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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"

20815 results found.

  1. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  2. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  3. EP250223a: CrAO ZTSH optical observation
  4. GRB 250225B: VLT optical and near-infrared candidate counterpart
  5. GRB 250225B: VLT/FORS2 candidate optical afterglow
  6. GRB 250225B: SVOM/GRM observation of a long burst
  7. EP250226a/GRB 250226A: GSP detects optical counterpart
  8. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  9. EP250226a / GRB 250226A: TRT optical counterpart observation
  10. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  11. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  12. EP250223a: GMG Optical Observation
  13. EP250225a: Einstein Probe detected of a fast X-ray transient
  14. GRB 250225B: Swift detection of a burst
  15. EP250223a: GROWTH-India Telescope optical observations
  16. EP250215A: J band upper limit by SYSU 80cm telescope
  17. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  18. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  19. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  20. EP250223a: Kinder optical follow-up observations
  21. GRB 250207a: ATCA Radio Upper Limits
  22. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  23. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  24. GRB 250222A: SVOM/GRM observation of a burst
  25. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  26. EP250223a: REM NIR upper limit
  27. EP250223a: TRT optical afterglow observation
  28. EP250223a: refined analysis of the EP-WXT and FXT observations
  29. EP250223a: 1.6m Mephisto and 50cm array observations
  30. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  31. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
  32. EP250223a: OASDG optical observations
  33. EP250223a: NOT optical afterglow candidate
  34. EP250223a: Einstein Probe detection of an X-ray transient
  35. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  36. GRB 250221A: Optical counterpart detection by LCO.
  37. EP250220a: EP-FXT follow-up observations
  38. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  39. GRB 250221A: GRANDMA/TAROT Detection
  40. GRB 250221A: Swift-XRT refined Analysis
  41. GRB 250221A: 1.6m Mephisto optical detection
  42. GRB 250221A: AKO Optical Upper Limit
  43. GRB 250221A: Swift/UVOT Detection
  44. EP250220a: Liverpool Telescope upper limits
  45. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  46. GRB 250221A: REM optical/NIR afterglow detection
  47. GRB 250221A: Enhanced Swift-XRT position
  48. EP250220a: 1.6m Mephisto observations
  49. EP250220a: Liverpool Telescope optical upper limits
  50. EP250220a: Optical upper limit with Kinder observations
  51. SVOM trigger sb25022102 is not an astrophysical event
  52. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  53. GRB 250221A: Swift detection of a burst with an optical counterpart
  54. EP250220a: Xinglong optical upper limit
  55. GRB 250219A: Swift/UVOT Upper Limits
  56. GRB 250219A: OHP/T193 optical upper limit
  57. GRB 250219A: NOT optical observations
  58. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  59. GRB 250219A: 1.6m Mephisto optical upper limits
  60. GRB 250219A: Swift-XRT observations
  61. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  62. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  63. GRB 250217C: Swift-XRT observations
  64. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  65. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  66. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  67. GRB 250217C: SVOM/GRM observation
  68. GRB 250217C: Fermi GBM Observation
  69. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  70. IPN triangulation of GRB 250217C (short)
  71. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  72. GRB 250213A: Swift-XRT observations
  73. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  74. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  75. GRANDMA/OPD observations of GRB250215A
  76. GRB 250215A / EP250215a: LCO detection of the afterglow
  77. EP250212a: FTW optical and NIR upper limits
  78. GRB 250215A: Swift/UVOT Upper Limits
  79. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  80. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  81. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  82. GRB 250215A: SVOM/GRM observation
  83. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  84. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  85. EP250207b: Xinglong optical upper limit
  86. EP250212a: Xinglong optical upper limit
  87. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  88. GRB 250205A: VIRT Optical Upper Limit
  89. GRB 250205A: Leavitt Observatory optical upper limit
  90. EP250207B: Chandra localization of the X-ray counterpart
  91. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  92. EP250207b: VLA radio upper limits
  93. EP250212a: Liverpool Telescope optical upper limits
  94. GRB250101A: Radio upper limits from GMRT observations
  95. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  96. EP250207B: GTC z-band Observations
  97. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  98. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  99. EP250207b: NOT optical counterpart candidate
  100. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT

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