[Paper Review] High resolution imaging of the X-ray afterglow of GRB970228 with ROSAT

F. Frontera, J. Greiner+7 more|arXiv (Cornell University)|Apr 25, 1998

Gamma-ray bursts and supernovae3 citations

TL;DR

This paper presents high-resolution X-ray imaging of the afterglow of GRB970228 using ROSAT's High-Resolution Imager, achieving a 10 arcsecond positional accuracy. The precise X-ray source position matches the optical transient within 2 arcseconds, confirming the common origin of the X-ray and optical afterglows and providing the most accurate localization of an X-ray afterglow to date.

ABSTRACT

We report results of a ROSAT High-Resolution Imager (HRI) observation of the X-ray error box given by the BeppoSAX Wide Field Camera for the gamma-ray burst that occurred on 1997 February 28. The observation started 10 days after the burst and ended three days later, with a total exposure of 34.3 ks. An X-ray source was detected within the 3' WFC error box and its position determined with a 10'' radius accuracy. The source position is in the BeppoSAX Narrow Field Instrument source error box and is coincident (to within 2'') with the optical transient associated with GRB970228. This is the most precise position obtained for an X-ray afterglow and confirms that the X-ray and optical afterglows have the same origin. We present the 0.1--2.4 keV combined HRI and BeppoSAX Low-Energy Concentrator Spectrometer decay light curve which can be well fit with a power-law. The decay is consistent with that measured at higher energies (2--10 keV) with the BeppoSAX Medium-Energy Concentrator Spectrometer.

Motivation & Objective

• To obtain high-resolution X-ray imaging of the X-ray afterglow of GRB970228 to improve source localization.
• To test the hypothesis that the X-ray afterglow and optical transient are co-located.
• To measure the X-ray light curve in the 0.1–2.4 keV energy band for comparison with higher-energy data.
• To confirm the consistency of decay behavior across different energy bands.
• To provide a precise astrometric reference for multi-wavelength studies of this gamma-ray burst.

Proposed method

• ROSAT HRI observed the BeppoSAX Wide Field Camera error box 10 days after the burst.
• The observation spanned 34.3 kiloseconds with a 10-day baseline.
• X-ray source position was determined with 10 arcsecond radius accuracy using HRI imaging.
• The X-ray light curve was constructed from combined HRI and BeppoSAX Low-Energy Concentrator Spectrometer data.
• A power-law decay model was fitted to the 0.1–2.4 keV light curve.
• The X-ray decay was compared with the 2–10 keV decay measured by the BeppoSAX Medium-Energy Concentrator Spectrometer.

Experimental results

Research questions

• RQ1 What is the precise X-ray position of the afterglow of GRB970228, and how does it compare to the optical transient?
• RQ2 Is the X-ray afterglow spatially coincident with the optical afterglow within the error budget?
• RQ3 Does the X-ray light curve in the soft band (0.1–2.4 keV) follow a power-law decay, and is it consistent with higher-energy decay?
• RQ4 What is the significance of the positional coincidence between X-ray and optical afterglows for understanding GRB emission mechanisms?
• RQ5 Can high-resolution X-ray imaging resolve the afterglow and improve astrometric calibration for future GRB studies?

Key findings

• An X-ray source was detected within the 3 arcminute BeppoSAX Wide Field Camera error box with a 10 arcsecond radius position accuracy.
• The X-ray source position is consistent with the optical transient associated with GRB970228, within 2 arcseconds.
• The X-ray afterglow light curve in the 0.1–2.4 keV band is well described by a power-law decay.
• The decay rate in the soft X-ray band is consistent with that measured in the 2–10 keV band by BeppoSAX.
• This is the most precise X-ray position ever obtained for an X-ray afterglow, confirming their common origin.
• The results support the interpretation that the X-ray and optical afterglows originate from the same physical region.