Searcharxiv⌕ Search

arXiv subjects

P. Jenke

Publications and source records attributed to P. Jenke.

17 recordsLinked to original sources
arXiv2021

The X-ray pulsar XTE J1858+034 observed with NuSTAR and Fermi/GBM: spectral and timing characterization plus a cyclotron line

Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the spectral and timing behavior of the neutron star can be studied in detail. We analyze a $NuSTAR$ observation of the XRP XTE J1858+034 during its outburst in 2019. The spectrum is fit with a phenomenological, a semi-empirical and a physical spectral model. A candidate cyclotron line is found at $48\,$keV, implying a magnetic field of $5.4\times10^{\rm 12}\,$G at the site of emission. This is also supported by the physical best-fit model. We propose an orbital period of about $81$ days based on the visual inspection of the X-ray outbursts recurrence time. Based on $Fermi$ Gamma-ray Burst Monitor data, the standard disk accretion-torque theory allowed us to infer a distance of $10.9\pm1.0\,$kpc. Pulse profiles are single-peaked and show a pulsed fraction that is strongly energy-dependent at least up to $40$ keV.

astro-ph.HE↗
arXiv2020

The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor

We review more than 10 years of continuous monitoring of accreting X-ray pulsars with the all-sky Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope. Our work includes data from the start of GBM operations in August 2008, through to November 2019. Pulsations from 39 accreting pulsars are observed over an energy range of $10-50\,$keV by GBM. The GBM Accreting Pulsars Program (GAPP) performs data reduction and analysis for each accreting pulsar and makes histories of the pulse frequency and pulsed flux publicly available. We examine in detail the spin histories, outbursts and torque behaviors of the persistent and transient X-ray pulsars observed by GBM. The spin period evolution of each source is analyzed in the context of disk-accretion and quasi-spherical settling accretion driven torque models. Long-term pulse frequency histories are also analyzed over the GBM mission lifetime and compared to those available from the previous BATSE all-sky monitoring mission, revealing previously unnoticed episodes in some of the analyzed sources (such as a torque reversal in 2S 1845-024). We obtain new, or update known, orbital solutions for three sources. Our results demonstrate the capabilities of GBM as an excellent instrument for monitoring accreting X-ray pulsars and its important scientific contribution to this field.

astro-ph.HE↗
arXiv2020

Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM

The accretion-powered X-ray pulsar GX 301-2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late December 2018, with contiguous observations by the NICER X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin-up of the pulsar discovered with the Fermi GBM. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15-35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of (27+38-27)% (90% confidence limit) averaged over all pulse phases. We discuss the spin-up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.

astro-ph.HE↗
arXiv2017

Studying the accretion geometry of EXO 2030+375 at luminosities close to the propeller regime

The Be X-ray binary EXO 2030+375 was in an extended low luminosity state during most of 2016. We observed this state with NuSTAR and Swift, supported by INTEGRAL observations as well as optical spectroscopy with the NOT. We present a comprehensive spectral and timing analysis of these data here to study the accretion geometry and investigate a possible onset of the propeller effect. The H-alpha data show that the circumstellar disk of the Be-star is still present. We measure equivalent widths similar to values found during more active phases in the past, indicating that the low-luminosity state is not simply triggered by a smaller Be disk. The NuSTAR data, taken at a 3-78 keV luminosity of ~6.8e35 erg/s (for a distance of 7.1 kpc), are well described by standard accreting pulsar models, such as an absorbed power-law with a high-energy cutoff. We find that pulsations are still clearly visible at these luminosities, indicating that accretion is continuing despite the very low mass transfer rate. In phase-resolved spectroscopy we find a peculiar variation of the photon index from ~1.5 to ~2.5 over only about 3% of the rotational period. This variation is similar to that observed with XMM-Newton at much higher luminosities. It may be connected to the accretion column passing through our line of sight. With Swift/XRT we observe luminosities as low as 1e34 erg/s during which the data quality did not allow us to search for pulsations, but the spectrum is much softer and well described by either a blackbody or soft power-law continuum. This softer spectrum might be due to the fact that accretion has been stopped by the propeller effect and we only observe the neutron star surface cooling.

astro-ph.HE↗
arXiv2016

Searching the Gamma-ray Sky for Counterparts to Gravitational Wave Sources: Fermi GBM and LAT Observations of LVT151012 and GW151226

We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candi- date LVT151012. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for char- acterizing the upper limits across a large area of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, dif- ferences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914.

astro-ph.HE↗
arXiv2016

Fermi GBM Observations of LIGO Gravitational Wave event GW150914

With an instantaneous view of 70% of the sky, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent partner in the search for electromagnetic counterparts to gravitational wave (GW) events. GBM observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914 reveal the presence of a weak transient above 50 keV, 0.4~s after the GW event, with a false alarm probability of 0.0022 (2.9$\sigma$). This weak transient lasting 1 s was not detected by any other instrument and does not appear connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. The duration and spectrum of the transient event are consistent with a weak short Gamma-Ray Burst arriving at a large angle to the direction in which Fermi was pointing, where the GBM detector response is not optimal. If the GBM transient is associated with GW150914, this electromagnetic signal from a stellar mass black hole binary merger is unexpected. We calculate a luminosity in hard X-ray emission between 1~keV and 10~MeV of $1.8^{+1.5}_{-1.0} \times 10^{49}$~erg~s$^{-1}$. Future joint observations of GW events by LIGO/Virgo and Fermi GBM could reveal whether the weak transient reported here is a plausible counterpart to GW150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short Gamma-Ray Bursts.

astro-ph.HE↗
arXiv2015

Construction of a Schwarzschild-Couder telescope as a candidate for the Cherenkov Telescope Array: status of the optical system

We present the design and the status of procurement of the optical system of the prototype Schwarzschild-Couder telescope (pSCT), for which construction is scheduled to begin in fall at the Fred Lawrence Whipple Observatory in southern Arizona, USA. The Schwarzschild-Couder telescope is a candidate for the medium-sized telescopes of the Cherenkov Telescope Array, which utilizes imaging atmospheric Cherenkov techniques to observe gamma rays in the energy range of 60Gev-60TeV. The pSCT novel aplanatic optical system is made of two segmented aspheric mirrors. The primary mirror has 48 mirror panels with an aperture of 9.6 m, while the secondary, made of 24 panels, has an diameter of 5.4 m. The resulting point spread function (PSF) is required to be better than 4 arcmin within a field of view of 6.4 degrees (80% of the field of view), which corresponds to a physical size of 6.4 mm on the focal plane. This goal represents a challenge for the inexpensive fabrication of aspheric mirror panels and for the precise alignment of the optical system as well as for the rigidity of the optical support structure. In this submission we introduce the design of the Schwarzschild-Couder optical system and describe the solutions adopted for the manufacturing of the mirror panels and their integration with the optical support structure.

astro-ph.IM↗
arXiv2014

Localization of Gamma-Ray Bursts using the Fermi Gamma-Ray Burst Monitor

The Fermi Gamma-ray Burst Monitor (GBM) has detected over 1400 Gamma-Ray Bursts (GRBs) since it began science operations in July, 2008. We use a subset of over 300 GRBs localized by instruments such as Swift, the Fermi Large Area Telescope, INTEGRAL, and MAXI, or through triangulations from the InterPlanetary Network (IPN), to analyze the accuracy of GBM GRB localizations. We find that the reported statistical uncertainties on GBM localizations, which can be as small as 1 degree, underestimate the distance of the GBM positions to the true GRB locations and we attribute this to systematic uncertainties. The distribution of systematic uncertainties is well represented (68% confidence level) by a 3.7 degree Gaussian with a non-Gaussian tail that contains about 10% of GBM-detected GRBs and extends to approximately 14 degrees. A more complex model suggests that there is a dependence of the systematic uncertainty on the position of the GRB in spacecraft coordinates, with GRBs in the quadrants on the Y-axis better localized than those on the X-axis.

astro-ph.IM↗
arXiv2013

The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 s is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

astro-ph.HE↗
arXiv2013

Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources

The Gamma ray Burst Monitor (GBM) on board Fermi Gamma-ray Space Telescope has been providing continuous data to the astronomical community since 2008 August 12. We will present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. Although the occultation technique is in principle quite simple, in practice there are many complications including the dynamic instrument response, source confusion, and scattering in the Earth's atmosphere, which will be described. We detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary/neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky monitors below 100 keV and is the only all-sky monitor above 100 keV. In our fourth year of monitoring, we have already increased the number of transient sources detected and expect several of the weaker persistent sources to cross the detection threshold. I will briefly discuss these new sources and what to expect from our five year occultation catalog.

astro-ph.HE↗
arXiv2013

Earth Occultation Imaging of the Low Energy Gamma-Ray Sky with GBM

The Earth Occultation Technique (EOT) has been applied to Fermi's Gamma-ray Burst Monitor (GBM) to perform all-sky monitoring for a predetermined catalog of hard X-ray/soft gamma-ray sources. In order to search for sources not in the catalog, thus completing the catalog and reducing a source of systematic error in EOT, an imaging method has been developed -- Imaging with a Differential filter using the Earth Occultation Method (IDEOM). IDEOM is a tomographic imaging method that takes advantage of the orbital precession of the Fermi satellite. Using IDEOM, all-sky reconstructions have been generated for ~sim 4 years of GBM data in the 12-50 keV, 50-100 keV and 100-300 keV energy bands in search of sources otherwise unmodeled by the GBM occultation analysis. IDEOM analysis resulted in the detection of 57 sources in the 12-50 keV energy band, 23 sources in the 50-100 keV energy band, and 7 sources in the 100-300 keV energy band. Seventeen sources were not present in the original GBM-EOT catalog and have now been added. We also present the first joined averaged spectra for four persistent sources detected by GBM using EOT and by the Large Area Telescope (LAT) on Fermi: NGC 1275, 3C 273, Cen A, and the Crab.

astro-ph.HE↗
arXiv2012

The Fermi-GBM X-ray burst monitor: thermonuclear bursts from 4U 0614+09

Thermonuclear bursts from slowly accreting neutron stars (NSs) have proven difficult to detect, yet they are potential probes of the thermal properties of the neutron star interior. During the first year of a systematic all-sky search for X-ray bursts using the Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope we have detected 15 thermonuclear bursts from the NS low-mass X-ray binary 4U 0614+09, when it was accreting at nearly 1% of the Eddington limit. We measured an average burst recurrence time of 12+/-3 d (68% confidence interval) between March 2010 and March 2011, classified all bursts as normal duration bursts and placed a lower limit on the recurrence time of long/intermediate bursts of 62 d (95% confidence level). We discuss how observations of thermonuclear bursts in the hard X-ray band compare to pointed soft X-ray observations, and quantify such bandpass effects on measurements of burst radiated energy and duration. We put our results for 4U 0614+09 in the context of other bursters and briefly discuss the constraints on ignition models. Interestingly, we find that the burst energies in 4U 0614+09 are on average between those of normal duration bursts and those measured in long/intermediate bursts. Such a continuous distribution in burst energy provides a new observational link between normal and long/intermediate bursts. We suggest that the apparent bimodal distribution that defined normal and long/intermediate duration bursts during the last decade could be due to an observational bias towards detecting only the longest and most energetic bursts from slowly accreting NSs.

astro-ph.HE↗
arXiv2011

GBM Monitoring of Cyg X-1 During the Recent State Transition

Cygnus X-1 is a high-mass x-ray binary with a black hole compact object. It is normally extremely bright in hard x-rays and low energy gamma rays and resides in the canonical hard spectral state. Recently, however, Cyg X-1 made a transition to the canonical soft state, with a rise in the soft x-ray flux and a decrease in the flux in the hard x-ray and low energy gamma-ray energy bands. We have been using the Gamma-Ray Burst Monitor on Fermi to monitor the fluxes of a number of sources in the 8--1000 keV energy range, including Cyg X-1. We present light curves of Cyg X-1 showing the flux decrease in hard x-ray and low energy gamma-ray energy bands during the state transition as well as the several long flares observed in these higher energies during the soft state. We also present preliminary spectra from GBM for the pre-transition state, showing the spectral evolution to the soft state, and the post-transition state.

astro-ph.HE↗
arXiv2011

X-Ray and Optical Observations of A 0535+26

We present recent contemporaneous X-ray and optical observations of the Be/X-ray binary system A\,0535+26 with the \textit{Fermi}/Gamma-ray Burst Monitor (GBM) and several ground-based observatories. These new observations are put into the context of the rich historical data (since $\sim$1978) and discussed in terms of the neutron star Be-disk interaction. The Be circumstellar disk was exceptionally large just before the 2009 December giant outburst, which may explain the origin of the unusual recent X-ray activity of this source. We found a peculiar evolution of the pulse profile during this giant outburst, with the two main components evolving in opposite ways with energy. A hard 30-70 mHz X-ray QPO was detected with GBM during this 2009 December giant outburst. It becomes stronger with increasing energy and disappears at energies below 25\,keV. In the long-term a strong optical/X-ray correlation was found for this system, however in the medium-term the H$_\alpha$ EW and the V-band brightness showed an anti-correlation after $\sim$2002 Agust. Each giant X-ray outburst occurred during a decline phase of the optical brightness, while the H$_\alpha$ showed a strong emission. In late 2010 and before the 2011 February outburst, rapid V/R variations are observed in the strength of the two peaks of the H$_\alpha$ line. These had a period of $\sim$\,25 days and we suggest the presence of a global one-armed oscillation to explain this scenario. A general pattern might be inferred, where the disk becomes weaker and shows V/R variability beginning $\sim$\,6 months following a giant outburst.

astro-ph.HE↗
arXiv2011

A 0535+26: an X-ray/Optical Tour

We compiled X-ray and Optical observations of the accreting X-ray binary system A 0535+262 since its discovery in 1975, that will allow us to shed light on the unpredictable behavior of this binary system. We present the data in terms of the Be-disk interaction with the neutron star companion. In addition, we show recent results from the continuous monitoring of this source by the Gamma-ray Burst Monitor(GBM), on board the Fermi observatory, since its launch in 2008 June 11.

astro-ph.HE↗
arXiv2009

All-Sky Earth Occultation Observations with the Fermi Gamma Ray Burst Monitor

Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog enters or exits occultation by the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. In addition, to Earth occultations, we have observed numerous occultations with Fermi's solar panels. We will present early results. Regularly updated results can be found on our website http://gammaray.nsstc.nasa.gov/gbm/science/occultation

astro-ph.HE↗