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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"

18399 results found.

  1. GRB 250320B: Fermi-LAT detection
  2. GRB 250321A: Swift/UVOT Upper Limits
  3. EP250321a: LCO optical counterpart detection
  4. EP250321a: Swift-XRT detection of an X-ray source
  5. Swift GRB 250321A: Global MASTER-Net observations report
  6. GRB 250321A: GOTO optical upper limits
  7. GRB 250321A: Swift-XRT localisation
  8. GRB 250321A: Fermi GBM Observation
  9. GRB 250321A: Swift detection of a burst
  10. GRB250312A: Swift/UVOT Upper Limits
  11. GRB 250317B: Swift-XRT observations
  12. GRB 250316A: Swift/UVOT Upper Limits
  13. GRB 250314A: REM optical/NIR upper limits
  14. GRB 250316A: AbAO AS-32 Optical Upper Limit
  15. GRB 250316A: Swift-XRT afterglow detection
  16. GRB 250316A: Fermi GBM Observation
  17. GRB 250316A: Swift-XRT observations
  18. GRB 250316A: Swift ToO observations
  19. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  20. GRB 250314A: EP-FXT afterglow detection
  21. GRB 250314A: Swift/UVOT Upper Limits
  22. GRB 250312B: GRBAlpha detection
  23. GRB 250314A: Swift XRT Detection
  24. GRB 250314A: NOT near-infrared candidate counterpart
  25. GRB 250312B: Fermi GBM Observation
  26. GRB 250313A: Swift-XRT observations
  27. Konus-Wind detection of GRB 250308A
  28. GRB 250313A: Fermi-LAT detection
  29. GRB 250313A: Swift ToO observations
  30. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  31. EP250304a: SVOM/VT optical observation
  32. EP250302a: Chandra X-ray Detection
  33. GRB 250312A: Swift-XRT refined Analysis
  34. GRB 250312A: Enhanced Swift-XRT position
  35. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  36. GRB 250226B: Fermi GBM Observation
  37. Swift GRB 250312A: Global MASTER-Net observations report
  38. GRB 250302A: Fermi GBM Observation
  39. GRB 250312A: Swift detection of a burst
  40. GRB 250223B: Fermi GBM Observation
  41. GRB 250311A: Swift-XRT observations
  42. GRB 250228A: Fermi GBM Observation
  43. GRB 230509B: 1.3m DFOT Optical observations
  44. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  45. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  46. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  47. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  48. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  49. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  50. EP250304a: Chandra detection
  51. GRB 250225B: Swift-BAT refined analysis
  52. GRB 250311A: Tiled Swift observations
  53. IPN triangulation of GRB 250308A (short)
  54. GRB 250309B: Swift-XRT refined Analysis
  55. GRB 250309B / AT2025dws: Swift-UVOT detection
  56. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  57. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  58. GRB 230509B: Tiled Swift observations
  59. GRB 250306A: EIRSAT-1 GMOD detection
  60. Konus-Wind detection of GRB 250306A
  61. GRB 250306A: Swift-BAT refined analysis
  62. GRB 250306A: NuSTAR detection of the prompt emission
  63. GRB 250306A: AstroSat CZTI detection
  64. Swift GRB 250306A: Global MASTER-Net observations report
  65. GRB 250306A: Swift detection of a burst
  66. IPN triangulation of GRB 250222A
  67. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  68. EP250304a: Swift-XRT detection of a fading X-ray source
  69. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  70. EP250302a: Swift/UVOT detection
  71. EP250302a: Swift-XRT observations of a fading X-ray source
  72. EP250228a: Optical observations with Kinder and Swift/UVOT
  73. GRB 250225B: EIRSAT-1 GMOD Detection
  74. GRB 250225B: VLT/HAWKI near-infrared observations
  75. EP250228a: updates on the EP observations
  76. EP250228a: Swift/XRT localisation
  77. GRB 250225B: INTEGRAL SPI-ACS detection
  78. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  79. GRB 250225B: Fermi GBM Observation
  80. GRB 250221A: ATCA Detections and Upper Limits
  81. GRB 250225B: REM NIR upper limits
  82. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  83. Konus-Wind detection of GRB 250225B
  84. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  85. GRB 250225B: VLT/FORS2 candidate optical afterglow
  86. GRB 250225B: SVOM/GRM observation of a long burst
  87. GRB 250221A: EP-FXT detection of the X-ray afterglow
  88. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  89. Swift GRB 250225B: Global MASTER-Net observations report
  90. GRB 250225B: Swift detection of a burst
  91. GRB 250221A: Swift-BAT refined analysis
  92. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  93. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  94. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  95. GRB 250207a: ATCA Radio Upper Limits
  96. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  97. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  98. GRB 250119B: VZLUSAT-2 detection
  99. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  100. GRB 250219A: EP-FXT afterglow detection

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