Insight-HXMT Observations of 4U 1636-536: Corona Cooling Revealed with Single Short Type-I X-Ray Burst

Abstract

Corona cooling was detected previously from stacking a series of short type I bursts that occurred during the low/hard state of an atoll outburst. Type I bursts are hence regarded as sharp probes used to better our understanding of the basic properties of the corona. The first Chinese X-ray satellite, Insight-HXMT, has a large detection area at hard X-rays that provides a unique opportunity to move further in this research field. We report the first detection of corona cooling by Insight-HXMT from a single short type I burst appearing during the flare of 4U 1636-536. This type I X-ray burst has a duration of ∼13 s and hard X-ray shortage is detected with a significance of 6.2σ in 40–70 keV. A cross-correlation analysis between the light curves of the soft and hard X-ray band shows that the corona shortage lags the burst emission by 1.6 ± 1.2 s. These results are consistent with those derived previously from stacking a large amount of bursts detected by RXTE/PCA within a series of flares of 4U 1636-536. Moreover, the broad bandwidth of Insight-HXMT also allows, for the first time, one to infer the burst influence upon the continuum spectrum via performing the spectral fitting of the burst, which points to the finding that hard X-ray shortage appears at around 40 keV in the continuum spectrum. These results suggest that the evolution of the corona, along with the outburst/flare of NS XRB, may be traced via analyzing a series of embedded type I bursts using Insight-HXMT.

Burst-induced coronal cooling in GS 1826–24

“…By stacking more than a hundred bursts from the IBIS/ISGRI instrument on board the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL; Winkler et al 2003), Kajava et al (2017) detected a clear flux drop above 40 keV in the light curves and spectra of the 4U 1728-34 hard-state bursts. Spectral evidence of X-ray burst-induced coronal cooling were also found in 4U 1636-536 by Chen et al (2018).…”

Insight-HXMT observations of the Crab pulsar

“…We selected the photons observed by small FoV detectors for ME because the large FoV was easily contaminated by a nearby source and the bright Earth. (Chen et al 2018;Huang et al 2018) Observations of the Crab pulsar were started on2017 August 27. The data in time range MJD 57992-58209 were employed in this work.…”

Overview to the Hard X-ray Modulation Telescope (Insight-HXMT) Satellite

“…Figure28 The spectrum of the onboard radioactive source 241 Am obtained by the ME pixels illuminated.…”