UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)

Permanent URI for this collectionhttp://hdl.handle.net/11603/7798

The Center for Space Sciences and Technology (CSST) is the administrative unit for UMBC’s participation in the CRESST consortium. The NASA Goddard Space Flight Center (NASA/GSFC), The University of Maryland College Park (UMCP), Catholic University, Howard University and Southeastern Universities Research Association (SURA) are our partners in the consortium.

The Center for Research and Exploration in Space Science & Technology (CRESST), is a cooperative agreement between the partner institutions. The CRESST consortium currently has over 120 PhD astronomers and astrophysicists working within the Astrophysics Science Division at GSFC.

CSST was formed in 2006 and currently has over 20 UMBC research faculty, several of which are affiliated to the physics department. The research conducted by the members of CSST focuses on (i) Astrophysical Data Reduction, Interpretation & Archiving, (ii) Space Science Technology: Development & Calibration, and (iii) Theoretical Astrophysics: Simulations & Software.

CSST maintains close relations with (and is housed within) the Physics Department at UMBC. Combined, UMBC astrophysics faculty and CSST scientists contribute to the Undergraduate & Graduate activities (including the Undergrad & Grad internships) by teaching & mentoring students.

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The bulk motion of gas in the core of the Centaurus galaxy cluster
(Nature, 2025-02) Audard, Marc; Awaki, Hisamitsu; Ballhausen, Ralf; Bamba, Aya; Behar, Ehud; Boissay-Malaquin, Rozenn; Brenneman, Laura; Brown, Gregory V.; Corrales, Lia; Costantini, Elisa; Cumbee, Renata; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Eckert, Dominique; Enoto, Teruaki; Eguchi, Satoshi; Ezoe, Yuichiro; Foster, Adam; Fujimoto, Ryuichi; Fujita, Yutaka; Fukazawa, Yasushi; Fukushima, Kotaro; Furuzawa, Akihiro; Gallo, Luigi; Garc�a, Javier A.; Gu, Liyi; Guainazzi, Matteo; Hagino, Kouichi; Hamaguchi, Kenji; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hell, Natalie; Hodges-Kluck, Edmund; Hornschemeier, Ann; Ichinohe, Yuto; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Kaastra, Jelle; Kallman, Timothy; Kara, Erin; Katsuda, Satoru; Kanemaru, Yoshiaki; Kelley, Richard; Kilbourne, Caroline; Kitamoto, Shunji; Kobayashi, Shogo; Kohmura, Takayoshi; Kubota, Aya; Leutenegger, Maurice; Loewenstein, Michael; Maeda, Yoshitomo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian; Mernier, Fran�ois; Miller, Eric D.; Miller, Jon M.; Mitsuishi, Ikuyuki; Mizumoto, Misaki; Mizuno, Tsunefumi; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard; Nakajima, Hiroshi; Nakazawa, Kazuhiro; Ness, Jan-Uwe; Nobukawa, Kumiko; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ogawa, Shoji; Ogorzalek, Anna; Okajima, Takashi; Ota, Naomi; Paltani, Stephane; Petre, Robert; Plucinsky, Paul; Porter, Frederick Scott; Pottschmidt, Katja; Sato, Kosuke; Sato, Toshiki; Sawada, Makoto; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall; Suzuki, Hiromasa; Szymkowiak, Andrew; Takahashi, Hiromitsu; Takeo, Mai; Tamagawa, Toru; Tamura, Keisuke; Tanaka, Takaaki; Tanimoto, Atsushi; Tashiro, Makoto; Terada, Yukikatsu; Terashima, Yuichi; Trigo, Mar�a D�az; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi G.; Uchida, Hiroyuki; Uchida, Nagomi; Uchida, Yuusuke; Uchiyama, Hideki; Ueda, Yoshihiro; Uno, Shinichiro; Vink, Jacco; Watanabe, Shin; Williams, Brian J.; Yamada, Satoshi; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yoneyama, Tomokage; Yoshida, Tessei; Yukita, Mihoko; Zhuravleva, Irina; Kondo, Marie; Werner, Norbert; Pl?ek, Tom�?; Sun, Ming; Hosogi, Kokoro; Majumder, Anwesh; XRISM collaboration
Galaxy clusters contain vast amounts of hot ionized gas known as the intracluster medium (ICM). In relaxed cluster cores, the radiative cooling time of the ICM is shorter than the age of the cluster. However, the absence of line emission associated with cooling suggests heating mechanisms that offset the cooling, with feedback from active galactic nuclei (AGNs) being the most likely source1,2. Turbulence and bulk motions, such as the oscillating (?sloshing?) motion of the core gas in the cluster potential well, have also been proposed as mechanisms for heat distribution from the outside of the core3,4. Here we present X-ray spectroscopic observations of the Centaurus galaxy cluster with the X-Ray Imaging and Spectroscopy Mission satellite. We find that the hot gas flows along the line of sight relative to the central galaxy, with velocities from 130?km?s?1 to 310?km?s?1 within about�30?kpc of the centre. This indicates bulk flow consistent with core gas sloshing. Although the bulk flow may prevent excessive accumulation of cooled gas at the centre, it could distribute the heat injected by the AGN and bring in thermal energy from the surrounding ICM. The velocity dispersion of the gas is found to be only ?120?km?s?1 in the core, even within about 10?kpc of the AGN. This suggests that the influence of the AGN on the surrounding ICM motion is limited in the cluster.
Detection of X-ray Emission from a Bright Long-Period Radio Transient
(2024-11-26) Wang, Ziteng; Rea, Nanda; Bao, Tong; Kaplan, David L.; Lenc, Emil; Wadiasingh, Zorawar; Hare, Jeremy; Zic, Andrew; Anumarlapudi, Akash; Bera, Apurba; Beniamini, Paz; Cooper, A. J.; Clarke, Tracy E.; Deller, Adam T.; Dawson, J. R.; Glowacki, Marcin; Hurley-Walker, Natasha; McSweeney, S. J.; Polisensky, Emil J.; Peters, Wendy M.; Younes, George; Bannister, Keith W.; Caleb, Manisha; Dage, Kristen C.; James, Clancy W.; Kasliwal, Mansi M.; Karambelkar, Viraj; Lower, Marcus E.; Mori, Kaya; Ocker, Stella Koch; P�rez-Torres, Miguel; Qiu, Hao; Rose, Kovi; Shannon, Ryan M.; Taub, Rhianna; Wang, Fayin; Wang, Yuanming; Zhao, Zhenyin; Bhat, N. D. R.; Dobie, Dougal; Driessen, Laura N.; Murphy, Tara; Jaini, Akhil; Deng, Xinping; Jahns-Schindler, Joscha N.; Lee, Y. W. J.; Pritchard, Joshua; Tuthill, John; Thyagarajan, Nithyanandan
Recently, a class of long-period radio transients (LPTs) has been discovered, exhibiting emission on timescales thousands of times longer than radio pulsars. Several models had been proposed implicating either a strong magnetic field neutron star, isolated white dwarf pulsar, or a white dwarf binary system with a low-mass companion. While several models for LPTs also predict X-ray emission, no LPTs have been detected in X-rays despite extensive searches. Here we report the discovery of an extremely bright LPT (10-20 Jy in radio), ASKAP J1832-0911, which has coincident radio and X-ray emission, both with a 44.2-minute period. The X-ray and radio luminosities are correlated and vary by several orders of magnitude. These properties are unique amongst known Galactic objects and require a new explanation. We consider a $\gtrsim0.5$ Myr old magnetar with a $\gtrsim 10^{13}$ G crustal field, or an extremely magnetised white dwarf in a binary system with a dwarf companion, to be plausible explanations for ASKAP J1832-0911, although both explanations pose significant challenges to formation and emission theories. The X-ray detection also establishes a new class of hour-scale periodic X-ray transients of luminosity $\sim10^{33}$ erg/s associated with exceptionally bright coherent radio emission.
Your smart home exchanged 3M messages: defining and analyzing smart device passive mode
(HAL, 2025-03) Badolato, Christian; Kullman, Kaur; Papadakis, Nikolaos; Bhatt, Manav; Bouloukakis, Georgios; Engel, Don; Yus, Roberto
The constant connectedness of smart home devices and their sensing capabilities pose a unique threat to individuals? privacy. While users may expect devices to exhibit minimal activity while they are not performing their intended functions, this is not necessarily the case, and traditional idle mode designations are insufficient to address the current landscape of smart home devices. To address this we propose a passive mode designation based on a comprehensive categorization of smart home devices. We then measure the network traffic of thirty-two devices in their respective passive modes. We find that 97% of the devices exhibit near-constant network activity in these modes (exchanging over 3M messages in 24 hours), with many of the devices initiating and responding to LAN communications with other devices, which potentially exposes users to privacy leakages.
Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST
(AAS, 2024-06-24) Rho, J.; Park, S.-H.; Arendt, R.; Matsuura, M.; Milisavljevic, D.; Temim, T.; De Looze, I.; Blair, W. P.; Rest, A.; Fox, O.; Ravi, A. P.; Koo, B.-C.; Barlow, M.; Burrows, A.; Chevalier, R.; Clayton, G.; Fesen, R.; Fransson, C.; Fryer, C.; Gomez, H. L.; Janka, H.-T.; Kirchschlager, F.; Laming, J. M.; Orlando, S.; Patnaude, D.; Pavlov, G.; Plucinsky, P.; Posselt, B.; Priestley, F.; Raymond, J.; Sartorio, N.; Schmidt, F.; Slane, P.; Smith, N.; Sravan, N.; Vink, J.; Weil, K.; Wheeler, J.; Yoon, S. C.
We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3?5.5 ?m) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar vi] and relatively weaker, variable strength ejecta lines of [Si ix], [Ca iv], [Ca v], and [Mg iv]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ?1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.
Extragalactic Magnetar Giant Flares: Population Implications, Rates, and Prospects for Gamma-Rays, Gravitational Waves, and Neutrinos
(AAS, 2025-02-17) Beniamini, Paz; Wadiasingh, Zorawar; Trigg, Aaron; Chirenti, Cecilia; Burns, Eric; Younes, George; Negro, Michela; Granot, Jonathan
Magnetar giant flares (MGFs) are the most energetic non-catastrophic transients known to originate from stellar objects. The first discovered events were nearby. In recent years, several extragalactic events have been identified, implying an extremely high volumetric rate. We show that future instruments with a sensitivity ?5 ? 10?9 erg cm?2 at ?1 MeV will be dominated by extragalactic MGFs over short gamma-ray bursts (sGRBs). Clear discrimination of MGFs requires intrinsic GRB localization capability to identify host galaxies. As MGFs involve a release of a sizable fraction of the neutron star's magnetic free energy reservoir in a single event, they provide us with invaluable tools for better understanding magnetar birth properties and the evolution of their magnetic fields. A major obstacle is to identify a (currently) small subpopulation of MGFs in a larger sample of more energetic and distant sGRBs. We develop the tools to analyze the properties of detected events and their occurrence rate relative to sGRBs. Even with the current (limited) number of events, we can constrain the initial internal magnetic field of a typical magnetar at formation to be B0 � 4 ? 1014?2 ? 1015 G. Larger samples will constrain the distribution of birth fields. We also estimate the contribution of MGFs to the gravitational-wave (GW) stochastic background. Depending on the acceleration time of baryon-loaded ejecta involved in MGFs, their GW emission may reach beyond 10 kHz and, if so, will likely dominate over other conventional astrophysical sources in that frequency range.
Hydrogen escaping from a pair of exoplanets smaller than Neptune
(Nature, 2025-02) Loyd, R. O. Parke; Schreyer, Ethan; Owen, James E.; Rogers, James G.; Broome, Madelyn I.; Shkolnik, Evgenya L.; Murray-Clay, Ruth; Wilson, David J.; Peacock, Sarah; Teske, Johanna; Schlichting, Hilke E.; Duvvuri, Girish M.; Youngblood, Allison; Schneider, P. Christian; France, Kevin; Giacalone, Steven; Batalha, Natasha E.; Schneider, Adam C.; Longo, Isabella; Barman, Travis; Ardila, David R.
Exoplanet surveys have shown a class of abundant exoplanets smaller than Neptune on close, <100-day orbits1,2,3,4. These planets form two populations separated by a natural division at about 1.8 R⊕ termed the radius valley. It is uncertain whether these populations arose from separate dry versus water-rich formation channels, evolved apart because of long-term atmospheric loss or a combination of both5,6,7,8,9,10,11,12,13,14. Here we report observations of ongoing hydrogen loss from two sibling planets, TOI-776 b (1.85 ± 0.13 R⊕) and TOI-776 c (2.02 ± 0.14 R⊕), the sizes of which near the radius valley and mature (1–4 Gyr) age make them valuable for investigating the origins of the divided population of which they are a part. During the transits of these planets, absorption appeared against the Lyman-α emission of the host star, compatible with hydrogen escape at rates equivalent to 0.03–0.6% and 0.1–0.9% of the total mass per billion years of each planet, respectively. Observations of the outer planet, TOI-776 c, are incompatible with an outflow of dissociated steam, suggesting both it and its inner sibling formed in a dry environment. These observations support the strong role of hydrogen loss in the evolution of close-orbiting sub-Neptunes5,6,7,8,15,16.
The Escape Probability of Photons Emitted in a Spherical Homogeneous Shell
(AAS, 2024-08) Dwek, Eli; Arendt, Richard
We present a general expression for calculating the escape probability of photons from a dusty homogeneous spherical shell.
The Green Monster Hiding in Front of Cas A: JWST Reveals a Dense and Dusty Circumstellar Structure Pockmarked by Ejecta Interactions
(AAS, 2024-11-12) De Looze, Ilse; Milisavljevic, Dan; Temim, Tea; Dickinson, Danielle; Fesen, Robert; Arendt, Richard; Chastenet, Jeremy; Orlando, Salvatore; Vink, Jacco; Barlow, Michael J.; Kirchschlager, Florian; Priestley, Felix D.; Raymond, John C.; Rho, Jeonghee; Sartorio, Nina S.; Scheffler, Tassilo; Schmidt, Franziska; Blair, William P.; Fox, Ori; Fryer, Christopher; Janka, Hans-Thomas; Koo, Bon-Chul; Laming, J. Martin; Matsuura, Mikako; Patnaude, Dan; Rela�o, M�nica; Rest, Armin; Schmidt, Judy; Smith, Nathan; Sravan, Niharika
JWST observations of the young Galactic supernova remnant Cassiopeia A revealed an unexpected structure seen as a green emission feature in colored composite MIRI F1130W and F1280W images?hence dubbed the Green Monster?that stretches across the central parts of the remnant in projection. Combining the kinematic information from NIRSpec and the MIRI Medium Resolution Spectrograph with the multiwavelength imaging from NIRCam and MIRI, we associate the Green Monster with circumstellar material (CSM) that was lost during an asymmetric mass-loss phase. MIRI images are dominated by dust emission, but their spectra show emission lines from Ne, H, and Fe with low radial velocities indicative of a CSM nature. An X-ray analysis of this feature in a companion paper supports its CSM nature and detects significant blueshifting, thereby placing the Green Monster on the nearside, in front of the Cas A supernova remnant. The most striking features of the Green Monster are dozens of almost perfectly circular 1??3? sized holes, most likely created by interaction between high-velocity supernova ejecta material and the CSM. Further investigation is needed to understand whether these holes were formed by small 8000?10,500 km s?1 N-rich ejecta knots that penetrated and advanced out ahead of the remnant?s 5000?6000 km s?1 outer blast wave or by narrow ejecta fingers that protrude into the forward-shocked CSM. The detection of the Green Monster provides further evidence of the highly asymmetric mass loss that Cas A?s progenitor star underwent prior to its explosion.
NICER observations of CXOU J005245.0-722844
(The Astronomer's Telegram, 2024-05-01) Jaisawal, G. K.; Guillot, S.; Ng, M.; Gendreau, K. C.; Arzoumanian, Z.; Hare, J.; Younes, George; Ferrara, E. C.; Ray, P. S.; Wadiasingh, Z.; Strohmayer, T. E.; Sanna, A.; Enoto, T.
Following the report of an X-ray outburst from CXOU J005245.0-722844 in the Small Magellanic Cloud (ATel #16631, #16633), NICER observed the source on the 28th and 29th of May 2024 for a total exposure of 4.9 ks. During the observation, the source count rate evolved from 84 to 46 counts per second in the 0.5-2 keV band.
Looking at Infrared Background Radiation Anisotropies with Spitzer: Large-scale Anisotropies and Their Implications
(AAS, 2025-02-06) Kashlinsky, A.; Arendt, Richard; Ashby, M. L. N.; Kruk, J.; Odegard, N.
We use Spitzer/IRAC deep-exposure data covering two significantly larger than before sky areas to construct maps suitable for evaluating source-subtracted fluctuations in the cosmic infrared background (CIB). The maps are constructed using the self-calibration methodology eliminating artifacts to sufficient accuracy, and subset maps are selected in each area containing approximately uniform exposures. These maps are clipped and removed of known sources and then Fourier transformed to probe the CIB anisotropies to new larger scales. The power spectrum of the resultant CIB anisotropies is measured from the data to >1�, revealing the component well above that from remaining known galaxies on scales . The fluctuations are demonstrated to be free of Galactic and solar system foreground contributions out to the largest scales measured. We discuss the proposed theories for the origin of the excess CIB anisotropies in light of the new data. Out of these, the model where the CIB fluctuation excess originates from the granulation power due to LIGO-observed primordial black holes as dark matter appears most successful in accounting for all observations related to the measured CIB power amplitude and spatial structure, including the measured coherence between the CIB and unresolved cosmic X-ray background (CXB). Finally we point out the use of the data to probe the CIB-CXB cross power to new scales and higher accuracy. We also discuss the synergy of these data with future CIB programs at shorter near-IR wavelengths with deep wide surveys and subarcsecond angular resolution as provided by Euclid and Roman space missions.
NICER, NuSTAR, and Swift-XRT observations of the Magnetar 1E 1841-045
(The Astronomer's Telegram, 2024-09-01) Younes, George; Hu, C.-P.; Enoto, T.; Gendreau, K. C.; Arzoumanian, Z.; Hare, J.; Ng, M.; Wadiasingh, Z.
Since the reported bursting activity of the magnetar 1E 1841-045 with Swift-BAT (ATEL #16784), Fermi-GBM (ATEL #16786), and NICER (ATEL #16789), we have acquired more NICER observations of the target, covering the time period 2024 August 20 at 23:28 to 2024 August 31 at 10:58 UT, for a total exposure of 27.6 ks. Additionally, we acquired a NuSTAR Directors Discretionary Time observation starting on 2024 August 29 at 04:21 UT for a total exposure of approximately 50 ks. Lastly, we analyze the Swift-XRT photon counting mode observation acquired beginning 2024-08-22 at 03:52 UT for a total of 1.8 ks. The NICER monitoring shows that the source bursting activity has strongly diminished since August 20. We detect only two faint bursts in addition to the ones reported in ATEL #16789.
NICER Confirms Burst Activity from the Magnetar 1E 1841-045
(The Astronomer's Telegram, 2024-08-24) Ng, M.; Younes, George; Hu, C.-P.; Enoto, T.; Begicarslan, B.; Guver, T.; Jaisawal, G. K.; Arzoumanian, Z.; Gendreau, K. C.; Wadiasingh, Z.
Swift/BAT reported the detection of possible burst activity from 1E 1841-045 at 19:01:18 UT on 2024 August 20 (GCN #37211). A subsequent notice reported three additional bursts detected by Swift/BAT over the next 24 hours, suggesting that the source has entered a bursting phase for the first time since Swift/BAT last detected it in 2016 (GCN #37222, ATel #16784). Follow-up Fermi/GBM observations detected 8 bursts, 3 of which were also reported by Swift/BAT (GCNs #37222, #37234, ATel #16786). Supplementing its biweekly monitoring campaign, NICER triggered observations of 1E 1841-045 starting on 2024 August 20 at 23:28 UT for a total exposure time of 4.6 ks.
Pulsed and Polarized X-Ray Emission From Neutron Star Surfaces
(Wiley, 2024-11-17) Baring, Matthew G.; Thi, Hoa Dinh; Younes, George; Hu, Kun
The intense magnetic fields of neutron stars naturally lead to strong anisotropy and polarization of radiation emanating from their surfaces, both being sensitive to the hot spot position on the surface. Accordingly, pulse phase-resolved intensities and polarizations depend on the angle between the magnetic and spin axes and the observer's viewing direction. In this paper, results are presented from a Monte Carlo simulation of neutron star atmospheres that uses a complex electric field vector formalism to treat polarized radiative transfer due to magnetic Thomson scattering. General relativistic influences on the propagation of light from the stellar surface to a distant observer are taken into account. The paper outlines a range of theoretical predictions for pulse profiles at different X-ray energies, focusing on magnetars and also neutron stars of lower magnetization. By comparing these models with observed intensity and polarization pulse profiles for the magnetar 1RXS J1708-40, and the light curve for the pulsar PSR J0821-4300, constraints on the stellar geometry angles and the size of putative polar cap hot spots are obtained.
TESSELLATE: Piecing Together the Variable Sky With TESS
(2025-02-24) Roxburgh, Hugh; Ridden-Harper, Ryan; Moore, Andrew; Montilla, Clarinda; Leicester, Brayden; Lane, Zachary G.; Freeburn, James; Rest, Armin; Bannister, Michele T.; Ridden-Harper, Andrew R.; Hubley, Lancia; Wang, Qinan; Hounsell, Rebekah; Cooke, Jeff; Coulter, Dave A.; Fausnaugh, Michael M.
We present TESSELLATE, a dedicated pipeline for performing an untargeted search documenting all variable phenomena captured by the TESS space telescope. Building on the TESSreduce difference imaging pipeline, TESSELLATE extracts calibrated and reduced photometric data for every full frame image in the TESS archive. Using this data, we systematically identify transient, variable and non-sidereal signals across timescales ranging from minutes to weeks. The high cadence and wide field of view of TESS enables us to conduct a comprehensive search of the entire sky to a depth of ~17 $m_i$. Based on the volumetric rates for known fast transients, we expect there to be numerous Fast Blue Optical Transients and Gamma Ray Burst afterglows present in the existing TESS dataset. Beyond transients, TESSELLATE can also identify new variable stars and exoplanet candidates, and recover known asteroids. We classify events using machine learning techniques and the work of citizen scientists via the Zooniverse Cosmic Cataclysms project. Finally, we introduce the TESSELLATE Sky Survey: a complete, open catalog of the variable sky observed by TESS.
Fermi-detection of gamma-ray Emissions from the Hot Coronae of Radio-quiet Active Galactic Nuclei
(2025-02-26) Collaboration, The Fermi-LAT; Wang, Jian-Min; Li, Jian; Liu, Jun-Rong; Rani, Bindu
Relativistic jets around supermassive black holes (SMBHs) are well-known powerful $\gamma$-ray emitters. In absence of the jets in radio-quiet active galactic nuclei (AGNs), how the SMBHs work in $\gamma$-ray bands is still unknown despite of great observational efforts made in the last 3 decades. Considering the previous efforts, we carefully select an AGN sample composed of 37 nearby Seyfert galaxies with ultra-hard X-rays for the goals of $\gamma$-ray detections by excluding all potential contamination in this band. Adopting a stacking technique, here we report the significant $\gamma$-ray detection (${\rm TS}=30.6$, or $5.2\,\sigma$) from the sample using 15-year Fermi-Large Area Telescope (LAT) observation. We find an average $\gamma$-ray luminosity of the sample as $(1.5\pm1.0)\times10^{40}{\,\rm erg\,s^{-1}}$ at energies from 1-300\,GeV. Limited by the well-known pair production from the interaction of $\gamma$-rays with low energy photons, $\gtrsim$ several GeV $\gamma$-rays are found to originate from an extended corona ($\sim 2.7\times 10^6\,R_{\rm g}$), whereas the canonical much more compact X-ray corona ($\sim 10\,R_{\rm g}$) is responsible for 1 to several GeV $\gamma$-rays. The finding of the compact region lends to strong supports to the long-time theoretical expectations, but the extended corona is beyond all the existing models. One promising scenario is that the electron-positron pairs produced in the compact X-ray corona would expand as fireball, similar to that in $\gamma$-ray bursts, forming the structure of extended corona.
The high energy X-ray probe (HEX-P): sensitive broadband X-ray observations of transient phenomena in the 2030s
(Frontiers, 2024-01-10) Brightman, Murray; Margutti, Raffaella; Polzin, Ava; Jaodand, Amruta; Hotokezaka, Kenta; Alford, Jason A. J.; Hallinan, Gregg; Kammoun, Elias; Mooley, Kunal; Masterson, Megan; Marcotulli, Lea; Rau, Arne; Wevers, Thomas; Younes, George; Stern, Daniel; Garc�a, Javier A.; Madsen, Kristin
HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10''<10?? FWHM) and broad spectral coverage (0.2?80 keV) with an effective area superior to NuSTAR above 10 keV to enable revolutionary new insights into a variety of astrophysical problems, especially those related to compact objects, accretion and outflows. HEX-P will launch at a time when the sky is being routinely scanned for transient gravitational wave, electromagnetic and neutrino phenomena that will require the capabilities of a sensitive, broadband X-ray telescope for follow up studies. These include the merger of compact objects such as neutron stars and black holes, stellar explosions, and the birth of new compact objects. A response time to target of opportunity observation requests of <24<24 hours and a field of regard of 3� steradians will allow HEX-P to probe the accretion and ejecta from these transient phenomena through the study of relativistic outflows and reprocessed emission, provide unique capabilities for understanding jet physics, and potentially revealing the nature of the central engine.
Rapid spin changes around a magnetar fast radio burst
(Springer Nature, 2024-02-14) Hu, Chin-Ping; Narita, Takuto; Enoto, Teruaki; Younes, George; Wadiasingh, Zorawar; Baring, Matthew G.; Ho, Wynn C. G.; Guillot, Sebastien; Ray, Paul S.; G�ver, Tolga; Rajwade, Kaustubh; Arzoumanian, Zaven; Kouveliotou, Chryssa; Harding, Alice K.; Gendreau, Keith C.
Magnetars are neutron stars with extremely high magnetic fields (?1014?gauss) that exhibit various X-ray phenomena such as sporadic subsecond bursts, long-term persistent flux enhancements and variable rotation-period derivative1,2. In 2020, a fast radio burst (FRB), akin to cosmological millisecond-duration radio bursts, was detected from the Galactic magnetar SGR?1935+2154 (refs. 3?5), confirming the long-suspected association between some FRBs and magnetars. However, the mechanism for FRB generation in magnetars remains unclear. Here we report the X-ray observation of two glitches in SGR?1935+2154 within a time interval of approximately nine hours, bracketing an FRB that occurred on 14 October 20226,7. Each glitch involved a significant increase in the magnetar?s spin frequency, being among the largest abrupt changes in neutron-star rotation8?10 observed so far. Between the glitches, the magnetar exhibited a rapid spin-down phase, accompanied by an increase and subsequent decline in its persistent X-ray emission and burst rate. We postulate that a strong, ephemeral, magnetospheric wind11 provides the torque that rapidly slows the star?s rotation. The trigger for the first glitch couples the star?s crust to its magnetosphere, enhances the various X-ray signals and spawns the wind that alters magnetospheric conditions that might produce the FRB.
The role of magnetar transient activity in time-domain and multimessenger astronomy
(Frontiers, 2024-07-09) Negro, Michela; Younes, George; Wadiasingh, Zorawar; Burns, Eric; Trigg, Aaron; Baring, Matthew
Time-domain and multimessenger astronomy (TDAMM) involves the study of transient and time-variable phenomena across various wavelengths and messengers. The Astro2020 Decadal Survey has identified TDAMM as the top priority for NASA in this decade, emphasizing its crucial role in advancing our understanding of the universe and driving new discoveries in astrophysics. The TDAMM community has come together to provide further guidance to funding agencies, aiming to define a clear path toward optimizing scientific returns in this research domain. This encompasses not only astronomy but also fundamental physics, offering insights into properties of gravity, the formation of heavy elements, the equation of state of dense matter, and quantum effects associated with extreme magnetic fields. Magnetars, neutron stars with the strongest magnetic fields in the universe, play a critical role in this context. We aim to underscore the significance of magnetars in TDAMM, highlighting the necessity of ensuring observational continuity, addressing current limitations, and outlining essential requirements to expand our knowledge in this field.
A Growing Braking Index and Spin-down Swings for the Pulsar PSR B0540?69
(AAS, 2024-09-23) Espinoza, Crist�bal M.; Kuiper, Lucien; Ho, Wynn C. G.; Antonopoulou, Danai; Arzoumanian, Zaven; Harding, Alice K.; Ray, Paul S.; Younes, George
The way pulsars spin down is not understood in detail, but a number of possible physical mechanisms produce a spin-down rate that scales as a power of the rotation rate (), with the power-law index n called the braking index. PSR B0540?69 is a pulsar that in 2011, after 16 yr of spinning down with a constant braking index of 2.1, experienced a giant spin-down change and a reduction of its braking index to nearly zero. Here, we show that, following this episode, the braking index monotonically increased during a period of at least 4 yr and stabilized at ?1.1. We also present an alternative interpretation of a more modest rotational irregularity that occurred in 2023, which was modeled as an anomalous negative step of the rotation rate. Our analysis shows that the 2023 observations can be equally well described as a transient swing of the spin-down rate (lasting ?65 days), and the Bayesian evidence indicates that this model is strongly preferred.
Timing and Spectral Evolution of the Magnetar 1E 1841-045 in Outburst
(2025-02-27) Younes, George; Lander, S. K.; Baring, M. G.; Bause, M. L.; Stewart, R.; Arzoumanian, Z.; Thi, H. Dinh; Enoto, T.; Gendreau, K.; Guver, T.; Harding, A. K.; Ho, W. C. G.; Hu, C.-P.; Kooten, A. van; Kouveliotou, C.; Lalla, N. Di; McEwen, Alexander; Negro, M.; Ng, Mason; Palmer, D. M.; Spitler, L. G.; Wadiasingh, Zorawar
We present the timing and spectral analyses of the NICER, NuSTAR, and IXPE observations of the magnetar 1E 1841-045 covering 82 days following its August 2024 bursting activity as well as radio observations utilizing MeerKAT and Effelsberg. We supplement our study with a historical NuSTAR and all 2024 pre-outburst NICER observations. The outburst is marked by an X-ray flux enhancement of a factor 1.6 compared to the historical level, predominantly driven by a newly-formed non-thermal emitting component with a photon index �=1.5. This flux showed a 20% decay at the end of our monitoring campaign. The radio monitoring did not reveal any pulsed radio emission with an upper-limit of 20 mJy and 50 mJy ms on the mean flux density and single pulse fluence, respectively. We detect a spin-up glitch at outburst onset with a ??=6.1?10?8 Hz and a ???=?1.4?10?14 Hz s?1, consistent with the near-universality of this behavior among the continuously-monitored magnetars. Most intriguingly, the 1E 1841-045 2-10 keV pulse profile is markedly different compared to pre-outburst; it shows a new, narrow (0.1 cycles) peak that appears to shift towards merging with the main, persistently-present, pulse. This is the second case of pulse-peak migration observed in magnetars after SGR 1830?0645, and the two sources exhibit a similar rate of phase shift. This implies that this phenomenon is not unique and might present itself in the broader population. The newly-formed peak for 1E 1841-045 is non-thermal, with emission extending to ?20 keV, in contrast to the case of SGR 1830?0645. Our results are consistent with an untwisting magnetic field bundle with migration towards the magnetic pole, perhaps accompanied by plastic motion of the crust.

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