generator (Evans et al. 2007, 2009) was utilized to construct X-ray light curves and source/background spectra, along with the relevant calibration files. The generator employed HEASOFT package (v. 6.29) and CALDB (v. 20230109).

Figure 1c presents the XRT image obtained from merging the event lists of all 16 observations. Within the circular source extraction region of a 30′′ radius (indicated by the green circle in the image), we identified 249 X-ray counts with energies ranging from 0.2 to 10 keV, of which only a few percent represented background counts.

For each of the 16 observations, UVOT magnitudes for the six filters (V:B:U:W1:M2:W2) were measured by applying the fappend (Blackburn et al. 1999) and uvotmaghist tools from HEASOFT (v. 6.31.1).

2.3. Chandra Data

To investigate the soft X-ray emission throughout the entire orbital phase of DQ Tau and complement the observations made by NuSTAR and Swift at periastron, additional X-ray data were obtained utilizing the Chandra X-ray Observatory (Weisskopf et al. 2002). The investigation involved 12 short Chandra imaging observations of DQ Tau away from periastron, with each observation lasting approximately 1.5 ksec. These observations were part of the Director’s Discretionary Time (DDT) program, with corresponding observation IDs ranging from 26464 to 26475.

Data were obtained between August 1 and August 14, 2022, covering an orbital phase range of 1.1 to 1.9. To mitigate potential pileup effects during anticipated Xray flares, a 1/8 sub-array of a single ACIS-I3 chip was employed (Garmire et al. 2003).

For the Chandra data reduction and analysis, CIAO v4.15(Fruscione et al. 2006) and CALDB v4.10.4 were utilized. The CIAO tools chandra repro and reproject obs were used to reprocess the data and merge the event images. Figure 1d displays the cutout of the merged Chandra-ACIS-I3 image of DQ Tau. Count rates and apparent fluxes were measured, and spectra and response files were generated using the srcflux tool. Within the circular source extraction region, with a radius of 2′′ (indicated by the green circle in the image), and within the energy band of (0.5 − 8) keV, net X-ray events were observed between 30 and 50 per observation in 8 instances. However, the remaining 4 consecutive observations (ObsIDs 26471, 26472, 26473, and 26474) exhibited higher net count levels, ranging from 61 to 781 counts per observation.

Figure 1. NuSTAR, Swift, and Chandra images of DQ Tau and its neighborhood. The color map, ranging from yellow to redto blue, indicates the intensity of X-rays with yellow and blue pixels representing more and less X-ray counts, respectively. Each figure panel has its own unique intensity scale. DQ Tau source extraction regions are marked by the green circles. (a) 13′ × 13′ image from the merged NuSTAR FPMA+FPMB event lists in the (3 − 10) keV energy band, and (b) in the (10 − 50) keV energy band. (c) 7′ × 7′ Swift-XRT cutout of DQ Tau’s neighborhood in the (0.2-10) keV band, which was obtained from the merged event lists of the 16 Swift observations. The other two X-ray objects visible in this image are the young stellar systems Haro 6-37 A,B and DR Tau, located to the north-east and south-east of DQ Tau, respectively. (d) 1′ × 1