arXiv subjects

S. Haemmerich

Publications and source records attributed to S. Haemmerich.

5 recordsLinked to original sources

arXiv2026

The SRG/eROSITA All-Sky Survey DR2: Cumulative X-ray catalogues from the first three surveys and multi-wavelength counterparts in the western Galactic hemisphere

The eROSITA telescope array on board the Spektrum-Roentgen-Gamma (SRG) mission began its all-sky survey program in December 2019, scanning the sky at an approximately six-month cadence. Here, we present new catalogues of point-like and extended X-ray sources derived from the first three completed eROSITA all-sky surveys (eRASS:3), covering the western Galactic hemisphere, which Germany's eROSITA consortium holds proprietary rights for. We describe the observational strategy, data processing, and analysis pipelines. We also characterise the resulting X-ray source populations. The eRASS:3 main catalogue contains nearly two million sources, including 1,911,744 point-like and 63,796 extended sources, detected in the 0.2-2.3 keV energy band, eROSITA's most sensitive energy window. This volume has doubled the X-ray source content of eRASS1 and provides a comprehensive census of X-ray-emitting objects across diverse astrophysical classes. We also released a secondary hard catalogue of nearly 15,000 sources detected in the harder 2.3-5.0 keV energy band. In addition, we released six catalogues, three for the main sample and three for the hard sample, in which we identify and classify the optical and infrared counterparts of eRASS:3 point-like sources. This approach delivers a homogeneous, high-quality identification of mostly extragalactic X-ray emitters; for example, we estimate that approximately 88% of the 1.4 million counterparts identified within the footprints of the Legacy Survey Imaging for DESI are extragalactic sources. This work has enabled the generation of samples optimised for completeness and purity, while expanding the discovery space for rare populations. The second data release (DR2) of the SRG/eROSITA all-sky survey is a catalogue-only release, comprising the catalogues presented in this work together with an updated version of the eROSITA upper flux limit server.

astro-ph.HE↗

arXiv2025

BlazEr1: The eROSITA Blazar Catalog. Blazars and Blazar Candidates in the First eROSITA Survey

Aims. eROSITA, on board the Spectrum Roentgen Gamma (SRG) spacecraft, performed its first X-ray all-sky survey (eRASS1) between December 2019 and June 2020. It detected about 930000 sources, providing us with an unprecedented opportunity for a detailed blazar census. We present the properties of blazars and blazar candidates in eRASS1 and the compilation of the eROSITA blazar catalog. Methods. We compiled a list of blazar and blazar candidates from the literature and matched it with the eRASS1 catalog, constructing the Blazars in eRASS1 (BlazEr1) catalog. For sources with more than 50 counts, we obtained their X-ray spectral properties. We compiled multiwavelength data from the radio to the gamma-ray regimes for all sources, including multiwavelength spectral indices and redshifts. The full catalog is available online. Results. We present the BlazEr1 catalog, containing 5865 sources, of which 2106 are associated with confirmed blazars. For 2966 sources, eROSITA provides the first X-ray data. The contamination from non-blazar sources of the entire sample is less than 11%. Most candidates exhibit properties typical for blazars. We present the properties of the entire X-ray detected blazar population, including the distributions of X-ray luminosities and photon indices, multiwavelength properties, and the blazar log N-log S distribution. Our catalog provides follow up targets, such as potential MeV and TeV blazars. Conclusions. The BlazEr1 catalog provides a compilation of X-ray detected blazars and blazar candidates. The catalog serves as a starting point for exploiting further eROSITA surveys using the same methodology, enabling us to study the X-ray variability and a large number of spectral energy distributions of blazars in the future.

astro-ph.HE↗

arXiv2024

An X-ray flaring event and a variable soft X-ray excess in the Seyfert LCRS B040659.9-385922 as detected with eROSITA

Extreme continuum variability in AGNs can indicate extreme changes in accretion flows onto supermassive black holes. We explore the multiwavelength nature of a continuum flare in the Seyfert LCRS B040659.9$-$385922. The all-sky X-ray surveys conducted by the eROSITA showed that its X-ray flux increased by a factor of roughly five over six months, and concurrent optical photometric monitoring with the ATLAS showed a simultaneous increase. We triggered a multiwavelength follow-up monitoring program (XMM, NICER; optical spectroscopy) to study the evolution of the accretion disk, broad-line region, and X-ray corona. During the campaign, X-ray and optical continuum flux subsided over roughly six months. We detected a soft X-ray excess near the flare peak and after it subsided, both exhibiting a power-law (nonthermal) behavior. We modeled the broadband optical/UV/X-ray spectral energy distribution at both the flare peak and post-flare times with the AGNSED model, incorporating thermal disk emission into the optical/UV and warm thermal Comptonization in the soft X-rays. Additionally, we find that the broad Heii $\lambda$4686 emission line fades significantly as the optical/UV/X-ray continuum fades, which could indicate a substantial flare of disk emission above 54 eV. We also observed a redshifted broad component in the H${\beta}$ emission line that is present during the high flux state of the source and disappears in subsequent observations. We witnessed a likely sudden strong increase in local accretion rate, which manifested itself via an increase in accretion disk emission and thermal Comptonization emission in the soft X-rays, followed by a decrease in accretion and Comptonized luminosity. The physical processes leading to such substantial variations are still an open question, and future continuous monitoring along with multi-wavelength studies will shed some light on it.

astro-ph.HE↗

arXiv2023

Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert

Context. Multiwavelength studies of transients in actively accreting supermassive black holes have revealed that large-amplitude variability is frequently linked to significant changes in the optical spectra -- a phenomenon known as changing-look AGN (CLAGN).} Aims. In 2020, the Zwicky Transient Facility detected a transient flaring event in the type 1.9 AGN LEDA 1154204, wherein brightness sharply increased by 0.55 mag in one month, then began to decay. Spectrum Roentgen Gamma (SRG)/eROSITA also observed the object as part of its all-sky X-ray surveys, after the flare had started decaying. Methods. We performed a three-year, multiwavelength follow-up campaign to track the source's spectral and temporal characteristics, during the post-flare fading. This campaign included optical spectroscopy, X-ray spectroscopy and photometry, and UV, optical, and IR continuum photometry. Results. Optical spectra taken near the flare peak revealed a broad double-peaked H$\beta$ emission and a blue continuum, both undetected in a 2005 archival spectrum; broad H$\beta$ had increased by a factor $>$5--6. Then, from late 2020 through 2023, broad Balmer line flux faded as the continuum faded, with Balmer decrement increasing by $\sim$2.2, consistent with the expected ionization response. The X-ray spectrum exhibits no significant spectral variability despite dramatic flux variation -- a factor of 17. There is no evidence of a soft X-ray excess, indicating an energetically unimportant warm corona. Conclusions. The transient event was likely triggered by a disk instability in a pre-existing AGN-like accretion flow, culminating in the observed multiwavelength variability -- X-rays via thermal Comptonization, BLR illumination, and IR dust echo -- and CLAGN event.

astro-ph.HE↗

arXiv2023

VLBI Scrutiny of a New Neutrino-Blazar Multiwavelength-Flare Coincidence

In the past years, evidence has started piling up that some high-energy cosmic neutrinos can be associated with blazars in flaring states. On February 26, 2022, a new blazar-neutrino coincidence has been reported: the track-like neutrino event IC220225A detected by IceCube is spatially coincident with the flat-spectrum radio quasar PKS 0215+015. Like previous associations, this source was found to be in a high optical and $γ$-ray state. Moreover, the source showed a bright radio outburst, which substantially increases the probability of a true physical association. We have performed six observations with the VLBA shortly after the neutrino event with a monthly cadence and are monitoring the source with the Effelsberg 100m-Telescope, and with the Australia Compact Telescope Array. Here, we present first results on the contemporary parsec-scale jet structure of PKS 0215+015 in total intensity and polarization to constrain possible physical processes leading to neutrino emission in blazars.

astro-ph.HE↗