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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"

18609 results found.

  1. GRB 250322A: VLT optical observations
  2. GRB 250322A: VLT near-infrared observations
  3. GRB 250322A: NOT optical upper limits
  4. GRB 250322A: Enhanced Swift-XRT position
  5. GRB 250322A: MASTER optical observation
  6. GRB 250322A: Swift detection of a short burst
  7. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  8. GRB 250225B: GECAM-A detection
  9. GRB 250312A: GECAM-A detection
  10. GRB 250321B: Swift ToO observations
  11. GRB 250321A: Swift-BAT refined analysis
  12. GRB 250321A: Swift-XRT refined Analysis
  13. GRB 250320B: Fermi-LAT detection
  14. GRB 250321A: Swift/UVOT Upper Limits
  15. EP250321a: LCO optical counterpart detection
  16. EP250321a: Swift-XRT detection of an X-ray source
  17. Swift GRB 250321A: Global MASTER-Net observations report
  18. GRB 250321A: GOTO optical upper limits
  19. GRB 250321A: Swift-XRT localisation
  20. GRB 250321A: Fermi GBM Observation
  21. GRB 250321A: Swift detection of a burst
  22. GRB250312A: Swift/UVOT Upper Limits
  23. GRB 250317B: Swift-XRT observations
  24. GRB 250316A: Swift/UVOT Upper Limits
  25. GRB 250314A: REM optical/NIR upper limits
  26. GRB 250316A: AbAO AS-32 Optical Upper Limit
  27. GRB 250316A: Swift-XRT afterglow detection
  28. GRB 250316A: Fermi GBM Observation
  29. GRB 250316A: Swift-XRT observations
  30. GRB 250316A: Swift ToO observations
  31. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  32. GRB 250314A: EP-FXT afterglow detection
  33. GRB 250314A: Swift/UVOT Upper Limits
  34. GRB 250312B: GRBAlpha detection
  35. GRB 250314A: Swift XRT Detection
  36. GRB 250314A: NOT near-infrared candidate counterpart
  37. GRB 250312B: Fermi GBM Observation
  38. GRB 250313A: Swift-XRT observations
  39. Konus-Wind detection of GRB 250308A
  40. GRB 250313A: Fermi-LAT detection
  41. GRB 250313A: Swift ToO observations
  42. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  43. EP250304a: SVOM/VT optical observation
  44. EP250302a: Chandra X-ray Detection
  45. GRB 250312A: Swift-XRT refined Analysis
  46. GRB 250312A: Enhanced Swift-XRT position
  47. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  48. GRB 250226B: Fermi GBM Observation
  49. Swift GRB 250312A: Global MASTER-Net observations report
  50. GRB 250302A: Fermi GBM Observation
  51. GRB 250312A: Swift detection of a burst
  52. GRB 250223B: Fermi GBM Observation
  53. GRB 250311A: Swift-XRT observations
  54. GRB 250228A: Fermi GBM Observation
  55. GRB 230509B: 1.3m DFOT Optical observations
  56. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  57. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  58. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  59. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  60. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  61. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  62. EP250304a: Chandra detection
  63. GRB 250225B: Swift-BAT refined analysis
  64. GRB 250311A: Tiled Swift observations
  65. IPN triangulation of GRB 250308A (short)
  66. GRB 250309B: Swift-XRT refined Analysis
  67. GRB 250309B / AT2025dws: Swift-UVOT detection
  68. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  69. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  70. GRB 230509B: Tiled Swift observations
  71. GRB 250306A: EIRSAT-1 GMOD detection
  72. Konus-Wind detection of GRB 250306A
  73. GRB 250306A: Swift-BAT refined analysis
  74. GRB 250306A: NuSTAR detection of the prompt emission
  75. GRB 250306A: AstroSat CZTI detection
  76. Swift GRB 250306A: Global MASTER-Net observations report
  77. GRB 250306A: Swift detection of a burst
  78. IPN triangulation of GRB 250222A
  79. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  80. EP250304a: Swift-XRT detection of a fading X-ray source
  81. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  82. EP250302a: Swift/UVOT detection
  83. EP250302a: Swift-XRT observations of a fading X-ray source
  84. EP250228a: Optical observations with Kinder and Swift/UVOT
  85. GRB 250225B: EIRSAT-1 GMOD Detection
  86. GRB 250225B: VLT/HAWKI near-infrared observations
  87. EP250228a: updates on the EP observations
  88. EP250228a: Swift/XRT localisation
  89. GRB 250225B: INTEGRAL SPI-ACS detection
  90. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  91. GRB 250225B: Fermi GBM Observation
  92. GRB 250221A: ATCA Detections and Upper Limits
  93. GRB 250225B: REM NIR upper limits
  94. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  95. Konus-Wind detection of GRB 250225B
  96. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  97. GRB 250225B: VLT/FORS2 candidate optical afterglow
  98. GRB 250225B: SVOM/GRM observation of a long burst
  99. GRB 250221A: EP-FXT detection of the X-ray afterglow
  100. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources

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