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Papers by Florian Hofmann
Astronomy & Astrophysics, 2016
Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters... more Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters of galaxies. The line has been discussed as a possible decay signature of 7.1 keV sterile neutrinos, which have been proposed as a dark matter candidate. We aim at putting constraints on the proposed line emission in a large sample of Chandra-observed clusters and obtain limits on the mixing-angle in a 7.1 keV sterile neutrino dark matter scenario. For a sample of 33 high-mass clusters of galaxies we merge all observations from the Chandra data archive. Each cluster has more than 100 ks of combined exposure. The resulting high signal-to-noise spectra are used to constrain the flux of an unidentified line emission at 3.55 keV in the individual spectra and a merged spectrum of all clusters. Results. We obtained very detailed spectra around the 3.55 keV range and limits on an unidentified emission line. Assuming all dark matter were made of 7.1 keV sterile neutrinos the upper limits on the mixing angle are sin^2(2Θ) < 10.1 × 10^−11 from ACIS-I, and < 40.3 × 10^−11 from ACIS-S data at 99.7 per cent confidence level. Conclusions. We do not find evidence for an unidentified emission line at 3.55 keV. The sample extends the list of objects searched for an emission line at 3.55 keV and will help to identify the best targets for future studies of the potential dark matter decay line with upcoming X-ray observatories like Hitomi (Astro-H), eROSITA, and Athena.
We confirm an optical nova candidate, designated PNV J00424629+4113517 by the optical discoverers... more We confirm an optical nova candidate, designated PNV J00424629+4113517 by the optical discoverers K. Nishiyama and F. Kabashima (Miyaki-Argenteus Observatory, Japan), as a bright source on three Swift UVOT UVW2 filter prediscovery images (central wavelength 192.8 nm, FWHM 65.7 nm) with about 815 s exposure (ObsID 00032702015) starting on 2013 Feb. 22.070, 22.137, and 22.204 UT with brightness increasing from magnitude 16.88± 0.05, 16.70± 0.05, to 16.41± 0.04, respectively.
In an observation of the M 31 central region with the X-ray telescope (XRT) on board the Swift sa... more In an observation of the M 31 central region with the X-ray telescope (XRT) on board the Swift satellite (ObsId 0035336069, start time 2012-09-13.16 UT, exposure 2.64 ks), we detect about 60 counts from a new X-ray transient at position RA = 00h42m47.21 Dec = +41d14'05.5" (± 3.0", J2000, 90% confidence) after correcting systematic offsets (Kaaret 2002, ApJ, 578, 114), which we name SWIFT J004247.2+411405.
Monitoring observations of the M 31 central region with the X-ray telescope (XRT) on board the Sw... more Monitoring observations of the M 31 central region with the X-ray telescope (XRT) on board the Swift satellite show a new outburst of an X-ray transient. The position of the transient was derived from the brightest observation after correcting systematic offsets (using the catalog of Kaaret 2002, ApJ, 578, 114) to RA = 00h42m47.96s, Dec = +41d11'14.9" (± 5", J2000, 90% confidence level). The transient is first detected in observation 0035336064, starting on 2012-08-12.48 UT.
In recent monitoring observations of the M31 centre with the Swift satellite, we find an X-ray tr... more In recent monitoring observations of the M31 centre with the Swift satellite, we find an X-ray transient at RA=00:42:57.0 Dec=+41🔞42 (J2000, ePOS=4.26", 90% confidence) that is likely associated with the X-ray binary candidate XMMM31 J004256.7+411843.
For all Chandra HRC-I observations a source catalogue was created and the energy flux of each sou... more For all Chandra HRC-I observations a source catalogue was created and the energy flux of each source in each observation was derived. Fluxes were calculated assuming a generic power law spectrum and Galactic foreground absorption for each source. (5 data files).
In the latest monitoring observations of the central region of the Andromeda Galaxy with the Ultr... more In the latest monitoring observations of the central region of the Andromeda Galaxy with the Ultra-violet/Optical Telescope (UVOT) on board the Swift satellite from 2012-05-24.62 UT to 2012-07-19.09 UT, we observe five recently discovered novae and one apparent UV variable. For all observations the UVOT uvw1 filter (181-321nm) is used. The following table shows UVOT uvw1 magnitudes (Vega system) and 1σ errors for each observed M 31 nova (see identification at the top of each column).
We report the discovery of a UV-transient (Swift J00431492+4119130) in a monitoring observation o... more We report the discovery of a UV-transient (Swift J00431492+4119130) in a monitoring observation of the central region of the Andromeda Galaxy (M 31) with the Ultra-violet/Optical Telescope (UVOT) on board the Swift satellite (ObsID 00035336120, starting 2013-09-11.01 UT). The source is located at RA 00h 43m 14.93s, Dec +41d 19' 13.0" (J2000, ePos=0.5", 90% confidence level). Light curve information for filters uvw1 (central wavelength: 260 nm) and uvm2 (225 nm) is given in the table below (Vega system, 1σ statistical uncertainties).
We report the discovery of a new X-ray transient (CXOU J004233.2+411742) in a Chandra HRC-I obser... more We report the discovery of a new X-ray transient (CXOU J004233.2+411742) in a Chandra HRC-I observation of the Andromeda Galaxy starting 2012-06-01.90 UT (ObsID 13281). The position of the source is RA = 00h42m33.26s Dec = +41d17'42.7" (± 0.5 arcsec, J2000). The source is also detected in a quasi simultaneous Swift X-ray telescope (XRT) observation starting 2012-06-01.77 UT (ObsID 00035336053).In a Swift XRT observation starting 2012-06-09.26 UT (ObsID 00035336054), one week later, the source had increased its luminosity by a factor of ~10.
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS ... more ABSTRACT We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback and cold fronts with an associated spiral structure. The cavity energetics imply they are powerful enough to compensate for cooling. Despite the evidence for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a few hundred solar masses per year cooling out of the X-ray phase, sufficient to power the emission line nebula. The coolest X-ray emitting gas and brightest nebula emission is offset by around 5 kpc from the radio and X-ray nucleus. Although the cluster has a regular appearance, its core shows density, temperature and pressure deviations over the inner 100 kpc, likely associated with the cold fronts. After correcting for ellipticity and projection effects, we estimate density fluctuations of ~4 per cent, while temperature, pressure and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ, able to accurately obtain thermodynamical cluster profiles, under the assumptions of hydrostatic equilibrium and spherical symmetry. The forward-fitting code compares model to observed profiles using Markov Chain Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius from the core, indicating a lack of hydrostatic equilibrium, deviations from spherical symmetry or non-thermal sources of pressure.
Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra H... more Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra HRC-I detector (about 0.1-10 keV energy range) from 2006 to 2012 with the main aim to detect X-rays from optical novae. We present a systematic analysis of all X-ray sources found in the 41 nova monitoring observations, along with 23 M 31 central field HRC-I observations available from the Chandra data archive starting in December 1999. Aims. Based on these observations, we studied the X-ray long-term variability of the source population and especially of X-ray binaries in M 31. Methods. We created a catalogue of sources, detected in the 64 available observations, which add up to a total exposure of about 1 Ms. To study the variability, we developed a processing pipeline to derive long-term Chandra HRC-I light curves for each source over the 13 years of observations. In the merged images we also searched for extended X-ray sources. Results. We present a point-source catalogue, containing 318 X-ray sources with detailed long-term variability information. 28 of which are published for the first time. The spatial and temporal resolution of the catalogue allows us to classify 115 X-ray binary candidates showing high X-ray variability or even outbursts in addition to 14 globular cluster X-ray binary candidates showing no significant variability. The analysis may suggest, that outburst sources are less frequent in globular clusters than in the field of M 31. We detected 7 supernova remnants, one of which is a new candidate and in addition resolved the first X-rays from a known radio supernova remnant. Besides 33 known optical nova/X-ray source correlations, we also discovered one previously unknown super-soft X-ray outburst and several new nova candidates. Conclusions. The catalogue contains a large sample of detailed long-term X-ray light curves in the M 31 central field, which helps to understand the X-ray population of our neighbouring spiral galaxy M 31.
Astronomy & Astrophysics, 2016
In high-resolution X-ray observations of the hot plasma in clusters of galaxies significant struc... more In high-resolution X-ray observations of the hot plasma in clusters of galaxies significant structures caused by AGN feedback, mergers, and turbulence can be detected. Many clusters have been observed by Chandra in great depth and at high resolution. Using archival data taken with the Chandra ACIS instrument the aim was to study thermodynamic perturbations of the X-ray emitting plasma and to apply this to better understand the thermodynamic and dynamic state of the intra cluster medium (ICM). Methods. We analysed deep observations for a sample of 33 clusters with more than 100 ks of Chandra exposure each at distances between redshift 0.025 and 0.45. The combined exposure of the sample is 8 Ms. Fitting emission models to different regions of the extended X-ray emission we searched for perturbations in density, temperature, pressure, and entropy of the hot plasma. For individual clusters we mapped the thermodynamic properties of the ICM and measured their spread in circular concentric annuli. Comparing the spread of different gas quantities to high-resolution 3D hydrodynamic simulations, we constrain the average Mach number regime of the sample to Mach 1D ≈ 0.16 ± 0.07. In addition we found a tight correlation between metallicity, temperature and redshift with an average metallicity of Z ≈ 0.3 ± 0.1 Z. Conclusions. This study provides detailed perturbation measurements for a large sample of clusters which can be used to study turbulence and make predictions for future X-ray observatories like eROSITA, Astro-H, and Athena.
articles by Florian Hofmann
Astronomy & Astrophysics, 2016
Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters... more Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters of galaxies. The line has been discussed as a possible decay signature of 7.1 keV sterile neutrinos, which have been proposed as a dark matter candidate. We aim at putting constraints on the proposed line emission in a large sample of Chandra-observed clusters and obtain limits on the mixing-angle in a 7.1 keV sterile neutrino dark matter scenario. For a sample of 33 high-mass clusters of galaxies we merge all observations from the Chandra data archive. Each cluster has more than 100 ks of combined exposure. The resulting high signal-to-noise spectra are used to constrain the flux of an unidentified line emission at 3.55 keV in the individual spectra and a merged spectrum of all clusters. Results. We obtained very detailed spectra around the 3.55 keV range and limits on an unidentified emission line. Assuming all dark matter were made of 7.1 keV sterile neutrinos the upper limits on the mixing angle are sin^2(2Θ) < 10.1 × 10^−11 from ACIS-I, and < 40.3 × 10^−11 from ACIS-S data at 99.7 per cent confidence level. Conclusions. We do not find evidence for an unidentified emission line at 3.55 keV. The sample extends the list of objects searched for an emission line at 3.55 keV and will help to identify the best targets for future studies of the potential dark matter decay line with upcoming X-ray observatories like Hitomi (Astro-H), eROSITA, and Athena.
We confirm an optical nova candidate, designated PNV J00424629+4113517 by the optical discoverers... more We confirm an optical nova candidate, designated PNV J00424629+4113517 by the optical discoverers K. Nishiyama and F. Kabashima (Miyaki-Argenteus Observatory, Japan), as a bright source on three Swift UVOT UVW2 filter prediscovery images (central wavelength 192.8 nm, FWHM 65.7 nm) with about 815 s exposure (ObsID 00032702015) starting on 2013 Feb. 22.070, 22.137, and 22.204 UT with brightness increasing from magnitude 16.88± 0.05, 16.70± 0.05, to 16.41± 0.04, respectively.
In an observation of the M 31 central region with the X-ray telescope (XRT) on board the Swift sa... more In an observation of the M 31 central region with the X-ray telescope (XRT) on board the Swift satellite (ObsId 0035336069, start time 2012-09-13.16 UT, exposure 2.64 ks), we detect about 60 counts from a new X-ray transient at position RA = 00h42m47.21 Dec = +41d14'05.5" (± 3.0", J2000, 90% confidence) after correcting systematic offsets (Kaaret 2002, ApJ, 578, 114), which we name SWIFT J004247.2+411405.
Monitoring observations of the M 31 central region with the X-ray telescope (XRT) on board the Sw... more Monitoring observations of the M 31 central region with the X-ray telescope (XRT) on board the Swift satellite show a new outburst of an X-ray transient. The position of the transient was derived from the brightest observation after correcting systematic offsets (using the catalog of Kaaret 2002, ApJ, 578, 114) to RA = 00h42m47.96s, Dec = +41d11'14.9" (± 5", J2000, 90% confidence level). The transient is first detected in observation 0035336064, starting on 2012-08-12.48 UT.
In recent monitoring observations of the M31 centre with the Swift satellite, we find an X-ray tr... more In recent monitoring observations of the M31 centre with the Swift satellite, we find an X-ray transient at RA=00:42:57.0 Dec=+41🔞42 (J2000, ePOS=4.26", 90% confidence) that is likely associated with the X-ray binary candidate XMMM31 J004256.7+411843.
For all Chandra HRC-I observations a source catalogue was created and the energy flux of each sou... more For all Chandra HRC-I observations a source catalogue was created and the energy flux of each source in each observation was derived. Fluxes were calculated assuming a generic power law spectrum and Galactic foreground absorption for each source. (5 data files).
In the latest monitoring observations of the central region of the Andromeda Galaxy with the Ultr... more In the latest monitoring observations of the central region of the Andromeda Galaxy with the Ultra-violet/Optical Telescope (UVOT) on board the Swift satellite from 2012-05-24.62 UT to 2012-07-19.09 UT, we observe five recently discovered novae and one apparent UV variable. For all observations the UVOT uvw1 filter (181-321nm) is used. The following table shows UVOT uvw1 magnitudes (Vega system) and 1σ errors for each observed M 31 nova (see identification at the top of each column).
We report the discovery of a UV-transient (Swift J00431492+4119130) in a monitoring observation o... more We report the discovery of a UV-transient (Swift J00431492+4119130) in a monitoring observation of the central region of the Andromeda Galaxy (M 31) with the Ultra-violet/Optical Telescope (UVOT) on board the Swift satellite (ObsID 00035336120, starting 2013-09-11.01 UT). The source is located at RA 00h 43m 14.93s, Dec +41d 19' 13.0" (J2000, ePos=0.5", 90% confidence level). Light curve information for filters uvw1 (central wavelength: 260 nm) and uvm2 (225 nm) is given in the table below (Vega system, 1σ statistical uncertainties).
We report the discovery of a new X-ray transient (CXOU J004233.2+411742) in a Chandra HRC-I obser... more We report the discovery of a new X-ray transient (CXOU J004233.2+411742) in a Chandra HRC-I observation of the Andromeda Galaxy starting 2012-06-01.90 UT (ObsID 13281). The position of the source is RA = 00h42m33.26s Dec = +41d17'42.7" (± 0.5 arcsec, J2000). The source is also detected in a quasi simultaneous Swift X-ray telescope (XRT) observation starting 2012-06-01.77 UT (ObsID 00035336053).In a Swift XRT observation starting 2012-06-09.26 UT (ObsID 00035336054), one week later, the source had increased its luminosity by a factor of ~10.
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS ... more ABSTRACT We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback and cold fronts with an associated spiral structure. The cavity energetics imply they are powerful enough to compensate for cooling. Despite the evidence for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a few hundred solar masses per year cooling out of the X-ray phase, sufficient to power the emission line nebula. The coolest X-ray emitting gas and brightest nebula emission is offset by around 5 kpc from the radio and X-ray nucleus. Although the cluster has a regular appearance, its core shows density, temperature and pressure deviations over the inner 100 kpc, likely associated with the cold fronts. After correcting for ellipticity and projection effects, we estimate density fluctuations of ~4 per cent, while temperature, pressure and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ, able to accurately obtain thermodynamical cluster profiles, under the assumptions of hydrostatic equilibrium and spherical symmetry. The forward-fitting code compares model to observed profiles using Markov Chain Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius from the core, indicating a lack of hydrostatic equilibrium, deviations from spherical symmetry or non-thermal sources of pressure.
Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra H... more Context. The central field of the Andromeda galaxy (M 31) has been monitored, using the Chandra HRC-I detector (about 0.1-10 keV energy range) from 2006 to 2012 with the main aim to detect X-rays from optical novae. We present a systematic analysis of all X-ray sources found in the 41 nova monitoring observations, along with 23 M 31 central field HRC-I observations available from the Chandra data archive starting in December 1999. Aims. Based on these observations, we studied the X-ray long-term variability of the source population and especially of X-ray binaries in M 31. Methods. We created a catalogue of sources, detected in the 64 available observations, which add up to a total exposure of about 1 Ms. To study the variability, we developed a processing pipeline to derive long-term Chandra HRC-I light curves for each source over the 13 years of observations. In the merged images we also searched for extended X-ray sources. Results. We present a point-source catalogue, containing 318 X-ray sources with detailed long-term variability information. 28 of which are published for the first time. The spatial and temporal resolution of the catalogue allows us to classify 115 X-ray binary candidates showing high X-ray variability or even outbursts in addition to 14 globular cluster X-ray binary candidates showing no significant variability. The analysis may suggest, that outburst sources are less frequent in globular clusters than in the field of M 31. We detected 7 supernova remnants, one of which is a new candidate and in addition resolved the first X-rays from a known radio supernova remnant. Besides 33 known optical nova/X-ray source correlations, we also discovered one previously unknown super-soft X-ray outburst and several new nova candidates. Conclusions. The catalogue contains a large sample of detailed long-term X-ray light curves in the M 31 central field, which helps to understand the X-ray population of our neighbouring spiral galaxy M 31.
Astronomy & Astrophysics, 2016
In high-resolution X-ray observations of the hot plasma in clusters of galaxies significant struc... more In high-resolution X-ray observations of the hot plasma in clusters of galaxies significant structures caused by AGN feedback, mergers, and turbulence can be detected. Many clusters have been observed by Chandra in great depth and at high resolution. Using archival data taken with the Chandra ACIS instrument the aim was to study thermodynamic perturbations of the X-ray emitting plasma and to apply this to better understand the thermodynamic and dynamic state of the intra cluster medium (ICM). Methods. We analysed deep observations for a sample of 33 clusters with more than 100 ks of Chandra exposure each at distances between redshift 0.025 and 0.45. The combined exposure of the sample is 8 Ms. Fitting emission models to different regions of the extended X-ray emission we searched for perturbations in density, temperature, pressure, and entropy of the hot plasma. For individual clusters we mapped the thermodynamic properties of the ICM and measured their spread in circular concentric annuli. Comparing the spread of different gas quantities to high-resolution 3D hydrodynamic simulations, we constrain the average Mach number regime of the sample to Mach 1D ≈ 0.16 ± 0.07. In addition we found a tight correlation between metallicity, temperature and redshift with an average metallicity of Z ≈ 0.3 ± 0.1 Z. Conclusions. This study provides detailed perturbation measurements for a large sample of clusters which can be used to study turbulence and make predictions for future X-ray observatories like eROSITA, Astro-H, and Athena.