George Ricker - Academia.edu (original) (raw)
Papers by George Ricker
AIP Conference Proceedings, 2004
We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremel... more We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S X /S γ) = 0.7, where S X and S γ are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E obs peak < 5.0 keV (99.7% probability upper limit) and no photons were detected above ∼ 10 keV. The burst is shorter at higher energies, which is
AIP Conference Proceedings, 2004
We present an upper limit on the brightness of the afterglow of the long GRB 030115 measured from... more We present an upper limit on the brightness of the afterglow of the long GRB 030115 measured from Infrared (IR) images taken with the Magellan Classic Cam instrument of Ks > 22 at 6.2 days after the burst. We also present measurments of the host galaxy of GRB 030115 from archival optical and IR HST images taken with the Advanced Camera for Surveys and the Near Infrared Camera and Multi Object Spectrometer 25+ days after the burst. GRB 030115 is classified as an Optically Dark Burst, as its afterglow was found in the J, H, and K IR bands after a null result was reported in the optical. This is the first HETE GRB to have its afterglow found initially in the IR.
Lecture Notes in Physics
The Explosive Transient Camera (ETC) is a dedicated wide-field sky monitor for short-duration opt... more The Explosive Transient Camera (ETC) is a dedicated wide-field sky monitor for short-duration optical transients. The ETC operates completely automatically, searching for transients in the night sky without the need for a human observer on site. Data products from the ETC include data from any transients detected, as well as CCD images of the fields-of-view observed. We report here the imaging by the ETC of the 2.5 error region of GRB 941014 90 seconds after the end of the burst.
X-Ray Optics, Instruments, and Missions III, 2000
Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured wi... more Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4-2.2 keV range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Neverthless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.
X-Ray Optics, Instruments, and Missions III, 2000
We have performed a series of measurements with the Physikalisch-Technische Bundesanstalt beamlin... more We have performed a series of measurements with the Physikalisch-Technische Bundesanstalt beamline of the electron storage ring BESSY I which provide the basis for the absolute calibration of the Advanced CCD Imaging Spectrometer (ACIS). ACIS is a prime focal plane instrument aboard the recently-launched Chandra X-ray Observatory. We have achieved an absolute detection efficiency knowledge accurate to better than 5% over the 0.3-4 keV band. We describe our measurement and analysis techniques, including our detector response modeling and pileup corrections. We summarize a variety of external and internal consistency checks which provide the basis for our error estimates. We discuss the factors limiting the accuracy of our measurements.
SPIE Proceedings, 2006
The Constellation-X Reflection Grating Spectrometer (RGS) is designed to provide high-throughput,... more The Constellation-X Reflection Grating Spectrometer (RGS) is designed to provide high-throughput, high-resolution spectra in the long wavelength band of 6 to 50 Å. In the nominal design an array of reflection gratings is mounted at the exit of the Spectroscopy X-ray Telescope (SXT) mirror module. The gratings intercept and disperse light to a designated array of CCD detectors. To achieve the throughput (A eff > 1000 cm 2 below 0.6 keV) and resolution (Δλ/λ > 300 below 0.6 keV) requirements for the instrument we are investigating two possible grating designs. The first design uses inplane gratings in a classical configuration that is very similar to the XMM-Newton RGS. The second design uses offplane gratings in a conical configuration. The off-plane design has the advantage of providing higher reflectivity and potentially, a higher spectral resolution than the in-plane configuration. In our presentation we will describe the performance requirements and the current status of the technology development.
SPIE Proceedings, 2007
We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission gratin... more We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission grating which is modeled to have superior efficiency. Here we outline a full instrument design proposed for Constellation-X which is expected to give resolving powers ~2000 (HEW). The spectrometer advantages include lower mass budget and smaller diffractor area, as well as order-of-magnitude more relaxed alignment tolerances for crucial degrees of freedom than reflection grating schemes considered in the past 1,2,3. The spectrometer readout is based on conventional CCD technology adapted to operate with very high speed and low power. This instrument will enable high resolution absorption and emission line spectroscopy in the critical band between 0.2 and 1.5 keV.
Solid State Sensor Arrays: Development and Applications II, 1998
We have performed precise measurements of X-ray absorption constants for all the thin films compr... more We have performed precise measurements of X-ray absorption constants for all the thin films comprising CCD gate structure, namely, phosphourous doped polysilicon, silicon dioxide, and silicon nitride. X-ray absorption of these films shows large oscillations around the corresponding absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a (JCD in the soft X-ray range deviates significantly from the generally assumed simple model predictions. In order to cover the range of energies from 60 eV to 3000 eV transmission measurements were performed at several synchrotron beamlines at ALS (Berkeley), PTB BESSY (Berlin), SRC (University of Wisconsin-Madison). A model of the CCD response with near edge X-ray absorption structure taken into account predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector were performed at BESSY for both frontside illuminated and backside illuminated CCDs for energies around the oxygen absorption edge. Experimental results were found to be in a good agreement with our model.
We propose an improved version of the redshift indicator developed by Atteia, which gets rid of t... more We propose an improved version of the redshift indicator developed by Atteia, which gets rid of the dependence on the burst duration and provides better estimates for high-redshift GRBs. We present first this redshift indicator, then its calibration with HETE-GRBs with known redshifts. We also provide an estimation of the redshift for 59 bursts, and we finally discuss the redshift
Proceedings of the SPIE - The International Society for Optical Engineering, 1999
Ve present results from recent measurements of the channel stop structures iii AXAI" C(Ds. We dis... more Ve present results from recent measurements of the channel stop structures iii AXAI" C(Ds. We discuss refinements of a technique that uses a tliiii metal film with small periodically spaced holes to restnct incident photons to welldefined regions of the pixel, providing a way to probe sub-pixel structure. By niaking nioiiochroiiiatic iiieastirenieiits at different energies, we can reliably deternune the width and thickness of the channel stop p+-type silicon implant and its insulating oxide layer.
X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy, 2003
SPIE Proceedings, 1999
The optical chain of the spectroscopic X-Ray telescopes aboard the Constellation-X spacecrafts em... more The optical chain of the spectroscopic X-Ray telescopes aboard the Constellation-X spacecrafts employs a reflective grating spectrometer to provide high resolution (E/zE '400) spectra for multiple spectra as a slitless spectrometer in the spectral feature rich, soft X-Ray band (0.2-2.3 keV). As a part of the spectroscopic readout array, we provide a zero-order camera that images the sky in the soft band inaccessible to the microcalorimeters. Technological enhancements required for producing the RGS instruments are described, along with prototype development progress, fabrication and testing results.
X-Ray and Gamma-Ray Instrumentation for Astronomy XI, 2000
Front side illuminated CCDs comprising focal plane of the Chandra X-ray telescope have suffered s... more Front side illuminated CCDs comprising focal plane of the Chandra X-ray telescope have suffered some radiation damage in the beginning of the mission. Measuremnts of CTI and dark current at different temperatures led us to conclusion that the type of damage is inconsistent with the much studied type of damage created by protons with energies higher than 10 MeV. Intensive ground based investigation showed that irradiation of a CCD with low energy protons (about 100 keY) results in the device characteristics similar to the oties of the flight chips (very low dark current, the shape of the CTI temperature dependence). We were able to reliably determine that only image section of the flight chips was damaged and therefore only fast transfer from image to frame store section was affected. We have developed several techniques in order to determine the parameters of the electron traps introduced into the transfer channel of the irradiated device. One of them is based on the analysis of the amplitude of the signal in the pixels trailing the pixel that absorbed an X-ray photon of known energy. Averaging over large number of photons allowed us to get high signal/noise ratio even for pixels with extremely low signal far behind the X-ray event. Performing this analysis at different temperatures we were able to measure trap density, emission time constant, and trap cross section. Another techique is based on the analysis of the tail behind the events of very high amplitude, such as cosmic ray hits. We have developed a new scheme of clocking the device which prevents several rows of image section from being ever read out and keeps them moving back and forth. This so-called "squeegee mode" improves CTI and can also be used to measure trap parameters, being especially effective in measuring long time constants. At least 4 different types of traps were detected, two of them with short time constants in the range from tens to a few hundred microseconds. The most damaging for the device performance are the traps with longer time constant in the millisecond range. The measurement of the trap parameters allows us to accurately model charge transfer inefficiency and helps to choose optimal operational parameters, and eventually will lead to techniques that may noticeably improve performance of a damaged CCD.
The Astrophysical Journal, 2005
We present high resolution X-ray spectroscopy of two recent GRB afterglows observed with the Low ... more We present high resolution X-ray spectroscopy of two recent GRB afterglows observed with the Low Energy Transmission Gratings on Chandra. The afterglows to GRBs 030328 and 041006 are detected beginning 15.33 and 16.8 hours after each burst, respectively, and are observed to fade in time during each ∼ 90 ksec observation. We fit for the continuum emission in each full data set and for the data sliced into half and quarter time sections. For both afterglows, the continuum emission is well described by an absorbed power-law model, and the model parameters describing the absorption and spectral slope do not appear to evolve in time. We perform a careful search for deviations from the model continua for the full and time-sliced data and find no evidence for significant (∼ > 3σ) narrow emission/absorption lines or edges. The lack of detections implies that line emission-if it is a general feature in GRB X-ray afterglows-occurs early (t ∼ 0.3 days in the source frame) and/or is short-lived (dt ∼ < 10 ksec). We also comment on synchrotron fireball models for the X-ray and optical data.
The Astrophysical Journal, 1971
On October 15-16, 1970, we carried out balloon X-ray observations from Australia (energies above ... more On October 15-16, 1970, we carried out balloon X-ray observations from Australia (energies above 15 keV). We detected a rapidly varying flux from a source at &300.7+0.5, bc=-2.2k2.7". Several flares with rise and decay times of a few minutes were recorded, A flux change of about a factor of five was recorded in 2.5 minutes. The highest flux observed in the energy range from 15-32 keV was % 10 keV ~m-~sec'l and the lowest, % 2 keV cm-2 sec". We also observed a source
The Astrophysical Journal, 2004
We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-Ray Monitor/French Gamma Telesco... more We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-Ray Monitor/French Gamma Telescope observations of the X-ray flash XRF 020903. This event was extremely soft: the ratio log ðS X =S Þ ¼ 0:7, where S X and S are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy of E obs peak < 5:0 keV (99.7% probability upper limit), and no photons were detected above 10keV.Theburstisshorterathigherenergies,whichissimilartothebehavioroflonggamma−raybursts(GRBs).WeconsiderthepossibilitythattheburstliesatveryhighredshiftandthatthelowvalueofEobspeakisduetothecosmologicalredshift,andshowthatthisisveryunlikely.WefindthatthepropertiesofXRF020903areconsistentwiththerelationbetweenthefluencesS(7−30keV)andS(30−400keV),foundbyBarraudetal.forGRBsandX−ray−richGRBs,andareconsistentwiththeextensionbyadecadeofthehardness−intensitycorrelationfoundbythesameauthors.AssumingthatXRF020903liesataredshiftz¼0:25,asimpliedbythehostgalaxyofthecandidateopticalandradioafterglowsofthisburst,wefindthatthepropertiesofXRF020903areconsistentwithanextensionbyafactor10 keV. The burst is shorter at higher energies, which is similar to the behavior of long gamma-ray bursts (GRBs). We consider the possibility that the burst lies at very high redshift and that the low value of E obs peak is due to the cosmological redshift, and show that this is very unlikely. We find that the properties of XRF 020903 are consistent with the relation between the fluences S(7-30 keV) and S(30-400 keV), found by Barraud et al. for GRBs and X-ray-rich GRBs, and are consistent with the extension by a decade of the hardness-intensity correlation found by the same authors. Assuming that XRF 020903 lies at a redshift z ¼ 0:25, as implied by the host galaxy of the candidate optical and radio afterglows of this burst, we find that the properties of XRF 020903 are consistent with an extension by a factor 10keV.Theburstisshorterathigherenergies,whichissimilartothebehavioroflonggamma−raybursts(GRBs).WeconsiderthepossibilitythattheburstliesatveryhighredshiftandthatthelowvalueofEobspeakisduetothecosmologicalredshift,andshowthatthisisveryunlikely.WefindthatthepropertiesofXRF020903areconsistentwiththerelationbetweenthefluencesS(7−30keV)andS(30−400keV),foundbyBarraudetal.forGRBsandX−ray−richGRBs,andareconsistentwiththeextensionbyadecadeofthehardness−intensitycorrelationfoundbythesameauthors.AssumingthatXRF020903liesataredshiftz¼0:25,asimpliedbythehostgalaxyofthecandidateopticalandradioafterglowsofthisburst,wefindthatthepropertiesofXRF020903areconsistentwithanextensionbyafactor300 of the relation between the isotropic-equivalent energy E iso and the peak E peak of the F spectrum (in the source frame of the burst) found by Amati et al. for GRBs. The results presented in this paper therefore provide evidence that X-ray flashes (XRFs), X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon. The results also impose strong constraints on models of XRFs and X-ray-rich GRBs.
Publications of the Astronomical Society of Japan, 2005
A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the H... more A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the High Energy Transient Explorer 2 satellite (HETE-2) at 02:44:19.17 UTC (9859.17 s UT) on 2002 August 13. The location was reported to the GRB Coordinates Network (GCN) about 4 min after the burst. In the prompt emission, the burst had a duration of approximately 125 s, and more than four peaks. We analyzed the time-resolved 2-400 keV energy spectra of the prompt emission of GRB 020813 using the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE) in detail. We found that the early part of the burst (17-52 s after the burst trigger) shows a depletion of low-energy photons below about 50 keV. It is difficult to explain the depletion by either synchrotron self-absorption or Comptonization. One possibility is that the low-energy depletion may be understood as a mixture of "jitter" radiation with the usual synchrotron radiation component.
Optical Engineering, 1998
We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate s... more We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate structure, namely, phosphorus doped polysilicon, silicon dioxide, and silicon nitride. The x-ray transmission of these films shows large oscillations with small changes in energy in the vicinity of the following absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a CCD in the soft x-ray range deviates significantly from simple model predictions based on Henke et al. (1993) mass absorption coefficients. The measurements covered the range of energies from 60 to 3000 eV, using synchrotron beamlines at the Advanced Light Source (ALS; Berkeley), Physikalisch-Technische Bundesanstalt BESSY (Berlin), the Synchrotron Radiation Center (SRC; University of Wisconsin-Madison). Our model of the CCD response includes near edge x-ray absorption structure and predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector at the BESSY synchrotron confirmed our model predictions for both frontside and backside illuminated CCDs.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
AIP Conference Proceedings, 2004
We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremel... more We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S X /S γ) = 0.7, where S X and S γ are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E obs peak < 5.0 keV (99.7% probability upper limit) and no photons were detected above ∼ 10 keV. The burst is shorter at higher energies, which is
AIP Conference Proceedings, 2004
We present an upper limit on the brightness of the afterglow of the long GRB 030115 measured from... more We present an upper limit on the brightness of the afterglow of the long GRB 030115 measured from Infrared (IR) images taken with the Magellan Classic Cam instrument of Ks > 22 at 6.2 days after the burst. We also present measurments of the host galaxy of GRB 030115 from archival optical and IR HST images taken with the Advanced Camera for Surveys and the Near Infrared Camera and Multi Object Spectrometer 25+ days after the burst. GRB 030115 is classified as an Optically Dark Burst, as its afterglow was found in the J, H, and K IR bands after a null result was reported in the optical. This is the first HETE GRB to have its afterglow found initially in the IR.
Lecture Notes in Physics
The Explosive Transient Camera (ETC) is a dedicated wide-field sky monitor for short-duration opt... more The Explosive Transient Camera (ETC) is a dedicated wide-field sky monitor for short-duration optical transients. The ETC operates completely automatically, searching for transients in the night sky without the need for a human observer on site. Data products from the ETC include data from any transients detected, as well as CCD images of the fields-of-view observed. We report here the imaging by the ETC of the 2.5 error region of GRB 941014 90 seconds after the end of the burst.
X-Ray Optics, Instruments, and Missions III, 2000
Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured wi... more Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4-2.2 keV range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Neverthless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.
X-Ray Optics, Instruments, and Missions III, 2000
We have performed a series of measurements with the Physikalisch-Technische Bundesanstalt beamlin... more We have performed a series of measurements with the Physikalisch-Technische Bundesanstalt beamline of the electron storage ring BESSY I which provide the basis for the absolute calibration of the Advanced CCD Imaging Spectrometer (ACIS). ACIS is a prime focal plane instrument aboard the recently-launched Chandra X-ray Observatory. We have achieved an absolute detection efficiency knowledge accurate to better than 5% over the 0.3-4 keV band. We describe our measurement and analysis techniques, including our detector response modeling and pileup corrections. We summarize a variety of external and internal consistency checks which provide the basis for our error estimates. We discuss the factors limiting the accuracy of our measurements.
SPIE Proceedings, 2006
The Constellation-X Reflection Grating Spectrometer (RGS) is designed to provide high-throughput,... more The Constellation-X Reflection Grating Spectrometer (RGS) is designed to provide high-throughput, high-resolution spectra in the long wavelength band of 6 to 50 Å. In the nominal design an array of reflection gratings is mounted at the exit of the Spectroscopy X-ray Telescope (SXT) mirror module. The gratings intercept and disperse light to a designated array of CCD detectors. To achieve the throughput (A eff > 1000 cm 2 below 0.6 keV) and resolution (Δλ/λ > 300 below 0.6 keV) requirements for the instrument we are investigating two possible grating designs. The first design uses inplane gratings in a classical configuration that is very similar to the XMM-Newton RGS. The second design uses offplane gratings in a conical configuration. The off-plane design has the advantage of providing higher reflectivity and potentially, a higher spectral resolution than the in-plane configuration. In our presentation we will describe the performance requirements and the current status of the technology development.
SPIE Proceedings, 2007
We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission gratin... more We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission grating which is modeled to have superior efficiency. Here we outline a full instrument design proposed for Constellation-X which is expected to give resolving powers ~2000 (HEW). The spectrometer advantages include lower mass budget and smaller diffractor area, as well as order-of-magnitude more relaxed alignment tolerances for crucial degrees of freedom than reflection grating schemes considered in the past 1,2,3. The spectrometer readout is based on conventional CCD technology adapted to operate with very high speed and low power. This instrument will enable high resolution absorption and emission line spectroscopy in the critical band between 0.2 and 1.5 keV.
Solid State Sensor Arrays: Development and Applications II, 1998
We have performed precise measurements of X-ray absorption constants for all the thin films compr... more We have performed precise measurements of X-ray absorption constants for all the thin films comprising CCD gate structure, namely, phosphourous doped polysilicon, silicon dioxide, and silicon nitride. X-ray absorption of these films shows large oscillations around the corresponding absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a (JCD in the soft X-ray range deviates significantly from the generally assumed simple model predictions. In order to cover the range of energies from 60 eV to 3000 eV transmission measurements were performed at several synchrotron beamlines at ALS (Berkeley), PTB BESSY (Berlin), SRC (University of Wisconsin-Madison). A model of the CCD response with near edge X-ray absorption structure taken into account predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector were performed at BESSY for both frontside illuminated and backside illuminated CCDs for energies around the oxygen absorption edge. Experimental results were found to be in a good agreement with our model.
We propose an improved version of the redshift indicator developed by Atteia, which gets rid of t... more We propose an improved version of the redshift indicator developed by Atteia, which gets rid of the dependence on the burst duration and provides better estimates for high-redshift GRBs. We present first this redshift indicator, then its calibration with HETE-GRBs with known redshifts. We also provide an estimation of the redshift for 59 bursts, and we finally discuss the redshift
Proceedings of the SPIE - The International Society for Optical Engineering, 1999
Ve present results from recent measurements of the channel stop structures iii AXAI" C(Ds. We dis... more Ve present results from recent measurements of the channel stop structures iii AXAI" C(Ds. We discuss refinements of a technique that uses a tliiii metal film with small periodically spaced holes to restnct incident photons to welldefined regions of the pixel, providing a way to probe sub-pixel structure. By niaking nioiiochroiiiatic iiieastirenieiits at different energies, we can reliably deternune the width and thickness of the channel stop p+-type silicon implant and its insulating oxide layer.
X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy, 2003
SPIE Proceedings, 1999
The optical chain of the spectroscopic X-Ray telescopes aboard the Constellation-X spacecrafts em... more The optical chain of the spectroscopic X-Ray telescopes aboard the Constellation-X spacecrafts employs a reflective grating spectrometer to provide high resolution (E/zE '400) spectra for multiple spectra as a slitless spectrometer in the spectral feature rich, soft X-Ray band (0.2-2.3 keV). As a part of the spectroscopic readout array, we provide a zero-order camera that images the sky in the soft band inaccessible to the microcalorimeters. Technological enhancements required for producing the RGS instruments are described, along with prototype development progress, fabrication and testing results.
X-Ray and Gamma-Ray Instrumentation for Astronomy XI, 2000
Front side illuminated CCDs comprising focal plane of the Chandra X-ray telescope have suffered s... more Front side illuminated CCDs comprising focal plane of the Chandra X-ray telescope have suffered some radiation damage in the beginning of the mission. Measuremnts of CTI and dark current at different temperatures led us to conclusion that the type of damage is inconsistent with the much studied type of damage created by protons with energies higher than 10 MeV. Intensive ground based investigation showed that irradiation of a CCD with low energy protons (about 100 keY) results in the device characteristics similar to the oties of the flight chips (very low dark current, the shape of the CTI temperature dependence). We were able to reliably determine that only image section of the flight chips was damaged and therefore only fast transfer from image to frame store section was affected. We have developed several techniques in order to determine the parameters of the electron traps introduced into the transfer channel of the irradiated device. One of them is based on the analysis of the amplitude of the signal in the pixels trailing the pixel that absorbed an X-ray photon of known energy. Averaging over large number of photons allowed us to get high signal/noise ratio even for pixels with extremely low signal far behind the X-ray event. Performing this analysis at different temperatures we were able to measure trap density, emission time constant, and trap cross section. Another techique is based on the analysis of the tail behind the events of very high amplitude, such as cosmic ray hits. We have developed a new scheme of clocking the device which prevents several rows of image section from being ever read out and keeps them moving back and forth. This so-called "squeegee mode" improves CTI and can also be used to measure trap parameters, being especially effective in measuring long time constants. At least 4 different types of traps were detected, two of them with short time constants in the range from tens to a few hundred microseconds. The most damaging for the device performance are the traps with longer time constant in the millisecond range. The measurement of the trap parameters allows us to accurately model charge transfer inefficiency and helps to choose optimal operational parameters, and eventually will lead to techniques that may noticeably improve performance of a damaged CCD.
The Astrophysical Journal, 2005
We present high resolution X-ray spectroscopy of two recent GRB afterglows observed with the Low ... more We present high resolution X-ray spectroscopy of two recent GRB afterglows observed with the Low Energy Transmission Gratings on Chandra. The afterglows to GRBs 030328 and 041006 are detected beginning 15.33 and 16.8 hours after each burst, respectively, and are observed to fade in time during each ∼ 90 ksec observation. We fit for the continuum emission in each full data set and for the data sliced into half and quarter time sections. For both afterglows, the continuum emission is well described by an absorbed power-law model, and the model parameters describing the absorption and spectral slope do not appear to evolve in time. We perform a careful search for deviations from the model continua for the full and time-sliced data and find no evidence for significant (∼ > 3σ) narrow emission/absorption lines or edges. The lack of detections implies that line emission-if it is a general feature in GRB X-ray afterglows-occurs early (t ∼ 0.3 days in the source frame) and/or is short-lived (dt ∼ < 10 ksec). We also comment on synchrotron fireball models for the X-ray and optical data.
The Astrophysical Journal, 1971
On October 15-16, 1970, we carried out balloon X-ray observations from Australia (energies above ... more On October 15-16, 1970, we carried out balloon X-ray observations from Australia (energies above 15 keV). We detected a rapidly varying flux from a source at &300.7+0.5, bc=-2.2k2.7". Several flares with rise and decay times of a few minutes were recorded, A flux change of about a factor of five was recorded in 2.5 minutes. The highest flux observed in the energy range from 15-32 keV was % 10 keV ~m-~sec'l and the lowest, % 2 keV cm-2 sec". We also observed a source
The Astrophysical Journal, 2004
We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-Ray Monitor/French Gamma Telesco... more We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-Ray Monitor/French Gamma Telescope observations of the X-ray flash XRF 020903. This event was extremely soft: the ratio log ðS X =S Þ ¼ 0:7, where S X and S are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy of E obs peak < 5:0 keV (99.7% probability upper limit), and no photons were detected above 10keV.Theburstisshorterathigherenergies,whichissimilartothebehavioroflonggamma−raybursts(GRBs).WeconsiderthepossibilitythattheburstliesatveryhighredshiftandthatthelowvalueofEobspeakisduetothecosmologicalredshift,andshowthatthisisveryunlikely.WefindthatthepropertiesofXRF020903areconsistentwiththerelationbetweenthefluencesS(7−30keV)andS(30−400keV),foundbyBarraudetal.forGRBsandX−ray−richGRBs,andareconsistentwiththeextensionbyadecadeofthehardness−intensitycorrelationfoundbythesameauthors.AssumingthatXRF020903liesataredshiftz¼0:25,asimpliedbythehostgalaxyofthecandidateopticalandradioafterglowsofthisburst,wefindthatthepropertiesofXRF020903areconsistentwithanextensionbyafactor10 keV. The burst is shorter at higher energies, which is similar to the behavior of long gamma-ray bursts (GRBs). We consider the possibility that the burst lies at very high redshift and that the low value of E obs peak is due to the cosmological redshift, and show that this is very unlikely. We find that the properties of XRF 020903 are consistent with the relation between the fluences S(7-30 keV) and S(30-400 keV), found by Barraud et al. for GRBs and X-ray-rich GRBs, and are consistent with the extension by a decade of the hardness-intensity correlation found by the same authors. Assuming that XRF 020903 lies at a redshift z ¼ 0:25, as implied by the host galaxy of the candidate optical and radio afterglows of this burst, we find that the properties of XRF 020903 are consistent with an extension by a factor 10keV.Theburstisshorterathigherenergies,whichissimilartothebehavioroflonggamma−raybursts(GRBs).WeconsiderthepossibilitythattheburstliesatveryhighredshiftandthatthelowvalueofEobspeakisduetothecosmologicalredshift,andshowthatthisisveryunlikely.WefindthatthepropertiesofXRF020903areconsistentwiththerelationbetweenthefluencesS(7−30keV)andS(30−400keV),foundbyBarraudetal.forGRBsandX−ray−richGRBs,andareconsistentwiththeextensionbyadecadeofthehardness−intensitycorrelationfoundbythesameauthors.AssumingthatXRF020903liesataredshiftz¼0:25,asimpliedbythehostgalaxyofthecandidateopticalandradioafterglowsofthisburst,wefindthatthepropertiesofXRF020903areconsistentwithanextensionbyafactor300 of the relation between the isotropic-equivalent energy E iso and the peak E peak of the F spectrum (in the source frame of the burst) found by Amati et al. for GRBs. The results presented in this paper therefore provide evidence that X-ray flashes (XRFs), X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon. The results also impose strong constraints on models of XRFs and X-ray-rich GRBs.
Publications of the Astronomical Society of Japan, 2005
A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the H... more A bright, long gamma-ray burst (GRB) was detected and localized by the instruments on board the High Energy Transient Explorer 2 satellite (HETE-2) at 02:44:19.17 UTC (9859.17 s UT) on 2002 August 13. The location was reported to the GRB Coordinates Network (GCN) about 4 min after the burst. In the prompt emission, the burst had a duration of approximately 125 s, and more than four peaks. We analyzed the time-resolved 2-400 keV energy spectra of the prompt emission of GRB 020813 using the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE) in detail. We found that the early part of the burst (17-52 s after the burst trigger) shows a depletion of low-energy photons below about 50 keV. It is difficult to explain the depletion by either synchrotron self-absorption or Comptonization. One possibility is that the low-energy depletion may be understood as a mixture of "jitter" radiation with the usual synchrotron radiation component.
Optical Engineering, 1998
We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate s... more We perform precise measurements of the x-ray transmission of the thin films comprising CCD gate structure, namely, phosphorus doped polysilicon, silicon dioxide, and silicon nitride. The x-ray transmission of these films shows large oscillations with small changes in energy in the vicinity of the following absorption edges: nitrogen K (400 eV), oxygen K (536 eV), silicon L and K (100 and 1840 eV, respectively). As a result, quantum efficiency of a CCD in the soft x-ray range deviates significantly from simple model predictions based on Henke et al. (1993) mass absorption coefficients. The measurements covered the range of energies from 60 to 3000 eV, using synchrotron beamlines at the Advanced Light Source (ALS; Berkeley), Physikalisch-Technische Bundesanstalt BESSY (Berlin), the Synchrotron Radiation Center (SRC; University of Wisconsin-Madison). Our model of the CCD response includes near edge x-ray absorption structure and predicts a very complicated shape of the energy dependence of the quantum efficiency around silicon and oxygen absorption edges. Experimental measurements of CCD quantum efficiency relative to a calibrated detector at the BESSY synchrotron confirmed our model predictions for both frontside and backside illuminated CCDs.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005