Galactic Plane Survey Research Articles

H i galaxy signatures in the SARAO MeerKAT galactic plane survey – II. The Local Void and its substructure

ABSTRACT The Local Void is one of the nearest large voids, located at a distance of 23 Mpc. It lies largely behind the Galactic Bulge and is therefore extremely difficult to observe. We use H i 21 cm emission observations from the SARAO MeerKAT Galactic Plane Survey (SMGPS) to study the Local Void and its surroundings over the Galactic longitude range 329° < ℓ < 55°, Galactic latitude |b| < 1.5°, and redshift cz < 7500 $\rm km \, s^{-1}$. We have detected 291 galaxies to median rms sensitivity of 0.44 mJy per beam per 44 $\rm km \, s^{-1}$ channel. We find 17 galaxies deep inside the Void, 96 at the border of the Void, while the remaining 178 galaxies are in average density environments. The extent of the Void is ∼58 Mpc. It is severely underdense for the longitude range 350° < ℓ < 35° up to redshift z < 4500 $\rm km \, s^{-1}$. The galaxies in the Void tend to have H i masses that are lower (by approximately 0.25 dex) than their average density counterparts. We find several potential candidates for small groups of galaxies, of which two groups (with 3 members and 5 members) in the Void show signs of filamentary substructure within the Void.

H i galaxy signatures in the SARAO MeerKAT Galactic Plane Survey – I. Probing the richness of the great attractor wall across the inner zone of avoidance

ABSTRACT This paper presents the first H i results extracted from the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) – a narrow strip (Δb ∼ 3°) along the southern Milky Way. The primary goal consisted in tracing the great attractor (GA) wall across the innermost zone of avoidance. We reduced a segment spanning the longitude range 302° ≤ ℓ ≤ 332° for the redshift range z ≤ 0.08. The superb SMGPS sensitivity (rms = 0.3–0.5 mJy beam−1 per 44 km s−1 channel) and angular resolution (∼31″ × 26″) lead to a detection limit of log(MH i/M⊙) ≥ 8.5 at the GA distance ($\mbox{$V_{\rm {hel}}$}\, \sim 3500{\!-\!}6500$ km s−1). A total of 477 galaxy candidates were identified over the full redshift range. A comparison of the few H i detections with counterparts in the literature (mostly HIZOA) found the H i fluxes and other H i parameters to be highly consistent. The continuation of the GA wall is confirmed through a prominent overdensity of N = 214 detections in the GA distance range. At higher latitudes, the wall moves to higher redshifts, supportive of a possible link with the Ophiuchus cluster located behind the Galactic Bulge. This deep interferometric H i survey demonstrates the power of the SMGPS in improving our insight of large-scale structures at these extremely low latitudes, despite the high obscuration and continuum background.

ALMA-IMF. VIII. Combination of Interferometric Continuum Images with Single-dish Surveys and Structural Analysis of Six Protoclusters

We present the combination of ALMA-IMF and single-dish continuum images from the MUSTANG-2 Galactic Plane Survey (MGPS90) at 3 mm and the Bolocam Galactic Plane Survey (BGPS) at 1 mm. Six and 10 out of the 15 ALMA-IMF fields are combined with MGPS90 and BGPS, respectively. The combination is made via the feathering technique. We used the dendrogram algorithm throughout the combined images, and performed further analysis in the six fields with the combination in both bands (G012.80, W43-MM1, W43-MM2, W43-MM3, W51-E, W51-IRS2). In these fields, we calculated spectral index maps and used them to separate regions dominated by dust or free–free emission, and then performed further structural analysis. We report the basic physical parameters of the dust-dominated (column densities, masses) and ionized (emission measures, hydrogen ionization photon rates) structures. We also searched for multiscale relations in the dust-dominated structures across the analyzed fields, finding that the fraction of mass in dendrogram leaves (which we label leaf mass efficiency (LME)) as a function of molecular gas column density follows a similar trend: a rapid, exponential-like growth, with maximum values approaching 100% in most cases. The observed behavior of the LME with the gas column is tentatively interpreted as an indicator of large star formation activity within the ALMA-IMF protoclusters. W51-E and G012.80 stand out as cases with comparatively large and reduced potential for further star formation, respectively.

A global view on star formation: The GLOSTAR Galactic plane survey

As part of the GLObal view of STAR formation in the Milky Way (GLOSTAR) survey, we present the high-resolution continuum source catalog for the regions (ℓ = 2° −28°, 36° −40°, 56° −60°, and |b| < 1.0°), observed with the Karl G. Jansky Very Large Array (VLA) in its B-configuration. The continuum images were optimized to detect compact sources on angular scales up to 4″, and have a typical noise level of 1σ ~ 0.08 mJy beam−1 for an angular resolution of 1″, which makes GLOSTAR currently the highest resolution as well as the most sensitive radio survey of the northern Galactic plane at 4–8 GHz. We extracted 13354 sources above a threshold of 5σ and 5437 sources above 7σ that represent the high-reliability catalog. We determined the in-band spectral index (α) for the sources in the 7σ-threshold catalog. The mean value is α = −0.6, which indicates that the catalog is dominated by sources emitting nonthermal radio emission. We identified the most common source types detected in radio surveys: 251 H II region candidates (113 new), 282 planetary nebulae (PNe) candidates (127 new), 784 radio star candidates (581 new), and 4080 extragalactic radio source candidates (2175 new). A significant fraction of H II regions and PNe candidates have α < −0.1 indicating that these candidates could contain radio jets, winds or outflows from high-mass and low-mass stellar objects. We identified 245 variable radio sources by comparing the flux densities of compact sources from the GLOSTAR survey and the Co-Ordinated Radio “N” Infrared Survey for High-mass star formation (CORNISH), and find that most of them are infrared quiet. The catalog is typically 95% complete for point sources at a flux density of 0.6 mJy (i.e., a typical 7σ level) and the systematic positional uncertainty is ≲ 0″.1.

The Swift Deep Galactic Plane Survey (DGPS) Phase I Catalog

The Swift Deep Galactic Plane Survey (DGPS) is a Swift Key Project consisting of 380 tiled pointings covering ∼40 deg2 of the Galactic plane between longitude 10 < ∣l∣ < 30 deg and latitude ∣b∣ < 0.5 deg. Each pointing has a 5 ks exposure, yielding a total of 1.9 Ms spread across the entire survey footprint. Phase I observations were carried out between 2017 March and 2021 May. The survey is complete to depth L X > 1034 erg s−1 to the edge of the Galaxy. The main survey goal is to produce a rich sample of new X-ray sources and transients, while also covering a broad discovery space. Here, we introduce the survey strategy and present a catalog of sources detected during Phase I observations. In total, we identify 928 X-ray sources, of which 348 are unique to our X-ray catalog. We report on the characteristics of sources in our catalog and highlight sources newly classified and published by the DGPS team.

Clump-scale Gas Infall in High-mass Star Formation: A Multitransition View with James Clerk Maxwell Telescope HCN (4–3) Mapping

Gas infall motions play a crucial role in high-mass star formation and are characterized by observable signatures of blueshifted asymmetric spectral line profiles (“blue profiles”). However, the connection between blue profiles and infall motions is unclear due to complex gas motions at parsec scales. In this study, we present the results of an HCN (4–3) mapping survey conducted with the James Clerk Maxwell Telescope, toward 38 massive clumps exhibiting blue profiles in HCO+ (3–2). We extract 34 HCN cores from the 38 observed fields. The core-averaged spectra show various line profiles, indicating that blue-profile HCO+ (3–2) does not guarantee the same in HCN (4–3). Through non-LTE radiative-transfer calculations, we attribute the low detection rate of high-J blue profiles to a combination of insufficient HCN (4–3) opacity and the intricate gas motion across different density layers. A comparison between the MALT90 and Bolocam Galactic Plane Survey line surveys highlights the importance of appropriate tracers, high spectral resolution, and column density thresholds when searching for blue profiles. We select 11 reliable infall candidates and adopt the Hill5 model to fit the infall velocity of 0.2–1.6 km s−1, corresponding to 5%–74% of freefall velocity. Assuming a spherically collapsing model, we estimate the median and mean mass infall rates to be 4.5 × 10−3 and 7.6 × 10−3 M ⊙ yr−1, respectively. The consistency of the mass infall rates among different transitions suggests a steady accretion process from the clump gas envelope to the inner region.

SRG/ART-XC Galactic Plane Survey near Galactic Longitude L 20◦ : Catalog of Sources

We present a catalog of sources detected by theMikhail Pavlinsky ART-XC telescope onboardthe SRG space observatory during the observations of the Galactic plane region near a longitude l 20◦(L20 field) in October 2019. The L20 field was observed four times in the scanning mode, which provideda uniform coverage of the sky region with a total area of 24 sq. deg with a median sensitivity of 8 ×10−13 erg s−1 cm−2 (at 50% detection completeness) in the 4–12 keV energy band. As a result, we havedetected 29 X-ray sources at a statistically significant level, 11 of which have not been detected previouslyby other X-ray observatories. Preliminary estimates show that four of themcan presumably be extragalacticin nature. We also show that the source SRGA J183220.1−103508 (CXOGSG J183220.8−103510) ismost likely a galaxy cluster containing a bright radio galaxy at redshift z 0.121.

PulsarX: A new pulsar searching package

Context. Pulsar surveys with modern radio telescopes are becoming increasingly computationally demanding. This is particularly true for wide field-of-view pulsar surveys with radio interferometers and those conducted in real or quasi-real time. These demands result in data analysis bottlenecks that can limit the parameter space covered by the surveys and diminish their scientific return. Aims. In this paper we address the computational challenge of ‘candidate folding’ in pulsar searching, presenting a novel, efficient approach designed to optimise the simultaneous folding of large numbers of pulsar candidates. We provide a complete folding pipeline appropriate for large-scale pulsar surveys that includes radio frequency interference mitigation, de-dispersion, folding, and parameter optimisation. Methods. By leveraging the fast discrete dispersion measure transform (FDMT) algorithm, we have developed an optimised and cache-friendly implementation that we term the pruned FDMT (pFDMT). This implementation is specifically designed for candidate folding scenarios where the candidates are broadly distributed in dispersion measure space. The pFDMT approach efficiently reuses intermediate processing results and prunes the unused computation paths, resulting in a significant reduction in arithmetic operations. In addition, we propose a novel folding algorithm based on the Tikhonov-regularised least squares method that can improve the time resolution of the pulsar profile. Results. We present the performance of its real-world application as an integral part of two major pulsar search projects conducted with the MeerKAT telescope: the MPIfR-MeerKAT Galactic Plane Survey (MMGPS) and the Transients and Pulsars with MeerKAT (TRAPUM) project. In our processing of approximately 500 candidates, the theoretical number of de-dispersion operations can be reduced by a factor of around 50 when compared to brute-force de-dispersion, which scales with the number of candidates.

Identification of 1RXS J165424.6-433758 as a Polar Cataclysmic Variable

We present the results of our X-ray, ultraviolet, and optical follow-up campaigns of 1RXS J165424.6-433758, an X-ray source detected with the Swift Deep Galactic Plane Survey. The source X-ray spectrum (Swift and NuSTAR) is described by thermal bremsstrahlung radiation with a temperature of kT = 10.1 ± 1.2 keV, yielding an X-ray (0.3–10 keV8) luminosity L X = (6.5 ± 0.8) × 1031 erg s−1 at a Gaia distance of 460 pc. Spectroscopy with the Southern African Large Telescope revealed a flat continuum dominated by emission features, demonstrating an inverse Balmer decrement, the λ4640 Bowen blend, almost a dozen He i lines, and He ii λ4541, λ4686, and λ5411. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, P orb = 2.87 hr, which fell well within the cataclysmic variable (CV) period gap between 2 and 3 hr. These features classify 1RXS J165424.6-433758 as a nearby polar magnetic CV.

A global view on star formation: The GLOSTAR Galactic plane survey

Context. Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation. Aims. We aim to investigate the properties of molecular gas structures on different linear scales with the 4.8 GHz formaldehyde (H2CO) absorption line in Cygnus X. Methods. As part of the GLOSTAR Galactic plane survey, we performed large-scale (7º×3º) simultaneous H2CO (11,0–11,1) spectral line and radio continuum imaging observations toward Cygnus X at λ ~6 cm with the Karl G. Jansky Very Large Array and the Effelsberg 100 m radio telescope. We used auxiliary HI, 13CO (1–0), dust continuum, and dust polarization data for our analysis. Results. Our Effelsberg observations reveal widespread H2CO (11,0–11,1) absorption with a spatial extent of ≳50 pc in Cygnus X for the first time. On large scales of 4.4 pc, the relative orientation between the local velocity gradient and the magnetic field tends to be more parallel at H2 column densities of ≳1.8×1022 cm−2. On the smaller scale of 0.17 pc, our VLA+Effelsberg combined data reveal H2CO (11,0–11,1) absorption only towards three bright HII regions. Our observations demonstrate that H2CO (11,0–11,1) is optically thin in general. The kinematic analysis supports the assertion that molecular clouds generally exhibit supersonic motions on scales of 0.17−4.4 pc. We show a non-negligible contribution of the cosmic microwave background radiation to the extended absorption features in Cygnus X. Our observations suggest that H2CO (11,0–11,1) can trace molecular gas with H2 column densities of ≳5 × 1021 cm−2 (i.e., AV ≳ 5). The ortho-H2CO fractional abundance with respect to H2 has a mean value of 7.0 × 10−10. A comparison of the velocity dispersions on different linear scales suggests that the velocity dispersions of the dominant −3 km s−1 velocity component in the prominent DR21 region are nearly identical on scales of 0.17−4.4 pc, which deviates from the expected behavior of classic turbulence.

A comparison of the Milky Way’s recent star formation revealed by dust thermal emission and high-mass stars

We present a comparison of the Milky Way’s star formation rate (SFR) surface density (∑SFR) obtained with two independent state-of-the-art observational methods. The first method infers ΣSFR from observations of the dust thermal emission from interstellar dust grains in far-infrared wavelengths registered in the Herschel infrared Galactic Plane Survey (Hi-GAL). The second method determines ΣSFR by modeling the current population of O-, B-, and A-type stars in a 6 kpc × 6 kpc area around the Sun. We find an agreement between the two methods within a factor of two for the mean SFRs and the SFR surface density profiles. Given the broad differences between the observational techniques and the independent assumptions in the methods for computing the SFRs, this agreement constitutes a significant advance in our understanding of the star formation of our Galaxy and implies that the local SFR has been roughly constant over the past 10 Myr.

Swift Deep Galactic Plane Survey classification of Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable

ABSTRACT Here, we present the results of our multiwavelength campaign aimed at classifying Swift J170800−402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with the Neil Gehrels Swift Observatory, Chandra X-ray Observatory, Neutron star Interior Composition Explorer (NICER), X-ray Multi-Mirror Mission (XMM–Newton), Nuclear Spectroscopic Telescope Array (NuSTAR), and the Southern African Large Telescope (SALT), as well as multiwavelength archival observations from Gaia, VST Photometric Hα Survey, and VISTA Variables in the Via Lactea. The source displays a periodicity of 784 s in our XMM–Newton observation. The X-ray spectrum (XMM–Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of kT ≈ 30 keV. The phase-folded X-ray light curve displays a double-peaked, energy-dependent pulse profile. We used Chandra to precisely localize the source, allowing us to identify and study the multiwavelength counterpart. Spectroscopy with SALT identified a Balmer H α line, and potential He i lines, from the optical counterpart. The faintness of the counterpart (r ≈ 21 AB mag) favours a low-mass donor star. Based on these criteria, we classify Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s.

The Galactic Population of Pulsar Wind Nebulae and the Contribution of Its Unresolved Component to the Diffuse High-Energy Gamma-ray Emission

In this work, we provide a phenomenological description of the population of galactic TeV pulsar wind nebulae (PWNe) based on suitable assumptions for their space and luminosity distribution. We constrain the general features of this population by assuming that it accounts for the majority of bright sources observed by H.E.S.S. Namely, we determine the maximal luminosity and fading time of PWNe (or, equivalently, the initial period and magnetic field of the pulsar powering the observed emission) by performing a statistical analysis of bright sources in the H.E.S.S. galactic plane survey. This allows us to estimate the total luminosity and flux produced by galactic TeV PWNe. We also evaluate the cumulative emission from PWNe that cannot be resolved by H.E.S.S., showing that this contribution can be as large as ∼40% of the total flux from resolved sources. We argue that also in the GeV domain, a relevant fraction of this population cannot be resolved by Fermi-LAT, providing a non-negligible contribution to the large-scale diffuse emission in the inner galaxy. This additional component could naturally account for a large part of the spectral index variation observed by Fermi-LAT, weakening the evidence of cosmic ray spectral hardening in the inner galaxy. Finally, the same result is obtained for PeV energy, for which the sum of the diffuse component, due to unresolved PWNe, and the truly diffuse emission well saturates the recent Tibet AS-γ data, without the need to introduce a progressive hardening of the cosmic-ray spectrum toward the galactic centre.

Dust emissions and OH masers: evidence for tracing advanced stages of HMPOs

We conducted a study using the Green Bank Telescope to investigate the correlation between OH masers and mm emission in high mass star forming regions (HMSFRs) using archival data from the Bolocam Galactic Plane Survey (BGPS) at 1.1 mm. Our objective was to gain insights into the physical characteristics, dynamics, and evolutionary status of these regions. Among the 27 OH maser sources examined, we found that 23 of them exhibited associations with multiple peaks of millimeter emission within a 30' radius. Notably, two high mass protostellar object candidates, namely IRAS 18089-1732 and IRAS 19035 + 0641, displayed consistent tracers. Interferometer observations further supported our findings. Compared to methanol masers, OH masers exhibited a lower level of consistency with mm sources, with a coincidence rate of 11% at offsets of 0.5 arcsec or less. At 3'' offset, 13 (48%) OH maser sources were found to be associated with mm continuum emission, with 11 previously classified as evolved HMSFRs. However, at larger offsets of 20'', the association rate increased significantly to 63%, indicating a broader spatial distribution of OH masers. This variation in offsets could be attributed to the presence of OH masers from different layers of the circumstellar disk. Our results suggest that the association between OH masers and mm emission may serve as a tracer for advanced stages of high mass protostellar objects. Future high angular resolution observations are recommended to enhance our understanding of this association.

FAST Polarization Mapping of the Supernova Remnant VRO 42.05.01

We have obtained the polarization data cube of the supernova remnant (SNR) VRO 42.05.01 at 1240 MHz using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). Three-dimensional Faraday synthesis is applied to the FAST data to derive the Faraday depth spectrum. The peak Faraday depth map shows a large area of enhanced foreground rotation measure (RM) of ∼60 rad m−2 extending along the remnant’s “wing” section, which coincides with a large-scale H i shell at −20 km s−1. The two depolarization patches within the “wing” region with RMs of 97 rad m−2 and 55 rad m−2 coincide with two H i structures in the H i shell. Faraday screen model fitting on the Canadian Galactic Plane Survey 1420 MHz full-scale polarization data reveals a distance of (0.7–0.8)d SNR in front of the SNR with enhanced regular magnetic field there. The highly piled-up magnetic field indicates that the H i shell at −20 km s−1 could originate from an old evolved SNR.

Large-scale velocity-coherent filaments in the SEDIGISM survey: Association with spiral arms and the fraction of dense gas

Context. Filamentary structures in the interstellar medium are closely related to star formation. It is possible that the dense gas mass fraction (DGMF) or clump formation efficiency in large-scale filaments determine whether or not they end up hosting star formation activity. Aims. We aim to automatically identify large-scale filaments, as well as characterizing them, investigating their association with Galactic structures, and studying their DGMFs. Methods. We used a modified minimum spanning tree (MST) algorithm to chain parsec-scale 13CO clumps previously extracted from the Structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium (SEDIGISM) survey. The MST connects nodes in a graph such that the sum of edge lengths is at a minimum. A modified MST also ensures the velocity coherence between nodes, so that the identified filaments are coherent in position-position-velocity (PPV) space. Results. We generated a catalog of 88 large-scale (&gt;10 pc) filaments in the inner Galactic plane (with −60° &lt; l &lt; 18° and |b| &lt; 0.5°). These SEDIGISM filaments are larger and less dense than MST filaments previously identified from the Bolocam Galactic Plane Survey (BGPS) and the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). We find that eight of the filaments run along spiral arms and can be regarded as the “bones” of the Milky Way. We also found three bones associated with the Local spur in PPV space. By compiling 168 large-scale filaments with available DGMF across the Galaxy, namely, an order of magnitude more than previously investigated, we find that DGMFs are not correlated with Galactic location. We also find that bones have higher DGMFs than other filaments.

The MPIfR–MeerKAT Galactic Plane Survey – I. System set-up and early results

ABSTRACT Galactic plane radio surveys play a key role in improving our understanding of a wide range of astrophysical phenomena. Performing such a survey using the latest interferometric telescopes produces large data rates necessitating a shift towards fully or quasi-real-time data analysis with data being stored for only the time required to process them. We present here the overview and set-up for the 3000-h Max-Planck-Institut für Radioastronomie (MPIfR)–MeerKAT Galactic Plane Survey (MMGPS). The survey is unique by operating in a commensal mode, addressing key science objectives of the survey including the discovery of new pulsars and transients and studies of Galactic magnetism, the interstellar medium and star formation rates. We explain the strategy coupled with the necessary hardware and software infrastructure needed for data reduction in the imaging, spectral, and time domains. We have so far discovered 78 new pulsars including 17 confirmed binary systems of which two are potential double neutron star systems. We have also developed an imaging pipeline sensitive to the order of a few tens of micro-Jansky ($\mu{\rm Jy}$) with a spatial resolution of a few arcseconds. Further science operations with an in-house built S-band receiver operating between 1.7 and 3.5 GHz are about to commence. Early spectral line commissioning observations conducted at S-band, targeting transitions of the key molecular gas tracer CH at 3.3 GHz already illustrate the spectroscopic capabilities of this instrument. These results lay a strong foundation for future surveys with telescopes like the Square Kilometre Array (SKA).

An infrared transient from a star engulfing a planet.

Planets with short orbital periods (roughly under 10 days) are common around stars like the Sun1,2. Stars expand as they evolve and thus we expect their close planetary companions to be engulfed, possibly powering luminous mass ejections from the host star3-5. However, this phase has never been directly observed. Here we report observations of ZTF SLRN-2020, a short-lived optical outburst in the Galactic disk accompanied by bright and long-lived infrared emission. The resulting light curve and spectra share striking similarities with those of red novae6,7-a class of eruptions now confirmed8 to arise from mergers of binary stars. Its exceptionally low optical luminosity (approximately 1035 erg s-1) and radiated energy (approximately 6.5 × 1041 erg) point to the engulfment of a planet of fewer than roughly ten Jupiter masses by its Sun-like host star. We estimate the Galactic rate of such subluminous red novae to be roughly between 0.1 and several per year. Future Galactic plane surveys should routinely identify these, showing the demographics of planetary engulfment and the ultimate fate of planets in the inner Solar System.

New eruptive variable(s) in the RAFGL 7009S H ii region

ABSTRACT Eruptions of young stellar objects (YSOs) are rare events, therefore a new outburst is always noteworthy. We present two new high-amplitude variable YSOs, J183421.85−055951.0 (#1) and J183421.39−055937.7 (#2), in the RAFGL 7009S star-forming region. We find them in the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Plane Survey data base, and supplement these data with archived infrared and millimetre photometric and spectral images and data from the Spitzer Infrared Array Camera, the K-band Multi-Object Spectrograph, and the Atacama Large Millimeter/submillimeter Array data bases. The outburst in #1 occurred in the period 2007–2011, during which the brightness increased by ∼2.7 mag in the K band and by ∼2.5 mag in the 3.6 μm band. The colour indices indicate a YSO in Class I/II evolutionary stage. After outburst, the K-band spectrum shows the CO band, Brγ, Mg i in absorption and H2 in emission – characteristics associated with a FU Orionis (FUors)-type eruptive variable. Object #1 is associated with an outflow detected in the near-infrared and millimetre ranges, mainly in the H2, SiO, HCO+, and HCN lines. Object #2 only shows high-amplitude variability in the K band (ΔK = 2.0 mag) while its colour indices before outburst indicate a YSO at an early evolutionary stage. There is no obvious outflow activity associated with this object. We classify #1 as a FUor-type eruptive variable based on the obtained data. The limited information on #2 makes it difficult to draw definite conclusions about the nature of its variability.

Detecting and characterizing pulsar haloes with the Cherenkov telescope array

ABSTRACTThe recently identified source class of pulsar haloes may be numerous and bright enough in the TeV energy range to constitute a large fraction of the sources that will be observed with the Cherenkov Telescope Array (CTA). In this work, we quantify the prospects for detecting and characterizing pulsar haloes in observations of the projected Galactic Plane Survey (GPS), using a simple phenomenological diffusion model for individual pulsar haloes and their population in the Milky Way. Our ability to uncover pulsar haloes and constrain their main physical parameters in the CTA GPS is assessed in the framework of a full spatial-spectral likelihood analysis of simulated survey observations, using the most recent estimates for the instrument response function and prototypes for the science tools. For a model setup representative of the halo around Geminga, we find that about three hundred objects could give rise to detectable emission in the GPS survey. Yet, only a third of them could be identified through their energy-dependent morphology, and only one-tenth of them would allow the derivation of strong constraints on key physical parameters like the magnitude or extent of suppressed diffusion around the pulsar. We also provide a list of known pulsars that could be hosting a detectable (Geminga-like) halo in the GPS and assess the robustness of our findings against several systematic uncertainties.