Browsing by Author "Mahabal, A. A."

Now showing 1 - 14 of 14
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    A Supernova Candidate from the Siding Spring Survey
    (2010) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Prieto, J.; Catelan , Marcio; Christensen, E.; McNaught, R.; Garradd, G.; Beshore, E. C.; Larson, S. M.
    We report the discovery of the first supernova candidate from the Siding Spring Survey (SSS) by the Catalina Real-time Transient Survey (CRTS). The detection has the following details: <table border=1 width=650 align=center> <tr><th>ID</th><th>Disc. Date</th><th>RA</th><th>Dec</th><th>Disc. Mag</th></tr> <tr align=center><td><a href='http://crts.caltech.edu/ATEL/SSS/1005080151534122262.atel.html'> SSS100508:210144-143830</a></td><td> 2010-05-08 </td><td> 21:01:44.10 </td><td> -14:38:30.5 </td><td> 16.4</tr> </table> The host galaxy, 2MFGC 15924 (=PGC 187888), has redshift z=0.0275 (Jones et al....
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    Alert Classification for the ALeRCE Broker System: The Real-time Stamp Classifier
    (2021) Carrasco-Davis, R.; Reyes, E.; Valenzuela, C.; Förster, F.; Estévez, P. A.; Pignata, G.; Bauer, F. E.; Reyes, I.; Sánchez-Sáez, P.; Cabrera-Vives, G.; Eyheramendy, S.; Catelan, Márcio; Arredondo, J.; Castillo-Navarrete, E.; Rodríguez-Mancini, D.; Ruz-Mieres, D.; Moya, A.; Sabatini-Gacitúa, L.; Sepúlveda-Cobo, C.; Mahabal, A. A.; Silva-Farfán, J.; Camacho-Iñiguez, E.; Galbany, L.
    We present a real-time stamp classifier of astronomical events for the Automatic Learning for the Rapid Classification of Events broker, ALeRCE. The classifier is based on a convolutional neural network, trained on alerts ingested from the Zwicky Transient Facility (ZTF). Using only the science, reference, and difference images of the first detection as inputs, along with the metadata of the alert as features, the classifier is able to correctly classify alerts from active galactic nuclei, supernovae (SNe), variable stars, asteroids, and bogus classes, with high accuracy (~94%) in a balanced test set. In order to find and analyze SN candidates selected by our classifier from the ZTF alert stream, we designed and deployed a visualization tool called SN Hunter, where relevant information about each possible SN is displayed for the experts to choose among candidates to report to the Transient Name Server database. From 2019 June 26 to 2021 February 28, we have reported 6846 SN candidates to date (11.8 candidates per day on average), of which 971 have been confirmed spectroscopically. Our ability to report objects using only a single detection means that 70% of the reported SNe occurred within one day after the first detection. ALeRCE has only reported candidates not otherwise detected or selected by other groups, therefore adding new early transients to the bulk of objects available for early follow-up. Our work represents an important milestone toward rapid alert classifications with the next generation of large etendue telescopes, such as the Vera C. Rubin Observatory....
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    Discovery and Classification of Transients from CRTS-II
    (2016) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Stern, D.; Catelan, Márcio; Christensen, E.; Larson, S. M.
    Following on from the Catalina Real-time Transient Survey (CRTS), the CRTS-II project has begun to search for transients and highly variable sources. As with CRTS, all detections will be made public immediately following discovery....
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    Discovery of Thousands of RR Lyrae by the Catalina Surveys
    (2013) Drake, Andrew J.; Djorgovski, S. G.; Catelan, Márcio; Torrealba, G.; Graham, M.; Mahabal, A. A.; Donalek, C.; Prieto, J.; McNaught, R.; Larson, S. M.; Christensen, E.; Beshore, E. C.
    We have performed an extensive search for RR Lyrae among the 500 million sources observed by the Catalina Surveys. We detect 23,000 type-ab RR Lyrae (of which 18,700 are new discoveries) from a region spanning 3/4 of the sky. By combining calibrated Catalina photometry with RR Lyrae absolute magnitude estimates, we derive accurate distances and investigate the spatial distribution of structures within the Galactic halo. We identify hundreds of new RR Lyrae belonging to the Sagittarius tidal streams system and compare their observed properties with predictions from existing N-body models. We discover significant evidence that firmly establishes the existence of a tidal stream reaching Galactocentric distances beyond 100 kpc. This stream remains to be explained by any Sagittarius model. For 1,500 of the RR Lyrae we find matches with targets observed by past SDSS spectroscopic surveys. Combining the radial velocities and metallicity estimates from the SDSS spectra, with photometric distances, we investigate the kinematics and abundances of halo tidal stream populations....
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    Results from the Catalina Real-time Transient Survey
    (2009) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M.; Williams, R.; Catelan, Marcio; Beshore, E.; Larson, S.; Christensen, E.
    The Catalina Real-time Transient Survey (CRTS) is a collaborative effort between Caltech and LPL that uses data from Catalina Sky Survey's 0.7m Schmidt telescope to search for optical transients. This survey currently covers a total of 26,000 square degrees on the sky between declinations -30 and 70. Observations covering 1200 square degrees are taken 21 nights per lunation and reach magnitudes of 19 to 20. CRTS is sensitive to transients with timescales from minutes to years since images are taken in sequences separated by 10 minutes and past observations date back over four years. Transient classification is performed using follow up imaging and spectroscopy in combination with VO-enabled archival analysis of CSS and Palomar Quest synoptic datasets and DSS, 2MASS, SDSS, GALEX and UKIDSS surveys. To date more than 600 unique transients have been identified by CRTS. These include more than 200 newly discovered Supernovae, Cataclysmic Variables and Blazars. Initial results of note include in the discovery of hyper-luminous supernovae, as well as a high rate of supernovae associated with intrinsically faint galaxies. In the near future we expect to expand the survey area and depth by utilizing data from two additional operational Catalina Sky Survey telescopes. All CRTS transients are discovered and distributed openly within minutes of observation using VOEvent technology as well as html tables, RSS feeds and GoogleSky (from VOEventNet.org). Astronomers will soon be able to automatically select transients of particular interest by using the personalized event selection available via the SkyAlert system....
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    Sixty Thousand Periodic Variables from the Catalina Surveys
    (2014) Drake, Andrew J.; Graham, M.; Djorgovski, S. G.; Catelan, Marcio; Mahabal, A. A.; Prieto, J.; Donalek, C.; Christensen, E. J.; Larson, S. M.; Boattini, A.; Gibbs, A.; Grauer, A. D.; Hill, R.; Kowalski, R.; Johnson, J.; Shelly, F.; Torrealba, G.
    We have performed an in-depth search for periodic variable stars within the photometry from the Catalina Surveys Data Releases. Our analysis reveals ~40,000 new periodic variable stars with brightness ranging from V=11 to 20, from a region covering ~20,000 square degrees on the sky. Each source is classified based on lightcurve morphology and multi-color photometry from WISE and SDSS. The variable stars discovered include eclipsing binaries, such as Algol, beta Lyrae, W UMa and WD+dM types, and pulsators including delta Scuti's, SX Phe, LPVs, RR Lyrae and Cepheids. We combine these sources with type-ab RR Lyrae from our prior analysis to produce a periodic variable catalog containing 60,000 stars. Using ~5,500 optical spectra from SDSS DR10 we determine the metallicities, surface gravities and radial velocities of the major types. The photometry, classifications and periods will all be made publicly available through the Catalina Surveys data release website....
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    Supernova 2011ke
    (2013) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Donalek, C.; Prieto, J.; Catelan, Marcio; Larson, S. M.; Christensen, E.; Inserra, C.; Smartt, S. J.; Fraser, M.; Young, D.; Smith, K.; Wright, D.; Kotak, R.; McCrum, M.; Magill, L.; Chen, T. -W.; Pastorello, A.; Benetti, S.; Valenti, S.; Bresolin, F.; Kudritzki, R.; Tonry, J.; Magnier, E.; Huber, M.; Chambers, K.; Kaiser, N.; Morgan, J.; Burgett, W.; Heasley, J.; Sweeney, W.; Waters, C.; Flewelling, H.; Stubbs, C.; Price, P. A.; Sollerman, J.; Taddia, F.; Ergon, M.; Leloudas, G.; Taubenberger, S.
    Report the Catalina Real-time Transient Survey discovery of an apparent supernova in V-band Catalina Sky Survey (CSS) images: SN 2011 UT R.A. (2000.0) Decl. Mag. 2011ke Apr. 25.4 13 50 57.78 +26 16 42.4 17.6 Nothing is visible at this position on a CSS image from 2011 Mar. 16 UT (limiting mag 19.5). C. Inserra, S. J. Smartt, M. Fraser, D. Young, K. Smith, D. Wright, R. Kotak, M. McCrum, L. Magill, and T.-W. Chen, Queen's University, Belfast; A. Pastorello and S. Benetti, Osservatorio Astronomico di Padova, Istituto Nazionale di Astrofisica; S. Valenti, Las Cumbres Observatory Global Telescope and University of California at Santa Barbara; F. Bresolin, R. Kudritzki, J. Tonry, E. Magnier, M. Huber, K. Chambers, N. Kaiser, J. Morgan, W. Burgett, J. Heasley, W. Sweeney, C. Waters, and H. Flewelling, University of Hawaii; C. Stubbs, Harvard University; P. A. Price, Princeton University; J. Sollerman, F. Taddia, and M. Ergon, Oscar Klein Centre, Stockholm; G. Leloudas, Dark Cosmology Centre, Copenhagen; and S. Taubenberger, Max-Planck-Institut fuer Astrophysik, Garching, report that they obtained a spectrogram of 2011ke on 2011 May 21 UT with the Telescopio Nazionale Galileo (+ DOLORES). The spectrum shows the clear presence of emission from the host galaxy of [O II], [O III], H-beta, and H-alpha. (The host galaxy is also clearly seen in images obtained via the Canada-France-Hawaii Telescope and the Sloan Digital Sky Survey.) A good match is obtained with the spectrum of SN 2010gx (cf. CBET 2413), a super-luminous type-Ic supernova, at a week after maximum light....
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    The Catalina Surveys Southern periodic variable star catalogue
    (2017) Drake, A. J.; Djorgovski, S. G.; Catelan, Márcio; Graham, M. J.; Mahabal, A. A.; Larson, S.; Christensen, E.; Torrealba, G.; Beshore, E.; McNaught, R. H.; Garradd, G.; Belokurov, V.; Koposov, S. E.
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    The First Optical Transient Discoveries from MLS (The Astronomer's Telegram, No.2318)
    (2009) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Catelan, Marcio; Beshore, E. C.; Larson, S. M.; Boattini, A.; Gibbs, A.; Grauer, A.; Hill, R.; Kowalski, R.; Christensen, E.
    We report on the discovery of optical transients by the Catalina Real-time Transient Survey (CRTS) in data from the Catalina Sky Survey's 1.5m Mount Lemmon Survey (MLS) telescope. The transients were discovered between 2009-11-11 and 2009-11-24 UT and have the following parameters....
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    The pre-Nova light curve of CSS081007:030559+054715
    (2009) Drake, A. J.; Beshore, E. C.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Catelan, Marcio; Larson, S. M.; Hill, R.; Gibbs, A.; Boattini, A.; Christensen, E.
    The Nova CSS081007:030559+054715 was discovered by the Catalina Real-time Transient Survey (CRTS) on Oct 07 2008 UT and followed photometrically with the Palomar-60 between Oct 9 and Dec 12 2008. It was first classified as a possible recurrent nova by Pejcha et al. (2008; ATEL#1825) and later as Oxygen/Neon nova by Prieto et al. (2008; ATel#1835). Beardmore et al. (2008; ATEL#1873) subsequently discovered significant X-ray emission and a 1.77 day period by monitoring it with SWIFT and Nelson et al. (2009; ATEL#1910) observed it with Chandra and found the object to exhibit a supersoft continuum superimposed with prominent emission lines. Goranskij and Metlova (2009; ATEL#1938) observed it optically in B,V and Rc between Dec. 3 2008 and Feb. 19 2009 and discovered two possible periods (1.694 and 0.6106 days). We have analyzed 117 pre-outburst CSS observations of the object taken on 34 nights between Oct 1 2005 and Mar 10 2008 UT. We find the the object exhibited variability well in excess of one magnitude during this time. However, we find no evidence for the post-outburst 1.77 day X-ray period signal observed by Beardmore et al. (2008; ATEL#1873) or the 0.6106 and 1.694 day optical periods observed by Goranskij and Metlova (2009; ATEL#1938). We find the best period for pre-outburst oscillations is 11.386 +/- 0.010 days. However, the data do not strongly constrain the periodic nature of the pre-outburst oscillations. On going CSS observations suggest that the Nova must not have begun the rapid decline noted by Goranskij and Metlova (2009; ATEL#1938) until after Jan 29th UT (rather the Jan. 22nd). Spectroscopic follow-up obtained with the SMARTs 1.5m telescope on Nov. 5th and is consistent with that of Prieto et al. (2008; ATel#1835).
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    The pre-Nova Lightcurve of KT Eri (Nova Eridani 2009)
    (2009) Drake, A. J.; Djorgovski, S. G.; Graham, M. J.; Mahabal, A. A.; Williams, R.; Wils, P.; Greaves, J.; Catelan, Marcio; Prieto, J.; Beshore, E. C.; Larson, S. M.; Boattini, A.; Gibbs, A.; Grauer, A.; Hill, R.; Kowalski, R.; Christensen, E.
    Here we report on historical observations of the pre-Nova source of KT Eri (Nova Eridani 2009). Following the detection of the possible Nova at mag 8.1 by Yamaoka et al. (2009, CBET#2050), we carried out a search of Catalina Sky Survey 0.7m data covering the location of this event. Photometry of the source was found with dates between 2005-01-17 and 2009-11-18 UT. The Nova was clearly seen in outburst in images taken on Nov.
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    Thirty Recent SN Candidates from CRTS
    (2012) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Prieto, J.; Catelan, Marcio; Christensen, E.; Larson, S. M.; Beshore, E. C.
    Further to ATel#4137, below we report the discovery of 30 supernova candidates by CRTS in Catalina Sky Survey data taken between 2012-09-13 and 2012-10-06 UT.
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    Thirty Three New SNe from CRTS
    (2011) Drake, A. J.; Mahabal, A. A.; Djorgovski, S. G.; Graham, M. J.; Williams, R.; Donalek, C.; Myers, A.; Prieto, J.; Catelan, Marcio; Christensen, E.; Beshore, E. C.; Larson, S. M.; Grauer, A.; Boattini, A.; Gibbs, A.; Hill, R.; Kowalski, R.
    Further to ATel#3188, we report the CRTS discovery of 33 new supernova candidates in data from the Catalina Sky Survey taken between 2011-02-23 and 2011-03-10 UT.
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    Three blue optical transients from CRTS
    (2011) Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Williams, R.; Donalek, C.; Prieto, J.; Catelan, Marcio; Christensen, E.; Beshore, E. C.; Larson, S. M.; McNaught, R. H.
    During the course of the CRTS survey, observations of poorly understood transient sources were undertaken with the Palomar 5m+DBSP on May 7 and May 8 UT. In addition to many SNe (ATEL#3340), three events were found exhibiting very blue continua.