arXiv subjects

F. Martinelli

Publications and source records attributed to F. Martinelli.

At least 19 recordsLinked to original sources

arXiv2023

Radiation Tolerance of SiGe BiCMOS Monolithic Silicon Pixel Detectors without Internal Gain Layer

A monolithic silicon pixel prototype produced for the MONOLITH ERC Advanced project was irradiated with 70 MeV protons up to a fluence of 1 x 10^16 1 MeV n_eq/cm^2. The ASIC contains a matrix of hexagonal pixels with 100 {\mu}m pitch, readout by low-noise and very fast SiGe HBT frontend electronics. Wafers with 50 {\mu}m thick epilayer with a resistivity of 350 {\Omega}cm were used to produce a fully depleted sensor. Laboratory tests conducted with a 90Sr source show that the detector works satisfactorily after irradiation. The signal-to-noise ratio is not seen to change up to fluence of 6 x 10^14 n_eq /cm^2 . The signal time jitter was estimated as the ratio between the voltage noise and the signal slope at threshold. At -35 {^\circ}C, sensor bias voltage of 200 V and frontend power consumption of 0.9 W/cm^2, the time jitter of the most-probable signal amplitude was estimated to be 21 ps for proton fluence up to 6 x 10 n_eq/cm^2 and 57 ps at 1 x 10^16 n_eq/cm^2 . Increasing the sensor bias to 250 V and the analog voltage of the preamplifier from 1.8 to 2.0 V provides a time jitter of 40 ps at 1 x 10^16 n_eq/cm^2.

physics.ins-det↗

arXiv2023

20 ps Time Resolution with a Fully-Efficient Monolithic Silicon Pixel Detector without Internal Gain Layer

A second monolithic silicon pixel prototype was produced for the MONOLITH project. The ASIC contains a matrix of hexagonal pixels with 100 {\mu}m pitch, readout by a low-noise and very fast SiGe HBT frontend electronics. Wafers with 50 {\mu}m thick epilayer of 350 {\Omega}cm resistivity were used to produce a fully depleted sensor. Laboratory and testbeam measurements of the analog channels present in the pixel matrix show that the sensor has a 130 V wide bias-voltage operation plateau at which the efficiency is 99.8%. Although this prototype does not include an internal gain layer, the design optimised for timing of the sensor and the front-end electronics provides a time resolutions of 20 ps.

physics.ins-det↗

arXiv2022

Testbeam Results of the Picosecond Avalanche Detector Proof-Of-Concept Prototype

The proof-of-concept prototype of the Picosecond Avalanche Detector, a multi-PN junction monolithic silicon detector with continuous gain layer deep in the sensor depleted region, was tested with a beam of 180 GeV pions at the CERN SPS. The prototype features low noise and fast SiGe BiCMOS frontend electronics and hexagonal pixels with 100 {\mu}m pitch. At a sensor bias voltage of 125 V, the detector provides full efficiency and average time resolution of 30, 25 and 17 ps in the overall pixel area for a power consumption of 0.4, 0.9 and 2.7 W/cm^2, respectively. In this first prototype the time resolution depends significantly on the distance from the center of the pixel, varying at the highest power consumption measured between 13 ps at the center of the pixel and 25 ps in the inter-pixel region.

physics.ins-det↗

arXiv2022

Picosecond Avalanche Detector -- working principle and gain measurement with a proof-of-concept prototype

The Picosecond Avalanche Detector is a multi-junction silicon pixel detector based on a $\mathrm{(NP)_{drift}(NP)_{gain}}$ structure, devised to enable charged-particle tracking with high spatial resolution and picosecond time-stamp capability. It uses a continuous junction deep inside the sensor volume to amplify the primary charge produced by ionizing radiation in a thin absorption layer. The signal is then induced by the secondary charges moving inside a thicker drift region. A proof-of-concept monolithic prototype, consisting of a matrix of hexagonal pixels with 100 $\mu$m pitch, has been produced using the 130 nm SiGe BiCMOS process by IHP microelectronics. Measurements on probe station and with a $^{55}$Fe X-ray source show that the prototype is functional and displays avalanche gain up to a maximum electron gain of 23. A study of the avalanche characteristics, corroborated by TCAD simulations, indicates that space-charge effects due to the large primary charge produced by the conversion of X-rays from the $^{55}$Fe source limits the effective gain.

physics.ins-det↗

arXiv2021

Efficiency and time resolution of monolithic silicon pixel detectors in SiGe BiCMOS technology

A monolithic silicon pixel detector prototype has been produced in the SiGe BiCMOS SG13G2 130 nm node technology by IHP. The ASIC contains a matrix of hexagonal pixels with pitch of approximately 100 $\mu$m. Three analog pixels were calibrated in laboratory with radioactive sources and tested in a 180 GeV/c pion beamline at the CERN SPS. A detection efficiency of $\left(99.9^{+0.1}_{-0.2}\right)$% was measured together with a time resolution of $(36.4 \pm 0.8)$ps at the highest preamplifier bias current working point of 150 $\mu$A and at a sensor bias voltage of 160 V. The ASIC was also characterized at lower bias voltage and preamplifier current.

physics.ins-det↗

arXiv2021

Latest results on quiescent and post-disruption runaway electron mitigation experiments at Frascati Tokamak Upgrade

Results from the last FTU campaigns on the deuterium large (wrt FTU volume) pellet REs suppression capability, mainly due to the induced burst MHD activity expelling REs seed are presented for discharges with 0.5 MA and 5.3T. Clear indications of avalanche multiplication of REs following single pellet injection on 0.36 MA flat-top discharges is shown together with quantitative indications of dissipative effects in terms of critical electrical field increase due to fan-like instabilities. Analysis of large fan-like instabilities on post-disruption RE beams, that seem to be correlated with low electrical field and background density drops, reveal their strong RE energy suppression capability suggesting a new strategy for RE energy suppression controlling large fan instabilities. We demonstrate how such density drops can be induced using modulated ECRH power on post-disruption beams.

physics.plasm-ph↗

arXiv2021

Multi-wavelength flare observations of the blazar S5 1803+784

The radio, optical, and $γ$-ray light curves of the blazar S5 1803+784, from the beginning of the {\it Fermi} Large Area Telescope (LAT) mission in August 2008 until December 2018, are presented. The aim of this work is to look for correlations among different wavelengths useful for further theoretical studies. We analyzed all the data collected by {\it Fermi} LAT for this source, taking into account the presence of nearby sources, and we collected optical data from our own observations and public archive data to build the most complete optical and $γ$-ray light curve possible. Several $γ$-ray flares ($\mathrm{F>2.3~10^{-7} ph(E>0.1 GeV)~cm^{-2}~s^{-1}}$) with optical coverage were detected, all but one with corresponding optical enhancement; we also found two optical flares without a $γ$-ray counterpart. We obtained two {\it Swift} Target of Opportunity observations during the strong flare of 2015. Radio observations performed with VLBA and EVN through our proposals in the years 2016-2020 were analyzed to search for morphological changes after the major flares. The optical/$γ$-ray flux ratio at the flare peak varied for each flare. Very minor optical V-I color changes were detected during the flares. The X-ray spectrum was well fitted by a power law with photon spectral index $α$=1.5, nearly independent of the flux level: no clear correlation with the optical or the $γ$-ray emission was found. The $γ$-ray spectral shape was well fitted by a power law with average photon index $α$= 2.2. These findings support an Inverse Compton origin for the high-energy emission of the source, nearly co-spatial with the optically emitting region. The radio maps showed two new components originating from the core and moving outwards, with ejection epochs compatible with the dates of the two largest $γ$-ray flares.

astro-ph.HE↗

arXiv2020

Time resolution and power consumption of a monolithic silicon pixel prototype in SiGe BiCMOS technology

SiGe BiCMOS technology can be used to produce ultra-fast, low-power silicon pixel sensors that provide state-of-the-art time resolution even without an internal gain mechanism. The development of such sensors requires the identification of the main factors that may degrade the timing performance and the characterisation of the dependance of the sensor time resolution on the amplifier power consumption. Measurements with a $ \mathrm{^{90}Sr} $ source of a prototype sensor produced in SG13G2 technology from IHP Microelectronics, shows a time resolution of 140 ps at an amplifier current of 7 $ \mathrmμ $A and 45 ps at higher power consumption. A full simulation shows that the resolution on the measurement of the signal time-over-threshold, used to correct for time walk, is the main factor affecting the timing performance.

physics.ins-det↗

arXiv2020

The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation

Among the four known transneptunian dwarf planets, Haumea is an exotic, very elongated, and fast rotating body. In contrast to the other dwarf planets, its size, shape, albedo, and density are not well constrained. Here we report results of a multi-chord stellar occultation, observed on 2017 January 21. Secondary events observed around the main body are consistent with the presence of a ring of opacity 0.5, width 70 km, and radius 2,287$_{-45}^{+75}$ km. The Centaur Chariklo was the first body other than a giant planet to show a ring system and the Centaur Chiron was later found to possess something similar to Chariklo's rings. Haumea is the first body outside the Centaur population with a ring. The ring is coplanar with both Haumea's equator and the orbit of its satellite Hi'iaka. Its radius places close to the 3:1 mean motion resonance with Haumea's spin period. The occultation by the main body provides an instantaneous elliptical limb with axes 1,704 $\pm$ 4 km x 1,138 $\pm$ 26 km. Combined with rotational light-curves, it constrains Haumea's 3D orientation and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea's largest axis is at least 2,322 $\pm$ 60 km, larger than thought before. This implies an upper limit of 1,885 $\pm$ 80 kg m$^{-3}$ for Haumea's density, smaller and less puzzling than previous estimations, and a geometric albedo of 0.51 $\pm$ 0.02, also smaller than previous estimations. No global N$_2$ or CH$_4$ atmosphere with pressures larger than 15 and 50 nbar (3-$σ$ limits), respectively, is detected.

astro-ph.EP↗

arXiv2019

Luminous Red Novae: Stellar Mergers or Giant Eruptions?

We present extensive datasets for a class of intermediate-luminosity optical transients known as "luminous red novae" (LRNe). They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC4490-2011OT1, M101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, Halpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (~6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. Halpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for LRNe. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between LRNe and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.

astro-ph.SR↗

arXiv2017

Mixing length scales of low temperature spin plaquettes models

Plaquette models are short range ferromagnetic spin models that play a key role in the dynamic facilitation approach to the liquid glass transition. In this paper we perform a rigorous study of the thermodynamic properties of two dimensional plaquette models, the square and triangular plaquette models. We prove that for any positive temperature both models have a unique infinite volume Gibbs measure with exponentially decaying correlations. We analyse the scaling of three a priori different static correlation lengths in the small temperature regime, the mixing, cavity and multispin correlation lengths. Finally, using the symmetries of the model we determine an exact self similarity property for the infinite volume Gibbs measure.

math-ph↗

arXiv2017

MN Draconis - peculiar, active dwarf nova in the period gap

Context: We present results of an extensive world-wide observing campaign of MN Draconis. Aims: MN Draconis is a poorly known active dwarf nova in the period gap and is one of the only two known cases of period gap SU UMa objects showing the negative superhumps. Photometric behaviour of MN Draconis poses a challenge for existing models of the superhump and superoutburst mechanisms. Therefore, thorough investigation of peculiar systems, such as MN Draconis, is crucial for our understanding of evolution of the close binary stars. Methods: To measure fundamental parameters of the system, we collected photometric data in October 2009, June-September 2013 and June-December 2015. Analysis of the light curves, $O-C$ diagrams and power spectra was carried out. Results: During our three observational seasons we detected four superoutburts and several normal outbursts. Based on the two consecutive superoutbursts detected in 2015, the supercycle length was derived P_sc = 74 +/- 0.5 days and it has been increasing with a rate of P_dot = 3.3 x 10^(-3) during last twelve years. Based on the positive and negative superhumps we calculated the period excess epsilon = 5.6% +/- 0.1%, the period deficit epsilon_ = 2.5% +/- 0.6%, and in result, the orbital period P_orb = 0.0994(1) days (143.126 +/- 0.144 min). We updated the basic light curve parameters of MN Draconis. Conclusions: MN Draconis is the first discovered SU UMa system in the period gap with increasing supercycle length.

astro-ph.SR↗

arXiv2016

MASTER OT J190519.41+301524.4: New Eclipsing Cataclysmic Variable of VY Scl Type

MASTER OT J190519.41+301524.4 was discovered as an optical transient of 15.7m by the Mobile Astronomical System of TElescope-Robots in March 2014. We report the results of photometric observations of this variable performed at Lajatico Astronomical Center in June-July 2015. The light curve is showing deep V-shaped eclipses with an amplitude of two magnitudes. The orbital period was determined to be 0.129694 d (3.113 h). Based on the archival observations and the shape of the orbital curve we suggest that MASTER OT J190519.41+301524.4 is a new cataclysmic variable of VY Scl type ("anti-nova") with an inclination angle close to 90 deg.

astro-ph.SR↗

arXiv2016

1RXS J161935.7+524630: New Polar with the Varying Accretion Modes on two Magnetic Poles

We report the discovery of a new cataclysmic variable DDE 32 identified with the ROSAT X-ray source 1RXS J161935.7+524630 in Draco. The variability was originally found by D. Denisenko on the digitized Palomar plates centered at the position of X-ray source. The photometric observations by F. Martinelli at Lajatico Astronomical Center in June 2015 have shown the large amplitude (nearly 2 magnitudes) variability with a period about 100.5 minutes. Using the publicly available Catalina Sky Survey data from 2005 to 2013 we have improved the value of period to 0.0697944 days. Comparison of the archival CRTS data with more recent observations from Lajatico shows the dramatic changes in the light curve shape. Instead of a single peak present in Catalina data before 2014, there were two peaks of nearly the same height during 2015. SDSS spectrum taken in June 2009 shows prominent Helium emission lines between the bright Balmer series. He II 4686 AA line has more than 30% effective width compared to H_beta line. All those features allow us to interpret 1RXS J161935.7+524630 as a magnetic cataclysmic variable (polar) with the accretion mode changing from one pole before 2014 to two poles in 2015.

astro-ph.SR↗

arXiv2016

Dead or Alive? Long-term evolution of SN 2015bh (SNhunt275)

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ -13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~ 1 yr after). In addition, we inspect archival images of the host galaxy up to ~ 21 yr before discovery, finding a burst ~ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.

astro-ph.SR↗

arXiv2015

Runaway Electron Control in FTU

Experimental results on the position and current control of disruption generated runaway electrons (RE) in FTU are presented. A scanning interferometer diagnostic has been used to analyze the time evolution of the RE beam radial position and its instabilities. Correspondence of the interferometer time traces, radial profile reconstructed via magnetic measurements and fission chamber signals are discussed. New RE control algorithms, which define in real-time updated plasma current and position references, have been tested in two experimental scenarios featuring disruption generated RE plateaus. Comparative studies among 52 discharges with disruption generated RE beam plateaus are presented in order to assess the effectiveness of the proposed control strategies as the RE beam interaction with the plasma facing components is reduced while the current is ramped-down.

physics.plasm-ph↗

arXiv2014

CzeV404 - an eclipsing dwarf nova in the period gap during its July 2014 superoutburst

Results of the CCD observations of CzeV404 Her are displayed. During the season of June-August 2014 we detected one outburst and one superoutburst of the star. Clear superhumps with the period of P_sh=0.10472(2) days were observed. The superhump period was decreasing with a high value of P_dot=-2.43(8) x 10^(-4). For 17 eclipses, we calculated an orbital period with the value of P_orb=0.0980203(6) days which indicates that CzeV404 Her belongs to period gap objects and it is the longest orbital period eclipsing SU UMa star. Based on superhump and orbital period determinations, the period excess 6.8 % +/- 0.02 % and the mass ratio q ~ 0.32 of the system were obtained.

astro-ph.SR↗

arXiv2014

Optical and X-ray behaviour of the high mass X-ray transient A0535+26/HDE245770 in February-March 2014

The optical behaviour of the Be star in the high-mass X-ray transient A0535+26/HDE245770 shows that at periastron the luminosity is typically enhanced by 0.02 to a few tenths magnitude, and the X-ray outburst occurs eight days after the periastron. Indeed, at the periastron an increase of the mass flux occurs. This sort of flush reaches the external part of the temporary accretion disk around the neutron star and moves to the hot central parts of the accretion disk and the neutron star surface. The time necessary for this way is dependent on the turbulent viscosity in the accretion disk, as discussed by Giovannelli, Bisnovatyi-Kogan, and Klepnev (2013) (GBK13). In this paper we will show the behaviour of this system in optical band around the predicted periastron passage on 21st February 2014, by using the GBK13 ephemeris that we used to schedule our spectroscopic and photometric optical observations. Spectroscopic unusual activity detected in the Balmer lines and the enhancement in the emission in B, V, and R bands around the periastron passage, and the subsequent X-ray event definitively demonstrate the existence of about 8 day delay between optical and X-ray flares.

astro-ph.HE↗