Observations of Cygnus X‐1 with the EXITE2 Hard X‐Ray Balloon Payload

Abstract

We present results from the second-generation Energetic X-ray Imaging Telescope (EXITE2) observations of the black hole X-ray binary Cyg X-1 during the experiment's 1997 and 2001 flights. The EXITE2 phoswich [NaI(Tl)/CsI(Na)] detector is designed to image cosmic X-ray sources in the hard X-ray band by using the codedaperture imaging technique from a high-altitude scientific balloon. The sky image reconstruction methodology used for EXITE2 is also discussed in detail. Background reduction (PSD rejection), subtractive flat-fielding, pixel shuffling, and image functions are introduced. During the observations from the EXITE2 1997 and 2001 flights, Cyg X-1 is easily detected in the 37-237 keV energy range. During the 1997 observations, the spectrum is well fitted by a Comptonization model. The spectral signatures and the observed 100 keV flux, together with the RXTE ASM light curve, indicate that the source was in the typical low state during this observation. Evidence is seen for hard X-ray variability on timescales on the order of 10 minutes. During the 2001 flight the spectrum is best fit by an extended power law with no observable cutoff. This is possible evidence of a transition to the high state, which is indeed seen in the RXTE ASM light curve shortly after our observation.

Luminescent properties of Ce:Gd3(Al,Ga,Mg,M)5O12 crystal (M = Zr, Hf)

“…Scintillation materials have been investigated and applied to many fields such as homeland security, medical imaging, oil well logging, and astronomy. [1][2][3][4][5] Some Compton cameras consist of scintillators, and these cameras can be applied to medical imaging or astronomy. [5][6][7][8][9][10][11][12][13][14] Ce-doped Gd 3 Al 2 Ga 3 O 12 (Ce:GAGG) was found to have high light yield (³46,000 photons/MeV) and good energy resolution (³4.9% at 662 keV, FWHM).…”

“…17) Although Ce:GAGG has good properties, its effective atomic number (Z eff ) is lower (below 54) than those of other conventional oxide crystals such as Ce:Gd 2 SiO 5 (Z eff = 59) and Ce:(Lu,Y) 2 SiO 5 (Z eff = 63). [18][19][20][21] Since the cross section of gamma-ray photo-absorption (gamma-ray stopping power) is proportional to Z eff , 4,5) the gamma-ray stopping power of Ce:GAGG is generally lower than those of other oxide scintillators.…”

Coded Aperture Imaging in High-energy Astrophysics

“…In order to obtain S from D, several approaches and algorithms have been discussed in the literature (see Skinner (2003) for a review) and used in specific instruments with specific detector systems and mask patterns (Hammersley et al 1992;Skinner et al 1987a;Krivonos et al 2010;Chou et al 2005;Hong 2002;Rideout and Skinner 1996). A widely used reconstruction method, described in this paper, is the correlation of the recorded data with a suitable decoding function that in general mimics the mask pattern.…”

A Novel Position-Sensitive Radiation Detector Using a Gaseous Photomultiplier and an UV Scintillator

“…Vacuum photomultiplier tubes (PMTs) are used in various fields such as high-energy physics [1], medical imaging [2], and gamma-ray astronomy [3]. Because a flat, large-area PMT cannot be produced easily, a large number of PMTs are necessary in applications that need large-area coverage.…”