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All-Sky Transient Detection Using the Night Sky Live! Network

Lior Shamir & Robert J. Nemiroff

AbstractReal-time detection of optical transients has an important role in modern astronomy. However, with the absence of a sustainable system constantly monitoring the entire sky, one can reasonably assume that many of the short timescale transients are not reported. Covering 90% of the global night sky at any given time, the Night Sky Live all-sky monitoring network provides an infrastructure capable of transient detection at real-time. The system takes an all-sky exposure every 236 seconds, rejects cosmic ray hits and bright planets and searches for optical transients by comparing the exposure to a canonical frame taken at the same sidereal time. The system alerts on persistent transients that rotate with the sky for at least 12 minutes (3 NSL exposures), or transients that are detected simultaneously by several Night Sky Live nodes covering the same portion of the sky. Currently, the Night Sky Live network can detect 5th magnitude optical transient.

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The Night Sky Live network is capable of creating a continuous record of the nighttime optical sky. Fully 2 steradians -- half the sky -- are monitored passively, without tracking. Currently, we have built and deployed 10 CONtinuous CAMeras (CONCAMs) at many of the world's premier observatories that together compose the Night Sky Live (NSL) network and provide continuous coverage for much of the nighttime sky. CONCAMs take 180-second exposures picture every 3 minutes and 56 seconds, and can detect stars down to visual magnitude 6.8 near the image center. CONCAMs provide near real-time pictures of the night sky, and have computers that process the images into additional information such as photometry analysis of the frames and all-sky atmospheric opacity maps. All images and files are uploaded to a main server, where they are archived and accessible to the public.

A panoramic image of the whole night sky is captured every 236 seconds using a super-wide angle fish-eye lens.

The FITS all-sky images captured by a CCD camera are sent over the internet to NightSkyLive.net server at Michigan Tech.

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Fuzzy Logic ModelUsing a fuzzy logic model celestial coordinates are transformed into image coordinates. This transformation enables the rejection of planets and variable stars.

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Fuzzy Logic-Based Cosmic Ray Hit Rejection

Bright Planets and Variable Stars (dM>1) Rejection

Canonical Image

Database

Comparison with a Set of Canonical Frames Taken

at the Same Sidereal Time

All-Sky Image

Transients

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Canonical Image Database

Images are added to the canonical image database based on the following algorithm:

1. Find all point spread functions in the image

2. Search the point spread functions of all stars brighter than 5.2 (V-mag) that should appear in the sky at the time the image was taken.

3. If the PSFs of 96% of the stars are found, the image is added to the database.

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Transients are alerted if they persist for 2 consecutive frames (~8 minutes), or detected By more than one CONCAM station at the same time.

Geocentric coordinates of transients from different stations are compared, and an alert is triggered in case of a match.

Transients 40 brighter than their local background are alerted. This criterion is comparable to ~5.5 visual magnitude in CONCAM3 systems.

Alert Criteria

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Geosynchronous Satellites

The picture shows a bright transient caused by a geosynchronous satellite recorded in Canary Islands. The transient is of visual magnitude ~2, and appeared in the sky for approximately 12 minutes (3 consecutive frames). In the period between September 16th 2003 and October 13th 2003, the transient appeared every day at the time and at the same location in the sky.

Geosynchronous Satellites

The transient recorded by both Haleakala and Mauna Kea CONCAMs at the same time and at the same region of the sky. The visual magnitude of the object was ~2.5, and the duration of the flash was around 15 minutes.

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Further investigation turned up that the flashing object is probably the satellite “Superbird A”, a failed Japanese communication satellite.

In the period between October 8th 2004 and October 19th 2004, the bright glint appeared every day at 6:57 UT.

Other periodic transients caused by geosynchronous satellites have been recorded in Mauna Kea, Haleakala, Canary Islands and Kitt Peak.

We discovered that each of the observatories recorded at least one bright (visual magnitude +2) >8 minutes glint from a geosynchronous satellite every day.

Geosynchronous Satellites

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Other SatellitesNight Sky Live!

NSL is capable of alerting other bright satellites glints such as Iridium satellites, HST, ISS, etc’.

The system can differentiate between short glints and longer glints (> 4 minutes).

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Education

The Night Sky Live infrastructure allows graduate, undergraduate and amateur astronomers to search for satellite glints, meteors and optical transients by writing their own customized software, using the software provided by NSL and even by observing the Night Sky Live images by eye.

Students can learn the notion of optical transients by observing and studying the different types of celestial flashes such as HST, IIS, geosynchronous satellites and meteors.

Available Educational ModulesAll modules (pdf format) can be downloaded at http://nightskylive.net/education

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Astrometry of MeteoroidsIntroductory Astronomy Lab Exercise

The Variability of PolarisIntroductory Astronomy Lab Exercise

Department of PhysicsMichigan Technological University1400 Townsend Dr.Houghton, MI 49931

Department of PhysicsMichigan Technological University1400 Townsend Dr.Houghton, MI 49931

Astrometry of MeteoroidsStudents are required to analyze the trajectory of meteors recorded simultaneously in two different observatories. Students first analyze the images to find a meteor trail, and then use parallax in order to obtain the altitude, direction, distance and the absolute length of the luminous trail.

The Variability of PolarisStudents are required to show that Polaris is a variable star by analyzing a series of measurements of the luminosity of Polaris. Students compare measurements taken at the same sidereal time and use statistical methods to achieve their goal.

Conclusions

• Performing all-sky transient detection allows a systematic monitoring and detection of bright transient visible to the unaided eye.

• The search for optical transients can be disturbed by glints from satellites. For instance, the flash reported by (Halliday, Feldman & Blackwell) in 1987 near the constellation Perseus appeared later to be a series of satellite glints (Schaefer et al., 1987). We found that bright (v=~+2) and persistent (8 minutes or longer) glints from geosynchronous satellites are not rare, and approximately one such glint is expected each night.

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References• Shamir, L., A Fuzzy Logic-Based Algorithm for Cosmic-ray Hit Rejection

From Single Images, 2005, AN, in press

• Shamir, L., Nemiroff, R. J., A Fuzzy Logic Based Algorithm For Finding Astronomical Objects in Wide-Angle Frames, 2005, Publications of the Astronomical Society of Australia, Vol. 22(2), p. 111-117, 2005

• Halliday, I., Feldman, P. A., Blackwell, A. T., Evidence from meteor patrol photographs for a nonastronomical origin of the reported optical flashes in Perseus, 1987, ApJ, Vol. 320, p. 153-155.

• Castro-Tirado et al., Detection of an optical transient following the 13 March 2000 short/hard gamma-ray burst, 2002, ApJ, Vol. 393, 55-59.

• Schaefer, B. E. et al., 1987, The Perseus Flasher and satellite glints, ApJ, Vol., 320, p. 398-404

• Schaefer, B. E., Pedersen, H., Gouiffes, C., Poulsen, J. M., Pizzichini, G., 1987, Optical flash background rates, A&AS, Vol. 174, p. 338-343.

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