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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

24608 results found.

  1. EP250223a: Swift/XRT localization
  2. EP250223a: NOT optical afterglow candidate
  3. EP250223a: Einstein Probe detection of an X-ray transient
  4. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  5. GRB 250221A: Optical counterpart detection by LCO.
  6. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  7. GRB 250221A: GRANDMA/TAROT Detection
  8. GRB 250221A: Swift-XRT refined Analysis
  9. GRB 250221A: NOT optical observations
  10. GRB 250221A: 1.6m Mephisto optical detection
  11. GRB 250221A: AKO Optical Upper Limit
  12. GRB 250221A: Swift/UVOT Detection
  13. EP250220a: Liverpool Telescope upper limits
  14. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  15. GRB 250221A: REM optical/NIR afterglow detection
  16. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  17. GRB 250221A: Enhanced Swift-XRT position
  18. EP250220a: 1.6m Mephisto observations
  19. EP250220a: Liverpool Telescope optical upper limits
  20. EP250220a: Optical upper limit with Kinder observations
  21. SVOM trigger sb25022102 is not an astrophysical event
  22. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  23. GRB 250221A: Swift detection of a burst with an optical counterpart
  24. Swift GRB250221.15: Global MASTER-Net OT detection
  25. EP250220a: Xinglong optical upper limit
  26. GRB 250219A: Swift/UVOT Upper Limits
  27. GRB 250219A: OHP/T193 optical upper limit
  28. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  29. GRB 250219A: 1.6m Mephisto optical upper limits
  30. GRB 250219A: Swift-XRT observations
  31. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  32. Konus-Wind detection of GRB 250215A / EP250215a
  33. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  34. GRB 250217C: Swift-XRT observations
  35. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  36. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  37. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  38. GRB 250217C: SVOM/GRM observation
  39. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  40. SVOM/sb25021804: SVOM detection of a long X-ray transient
  41. GRB 250213A: Swift-XRT observations
  42. GRB 250216A: AstroSat CZTI detection
  43. GRB 250217C: AstroSat CZTI detection of a short burst
  44. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  45. GRANDMA/OPD observations of GRB250215A
  46. GRB 250215A / EP250215a: LCO detection of the afterglow
  47. GRB 250215A: Swift/UVOT Upper Limits
  48. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  49. GRB 250215A: Fermi GBM Observation
  50. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  51. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  52. GRB 250215A: Swift-XRT refined Analysis
  53. GRB 250215A: SVOM/GRM observation
  54. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  55. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  56. EP250207b: Xinglong optical upper limit
  57. EP250212a: Xinglong optical upper limit
  58. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  59. EP250212a: Global MASTER-Net observations report
  60. GRB 250205A: VIRT Optical Upper Limit
  61. GRB 250205A: Leavitt Observatory optical upper limit
  62. EP250207B: Chandra localization of the X-ray counterpart
  63. EP250212a: Liverpool Telescope optical upper limits
  64. GRB250101A: Radio upper limits from GMRT observations
  65. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  66. EP250207B: GTC z-band Observations
  67. Fermi GRB 250212A: Global MASTER-Net observations report
  68. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  69. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  70. Fermi trigger No 760945500: Global MASTER-Net observations report
  71. EP250207b: NOT optical counterpart candidate
  72. GRB 250211B: A long GRB detected by INTEGRAL
  73. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  74. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  75. LIGO/Virgo/KAGRA S250211be: Updated Sky localization
  76. GRB 250207A: Fermi GBM Observation
  77. GRB 250206A: Fermi GBM Observation
  78. GRB 250205A / EP250205A: radio detection with the VLA
  79. EP250207b: Tentative z-band brightening source
  80. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  81. Konus-Wind detection of GRB 250206A
  82. GRB 250210A: SVOM/GRM observation of a long burst
  83. EP250207b: Liverpool Telescope possible optical counterpart
  84. LIGO/Virgo/KAGRA S250211be: Identification of a GW compact binary merger candidate
  85. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  86. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  87. GRB 250207A: Skynet optical afterglow observations
  88. GRB 241128A: VIRT Optical Upper Limit
  89. EP250207b: Gemini GMOS-N z-band observations
  90. EP250207A: Upper limits from Fermi-GBM Observations
  91. EP250207b: a new X-ray transient detected by Einstein Probe
  92. GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
  93. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  94. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube
  95. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report
  96. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  97. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER
  98. LIGO/Virgo/KAGRA S250206dm: Optical observations of candidate AT 2025bbo with Kinder
  99. Fermi-LAT Gamma-ray Observations of IceCube-250207A
  100. GRB 250207A: 1.3m DFOT Optical observations

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